Scholarly article on topic 'A comprehensive overview about recycling rubber as fine aggregate replacement in traditional cementitious materials'

A comprehensive overview about recycling rubber as fine aggregate replacement in traditional cementitious materials Academic research paper on "Civil engineering"

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Abstract of research paper on Civil engineering, author of scientific article — Alaa M. Rashad

Abstract Currently, the need to incorporate recycled materials such as rubber in building products is becoming more important than ever before. The use of waste rubber in mortar/concrete mixtures creates landfill avoidance and decreases the depletion of virgin raw materials. Waste rubber can be used as a part of fine aggregate, coarse aggregate or both aggregates. It can be used as an additive to Portland cement (PC). This paper presents an overview of the previous researches carried out on the use of waste rubber as partially or fully natural fine aggregate replacement in traditional mortar/concrete mixtures based on PC. The effects of rubber sand on workability, setting time, bleeding, density, strength, impact energy, impact load, toughness, ductility, shrinkage, abrasion resistance, freeze/thaw resistance, fire resistance, thermal insulation, carbonation resistance, corrosion resistance, water absorption, porosity, chloride ion penetration, resistance to aggressive environmental, energy absorption, sound absorption, electrical resistance and cracking resistance of rubberised mortar/concrete were reviewed.

Academic research paper on topic "A comprehensive overview about recycling rubber as fine aggregate replacement in traditional cementitious materials"

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International Journal of Sustainable Built Environment (2015) xxx, xxx-xxx

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Review Article

A comprehensive overview about recycling rubber as fine aggregate replacement in traditional cementitious materials

Alaa M. Rashad *

Building Materials Research and Quality Control Institute, Housing & Building National Research Center, HBRC, Cairo, Egypt

Received 16 April 2015; accepted 24 November 2015

Abstract

Currently, the need to incorporate recycled materials such as rubber in building products is becoming more important than ever before. The use of waste rubber in mortar/concrete mixtures creates landfill avoidance and decreases the depletion of virgin raw materials. Waste rubber can be used as a part of fine aggregate, coarse aggregate or both aggregates. It can be used as an additive to Portland cement (PC). This paper presents an overview of the previous researches carried out on the use of waste rubber as partially or fully natural fine aggregate replacement in traditional mortar/concrete mixtures based on PC. The effects of rubber sand on workability, setting time, bleeding, density, strength, impact energy, impact load, toughness, ductility, shrinkage, abrasion resistance, freeze/thaw resistance, fire resistance, thermal insulation, carbonation resistance, corrosion resistance, water absorption, porosity, chloride ion penetration, resistance to aggressive environmental, energy absorption, sound absorption, electrical resistance and cracking resistance of rubberised mortar/concrete were reviewed.

© 2015 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved.

Keywords: Waste rubber; Fine aggregate; Fresh properties; Mechanical strength; Durability

Contents

1. Introduction..............................................................................................................................................................00

2. Workability, setting time, segregation and bleeding........................................................................................................00

2.1. Rubberised mortars............................................................................................................................................00

2.2. Rubberised concretes..........................................................................................................................................00

3. Density......................................................................................................................................................................00

3.1. Fresh density....................................................................................................................................................00

3.2. Hardened density..............................................................................................................................................00

4. Mechanical strength....................................................................................................................................................00

* Tel./fax: +20 (2)33351564, +20 (2)33367179. E-mail addresses: alaarashad@yahoo.com, a.rashad@hbrc.edu.eg Peer review under responsibility of The Gulf Organisation for Research and Development.

http://dx.doi.org/10.1016/j.ijsbe.2015.1L003

2212-6090/© 2015 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved.

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4.1. Rubberised mortars............................................................................................................................................00

4.1.1. Replacement levels up to 15%.........................................................00

4.1.2. Replacement levels upto 35%..........................................................00

4.1.3. Replacement levels up to 60%.........................................................00

4.2. Rubberised concretes ..........................................................................................................................................00

4.2.1. Replacement levels upto 15%..........................................................00

4.2.2. Replacement levels up to 25% ......................................................... 00

4.2.3. Replacement levels up to 33.3%........................................................ 00

4.2.4. Replacement levels upto 50%.......................................................... 00

4.2.5. Replacement levels upto 100%......................................................... 00

5. Impact energy and impact load....................................................................................................................................00

6. Toughness..................................................................................................................................................................00

7. Ductility and strain capacity........................................................................................................................................00

8. Shrinkage..................................................................................................................................................................00

9. Abrasion resistance....................................................................................................................................................00

10. Freeze/thaw and ageing resistance..............................................................................................................................00

11. Fire resistance and thermal insulation........................................................................................................................00

12. Carbonation resistance..............................................................................................................................................00

13. Corrosion resistance..................................................................................................................................................00

14. Water absorption, porosity and chloride ion penetration..............................................................................................00

15. Resistance to aggressive environmental ......................................................................................................................00

16. Energy absorption....................................................................................................................................................00

17. Sound absorption......................................................................................................................................................00

18. Electrical resistance ..................................................................................................................................................00

19. Cracking resistance....................................................................................................................................................00

20. Usability of rubberised mortar/concrete......................................................................................................................00

21. Remarks..................................................................................................................................................................00

References ................................................................................................................................................................00

1. Introduction

As known, waste generation in the EU was estimated to stand at over 1.43 billion tonnes per year and was increasing at rates comparable to those of economic growth (Daniel et al., 2013). Consequently, waste reduction and recycling are very important elements in a waste management framework because they help to conserve natural resources and reduce the demand for valuable landfill space. Waste rubber is one of the significant wastes which has been a major concern in the world. Data that were collected from the literature has shown that in 2005, over 10 billion tyres are discarded worldwide every year (Alamo-NoleLuis et al., 2011). According to Colom et al. (2007), it was estimated that around 1 billion tyres are withdrawn from use each year. It was estimated that 1000 million tyres reach the end of their useful life every year. By the year 2030, the number can reach up to 1200 million tyres representing almost 5000 million tyres (including stock piled) to be discarded on a regular basis (Pacheco-Torgal et al., 2012). In the United States, for example, there were 2-3 billion tyres deposited in landfills per year (Humphrey, 1995) and 275 million scrap tyres stockpiled across the country, with an increase of 290 million tyres generated per year (Batayneh et al., 2008). It was estimated that one car tyre per person was discarded each year in the developed world and hence 1 billion waste tyres were disposed globally each year (Daniel et al., 2013). It

was estimated that approximately 4 billion of waste tyres were in landfills and stockpiles worldwide (Business Council for Sustainable Development, 2011).

The US Environmental Protection Agency reported that 290 million scrap tyres were generated in 2003. Of the 290 million, 45 million of these scrap tyres were used to make automotive and truck tyre re-treads. In Europe every year, 355 million tyres are produced in 90 plants, representing 24% of world production (Davide Lo, 2013). In addition the EU has millions of used tyres that have been illegally dumped or stockpiled. The inadequate disposal of tyres may, in some cases, pose a potential threat to human health (fire risk, haven for rodents or other pests such as mosquitoes) and increase environmental risks. Most countries, in Europe and worldwide, have relied on land filling to dispose of used tyres but the limited space and their potential for reuse has led to many countries imposing a ban on this practice. The current estimate for these historic stockpiles throughout the EU stands at 5.5 million tonnes (1.73 times the 2009 annual used tyres arising) and the estimated annual cost for the management of ELTs is estimated at € 600 million (Davide Lo, 2013).

In UK, approximately 37 million tyres were used annually in 2002. This number continues to grow (Martin, 2001). In Thailand, the record of the year 2000 alone indicated a consumption of approximately 250,000 metric tonnes of rubber products. About 38% of this (94,000 metric tonnes) were vehicle tyres. These numbers keep on increas-

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Figure 1. Waste rubber landfill.

117 ing every year with the numbers of vehicles, as do the

118 future problems relating to waste tyres (Sukontasukkul

119 and Chaikaew, 2006). In Taiwan, over 100,000 tonnes of

120 waste tyres are annually generated, and this number is

121 increasing (Yung et al., 2013). In Australia, the trend for

122 accumulated waste tyres was rising at a rate of 2% and it

123 was estimated more than 20 million tyres were accumulated

124 in landfills by year 2010 (Mohammadi et al., 2014). In

125 France, over 10 million scrap-tyres per year were produced

126 (Rafat and Naik Tarun, 2004). The used rubber tyres in

127 Singapore are sent to the incineration plants for disposal

128 and burning. Based on waste statistics and recycling rate

129 for 2008 (Sook-Fun and Seng-Kiong, 2009), from a total

130 scrap tyre waste output of 25,100, 3000 tonnes were dis-

131 posed of, whereas 22,100 were recycled such that the recy-

132 cling rate of this waste was approximately 88%. In Spain,

133 42% of worn tyres generated have been destined to energy

134 recovery, mainly in cement kilns, 10% have been reused

135 and 48% have been destined to material recovery in 2011

136 (Eiras et al., 2014). In 2010 the EU27 plus Turkey pro-

137 duced about 4.5 million tonnes of tyres, estimated at

138 17 million tonnes. From this amount, it is assessed that

139 more than 3.2 million tonnes of waste tyres are discarded

140 annually and for this reason the disposal of waste tyres is

considered as an increasing environmental and economic 141

problem (Williams et al., 1995). 142

Most of waste tyres are landfill disposed, which is the 143

most common method (Fig. 1). This method will be drasti- 144

cally reduced in the near future due to the recent introduc- 145

tion of European Union directives that include significant 146

restrictions on this practice in favour of alternatives ori- 147

ented towards material and energy recovery. In addition, 148

the disposal of used tyres in landfills, stockpiles or illegal 149

dumping grounds increases the risk of accidental fires with 150

uncontrolled emission of potentially harmful compounds 151

(Yung et al., 2013). In order to properly dispose of these 152

millions of waste tyres, the use of innovative techniques 153

to recycle them is important. However, a significant pro- 154

portion of the waste tyres are used in civil engineering 155

applications such as road and rail foundations and 156

embankments (0.24 million tonnes) re-treaded (0.26 million 157

tonnes) or exported (0.33 million tonnes) each year 158

(ETRMA, 2011). Recycled waste tyres are used for ener- 159

getic purposes in cement kilns (Rafat and Naik Tarun, 160

2004), incinerated for the production of electricity 161

(Oikonomou and Mavridou, 2009), used as an additive to 162

PC mortar/concrete (Mercedes del Rio et al., 2007; 163

Al-Akhras and Samadi, 2004; Benazzouk et al., 2004), as 164

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a light weight filler (Chen et al., 2013), as crush barriers, bumpers and artificial reefs, etc. (Xiang and Baoshan, 2014).

The worldwide consumption of natural sand as a fine aggregate in mortar/concrete production is very high and several developing countries have encountered some strain in the supply of natural sand in order to meet the increasing needs of infrastructural development in recent years. In many countries there is a scarcity of natural fine aggregate which is suitable for construction. In general, in the last 15 years, it has become clear that the availability of good quality natural sand is decreasing (Rashad Alaa, 2013, 2014). The shortage of resources of natural sand opened the door for using by-products as fine aggregate. Reuse of waste rubber as a partial or full replacement of fine aggregate in construction activities not only reduces the demand for extraction of natural raw materials, but also saves landfill space.

Already the literature has useful review papers related to properties of concrete containing scrap-tyre rubber (Rafat and Naik Tarun, 2004), mechanical properties of rubber (Pusca et al., 2010), fresh/hardened properties of rubberised and self-compacting rubberised concrete (Najim and Hall, 2010), pyrolysis of waste tyres (Williams Paul, 2013), recycled tyre rubber modified bitumens for road asphalt mixtures (Davide Lo, 2013) and recycling of waste tyre rubber in asphalt and Portland cement concrete (Xiang and Baoshan, 2014). On the other hand, there is no published literature review paper that reviewed the previous works carried out on the properties of mortar/concrete when fine aggregate was partially or fully replaced with waste rubber. So that, the current review aims to review the previous works carried out on the effect of partial or full replacement of fine aggregate, in traditional mortar/concrete based on PC, with waste rubber on some properties of mortar/concrete. The effects of rubber sand on workability, setting time, bleeding, density, strength, impact energy, impact load, toughness, ductility, shrinkage, abrasion resistance, freeze/thaw resistance, fire resistance, thermal insulation, carbonation resistance, corrosion resistance, water absorption, porosity, chloride ion penetration, resistance to aggressive environmental, energy absorption, sound absorption, electrical resistance and cracking resistance of rubberised mortar/concrete were reviewed.

2. Workability, setting time, segregation and bleeding

2.1. Rubberised mortars

Al-Akhras and Samadi (2004) partially replaced natural sand in mortar mixtures with tyre rubber ash (size 0.15 mm) at levels of 0%, 2.5%, 5%, 7.5% and 10%, by weight. The results showed a reduction in the workability with increasing rubber ash sand content. The reduction in the flow was 7.14%, 12.86%, 19.28% and 25% with the inclusion of 2.5%, 5%, 7.5% and 10% rubber ash sand, respectively. The setting time increased with increasing rubber ash sand content. Marques et al. (2008) partially replaced natural sand in mortar mixtures with rubber (passed in sieve 0.8 mm) at levels of 0% and 12%, by volume. Fixed w/c ratio was used. They reported that the inclusion of rubber sand decreased the workability. Topcu and Demir (2007) studied the workability, by flow, of mortar mixtures containing rubber with particles sizes of either 1-0 mm or 4-1 mm as natural sand replacement at levels of 0%, 10%, 20%, 30% and 40%, by volume. The results showed a reduction in the flow with increasing rubber sand content. The reduction in the flow was 4.84%, 12.9%, 22.04% and 24.19% with the inclusion of rubber sand with particle sizes of 0-1 mm or 1-4 mm. Pierce and Blackwell (2003) partially replaced natural fine aggregate in mortar mixtures with crumb rubber (size 0.6 mm) at levels ranging from 32% to 57%, by volume. They reported that crumb rubber contents as high as 57% can be mixed in flowable fill without noticeable rubber segregation, but there was measurable bleeding. Uygunoglu and Topcu (2010) partially replaced natural sand (size 4-0 mm) with scrap tyre rubber (size 4-1 mm) in self-consolidating mortar mixtures at levels of 0%, 10%, 20%, 30%, 40% and 50%, by weight. Various w/c ratios were used. They reported that the workability of the mixtures decreased by using scrap rubber particles with low and high volumes. The workability of rubberised mixture dramatically decreased for 50% rubber sand. Pelisser et al. (2012) reported a reduction in the flow table of mortar mixtures containing recycled tyre rubber (maximum size 2.4 mm) as natural sand (maximum size 2.4 mm) replacement at a level of 20%, by volume, whilst the inclusion of 40% and 60% rubber sand increased the flow table. Table 1 summarises the mentioned studies about the effect of

Table 1

Effect of rubber sand on the workability and bleeding of mortar mixtures.

References

Rubber content (%)

Size (mm)

Effect

Al-Akhras and Samadi (2004)

Marques et al. (2008) Topcu and Demir (2007) Pierce and Blackwell (2003) Uygunoglu and Topcu (2010) Pelisser et al. (2012)

2.5, 5, 7.5 and 10 12

10, 20, 30 and 40 32-57

10, 20, 30, 40 and 50 20, 40 and 60

Passed in sieve 0.Î 1-0 and 4-1 0.6 4-0 2.4

Reduced workability Increased setting time Reduced workability Reduced workability Increased bleeding Reduced workability 20% Reduced workability - 40% and 60% increased workability

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rubber sand on the workability and bleeding of mortar mixtures.

2.2. Rubberised concretes

Wang et al. (2013) reported an increase in the cumulative bleeding with the inclusion of rubber (size 4.75 mm) as natural sand replacement in concrete mixtures at levels of 10%, 20%, 30% and 40%, by volume. The cumulative bleeding increased as the amount of rubber replacement increased.

Mohammadi et al. (2014) accomplished trial concrete mixtures when w/c ratio was 0.35 in which natural sand was partially substituted with crumb rubber at levels of 0%, 20% and 40%, by volume. The workability decreased with increasing rubber sand content. Albano et al. (2005) partially replaced natural sand in concrete mixtures with recycled rubber from automobile tyre at levels of 0%, 5% and 10%, by weight, with particle sizes of 0.29 mm and 0.59 mm. The workability decreased with increasing rubber sand content. The reduction in the slump value was 87.5% and 93.75% with the inclusion of 5% and 10% rubber sand with a particle size of 0.29 mm or 0.59 mm, respectively. They also reported that no segregation was observed in rubberised mixtures. Holmes et al. (2014) reported a reduction in the workability of concrete mixtures by replacing natural sand with crumb rubber (size 4.75-0.425 mm) at a level of 7.5%. Guo et al. (2014) partially replaced natural sand in concrete mixtures, containing crushed recycled concrete as coarse aggregate, by crumb rubber (size 1.4-0.85 mm). Natural sand was partially replaced with crumb rubber at levels of 0%, 4%, 8%, 12% and 16%, by volume. Fixed w/c ratio and fixed dosage of naphthalene-based high-range water-reducing were used. Results showed that the inclusion of 4% rubber sand exhibited similar workability to the control mixture. For the remaining replacement levels, the workability decreased with increasing rubber sand content. Youssf et al. (2014) partially replaced natural sand in concrete mixtures with crumb rubber (size 2.36 and 1.18 mm) at levels of 0% 5%, 10% and 20%, by volume. Fixed w/c ratio and fixed dosage of superplasticiser (SP) were used. Results showed that the inclusion of 5% rubber sand exhibited similar workability to the control mixture. For the remaining replacement levels, the workability decreased with increasing rubber sand content. Raj et al. (2011) partially replaced natural sand (maximum size 4.75 mm) with rubber (maximum size 4.75 mm) in SCC mixtures at levels of 0%, 5%, 10%, 15% and 20%, by volume. Various w/b ratios, various dosages of SP and viscosity-modifying admixture were used. They reported a reduction in the workability with increasing rubber sand content. The average reduction in the flow value was approximately 0.47%, 0.94%, 1.96% and 8% with the inclusion of 5%, 10%, 15% and 20% rubber sand, respectively. The flow value decreased with increasing rubber sand content, whilst the V-funnel time and L-box increased with increasing rubber sand content. Ganesan et al. (2013)

studied the slump flow of SCC mixtures containing rubber (maximum size 4.75 mm), after suitable treatment with Poly Vinyl Alcohol, as natural sand (maximum size 4.75 mm) replacement at levels of 0%, 15% and 20%, by volume. The results showed a reduction in the slump flow with the inclusion of rubber sand. The reduction in the slump flow was 1.43% and 2.14% with the inclusion of 15% and 20% rubber sand, respectively.

Gesoglu and Guneyisi (2007) partially replaced natural fine and coarse aggregate in concrete mixtures with crumb rubber (grading close to fine aggregate) and tyre chips, respectively, at levels of 0%, 5%, 15% and 25%, by total aggregate volume. Fixed w/b ratio and fixed dosage of SP were used. The results showed a reduction in the workability with increasing rubber sand content. Ozbay et al. (2011) partially replaced natural crushed limestone sand in concrete mixtures with crumb rubber (size 3-0 mm) at levels of 0%, 5%, 15% and 25%, by volume. Fixed w/c ratio of 0.4 and fixed dosage of SP were used. They reported that the inclusion of rubber sand reduced the workability. The reduction in the slump value was 2.27%, 9.1% and 15.91% with the inclusion of 5%, 15% and 25% rubber sand, respectively. Guneyisi (2010) partially replaced natural sand (maximum size 5 mm) in SCC mixtures with crumb rubber (similar to the natural sand gradation) at levels of 5%, 15% and 25%, by volume. Fixed w/b ratio and various dosages of SP were used. Results showed a reduction in the workability with increasing rubber sand content. They also partially replaced cement with FA at levels of 0%, 20%, 40% and 60%, by weight. They reported that the inclusion of FA amended the fresh properties of the rubberised SCC mixtures. More amended mixture was obtained with increasing the FA content. Initial and final setting times increased with increasing rubber sand content and FA content.

Rahman et al. (2012) partially replaced natural sand in SCC mixtures with rubber (size 4-1 mm) at a level of 28%, by volume. Fixed w/c ratio with two dosages of SP was used. Results showed a reduction in the workability with the inclusion of rubber sand. Topcu and Demir (2007) studied the workability of concrete mixtures containing rubber (size 4-1 mm) as a natural sand replacement at levels of 0%, 10%, 20% and 30%, by volume. Results showed a reduction in the workability with increasing rubber sand content. The reduction in the slump value was 3.1%, 6.2% and 8.53% with the inclusion of 10%, 20% and 30% rubber sand, respectively. Karahan et al. (2012) partially replaced natural sand in SCC mixtures with crumb rubber (size 4.75-0.15 mm) at levels of 0%, 10%, 20% and 30%, by volume. Fixed w/b ratio of 0.32 and various dosages of HRWR were used. Results showed a reduction in the filling and passing ability of SCC mixtures with the inclusion of rubber sand. Grdic et al. (2014) reported a reduction in the workability of concrete mixtures by partially replacing natural sand with rubber (size 4-0.5 mm) at levels of 10%, 20% and 30%, by volume. Guneyisi et al. (2004) studied the workability of concrete mixtures

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365 containing crumb rubber (maximum particle size 4 mm) as

366 natural fine aggregate replacement and tyre chips (size 40367 10 mm) as natural coarse aggregate replacement at levels

368 ranging from 2.5% to 50%, by total aggregate volume. Var-

369 ious w/c ratios were used. They reported a reduction in the

370 workability with the inclusion of rubber aggregate. This

371 reduction increased as the content of rubber aggregate

372 increased.

373 Batayneh et al. (2008) studied the workability of con-

374 crete mixtures containing crumb rubber. Natural sand (size

375 4.75-0.15 mm) was replaced with crumb rubber (size

376 4.75-0.15 mm) at levels of 0%, 20%, 40%, 60%, 80% and

377 100%, by volume. Results showed a reduction in the

378 workability with the inclusion of rubber sand. This reduc-

379 tion increased with increasing rubber sand content. The

380 reduction in the slump value was 19.42%, 52.61%, 76.5%,

381 86.33% and 93.76% with the inclusion of 20%, 40%, 60%,

382 80% and 100% rubber sand, respectively. Taha et al.

383 (2008) replaced natural sand in concrete mixtures with

384 crumb rubber (size 5-1 mm) at levels of 0%, 25%, 50%,

385 75% and 100%, by volume. Fixed w/c ratio was used.

386 Results showed a reduction in the workability with the

387 inclusion of rubber sand. This reduction increased with

388 increasing rubber sand content. The reduction in the slump

389 value was approximately 13.33%, 40%, 66.67% and 80%

390 with the inclusion of 25%, 50%, 75% and 100% rubber

391 sand, respectively. Khatib and Bayomy (1999) studied the

392 workability of concrete mixtures containing crumb rubber

393 (gradation close to the natural sand) as natural sand

394 replacement. Natural sand was replaced with crumb rubber

395 at levels ranging from 5% to 100%, by volume. Results

396 showed that the workability decreased with increasing rub-

397 ber sand content.

398 On the other hand, Pelisser et al. (2012) partially

399 replaced natural sand in concrete mixtures with recycled

400 tyre rubber (size < 4.8 mm) at levels of 0%, 10%. Fixed

401 w/c ratio and various dosages of plasticiser were used.

402 They reported an increase in the workability with the inclu-

403 sion of rubber sand. The increase in the slump value was

404 63.63% with the inclusion of rubber sand. Bravo and de

405 Brito (2012) partially replaced natural sand in concrete

406 mixtures with rubber aggregate made from used tyres (with

407 the same size of the natural sand) at levels of 0%, 5%, 10%

408 and 15%, by volume. Various w/c ratios were used. Results

409 showed a reduction in the workability with the inclusion of

410 5% and 15% rubber sand, whilst the inclusion of 10% rub-

411 ber sand increased it. Onuaguluchi and Panesar (2014) par-

412 tially replaced natural fine aggregate in concrete mixtures

413 with crumb rubber (size ^86% of rubber particles smaller

414 than 2.3 mm) at levels of 0%, 5%, 10% and 15%, by vol-

415 ume. Fixed w/c ratio and fixed dosage of HRWR were

416 used. Results showed an increase in the workability with

417 the inclusion of rubber sand. The workability increased

418 with increasing rubber sand content. Antil et al. (2014)

419 reported an increase in concrete mixture workability by

420 partially replacing natural sand with 5% and 10% crumb

421 rubber (size 4.75-0.075 mm), by volume, whilst the inclu-

sion of 15% and 20% rubber sand reduced it. Parveen 422

et al. (2013) partially replaced natural sand in concrete mix- 423

tures with crumb rubber (size 4.75-0.075 mm) at levels of 424

0%, 5%, 10%, 15% and 20%, by volume. Results showed 425

an increase in the workability with the inclusion of 5% 426

and 10% rubber sand, whilst the inclusion of 15% and 427

20% rubber sand decreased it. Balaha et al. (2007) reported 428

higher workability of concrete mixtures containing ground 429

waste tyre rubber (size < 4 mm) as partial replacement of 430

natural sand at levels of 0%, 5%, 10%, 15% and 20%, by 431

volume. Results showed an increase in the workability as 432

rubber sand content increased. Azmi et al. (2008) reported 433

an increase in the workability of concrete mixtures by 434

replacing natural sand with crumb rubber (size 2.36- 435

2 mm) at levels of 0%, 10%, 15%, 20% and 30%, by volume. 436

The workability increased with increasing rubber sand 437

content. 438

Wang et al. (2013) studied the workability and initial 439

setting time of low strength rubber concrete (CLSRC) mix- 440

tures and low strength lightweight concrete (CLSRLC) 441

mixtures at different contents of rubber. Natural sand 442

was partially replaced with rubber (size 4.75 mm) at levels 443

of 0%, 10%, 20%, 30% and 40%, by volume. Fixed w/b 444

ratio and fixed dosage of accelerating agent were used. 445

For CLSRC mixtures, the results showed 3.46% increase 446

in the slump value with the inclusion of 10% rubber sand, 447

whilst the reduction in the slump value reached 4.33%, 448

1.3% and 14.72% with the inclusion of 20%, 30% and 449

40% rubber sand, respectively. The slump flow increased 450

with the inclusion of 10% and 20% rubber sand, whilst 451

the inclusion of 30% and 40% rubber sand decreased it. 452

The initial setting time increased with increasing rubber 453

sand content. The increase in the initial setting time was 454

8%, 15.47%, 28.27% and 42.4% with the inclusion of 455

10%, 20%, 30% and 40% rubber sand, respectively. For 456

CLSRLC mixtures, the results showed an 8% increase in 457

the slump value with the inclusion of either 10% or 20% 458

rubber sand, whilst the reduction in the slump value 459

reached 12% and 14% with the inclusion of 30% and 40% 460

rubber sand, respectively. The initial setting time results 461

showed similar trend as CLSRC mixtures. Topcu and 462

Saridemir (2008) partially replaced natural fine aggregate 463

in concrete mixtures by rubber with two particle sizes of 464

1-0 mm and 4-1 mm at levels of 0%, 15%, 30% and 45%, 465

by volume. They reported that with the increase of rubber 466

content in concrete mixtures as fine aggregate replacement, 467

the flow table value increased. The greatest flow table value 468

was observed in the coarse rubberised concrete mixture as 469

8.33%, whilst the smallest was observed in the fine rub- 470

berised concrete mixture as 1.08%. Turgut and Yesilata 471

(2008) partially replaced natural sand in concrete block 472

mixtures with rubber (size 4.75-0.075 mm) at levels ranging 473

from 10% to 70% with an increment of 10%, by volume. 474

Results showed an increase in the workability with the 475

inclusion of rubber sand up to 40%, whilst the inclusion 476

of 50-70% rubber sand decreased it. Khaloo et al. (2008) 477

studied the workability of concrete mixtures containing 478

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Table 2

Effect of rubber sand on the workability, setting time, segregation and bleeding of concrete mixtures.

References Rubber content (%) Size (mm) Effect

Wang et al. (2013) 10, 20, 30 and 40 4.75 - Increased bleeding

Mohammadi et al. (2014) 20 and 40 - - Reduced workability

Albano et al. (2005) 5 and 10 0.29 and 0.59 - Reduced workability

- No segregation

Holmes et al. (2014) 7.5 4.75-0.425 - Reduced workability

Guo et al. (2014) 4, 8, 12 and 16 1.4-0.85 - Reduced workability

Youssf et al. (2014) 5, 10 and 20 2.36 and 1.18 - Reduced workability

Rajet al. (2011) 5, 10, 15 and 20 4.75 - Reduced workability

Ganesan et al. (2013) 15 and 20 4.75 - Reduced workability

Gesoglu and Guneyisi (2007) 5, 15 and 25 Close to fine aggregate - Reduced workability

Ozbay et al. (2011) 5, 15 and 25 3-0 - Reduced workability

Guneyisi (2010) 5, 15 and 25 Similar to sand gradation - Reduced workability

- Increased initial and final setting time

- FA amended fresh properties and increased setting time

Rahman et al. (2012) 28 4-1 - Reduced workability

Topcu and Demir (2007) 10, 20 and 30 4-1 - Reduced workability

Karahan et al. (2012) 10, 20 and 30 4.75-0.15 - Reduced workability

GrdiC et al. (2014) 10, 20 and 30 4-0.5 - Reduced workability

Batayneh et al. (2008) 20, 40, 60, 80 and 100 4.75-0.15 - Reduced workability

Taha et al. (2008) 25-100 5-1 - Reduced workability

Khatib and Bayomy (1999) 5-100 Close to sand - Reduced workability

Pelisser et al. (2011) 10 <4.8 - Increased workability

Bravo and de Brito (2012) 5, 10 and 15 Similar to sand gradation - 5% and 15% reduced workability

- 10% increased workability

Onuaguluchi and Panesar (2014) 5, 10 and 15 ~86% smaller than 2.3 mm - Increased workability

Antil et al. (2014) 5, 10, 15 and 20 4.75-0.075 - 5% and 10% increased workability

- 15% and 20% reduced workability

Parveen et al. (2013) 5, 10, 15 and 20 4.75-0.075 - 5% and 10% increased workability

- 15% and 20% reduced workability

Balaha et al. (2007) 5, 10, 15 and 20 <4 - Increased workability

Azmi et al. (2008) 10, 15, 20 and 30 2.36-2 - Increased workability

Wang et al. (2013) 10, 20, 30 and 40 4.75 For CLSRC

- Increased initial setting time

- 10% increased workability

- 20%, 30% and 40% reduced workability

Wang et al. (2013) 10, 20, 30 and 40 4.75 For CLSRLC

- Increased initial setting time

- 10% and 20% increased workability

- 30% and 40% reduced workability

Topcu and Saridemir (2008) 15, 30 and 45 1-0 and 4-1 - Increased workability

Turgut and Yesilata (2008) 10-70 4.75-0.075 - Up to 40% increased workability

—50-70% reduced workability

Khaloo et al. (2008) 25, 50, 75 and 100 4.75 - 25%, 50% and 75% increased workability

Figure 2. Research numbers versus the effect of waste rubber sand on the workability of mixtures.

crumb rubber. Natural sand (maximum size 4.75 mm) was replaced with crumb rubber (maximum size 4.75 mm) at levels of 0%, 25%, 50%, 75% and 100%, by volume. Results showed an increase in the workability with the inclusion of 25%, 50% and 75% rubber sand. The inclusion of 25% rubber sand showed the highest workability followed by 75% and 50%, respectively. On the other hand, the inclusion of 100% rubber sand significantly decreased it. Table 2 summarises the mentioned studies about the effect of rubber sand on the workability, setting time, segregation and bleeding of concrete mixtures.

From the above review of the literature in Sections 2.1 and 2.2, it can be noted that several studies reported that the inclusion of waste rubber sand in the mixture reduced the workability (Fig. 2). This may be related to the higher

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water absorption of rubber sand compared to natural sand. The reduction in the workability is mainly depending on rubber content and its particle size. On the contrary, few studies believed that the inclusion of rubber to the mixture increased the workability (Fig. 2). It is worth mentioning that a few other studies believed that some rubber sand contents reduced workability, whilst other contents increased it (Pelisser et al., 2012; Balaha et al., 2007; Khaloo et al., 2008). The reduction in the workability of the mixture with the inclusion of rubber sand is one of disadvantages of using this recycled material.

3. Density

3.1. Fresh density

Skripkiunas et al. (2007) partially replaced natural sand in concrete mixtures with rubber (size 1-0 mm) at levels of 0% and 3.2%, by weight. Fixed w/c ratio and fixed dosage of SP were used. The concrete mixture density reduced by 0.66% with the inclusion of rubber sand. Albano et al. (2005) reported a reduction in the fresh density of concrete mixtures containing rubber from automobile at levels of 5% and 10%, by weight. The reduction in the fresh density was 20.33% and 29.58% with the inclusion of 5% and 10% rubber sand with a particle size of 0.59 mm, whilst it was 22.51% and 38.2%, respectively with the inclusion of rubber sand with a particle size of 0.29 mm. Pedro et al. (2013) reported a reduction in the fresh density of mortar mixtures by replacing natural sand with shredded rubber (size 4.75-0.15 mm) at different levels, by volume. This reduction increased with increasing rubber sand content. The reduction in the fresh density was 4.17%, 7.21% and 10% with the inclusion of 5%, 10% and 15% rubber sand, respectively. Bravo and de Brito (2012) reported a reduction in the fresh density of concrete mixtures containing rubber made from used tyres (with the same size of the natural sand) as natural sand replacement at levels of 0%, 5%, 10% and 15%, by volume. This reduction in the fresh density increased with increasing rubber sand content. Gesoglu et al. (2014) reported approximately 1.41% and 6.85% reduction in the fresh density of concrete mixtures by partially replacing natural aggregate with rubber (size 4 mm) at levels of 10% and 20%, by total aggregate volume, respectively. Thomas et al. (2014) reported a reduction in the fresh density of concrete mixtures by partially replacing natural sand with discarded tyre rubber (40% powder from mesh 30, 35% size 2-0.8 mm and 25% size 4-2 mm) up to 20%. This reduction increased with increasing rubber sand content. The reduction ranging from 1% with the inclusion of 2.5% rubber sand to 13.23% with the inclusion of 20% rubber sand, at w/c ratio of 0.4. Balaha et al. (2007) reported a reduction in the fresh unit weight of concrete mixtures by partially replacing natural sand with ground waste tyre rubber (size <4 mm) at levels of 5%, 10%, 15% and 20%, by volume. This reduction increased as the rubber sand content increased. Gesoglu and Guneyisi

(2007) reported a reduction in the fresh unit weight of concrete mixtures containing crumb rubber (grading close to the natural fine aggregate) and tyre chips as fine and coarse aggregate replacement, respectively, at levels of 0%, 5%, 15% and 25%, by total aggregate volume. The fresh unit weight decreased as the rubber content increased. Ozbay et al. (2011) reported a reduction in the fresh unit weight of concrete mixtures with the inclusion of crumb rubber (size 3-0 mm) as natural fine aggregate replacement. The reduction in the fresh unit weight was 0.91%, 3.32% and 5% with the inclusion of 5%, 15% and 25% rubber sand, respectively. Grdic et al. (2014) reported a reduction in the fresh density of concrete mixtures by partially replacing natural sand with rubber (size 4-0.5 mm) at levels of 10%, 20% and 30%, by volume. The reduction in the fresh density increased with increasing rubber sand content. The reduction in the fresh density was 3.8%, 9.3% and 13.3% with the inclusion of 10%, 20% and 30% rubber sand, respectively.

Fadiel et al. (2014) partially replaced natural sand in mortar mixtures with crumb rubber with different sizes at levels of 10%, 20%, 30% and 40%, by weight. Fixed w/c ratio was used. Results showed a reduction in the fresh unit weight of mortar mixtures with the inclusion of rubber sand. The reduction in the fresh unit weight was 10%, 20.94%, 27.1% and 35.37% with the inclusion of 10%, 20%, 30% and 40% rubber sand (size 0.6-0 mm), respectively, whilst the inclusion of rubber sand with a size of 2-0.84 mm reduced it by 6.1%, 15.88%, 21.59% and 29.46%, respectively. Mohammadi et al. (2014) reported a reduction in the fresh density of concrete mixtures by partially substituted natural sand with crumb rubber (after treatment in water-soaking) at levels of 10%, 20%, 30% and 40%, by volume. This reduction increased with increasing rubber sand content. At w/c ratio of 0.45, the reduction in the fresh density was approximately 2.47%, 4.81%, 7.42% and 11.81% with the inclusion of 10%, 20%, 30% and 40% rubber sand, respectively. Topcu and Saridemir

(2008) reported that rubber (size 1-0 mm or 4-1 mm) at levels of 15%, 30% and 45% as natural fine aggregate replacement, by volume, decreased the fresh unit weight

Figure 3. Effect rubber content on the fresh unit weight of concrete mixtures (Topcu and Saridemir, 2008).

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Table 3

Effect of rubber sand on the reduction percentage of the fresh unit weight of concrete mixtures.

References

Rubber content (%)

Size (mm)

% Reduction

Skripkiunas et al. (2007) Albano et al. (2005) Albano et al. (2005) Pedro et al. (2013) Gesoglu et al. (2014) Thomas et al. (2014) Ozbay et al. (2011) Grdic et al. (2014) Fadiel et al. (2014) Fadiel et al. (2014) Mohammadi et al. (2014) Topcu and Saridemir (2008) Topcu and Saridemir (2008) Taha et al. (2008) Khaloo et al. (2008) Batayneh et al. (2008)

5 and 10 5 and 10 5, 10 and 15 10 and 20 2.5-20 5, 15 and 25 10, 20 and 30 10, 20, 30 and 40 30 and 40 30 and 40

10 10 45 45 25 25

20, 20,

75 and 100 75 and 100

20, 40, 60, 80 and 100

1-0 0.59 0.29

4.75-0.15 4

Mesh 30, 2-0.8 mm, 4-2 mm

4-0.5 0.6-0 2-0.84

Maximum 4.75 4.75-0.15

20.33 and 29.58

22.51 and 38.2

4.17, 7.21 and 10

1.41 and 6.85

From 1 to 13.22

0.91, 3.32 and 5

3.8, 9.3 and 13.3

10, 20.94, 27.1 and 35.37

6.1, 15.88, 21.59 and 29.46

2.47, 4.81, 7.42 and 11.81

I.13 16.92

II.57, 14.35, 17.13 and 21.48 15.46, 28.66, 34 and 34.79

7.59, 13.78, 17.17, 23.69 and 27.44

of concrete mixtures (Fig. 3). The reduction in the fresh unit weight values of coarse rubberised concrete mixtures was greater than that of fine rubberised concrete mixtures. The greater reduction in the fresh unit weight values was observed in coarse rubberised concrete mixture as 16.92%, whilst the smallest was observed in fine rubberised concrete mixture as 1.13%. Guneyisi et al. (2004) reported a reduction in the fresh unit weight of concrete mixtures containing rubber (maximum particle size 4 mm) as natural fine aggregate replacement and tyre chips (size 40-10 mm) as natural coarse aggregate replacement at levels ranging from 2.5% to 50%, by total aggregate volume. This reduction increased as the rubber aggregate content increased. Taha et al. (2008) reported a reduction in the fresh unit weight of concrete mixtures by replacing natural sand, up to 100%, with rubber (size 5-1 mm). The fresh density decreased with increasing rubber sand content. The reduction in the fresh density was approximately 11.57%, 14.35%, 17.13% and 21.48% with the inclusion of 25%, 50%, 75% and 100% rubber sand, respectively. Khaloo et al. (2008) found a reduction in the fresh unit weight of concrete mixtures by replacing natural sand (maximum size 4.75 mm) with crumb rubber (maximum size 4.75 mm) at levels of 25%, 50%, 75% and 100%, by volume. This reduction increased as the rubber sand content increased. The reduction in the fresh unit weight was approximately 15.46%, 28.66%, 34% and 34.79% with the inclusion of 25%, 50%, 75% and 100% rubber sand, respectively. Batayneh et al. (2008) found a reduction in the fresh unit weight of concrete mixtures by replacing natural sand (size 4.75-0.15 mm) with crumb rubber (size 4.75-0.15 mm), by volume. This reduction increased as the rubber sand content increased. The reduction in the fresh unit weight was 7.59%, 13.78%, 17.17%, 23.69% and 27.44% with the inclusion of 20%, 40%, 60%, 80% and 100% rubber sand, respectively. Table 3 summarises the mentioned studies about the effect of rubber sand on the reduction percentage of the fresh unit weight of concrete mixtures.

3.2. Hardened density

Pierce and Blackwell (2003) reported a reduction in the mortar mass density by partially replacing natural fine aggregate with crumb rubber (size 0.6 mm) at levels ranging from 32% to 57%, by volume. This reduction increased as the rubber sand content increased. Mohammed et al. (2012) reported that hollow concrete blocks containing rubber (size 0.6 mm) as natural sand replacement produced lightweight blocks compared to the normal weight hollow blocks. Skripkiunas et al. (2007) partially replaced natural sand in concretes with rubber (size 1-0 mm) at levels of 0% and 3.2%, by weight. The hardened density of concrete reduced by 0.85% with the inclusion of rubber sand. Pelisser et al. (2011) found a 13% reduction in the concrete density by partially replacing natural sand with 10% recycled tyre rubber (size < 4.8 mm). Sukontasukkul and Chaikaew (2006) partially replaced natural fine and coarse aggregate with crumb rubber in concrete blocks at levels of 0%, 10% and 20%, by weight. Results showed a reduction in the dry density of the specimens with increasing rubber sand content. Raj et al. (2011) reported a reduction in the hardened density of SCCs by partially replacing natural sand with rubber (maximum size 4.75 mm) at levels of 0%, 5%, 10%, 15% and 20%, by volume. This reduction increased with increasing rubber sand content.

Pedro et al. (2013) reported a reduction in the dry bulk density of mortar specimens by partially replacing natural sand with shredded rubber (size 4.75-0.15 mm) at different levels, by volume. This reduction increased with increasing rubber sand content. The reduction in the 28 days dry bulk density was 4.32%, 7.45% and 9.9% with the inclusion of 5%, 10% and 15% rubber sand, respectively, whilst, it reached 4.83%, 7.8% and 11.11% at the age of 90 days, respectively. Onuaguluchi and Panesar (2014) reported a reduction in the dry unit weight of concretes with the inclusion of crumb rubber (size ^86% smaller than 2.3 mm) as natural fine aggregate replacement, by volume. The reduc-

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Figure 4. Effect of rubber sand content on the dry unit weight of CLSRC and CLSRLC (Wang et al., 2013).

664 tion in the dry unit weight was 1.75%, 2.58% and 7% with

665 the inclusion of 5%, 10% and 15% rubber sand, respec-

666 tively. Corinaldesi et al. (2011) employed styrene butadiene

667 rubber (SBR) or waste rubber-shoe (SR) as a part of fine

668 aggregate in mortars. Natural sand (size 5-0 mm) was par-

669 tially replaced with either SBR (size 12-0 mm) or SR (size

670 8-0 mm) at levels of 0%, 10% and 30%, by volume. The dry

671 unit weight of the mortars decreased with increasing rubber

672 sand content. The reduction in the dry unit weight was

673 3.84% and 16.35% with the inclusion of 10% and 30%

674 SBR sand, respectively, whilst it was 2.86% and 13.54%

675 with the inclusion of 10% and 30% SR sand, respectively.

676 Sukontasukkul (2009) partially replaced natural sand in

677 concretes with two different particle sizes of rubber at levels

678 of 0%, 10%, 20% and 30%, by volume. The sizes of crumb

679 rubber were No. 6 (passing sieve No. 6) and No. 26 (pass-

680 ing sieve No. 26). Results showed a reduction in the hard-

681 ened density of concrete specimens with increasing rubber

682 sand content. The reduction in the hardened density was

683 approximately 14.23%, 16.6% and 19.76% with the inclu-

684 sion of 10%, 20% and 30% rubber sand with large size,

685 respectively, whilst it was approximately 17.39%, 22.13%

686 and 28.06%, respectively, with the inclusion of rubber sand

687 with small size. In another investigation, Sukontasukkul

688 and Tiamlom (2012) partially replaced natural sand in con-

689 cretes with two different particle sizes of rubber at levels of

690 0%, 10%, 20% and 30%, by volume. The sizes of crumb

691 rubber were No. 6 (passing sieve No. 6) and No. 26 (pass-

692 ing sieve No. 26). Results showed a reduction in the hard-

693 ened density of concrete specimens with increasing rubber

694 sand content. The reduction in the hardened density was

695 approximately 3.66%, 9.76% and 12.19% with the inclusion

696 of 10%, 20% and 30% rubber sand with large size, respec-

697 tively, whilst it was approximately 9.76%, 13.42% and

698 16.46%, respectively, with the inclusion of rubber sand with

699 small size. Grdic et al. (2014) reported a reduction in the

700 hardened density of concrete specimens by partially replac-

701 ing natural sand with rubber (size 4-0.5 mm) at levels of

702 10%, 20% and 30%, by volume. The reduction in the hard-

703 ened density increased with increasing rubber sand content.

The reduction in the hardened density was 4.64%, 9.49% 704

and 13.2% with the inclusion of 10%, 20% and 30% rubber 705

sand, respectively. Hilal (2011) reported a reduction in the 706

hardened density of foamed concrete specimens by 707

partially replacing natural sand with crumb rubber (size 708

5-0.7 mm) at levels of 20% and 30%, by weight. The reduc- 709

tion in the 28 days density was 6.4% and 10.4% with the 710

inclusion of 20% and 30% rubber sand, respectively. 711

Fadiel et al. (2014) partially replaced natural sand in 712

mortars with crumb rubber (size 0.6-0 or 2-0.84) at levels 713

of 10%, 20%, 30% and 40%, by weight. Fixed w/c ratio was 714

used. Results showed a reduction in the dry density of 715

mortar specimens with the inclusion of rubber sand. The 716

reduction in the density reached 8%, 20.66%, 28% and 717

39% with the inclusion of 10%, 20%, 30% and 40% rubber 718

sand (size 0.6-0 mm), respectively, whilst the inclusion of 719

rubber sand with size of 2-0.84 mm reduced it by 3.25%, 720

13.94%, 21.21% and 30.1%, respectively. Gisbert et al. 721

(2014) partially replaced natural sand in mortars with 722

two different fineness of crumb rubber at levels of 0%, 723

10%, 20%, 30% and 40%, by weight. 80% of residue was 724

retained in the size of 0.25 mm for fine rubber particles, 725

whilst 80% of residue was retained in the size of 2.0 mm 726

for coarse rubber particles. Results showed a reduction in 727

the density with the inclusion of rubber sand. The reduc- 728

tion in the density was 9.62%, 12.14%, 14% and 17.14% 729

with the inclusion of 10%, 20%, 30% and 40% fine rubber 730

sand, respectively, whilst it was 17.35%, 11.74%, 21.48% 731

and 28.64% with the inclusion of coarse rubber sand, 732

respectively. 733

t Wang et al. (2013) reported a reduction the unit weight 734

of concrete specimens by replacing natural sand with rub- 735

ber (size 4.75 mm) at levels ranging from 0% to 40%, by 736

volume. This reduction increased as the content of rubber 737

sand increased (Fig. 4). Turki et al. (2009) partially 738

replaced natural sand (size 2-0 mm) in concretes with rub- 739

ber made from shredded worn tyres (size 4-1 mm) upto 740

50%, by volume. They reported a reduction in the dry bulk 741

density of concretes with increasing rubber sand content. 742

The reduction in the dry bulk density was 2.76%, 6.4%, 743

13.43%, 16.78% and 22.3% with the inclusion of 10%, 744

20%, 30%, 40% and 50% rubber sand, respectively. 745

Uygunoglu and Topcu (2010) reported a reduction in the 746

dry unit weight of mortars containing scrap tyre rubber 747

(size 4-1 mm) as natural sand replacement (size 4-0 mm) 748

at levels ranging from 10% to 50%, by weight. This reduc- 749

tion increased with increasing rubber sand content. At w/b 750

ratio of 0.4, the reduction in the dry unit weight was 751

approximately 3.9%, 4.44%, 8.81%, 11.35% and 16% with 752

the inclusion of 10%, 20%, 30%, 40% and 50% rubber sand, 753

respectively. Ling, 2011 studied the hardened density of 754

concrete blocks manufactured with different w/c ratios of 755

0.45, 0.5 and 0.55 containing rubber (size 5-1 mm) as nat- 756

ural sand (size 4 mm) replacement at levels ranging from 757

5% to 50%, by volume. Results showed a reduction in the 758

hardened density with increasing rubber sand content at 759

all w/c ratios. At w/c ratio of 0.45, the reduction in the 760

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hardened density was 0.88%, 1.95%, 2.59%, 3.71%, 4.59%, 6.54%, 7.28% and 7.65% with the inclusion of 5%, 10%, 15%, 20%, 25%, 30%, 40% and 50% rubber sand, respectively, whilst it was 1.27%, 2.08%, 1.72%, 3.21%, 3.57%, 5.34%, 5.83% and 8.41%, respectively, at w/c ratio of 0.55. Turki et al. (2009) partially replaced natural sand (size 2-0 mm) in mortars with rubber (size 4-1 mm, maximum grain size was 3.15 mm) at levels of 0%, 10%, 30% and 50%, by volume. Fixed w/c ratio of 0.5 was used. Results showed a reduction in the dry bulk density of mortar specimens with increasing rubber sand content. The reduction in the dry bulk density was 3.64%, 16.3% and 20.85% with the inclusion of 10%, 30% and 50% rubber sand, respectively.

Eiras et al. (2014) reported a reduction in the dry bulk density of mortars by partially replacing natural sand with crumb rubber (size ^0.08-1.3 mm) at levels of 40%, 50% and 60%, by volume. The reduction in the dry bulk density was approximately 18.69%, 25.23% and 27.1% with the inclusion of 40%, 50% and 60% rubber sand, respectively. Turgut and Yesilata (2008) reported a reduction in the unit weight of concrete blocks by partially replacing natural sand with crumb rubber (4.75-0.075 mm) at different levels, by volume. The reduction of the unit weight increased with increasing rubber sand content. The reduction in the unit weight was 2.76%, 6.45%, 10.14%, 15.21%, 20.28%,

26.27% and 29.49% with the inclusion of 10%, 20%, 30%, 40%, 50%, 60% and 70% rubber sand, respectively. El-Gammal et al. (2010) replaced natural sand in concretes with crumb rubber (size ^ 5-0.2 mm) at levels of 0%, 50% and 100%, by weight. Results showed a reduction in the density of concrete specimens with the inclusion of rubber sand. The reduction reached 9.42% and 13.45% with the inclusion of 50% and 100% rubber sand, respectively. Atahan and Yiice (2012) replaced natural fine aggregate and coarse aggregate in concretes with crumb rubber at levels of 0%, 20%, 40%, 60%, 80% and 100%, by volume. The small rubber particles that were used to replace natural sand passed mesh sizes of 10 and 20, whilst large rubber particles that passed through a 13 mm screen were used to replace natural coarse aggregate. The unit weight of the concrete specimens decreased with increasing rubber aggregate content. The reduction in the unit weight was approximately 10.39%, 16.24%, 20.78%, 35.26% and 42.86% with the inclusion of 20%, 40%, 60%, 80% and 100% rubber sand, respectively. Taha et al. (2008) reported a reduction in the hardened density of concretes by replacing natural sand, up to 100%, with rubber (size 5-1 mm). The hardened density decreased with increasing rubber sand content. The reduction in the hardened density was 9.35%, 13.36%, 16.44% and 19.16% with the inclusion of 25%, 50%, 75% and 100% rubber sand, respectively. On

Table 4

Effect of rubber content on the dry unit weight of mortars and concretes.

References Rubber content (%) Size (mm) Type % Reduction

Skripkiunas et al. (2007) 3.2 1-0 Concrete 0.85

Pelisser et al. (2011) 10 <4.8 Concrete 13

Pedro et al. (2013) 5, 10 and 15 4.75-0.15 Mortar 4.32, 7.45 and 9.9

Onuaguluchi and Panesar 5, 10 and 15 ~86% smaller than Concrete 1.75, 2.58 and 7

(2014) 2.3 mm

Corinaldesi et al. (2011) 10 and 30 (SBR) 12-0 Mortar 3.84 and 16.35

Corinaldesi et al. (2011) 10 and 30 (SR) 8-0 Mortar 2.86 and 13.54

Sukontasukkul (2009) 10, 20 and 30 Passing sieve No. 6 Concrete 14.23, 16.6 and 19.76

Sukontasukkul (2009) 10, 20 and 30 Passing sieve No. 26 Concrete 17.39, 22.13 and 28.06

Sukontasukkul and Tiamlom 10, 20 and 30 Passing sieve No. 6 Concrete 3.66, 9.76 and 12.19

(2012)

Sukontasukkul and Tiamlom 10, 20 and 30 Passing sieve No. 26 Concrete 9.76, 13.42 and 16.46

(2012)

Grdic et al. (2014) 10, 20 and 30 4-0.5 Concrete 4.64, 9.49 and 13.2

Hilal (2011) 20 and 30 5-0.7 Concrete 6.4 and 10.4

Fadiel et al. (2014) 10, 20, 30 and 40 0.6-0 Mortar 8, 20.66, 28 and 39

Fadiel et al. (2014) 10, 20, 30 and 40 2-0.84 Mortar 3.25, 13.94, 21.21 and 30.1

Gisbert et al. (2014) 10, 20, 30 and 40 80% returned 0.25 Mortar 9.62, 12.14, 14 and 17.14

Gisbert et al. (2014) 10, 20, 30 and 40 80% returned 2 Mortar 17.35, 11.74, 21.48 and 28.64

Turki et al. (2009) 10, 20, 30, 40 and 50 4-1 Concrete 2.76, 6.4, 13.43, 16.78 and 22.3

Uygunoglu and Topcu (2010) 10, 20, 30, 40 and 50 4-1 Mortar 3.9, 4.44, 8.81, 11.35 and 16 (w/c = 0.4)

Ling (2011) 5, 10, 15, 20, 25, 30, 40 5-1 Concrete 0.88, 1.95, 2.59, 3.71, 4.59, 6.54, 7.28 and 7.65 (w/

and 50 c = 0.45)

Ling (2011) ■5, 10, 15, 20, 25, 30, 40 5-1 Concrete 1.27, 2.08, 1.72, 3.21, 3.57, 5.34, 5.83 and 8.41 (w/

and 50 c = 0.55)

Turki et al. (2009) 10, 30 and 50 4-1 Mortar 3.64, 16.3 and 20.85

Eiras et al. (2014) 40, 50 and 60 ~0.08-1.3 Mortar 18.69, 25.23 and 27.1

Turgut and Yesilata (2008) 10-70 4.75-0.075 Concrete 2.76-29.49

El-Gammal et al. (2010) 50 and 100 ~5-0.2 Concrete 9.42 and 13.45

Taha et al. (2008) 25, 50, 75 and 100 5-1 Concrete 9.35%, 13.36%, 16.44% and 19.16%

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the other hand, Ling (2012) reported an increase in the hardened density of concrete with the inclusion of 10% rubber as natural sand replacement, by volume, whilst the inclusion of 20% and 30% rubber sand decreased it. The hardened density increased by 3.63% with the inclusion of 10% rubber sand, whilst the inclusion of 20% and 30% rubber sand decreased it by 3.34% and 7%, respectively. Table 4 summarises the mentioned studies about the effect of rubber sand on the dry unit weight of mortars and concretes.

From the above review of the literature in Sections 3.1 and 3.2, it can be noted that the inclusion of rubber sand in the mixture decreased the fresh and hardened density. This reduction in the density is related to the physical properties of rubber, since it has lower density than natural sand, hence it occupies greater volume (Albano et al., 2005). This effect is more pronounced for smaller rubber particles, due to the greater porosity of the composite obtained; this means greater quantity of spaces filled with water within the interface rubber-concrete (Albano et al., 2005). Gesoglu and Giineyisi (2007), Turki et al. (2009) and Thomas et al. (2014) related the reduction in the unit weight of the rubberised mixture to the lower specific gravity of rubber. Raj et al. (2011) related the reduction in the hardened density of rubberised concrete to the relatively lower density of rubber compared to natural sand. Taha et al. (2008) attributed the reduction in the fresh and hardened unit weight of rubberised concrete to two factors: first, the ability of rubber particles to entrap air in its jagged surface texture; and second, to the low specific gravity of the rubber particles compared to conventional aggregate. The reduction in the density with the inclusion of rubber sand is one advantage of using this recycled material. This also could be a courage factor to use rubber sand in concrete in some engineering applications such as lightweight concrete.

4. Mechanical strength

4.1. Rubberised mortars

4.1.1. Replacement levels up to 15%

Al-Akhras and Samadi (2004) reported an increase in the compressive and flexural strength at ages of 3, 7, 28 and 90 days by partially replacing natural sand in mortars with rubber ash (size 0.15 mm) at levels of 2.5%, 5%, 7.5% and 10%, by weight. The strength increased with increasing rubber ash content. The enhancement in the 28 day com-pressive strength was 12%, 14%, 23% and 40% with the inclusion of 2.5%, 5%, 7.5% and 10% rubber ash sand, respectively, whilst the enhancement in the 28 days flexural strength was 12%, 27%, 32% and 43%, respectively. On the other hand, Segre et al. (2004) studied flexural strength of mortars containing 10% rubber (size 0.2 mm) as natural sand replacement, by weight. Results showed 25% reduction in the flexural strength with the inclusion of rubber sand. Marques et al. (2008) reported a reduction in the

compressive strength, splitting tensile strength and modulus of elasticity of mortars, at ages of 7, 28, 56 and 90 days, by partially replacing 12% natural sand with rubber (passed in sieve 0.8 mm), by volume. Oikonomou and Mavridou (2009) partially replaced natural sand in mortars with worn automobile tyre rubber (size 1.18-0.75 mm) at levels of 0%, 2.5%, 5%, 7.5%, 10%, 12.5% and 15%, by weight. Fixed w/c ratio was used. Results showed a reduction in the compressive strength and flexural strength with the inclusion of rubber sand. The reduction in the compressive strength was 24.12%, 47.66%, 60.37%, 72.71%, 76.2% and 78.89% with the inclusion of 2.5%, 5%, 7.5%, 10%, 12.5% and 15% rubber sand, respectively, whilst the reduction in the flexural strength was 16.67%, 36.67%, 41.67%, 52.22%, 61.11% and 67.78%, respectively. Pedro et al. (2013) reported a reduction in the compressive strength, flexural strength and modulus of elasticity by partially replacing natural sand in mortars with shredded rubber (size 4.75-0.15) mm at levels of 5%, 10% and 15%, by volume. The reduction in the 28 days compressive strength was 9%, 35.31% and 40.28% with the inclusion of 5%, 10% and 15% rubber sand, respectively. The reduction in the modulus of elasticity at the age of 28 days was 11.79%, 28.23% and 31.744% with the inclusion of 5%, 10% and 15% rubber sand, respectively, whilst it was 20.16%, 32.9% and 43.51% at the age of 90 days, respectively.

4.1.2. Replacement levels upto 35%

Turatsinze et al. (2006) partially replaced natural sand (maximum grain size 4 mm) in mortars with shredded non-reusable tyres (maximum grain size 4 mm) at levels of 0%, 20% and 30%, by volume. Fixed w/c ratio and fixed colloidal admixture were used. The results showed a reduction in the compressive strength, tensile strength and elastic modulus with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. The reduction in the 28 day compressive strength was 57.89% and 78.95% with the inclusion of 20% and 30% rubber sand, respectively, whilst the reduction in the 28 day tensile strength was 40% and 70%, respectively. The reduction in the 28 day compressive elastic modulus was 38.37% and 59.16% with the inclusion of 20% and 30% rubber sand, respectively, whilst the reduction in the tensile elastic modulus was 47.25% and 77.59%, respectively. Aules (2011) partially replaced natural sand (maximum size 4.75 mm) in mortars with crumb rubber (maximum size 4.75 mm) at levels ranging from 0% to 30% with an increment of 5%, by volume. Fixed w/c ratio was used. Results showed a reduction in the modulus of elasticity, compressive strength and flexural strength with increasing rubber sand content. The reduction in the compressive strength was approximately 23.81%, 46.02%, 53.97%, 58.73%, 59.52% and 57.93% with the inclusion of 3%, 10%, 15%, 20%, 25% and 30% rubber sand, respectively, whilst the reduction in the flexural strength was approximately 1.3%, 3.91%, 13.17%, 20.5%, 28.94% and 39.48%, respectively.

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Turatsinze et al. (2007) partially replaced natural sand (maximum size 4 mm) in mortars with rubber (maximum size 4 mm), obtained from shredded non-reusable, at levels of 0%, 20% and 30%, by volume. Fixed w/b ratio, fixed dosage of plasticiser and fixed dosage of stabiliser were used. Results showed a large reduction in the compressive strength, tensile strength and modulus of elasticity with the inclusion of rubber sand. The reduction in the compressive strength was 57.89% and 78.95% with the inclusion of 20% and 30% rubber, respectively, whilst the reduction in the tensile strength was 40% and 66.67%, respectively. The reduction in the compressive elasticity modulus (static elastic modulus) was 38.37% and 59.16% with the inclusion of 20% and 30% rubber, respectively. Similar results were also obtained by Turatsinze et al. (2005).

Correia et al. (2010) reported a reduction in the com-pressive strength of mortars by replacing part of natural sand (particle size below 2.4 mm) with waste vulcanised rubber scrap particles (size below 1.2 mm) at levels of 10%, 20% and 30%, by weight. At w/c ratio of 0.55, the reduction in the 28 day compressive strength was 34.03%, 48.62% and 48.16% with the inclusion of 10%, 20% and 30%, respectively. Corinaldesi et al. (2011) reported a reduction in the 28 day compressive strength and flexural strength of mortars containing (SBR) or (SR) as natural sand replacement. Natural sand (size 5-0 mm) was partially replaced with either SBR (size 12-0 mm) or SR (size 8-0 mm) at levels of 0%, 10% and 30%, by volume. The reduction in the 28 day compressive strength was approximately 30.12% and 56.63% with the inclusion of 10% and 30% SBR sand, respectively, whilst it was approximately 21.92% and 42.87% with the inclusion of 10% and 30% SR sand, respectively. Nguyen et al. (2010) partially replaced sand in mortars with rubber at levels of 0%, 20% and 30%, by volume. They found a reduction in the 28 day compressive strength, tensile strength and Young's modulus with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. The reduction in the compressive strength was 46.48% and 59% with the inclusion of 20% and 30% rubber sand, respectively, whilst the reduction in the tensile strength was 19.63% and 34.35%, respectively. The reduction in the Young's modulus was 36.51% and 47.3% with the inclusion of 20% and 30% rubber sand, respectively. Sallam et al. (2008) reported a reduction in the compressive strength and splitting tensile strength of concretes by replacing natural sand with crumb rubber (size 5-0.16) at different levels, by volume. The reduction in the 28 day compressive strength was 6.25%, 16.03% and 20.91% with the inclusion of 10%, 20%, 30% rubber sand, respectively, whilst the reduction in the 28 day splitting tensile strength was 14.13%, 28.26% and 41.1%, respectively.

Jingfu and Yongqi (2008) studied flexural strength, at ages of 3, 7 and 28 days, of mortars containing rubber (average size 1.5 mm) as partially natural sand replacement at levels of 0%, 8%, 16%, 21% and 31.2%, by volume. Fixed w/c ratio was used. Results showed a reduction in the flex-

ural strength with the inclusion of rubber sand. The reduction in the 28 day flexural strength was 14.81%, 25.92%, 40.74% and 59.26% with the inclusion of 8%, 16%, 21% and 31.2% rubber sand, respectively. Abdulla and Ahmed (2011) partially replaced natural sand in mortars with crumb rubber (size 2.36-2 mm) at levels ranging from 0% to 30%, by volume. Fixed w/c ratio of 0.4 was used. Results showed a reduction in the compressive strength, modulus of rupture, static modulus of elasticity and dynamic modulus of elasticity with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. In another investigation, Abdulla et al. (2010) partially replaced sand in mortars with crumb rubber (size 22.36 mm) at levels ranging from 0% to 35%, by volume. Fixed w/c ratio of 0.3 and fixed dosage of SP were used. They reported that the compressive strength, flexural strength and modulus of elasticity decreased with increasing rubber sand content.

4.1.3. Replacement levels up to 60%

Huang et al. (2013) studied the compressive strength, tensile strength and elastic modulus of ECC containing rubber (size 0.15-0 mm) as partially replacement of iron ore tailings (average size 0.135 mm) that were used as aggregate at levels of 0%, 10%, 20%, 30% and 40%, by volume. Results showed a reduction in the compressive strength, tensile strength and elastic modulus in the inclusion of rubber sand. This reduction increased with increasing rubber sand content. The reduction in the compressive strength was 63% and 74.14% with the inclusion of 10% and 40% rubber sand. The reduction in the tensile strength was 28.57%, 30.61%, 34.69% and 36.73% with the inclusion of 10%, 20%, 30% and 40% rubber, respectively. Gisbert et al. (2014) reported a reduction in the compressive strength, bending strength, tension strength and Young's modulus of mortars by partially replacing natural sand with crumb rubber at different levels. The reduction in the compressive strength was 63.75%, 71.2%, 77.74% and 90.22% with the inclusion of 10%, 20%, 30% and 40% coarse rubber sand (80% of residue is retained in the size of 2.0 mm), respectively, whilst it was 73.77%, 93.37%, 93.75% and 96.82% with the inclusion of fine rubber sand (80% of residue is retained in the size of 0.25 mm). The reduction in the Young's modulus was 35.27%, 51.51%, 65.97%, 77.33% and 91% with the inclusion of 10%, 15%, 20%, 30% and 40% coarse crumb rubber sand, respectively, whilst it was 55.28%, 71.35%, 92.19%, 96.16% and 97.77%, respectively, with the inclusion of fine rubber sand.

Uygunoglu and Topcu (2010) reported that partially replacement of natural sand (size 4-0 mm) in self-consolidating mortars with rubber (size 4-1 mm) at levels ranging from 10% to 50%, by weight, decreased the com-pressive strength, flexural strength and dynamic modulus of elasticity. This reduction increased with increasing rubber sand content. At w/b ratio of 0.4, the reduction in the 28 day compressive strength was approximately 8.36%, 32.72%, 41.41%, 44.9% and 48.38% with the inclu-

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sion of 10%, 20%, 30%, 40% and 50% rubber sand, respectively. The reduction in the dynamic modulus of elasticity was 47.4% with the inclusion of 50% rubber sand. Topcu and Saridemir (2008) employed two different sizes of rubber (1-0 mm and 4-1 mm) as a part of natural fine aggregate in mortars. Natural sand was partially replaced with rubber at levels of 0%, 10%, 15%, 20%, 30%, 45% and 50%, by volume. They reported a reduction in the compres-sive strength and flexural strength with the inclusion of rubber sand. This reduction increased as the rubber sand content increased. The reduction in the compressive strength and flexural strength of rubberised mortars was greater in the coarse rubber mortars. Turki et al. (2009) partially replaced natural sand (size 2-0 mm) with rubber made from shredded worn tyres (size 4-1 mm) at levels of 0%, 10%, 20%, 30%, 40% and 50%, by volume. Various w/c ratios were used. Results showed a reduction in the compressive strength and flexural strength with the inclusion of rubber sand. The reduction in the compressive strength was 20.82%, 24.36%, 42.74%, 65.1% and 79.18% with the inclusion of 10%, 20%, 30%, 40% and 50% rubber sand, respectively, whilst the reduction in the flexural strength was 38.39%, 38.39%, 53.22%, 65.48%, and 63.87%, respectively. Turki et al. (2009) reported a reduction in the static and dynamic elastic Young's modulus values of mortars containing rubber (size 4-1 m, maximum grain size was 3.15 mm) as natural sand (size 2-0 mm) replacement at levels of 10%, 30% and 50%, by volume. The reduction in the static Young's modulus was 60%, 80% and 90.67% with the inclusion of 10%, 20% and 50% rubber sand, respectively, whilst the reduction in the dynamic Young's modulus was 13.21%, 56.49% and 67.44%, respectively. Pierce and Blackwell (2003) partially replaced natural fine aggregate in mortars with crumb rubber (size 0.6 mm) at levels ranging from 32% to 57%, by volume. They reported a reduction in the compressive strength with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. Pelisser et al. (2012) reported a reduction in the compressive strength by replacing natural sand in mortars with recycled tyre rubber (maximum size 2.4 mm) at levels of 0%, 20%, 40% and 60%, by volume. The reduction in the compressive strength increased with increasing rubber sand content (Fig. 5). Eiras et al. (2014) reported a reduction in the com-pressive strength and flexural strength of mortars by partially replacing natural sand with 40%, 50% and 60% crumb rubber (size ^0.08-1.3 mm), by volume. The reduction in the compressive strength was 77.85%, 79.72% and 88.87% with the inclusion of 40%, 50% and 60% rubber sand, respectively, whilst the reduction in the flexural strength was 76.97%, 79.56% and 88.86%, respectively.

4.2. Rubberised concretes

4.2.1. Replacement levels upto 15%

Skripkiunas et al. (2007) reported a reduction in the concrete compressive strength, static modulus of elasticity and

40 _ 36

£ 24 tt « 20 'Ci

E 12 o

0 20 40 60

Rubber content(%)

Figure 5. Effect of rubber content on the compressive strength of mortars (Pelisser et al., 2012).

dynamic modulus of elasticity by 1.46%, 10.82% and 2.47% with the inclusion of 3.2% rubber (size 1-0 mm) as natural sand replacement, by weight, respectively. Holmes et al. (2014) reported a reduction in the compressive strength and Young's modulus of concretes by partially replacing natural sand with crumb rubber (size 4.75-0.425 mm) at a level of 7.5%. On the other hand, the flexural strength increased with the inclusion of rubber sand. They related this enhancement in the flexural strength to the ductile failure of rubber specimens compared to brittle failure of the control. Pelisser et al. (2011) reported 67% and 49% reduction in the 28 day compressive strength and elastic modulus, respectively, of concrete containing 10% recycled tyre rubber (size < 4.8 mm) as natural sand replacement. Chunlin et al. (2011) reported 5.73% and 29.47% reduction in the 28 days compressive and flexural strength, respectively, by partially replacing natural sand in concretes with 10% crumb rubber (size 5-1 mm), by volume. Albano et al. (2005) reported a reduction in the compressive strength and flexural strength by partially replacing natural sand in concretes with recycled rubber from automobile tyre at levels of 5% and 10%, by weight. The reduction in the compressive strength was 61.54% and 88.5% with the inclusion of 5% and 10% rubber sand with a particle size of 0.59 mm, respectively, whilst it was 70.97% and 97.43%, respectively, with a particle size of 0.29 mm. Lijuan et al. (2014) partially replaced natural sand in concretes with rubber at levels of 0%, 2%, 4%, 6%, 8% and 10%, by cement mass. They used different rubber sizes (4, 2, 0.864, 0.535, 0.381, 0.221 and 0.173 mm). They concluded that the inclusion of rubber weakened the axial compressive strength. The axial com-pressive strength and elastic modulus of the concrete specimens decreased with increasing rubber content and decreasing rubber particle size. Azevedo et al. (2012) partially replaced natural sand in HPCs with tyre rubber waste (dimensions between 2.4 and 1 mm) at levels of 0%, 5%, 10% and 15%, by weight. The compressive strength results at ages of 7 and 28 days decreased with increasing rubber sand content. The reduction in the 28 day compressive

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strength was approximately 31.53%, 54.36% and 64.63% with the inclusion of 5%, 10% and 15% rubber sand, respectively. Ganesan et al. (2012) reported 15.3%, 14.24% and 22.4% in the 28 day compressive strength of concretes by partially replacement of natural sand with 15% rubber (size < 4.75 mm) when cement content was 277, 339 and 441 kg/m3, respectively.

Bravo and de Brito (2012) partially replaced natural sand in concretes with rubber aggregate made from used tyres (with the same size of the natural sand) at levels of 0%, 5%, 10% and 15%, by volume. Various w/c ratios were used. The results showed a reduction in the 28 day com-pressive strength with the inclusion of rubber sand. The compressive strength decreased with increasing rubber sand content. Ghaly and Cahill (2005) partially replaced natural sand in concretes with crumb rubber (size 21 mm) at levels of 0%, 5%, 10% and 15%, by volume. Various w/c ratios of 0.47, 0.54 and 0.61 were used. They reported a reduction in the compressive strength with the inclusion of rubber sand. Najim and Hall (2012) reported a reduction in the compressive strength, flexural strength, splitting tensile strength, Young's modulus of elasticity and dynamic modulus of elasticity with the inclusion of crumb rubber (size 6-2 mm) in SCCs as natural sand replacement, by weight. The reduction in the compressive strength was 41.75, 52.35% and 67.65% with the inclusion of 5%, 10% and 15% rubber sand, respectively. Onuaguluchi and Panesar (2014) partially replaced natural fine aggregate in concretes with crumb rubber (size ^86% smaller 2.3 mm) at levels of 0%, 5%, 10% and 15%, by volume. Fixed w/c ratio and fixed dosage of HRWR were used. Results showed a reduction in the compressive strength, splitting tensile strength and elastic modulus with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. The reduction in the com-pressive strength was 6.93%, 13.86% and 39.85% with the inclusion of 5%, 10% and 15% rubber sand, respectively, whilst the reduction in the splitting tensile strength was 5.71%, 11.43% and 34.28%, respectively. The reduction in the elastic modulus was 14.51%, 20.21% and 29.27% with the inclusion of 5%, 10% and 15% rubber sand, respectively. Bowland et al. (2012) reported a reduction in the compressive strength of concrete by partially replacing natural sand with ground rubber (maximum size 0.25 mm) at levels of 5%, 10% and 15%, by volume. This reduction increased with increasing rubber sand content.

4.2.2. Replacement levels up to 25%

Guo et al. (2014) reported a reduction in the compressive strength and Young's modulus of concrete mixtures, containing crushed recycled concrete as coarse aggregate, by partially replacing natural sand with crumb rubber (size 1.4-0.85 mm) at levels of 4%, 8%, 14% and 16%, by volume. The reduction in the compressive strength was 4.57%, 23.34%, 26.84% and 30.21% with the inclusion of 4%, 8%, 14% and 16% rubber sand, respectively. Jingfu et al. (2009) partially replaced natural sand in concretes

with rubber (size 1.5 mm) at levels of 50, 80, 100 and 120 Kg/m3. The tyre rubber particles were incorporated by replacing the same volume of natural sand. Various w/c ratios and various dosages of plasticiser were used. The results showed a reduction in the compressive strength, tensile elastic modulus and compressive elastic modulus with the inclusion of rubber sand. The reduction in the 28 day compressive strength was 4.37%, 1.46% and 14.56% with the inclusion of 50, 80, 100 and 120 kg/m3 rubber sand, respectively. On the other hand, the inclusion of rubber sand increased the 28 day flexural strength by 0.25%, 11.31% and 22.36%, respectively. Yi and Fan (2009) reported 8.5% reduction in the ultimate flexural strength by partially replacing natural sand in concretes with 60 kg/m3 rubber. Parveen et al. (2013) reported a reduction in the compressive strength, flexural strength and splitting tensile strength of concretes by partially replacing natural sand with crumb rubber (size 4.75-0.075 mm) at different levels, by volume. This reduction increased with increasing rubber sand content. The reduction in the compressive strength was 11.05%, 23.48%, 31.49% and 37.29% with the inclusion of 5%, 10%, 15% and 20% rubber sand, respectively. Gesoglu et al. (2014) partially replaced natural aggregate in concretes with crumb rubber (size either 4 mm or 2 mm) at levels of 0%, 10% and 20%, by total aggregate volume. The results showed a reduction in the compressive strength, splitting tensile strength and modulus of elasticity with the inclusion of rubber aggregate. This reduction increased with increasing rubber aggregate content. The reduction in the compressive strength was 18.94% and 44.1%, respectively, with the inclusion of rubber aggregate (size 4 mm), whilst it was 7.85% and 38.57% with the inclusion of rubber aggregate (size 2 mm). Mohammadi et al. (2014) partially replaced natural sand in concretes with crumb rubber at levels of 0% and 20%, by volume, when w/c ratio was 0.45. There were two cases for the crumb rubber either as received without treatment or after treatment in water-soaking. Results showed a reduction in the com-pressive strength and flexural strength with the inclusion of rubber sand at ages of 7, 28 and 56 days. The treated rubberised concrete showed higher strength than the corresponding untreated one. The reduction of the 28 day com-pressive strength with the inclusion of untreated rubber sand was 51.44%, whilst it was 44.6% for treated rubber sand. Youssf et al. (2014) reported an increase in the com-pressive strength, tensile strength and modulus of elasticity by partially replacing sand in concretes with 5% and 10% crumb rubber (size 2.36 and 1.18 mm), by volume, whilst the inclusion of 20% rubber sand decreased them. On the other hand, the inclusion of 5%, 10% and 20% rubber (size 2.36-0.15 mm) decreased the compressive strength and the modulus of elasticity. The reduction in the 28 day compressive strength was 18%, 20% and 37% with the inclusion of 5%, 10% and 20% rubber sand. Raj et al. (2011) reported a reduction in the compressive strength, splitting tensile strength and modulus of elasticity by partially replacing natural sand, upto 20% by volume, in SCCs with rubber

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16 A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

1243 (maximum size 4.75 mm). This reduction increased as the

1244 rubber sand content increased. Balaha et al. (2007) studied

1245 the possibility of the usage of ground waste tyre rubber

1246 (size < 4 mm) as natural sand replacement in concretes

1247 containing different cement contents. Natural sand was

1248 partially replaced with rubber at levels of 0%, 5%, 10%,

1249 1 5% and 20%, by volume. Results showed a reduction in

1250 the compressive strength with the inclusion of rubber sand.

1251 At cement content of 400 kg/m3, the reduction in the com-

1252 pressive strength was approximately 6.95%, 12.58%,

1253 1 8.57% and 28.48% with the inclusion of 5%, 10%, 15%

1254 and 20% rubber sand, respectively. Sukontasukkul and

1255 Chaikaew (2006) partially replaced natural fine and coarse

1256 aggregates with crumb rubber in concrete blocks at levels

1257 of 0%, 10% and 20%, by weight. Results showed a reduc-

1258 tion in the compressive strength and flexural strength with

1259 the inclusion of rubber aggregate. This reduction increased

1260 as the rubber aggregate content increased. Antil et al.

1261 (2014) reported 11.1%, 23.54%, 31.85% and 37.39% reduc-

1262 tion in the 28 day compressive strength of concretes by par-

1263 tially replacing natural sand with crumb rubber (size 4.751264 0.075 mm) at levels of 5%, 10%, 15% and 20%, by volume,

1265 respectively. Yung et al. (2013) partially replaced natural

1266 sand in SCCs with waste tyre rubber at levels of 0%, 5%,

1267 1 0%, 15% and 20%, by volume. Two different particle sizes

1268 of 0.6 mm and 0.3 mm of the rubber were used. Fixed w/c

1269 ratio and fixed dosage of binding agent were used. Results

1270 showed a reduction in the 1, 7, 28, 56 and 91 day compres-

1271 sive strength with the inclusion of rubber sand. The reduc-

1272 tion in the 28 day compressive strength was 9.67%, 22.39%,

1273 16.12% and 28.9% with the inclusion of 5%, 10%, 15% and

1274 20% rubber sand with a particle size of 0.6 mm, respec-

1275 tively, whilst it was 3.52%, 26.63%, 27.03% and 31.71%

1276 with the inclusion of rubber sand with a particle size of

1277 0.3 mm, respectively.

1278 Ganesan et al. (2013) studied the compressive strength,

1279 static flexural strength and fatigue flexural strength of rub-

1280 berised SCCs. Natural sand was partially replaced with

1281 rubber (maximum size 4.75 mm) at levels of 15% and

1282 20%, by volume. In fatigue testing, the maximum stress

1283 level applied to specimens ranging from 90% to 60% of

1284 the static flexural strength. The tests were terminated when

1285 the failure of specimens occurred or the number of cycles

1286 exceeded 2 million. Results showed a reduction in the com-

1287 pressive strength at ages of 7 and 28 days with the inclusion

1288 of rubber sand. The reduction in the 28 day compressive

1289 strength was 6.85% and 13.35% with the inclusion of 15%

1290 and 20% rubber sand, respectively. On the other hand,

1291 the static flexural strength increased with the inclusion of

1292 rubber sand. The increment in the static flexural strength

1293 was 14.69% and 9.73% with the inclusion of 15% and

1294 20% rubber sand, respectively. This may be due to the bet-

1295 ter tensile load carrying capacity of rubber particles. The

1296 fatigue flexural increased with increasing rubber sand con-

1297 tent. The increment in the fatigue flexural was 12.87% and

1298 1 5.84% with the inclusion of 15% and 20% rubber sand,

1299 respectively. They also reported that the static flexural

and fatigue flexural can be modified by adding 0.5% and 1300

0.75% steel fibres, by volume. Raj et al. (2011) reported 1301

that the average reduction in the compressive strength of 1302

SCCs containing rubber (maximum size 4.75 mm) as natu- 1303

ral sand replacement at levels of 5%, 10%, 15% and 20%, 1304

by volume, was 8%, 16%, 23% and 40%, respectively. The 1305

same trend was observed for splitting tensile strength, flex- 1306

ural strength and modulus of elasticity. 1307

Al-Tayeb et al. (2013) reported a reduction in the com- 1308

pressive strength, splitting tensile strength and elastic mod- 1309

ulus of concretes containing crumb rubber (size 1 mm) as 1310

natural sand replacement at levels of 5%, 10% and 20%, 1311

by volume. The reduction in the compressive strength 1312

was 5.35%, 14.48% and 20.21% with the inclusion of 5%, 1313

10% and 20% rubber sand, respectively, whilst the reduc- 1314

tion in the splitting tensile strength was 11%, 13.69% and 1315

16.67%, respectively. The reduction in the elastic modulus 1316

was 8.32%, 15.1% and 22.2% with the inclusion of 5%, 1317

10% and 20% rubber sand, respectively. Thomas et al. 1318

(2014) reported a reduction in the compressive strength 1319

and flexural strength of concretes containing discarded tyre 1320

rubber (40% powder from mesh 30, 35% size 0.8-2 mm and 1321

25% size 2-4 mm) as natural sand replacement up to 20%. 1322

The strength decreased with increasing rubber sand con- 1323

tent. The reduction in the 28 day compressive strength, at 1324

w/c ratio of 0.4, was 3.53%, 11.76%, 12.94%, 21.17%, 1325

29.41%, 41.18%, 94.52% and 52.94%, with the inclusion 1326

of 2.5%, 5%, 7.5%, 10%, 12.5%, 15%, 17.5% and 20% rub- 1327

ber sand, respectively, whilst the reduction in the 28 day 1328

flexural strength was 2.26%, 5.83%, 9.77%, 14.28%, 1329

15.79%, 24.1% and 24.81%, respectively. Guneyisi (20 1 0) 1330

reported a reduction in the compressive strength of SCCs 1331

containing crumb rubber (similar to the natural sand gra- 1332

dation) as natural sand replacement at levels of 5%, 15% 1333

and 25%, by volume. The compressive strength decreased 1334

as the rubber sand content increased. Ozbay et al. (2011) 1335

reported a reduction in the compressive strength of con- 1336

crete by partially replacing natural sand with crumb rubber 1337

(grain size 3-0 mm) at levels of 5%, 15% and 25%, by vol- 1338

ume. The compressive strength decreased with increasing 1339

rubber sand content. The reduction in the compressive 1340

strength was approximately 4.47%, 10% and 25.98% with 1341

the inclusion of 5%, 15% and 25% rubber sand, respec- 1342

tively. Gesoglu and Guneyisi (2011) partially replaced nat- 1343

ural fine aggregate in SCCs with crumb rubber 1344

(size <4 mm) at levels of 0%, 5%, 15% and 25%, by vol- 1345

ume. They reported a reduction in the compressive strength 1346

with the inclusion of rubber sand. This reduction increased 1347

with increasing rubber sand content. Gesoglu and Guneyisi 1348

(2007) reported a reduction in the compressive strength of 1349

concretes containing crumb rubber (grading close to the 1350

natural fine aggregate) and tyre chips as fine and coarse 1351

aggregate replacement, respectively, at levels of 5%, 15% 1352

and 25%, by total aggregate volume. This reduction 1353

increased as the rubber aggregate content increased. They 1354

also reported that the compressive strength can be modified 1355

by replacing 10% of cement with silica fume (SF). 1356

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4.2.3. Replacement levels up to 33.3%

Rahman et al. (2012) reported a reduction in the com-pressive strength, dynamic modulus and dynamic shear modulus by partially replacing natural sand in SCCs with rubber (size 4-1 mm) at levels of 0% and 28%, by volume. Grinys et al. (2012) partially replaced natural sand in concretes with crumb rubber (size 2-1 mm) at levels of 0%, 5%, 10%, 20% and 30%, by total aggregate volume. Fixed w/c ratio and fixed dosage of SP were used. Results showed a reduction in the compressive strength and flexural strength with the inclusion of crumb rubber sand. The reduction in the compressive strength was 25%, 37.5%, 65.62% and 82.81% with the inclusion of 5%, 10%, 20% and 30% rubber sand, respectively, whilst the reduction in the flexural strength was 21.42%, 28.35%, 44.53% and 59.63%, respectively. The splitting tensile strength increased by 0.86% and 7.47% with the inclusion of 5% and 10% rubber sand, respectively, whilst it decreased by 11.49% and 49.13% with the inclusion of 20% and 30% rubber sand, respectively. Azmi et al. (2008) reported a reduction in the compressive strength, flexural strength, splitting tensile strength and modulus of elasticity by partially replacing natural sand in concretes with crumb rubber (size 2.35-2 mm) at different levels, by volume. The reduction in the 28 day compres-sive strength was 8.02%, 13.85%, 27.86% and 50.49% with the inclusion of 10%, 15%, 20% and 30% rubber sand, respectively. The reduction in the 28 day modulus of elasticity was 32.4%, 41.19% and 45.93% with the inclusion of 10%, 15%, 20% and 30% rubber sand, respectively. Grdic et al. (2014) partially replaced natural sand in concretes with crumb rubber (size 4-0.5 mm) at levels of 0%, 10%, 20% and 30%, by volume. Results showed a reduction in the compressive strength, flexural strength and bond strength with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. The reduction in the 28 day compressive strength was 36%59.9% and 70.5% with the inclusion of 10%, 20% and 30% rubber sand, respectively, whilst the reduction in the 28 day flexu-ral strength was 20.1%, 34.41% and 55.2%, respectively. The reduction in the 28 day bond strength was 14.6%, 30.4% and 51% with the inclusion of 10%, 20% and 30% rubber sand, respectively. Mohammadi et al. (2014) partially replaced natural sand in concretes with crumb rubber at levels of 0% and 30%, by volume, when w/c ratio was 0.4. There were two cases for the crumb rubber either as received without treatment or after treatment in water-soaking. Results showed a reduction in the compressive strength and flexural strength with the inclusion of rubber sand at ages of 7, 28 and 56 days. The treated rubberised concrete showed higher strength than the corresponding untreated one. The reduction the 28 day compressive strength with the inclusion of untreated rubber sand was 56.51%, whilst it was 50.95% for treated rubber sand. Hilal (2011) partially replaced natural sand in foamed concretes with crumb rubber (size 5-0.7 mm) at levels of 0%, 20% and 30%, by weight. Results showed a reduction in the compressive strength, splitting tensile strength and flex-

ural strength at ages of 7, 21 and 28 days with the inclusion of rubber sand. The reduction in the 28 day compressive strength was 20.86% and 37.77% with the inclusion of 20% and 30% rubber sand, respectively, whilst the reduction in the splitting tensile strength was 21.93% and 46.45%, respectively. The reduction in the flexural strength was 34.79% and 47.95% with the inclusion of 20% and 30% rubber sand, respectively. Ling (2012) partially replaced natural sand (maximum particle size < 4.75 mm) in concrete paving blocks manufactured with compaction method with crumb rubber (size 3-1 mm and 5-1 mm) at levels of 0%, 10%, 20% and 30%, by volume. Various w/c ratios and fixed dosage of SP were used. Results showed an increase in the compressive strength and modulus of rupture (bending strength "flexural strength") at replacement level of ~10%>. On the other hand, a reduction in the com-pressive strength and bending strength was obtained at replacement levels of 20% and 30%. The enhancement in the compressive strength and bending strength with the inclusion of 10% rubber sand was 36.65% and 14.16%, respectively. The reduction in the compressive strength was 49.84% and 62.38% with the inclusion of 20% and 30% rubber sand, respectively, whilst the reduction in the bending strength was 28.1% and 44.66%, respectively. Karahan et al. (2012) reported a reduction in the compres-sive strength, flexural strength, splitting strength and bond strength of SCCs by partially replacing natural sand with crumb rubber (size 4.75-0.15 mm) at levels of 10%, 20% and 30%, by volume. The reduction in the compressive strength was 21.24%, 30.97% and 53.32% with the inclusion of 5%, 10% and 20% rubber sand, respectively, whilst the reduction in the flexural strength was 8.47%, 18.64% and 35.59%, respectively. The reduction in the splitting strength was 5.71%, 11.43% and 22.86% with the inclusion of 5%, 10% and 20% rubber sand, respectively, whilst the reduction in the bond strength was 22.39%, 26.86% and 28.36%, respectively.

Sukontasukkul and Tiamlom (2012) reported a reduction in the compressive strength and elastic modulus of concretes by partially replacing natural sand with rubber at levels of 10%, 20% and 30%, by volume, (Fig. 6). There were two particle sizes of rubber namely large size (passing sieve 6) and small rubber size (passing sieve 26). Specimens containing large rubber size showed higher compressive strength and modulus of elasticity than those containing small rubber size. The reduction in the compressive strength was approximately 42.48%, 65.1% and 78.77% with the inclusion of 10%, 20% and 30% large size rubber sand, respectively, whilst the reduction in the elastic modulus was approximately 17.95%, 33.33% and 53.85%, respectively. Bignozzi and Sandrolini (2006) reported a reduction in the compressive strength and dynamic elastic modulus of SCCs by partially replacing natural sand with 22.2% and 33.3% rubber (size 55% 2-0.5 mm and 45% 0.7-0.5 mm), by volume. The reduction in the 28 day com-pressive strength was 25.15% and 38.79% with the inclusion of 22.2% and 33.3% rubber sand, respectively, whilst the

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IT 45 &40

t* w>30

■ Compressive strength (MPa) □ Elastic modulus (MPa)

n 1 1 n

n -1 □ 1 l-l

1 1 1 1 1

35000 30000

25000 g,

20000 % 5

15000 I

10000 c

5000 g

0000000000

Q_*-CMCO*-CMCOT-CMCO

KKKKttCtQicrCE

OOOOOOOUO (OCDCDCDCDCDCDCDCD CM CM Cvj CM CM CM

Concrete type 10 ® ®

Figure 6. Effect of rubber sand content on compressive strength and elastic modulus of concretes (Sukontasukkul and Tiamlom, 2012).

reduction in the dynamic elastic modulus was 19.39% and 27.57%, respectively.

4.2.4. Replacement levels upto 50%

Valadares et al. (2012) partially replaced natural sand in concretes with shredded rubber (size 4 mm) at levels of 0%, 12.5%, 24.15% and 35.77%, by volume. Various w/c ratios were used. Results showed a reduction in the compressive strength, splitting tensile strength and modulus of elasticity with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. The reduction in the 28 day compressive strength was 19.82%, 35.15% and 51.89% with the inclusion of 12.5%, 24.15% and 35.77% rubber sand, respectively, whilst the reduction in the 28 day splitting tensile strength was 23.53%, 38.23% and 44.12%, respectively. The reduction in the 28 day modulus of elasticity was 15.76%, 28.57% and 38.18% with the inclusion of 12.5%, 24.15% and 35.77% rubber sand, respectively. Wang et al. (2013) partially replaced natural sand in CLSRC and CLSRLC with rubber (size 4.75 mm) at levels ranging from 0% to 40%, by volume. Results showed a reduction in the compressive strength with the inclusion of rubber sand. This reduction increased with increasing rubber sand content. For CLSRC, the reduction in the compressive strength was approximately 9.51%, 36.94%, 38.03% and 48.92% with the inclusion of 10%, 20%, 30% and 40% rubber sand, respectively, whilst it was 22.18%, 42.45%%, 50.51% and 63.31%, respectively, for CLSRLC. Mohammadi et al. (2014) reported a positive effect of 30% and 40% crumb rubber (treated in water-soaking) as natural sand replacement, by volume, in concretes on fatigue behaviour, whilst 10% and 20% crumb rubber sand showed a negative effect (Fig. 7). Topcu (1995) studied the performance of concrete with rubber (size 1-0 mm and 4-1 mm) aggregate made from used tyres. The proportions of the rubber were between 0% and 45%, by volume. The author observed that the compressive strength at ages of 7 and 28 days did not significantly change below 15% replacement ratio, whilst the mechanical strength worsened for a larger rubber ratio. Mohammed et al. (2012) reported

Figure 7. Cycles number before failure versus rubber content (Mohammadi et al., 2014).

a reduction in compressive strength and splitting tensile 1510

strength of hollow concrete blocks by partially replacing 1511

natural sand with rubber (size 0.6 mm) at levels of 10%, 1512

25% and 50%, by volume. This reduction increased with 1513

increasing rubber sand content. 1514

Ling (2012) reported a reduction in the compressive 1515

strength of concrete blocks at ages of 7 and 28 days by 1516

replacing natural sand (size 4 mm) with rubber (size 5- 1517

1 mm) at levels ranging from 5% to 50%, by volume. Dif- 1518

ferent w/b ratios of 0.45, 0.5 and 0.55 were used. This 1519

reduction increased with increasing rubber sand content. 1520

The reduction in the 28 day compressive strength at w/c 1521

ratio of 0.45 was 2.27%, 18.83%, 24.35%, 33.77%, 1522

35.39%, 48.7%, 65.91% and 69.165% with the inclusion of 1523

5%, 10%, 15%, 20%, 25%, 30%, 40% and 50% rubber sand, 1524

respectively. Guneyisi et al. (2004) reported a reduction in 1525

the 90 day compressive strength, splitting tensile strength 1526

and modulus of elasticity of concretes containing crumb 1527

rubber (maximum particle size 4 mm) as natural fine aggre- 1528

gate replacement and tyre chips (size 40-10 mm) as natural 1529

coarse aggregate replacement at levels ranging from 2.5% 1530

to 50%, by total aggregate volume. At w/c ratio of 0.6, 1531

the reduction in the compressive strength was 12.64%, 1532

22.86%, 40.89%, 54.83%, 69.89% and 86.8% with the inclu- 1533

sion of 2.5%, 5%, 10%, 15%, 25% and 50% rubber aggre- 1534

gate, respectively, whilst the reduction in the splitting 1535

tensile strength was 9.68%, 12.9%, 19.35%, 32.26%, 1536

48.39% and 77.42%, respectively. The reduction in the 1537

modulus of elasticity was 1.71%, 12.39%, 16.92%, 1538

36.29%, 61.32% and 81.57% with the inclusion of 2.5%, 1539

5%, 10%, 15%, 25% and 50% rubber aggregate, respec- 1540

tively. They also reported that the values of compressive 1541

strength, splitting tensile strength and modulus of elasticity 1542

can be improved by replacing part of cement with SF 1543

(Fig. 8). 1544

4.2.5. Replacement levels upto 100% 1545

Turgut and Yesilata (2008) reported a reduction in the 1546

compressive strength, flexural strength and splitting 1547

strength of concrete blocks by replacing natural sand with 1548

crumb rubber (size 4.75-0.075 mm) at different levels, by 1549

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Figure 8. Effect of rubber aggregate content on the compressive strength of concretes.

volume. The reduction in the compressive strength was 12.54%, 33.1%, 57.49%, 69.34%, 81.18% and 84.67% with the inclusion of 10%, 20%, 30%, 40%, 50%, 60% and 70% rubber sand, respectively, whilst the reduction in the splitting strength was 15.17%, 34.48%, 42.41%, 53.1%, 70%, 85.17% and 85.86%, respectively. Issa and Salem (2013) prepared concrete mixtures containing natural sand and crushed sand as fine aggregate (natural sand to crushed sand ratio was 33.33%: 66.66%). Crushed sand was replaced by crumb rubber (size 2.54-0.075 mm) at levels of 0%, 15%, 25%, 50% and 100%, by volume. In addition, all fine aggregate was replaced with crumb rubber at level of 100%, by volume. Fixed w/c ratio and fixed dosage of SP were used. Results showed a reduction in the compres-sive strength at ages of 7 and 28 days with the inclusion of rubber sand. The reduction in the 28 day compressive strength was 17.85%, 36%, 58.15% and 83.69% by replacing crushed sand at levels of 15%, 25%, 50% and 100%, respectively, whilst it was 96% by replacing full fine aggregate with rubber sand. Taha et al. (2008) reported a reduction in the compressive strength at ages of 7 and 28 days of concretes containing rubber (size 5-1 mm) as natural sand replacement at levels of 25%, 50%, 75% and 100%, by volume. This reduction increased as the rubber sand content increased. The reduction in the 28 day compressive strength was approximately 14.51%, 24.21%, 49.75% and 67.4% with the inclusion of 25%, 50%, 75% and 100% rubber sand, respectively. El-Gammal et al. (2010) replaced natural sand in concretes with crumb rubber (size ~ 50.2 mm) up to 100%, by weight. Results showed a reduction in the compressive strength with the inclusion of rubber sand. The reduction in the compressive strength was 80.33% and 81.64% with the inclusion of 50% and 100% rubber sand, respectively. Atahan and Ytice (2012) reported a reduction in the compressive strength and elastic modulus of concretes by replacing natural fine aggregate and coarse aggregate with crumb rubber at levels of 0%, 20%, 40%, 60%, 80% and 100%, by volume. This reduction increased with increasing rubber aggregate. The reduction in the compressive strength was approximately 57.96%, 65.61%, 75.8%, 87.26% and 92.35% with the inclusion of

20%, 40%, 60%, 80% and 100% rubber aggregate, respectively.

Khaloo et al. (2008) reported a reduction in the com-pressive strength and tangential modulus of elasticity of concretes by replacing natural sand (maximum size 4.75 mm) with crumb rubber (maximum size 4.75 mm) at levels of 25%, 50%, 75% and 100%, by volume. The reduction in the compressive strength was 79.33%, 96%, 97.37%, 98.21% with the inclusion of 25%, 50%, 75% and 100% rubber sand, whilst the reduction in the tangential modulus of elasticity was 84.48%, 95.82%, 98.51% and 99.46%, respectively. Batayneh et al. (2008) reported a reduction in the compressive strength, splitting tensile strength and flexural strength of concretes containing rubber (size 4.750.15 mm) as natural sand replacement, by volume. The reduction in the compressive strength was 25.15%, 51.56%, 68.14%, 82.35% and 90.13% with the inclusion of 20%, 40%, 60%, 80% and 100% rubber sand, respectively, whilst the reduction in the splitting tensile strength was 34.75%, 47.87%, 66.67%, 81.1% and 92.19%, respectively. The reduction in the flexural strength was 30.7%, 44.56%, 62.5%, 79.1% and 82.61% with the inclusion of 20%, 40%, 60%, 80% and 100% rubber sand, respectively. Khatib and Bayomy (1999) reported a reduction in the 7 and 28 day compressive strength and flexural strength of concretes containing crumb rubber (gradation close to the natural sand) as natural sand replacement. Natural sand was replaced with crumb rubber at levels ranging from 5% to 100%, by volume. Results showed a reduction in the compressive strength and flexural strength with the inclusion of rubber sand. This reduction increased as the rubber sand content increased.

From the above review of the literature in Sections 4.1 and 4.2, it can be noted that the inclusion of rubber sand in the mixture decreased the mechanical strength. This reduction in the mechanical strength may be related to the bond defects between rubber sand and the matrix (Fig. 9) Turatsinze et al., 2006. Corinaldesi et al. (2011)

Figure 9. Bond defect (B.D.) between rubber aggregate (R.A.) and cement matrix (Turatsinze et al., 2006).

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Figure 10. SEM observation of the interfacial zone between cement paste and SBR particles (Corinaldesi et al., 2011).

related the low strength of rubberised mortar to the low quality of the interfacial transition zone (ITZ) between rubber particles and cement paste (Fig. 10). Turki et al. (2009) related the low strength of rubberised mortar to the void space between rubber aggregate and cement matrix (Fig. 11). Albano et al. (2005) related the low strength to the increased porosity or weakness points in rubberised concrete matrix. Raj et al. (2011) related the low strength of rubberised concrete to the weak interface or the transition zone of the rubberised mortar and the conventional coarse aggregates. These weak interfaces acted as the originators of micro-cracks which eventually grew to macro size, leading to failure under compression. Thomas et al. (2014) related the low strength of rubberised concrete to the smooth surfaces of the rubber particles (Fig. 12) that led to a weak bond with the cement paste. Taha et al. (2008) related the low strength of rubberised concrete to three main reasons: first, the deformability of the rubber particles compared with the surrounding cement paste, that results in initiating cracks around the rubber particles in a fashion similar to that occuring with air voids in normal concrete; second, due to the weak bond between rubber particles and the cement paste; third, due to the possible reduction of the concrete matrix density which depends

Figure 12. SEM images of rubberised concrete (20% substitution) (Thomas et al., 2014).

greatly on the density, size and hardness of the aggregate. 1653

Many studies (Ozbay et al., 2011; Karahan et al., 2012; 1654 Taha et al., 2008; Khatib and Bayomy, 1999; Eldin and 1655

Senouci, 1993; Lee et al., 1998; Chung and Hong, 1999) 1656 related the low strength of rubberised mixture to the weak 1657 bond between rubber particles and cement paste, and 1658 increased matrix porosity. The reduction in the strength 1659 by using rubber sand is one of the shortcomings of using 1660

this recycled material which limits its wide use by engineers. 1661 To alleviate this problem, some studies (Gesoglu and 1662

Guneyisi, 2007; Giineyisi et al., 2004) recommended to 1663 replace part of cement with SF to mitigate the degradation 1664

in strength caused by rubber sand. Others (Bowland et al., 1665 2012) recommended to mix rubber particles with latex 1666

before they are added to the concrete/mortar aiming to 1667 improve the strength. However, few studies have proposed 1668

to improve the rubber-cementitious matrix bond (Li et al., 1669 1998), notably treating the rubber particles with NaOH 1670 aqueous solution (Segre and Joekes, 2000). However, the 1671 results that they obtained showed that the strength benefit 1672

due to the rubber treatment was small. 1673

5. Impact energy and impact load 1674

Taha et al. (2008) replaced natural sand in concretes 1675 with rubber (size 5-1 mm) at levels of 25%, 50%, 75% 1676 and 100%, by volume. They reported that the impact 1677

Figure 11. Adherence of ITZ of rubber-free and rubber aggregate mortar with 30% of substituted rubber aggregate (Turki et al., 2009).

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1678 energy improved with the inclusion of rubber sand up to

1679 50%. A further increase in the rubber sand content beyond

1680 this level led to a reduction in the impact strength. Sallam

1681 et al. (2008) partially replaced natural sand in concretes

1682 with crumb rubber (size 5-0.16 mm) at levels of 10%,

1683 20% and 30%, by volume. They reported that the presence

1684 of crumb rubber increased the resistance of concrete to

1685 crack initiation under the impact load. Al-Tayeb et al.

1686 (2013) reported that the inclusion of crumb rubber (size

1687 1 mm) in concretes at levels of 5%, 10% and 20%, by vol-

1688 ume, as natural sand replacement improved the impact

1689 load behaviour. They also reported an increase in the frac-

1690 ture energy (static test) of concretes with the inclusion of

1691 rubber sand. The enhancement in the fracture energy was

1692 34.61%, 38.46% and 46.15% with the inclusion of 5%,

1693 1 0% and 20% rubber sand, respectively. Maher et al.

1694 (2013) partially replaced natural sand in concrete beams

1695 with crumb rubber (specific area 0.0266 m2/g) at levels of

1696 0%, 5%, 10% and 20%, by volume. Fixed w/c ratio was

1697 used. They reported that the impact tup load, inertial load

1698 and bending load of concrete increased with increasing

1699 rubber sand content, whilst static peak bending decreased.

1700 The fracture energy increased with increasing rubber sand

1701 content. Gesoglu et al. (2014) partially replaced natural

1702 aggregate in concretes with crumb rubber (size either

1703 4 mm or 2 mm) at levels of 0%, 10% and 20%, by total

1704 aggregate volume. Results showed an increase in the frac-

1705 ture energy with the inclusion of rubber aggregate (size

1706 4 mm). The fracture energy increased by 1.38 and 1.33

1707 times greater with the inclusion of 10% and 20% rubber

1708 aggregate, respectively. On the other hand, the inclusion

1709 of 10% and 20% rubber aggregate with a size of 2 mm

1710 decreased fracture energy by 26.2% and 18.5%, respec-

1711 tively. Pedro et al. (2013) partially replaced natural sand

1712 in mortars with shredded rubber (size 4.74-0.15 mm) at

1713 levels of 5%, 10% and 15%, by volume. They reported that

1714 the inclusion of rubber sand improved impact behaviour in

1715 which crack width decreased. Vadivel et al. (2014) reported

1716 an improvement in the impact resistance of concrete spec-

1717 imens by partially replacing natural sand with 6% rubber

1718 (size ^4.75-0.1 mm), by weight.

1719 Atahan and Yiice (2012) replaced natural fine aggregate

1720 and coarse aggregate in concretes with crumb rubber at

1721 levels of 0%, 20%, 40%, 60%, 80% and 100%, by volume.

1722 Results showed that the maximum impact load decreased

1723 with increasing rubber aggregate content. The inclusion

1724 of 100% rubber showed 71.6% maximum load lower than

1725 that of the control. The total time of impact increased with

1726 increasing rubber aggregate content. Over 600% difference

1727 in impact time was achieved with 100% rubber aggregate.

1728 Sukontasukkul et al. (2013) partially replaced natural sand

1729 in concrete panels with rubber at levels of 25% and 50%, by

1730 volume fractions. They reported that rubberised concrete

1731 panels can absorb impact energy from the bullets and

1732 reduce the damage.

1733 From the above review of the literature in this section, it

1734 can be noted that the inclusion of rubber sand in the mix-

ture, upto 50%, improved impact energy. Rubber sand, 1735

upto 20% improved impact load behaviour. The improve- 1736

ment in the impact energy and impact load of concrete with 1737

the inclusion of rubber sand is one advantage of using this 1738

recycled material. 1739

6. Toughness 1740

Sukontasukkul and Chaikaew (2006) reported an 1741

increase in the toughness with the inclusion of rubber as nat- 1742

ural fine aggregate and coarse aggregate replacement. Najim 1743

and Hall (2012) partially replaced natural sand in SCCs with 1744

crumb rubber (size 6-2 mm) at levels of 0%, 5%, 10% and 1745

15%, by weight. They reported that there was a general ten- 1746

dency for all crumb rubber aggregate replacements to signif- 1747

icantly increase all toughness indices (I5, I10 and I20). The 1748

increase in I5 was 53.94%, 16.97% and 33.64% with the 1749

inclusion of 5%, 10% and 15% rubber sand, respectively, 1750

whilst the increase in I20 was 117.84%, 53.28% and 1751

102.58%, respectively. The inclusion of 5% rubber showed 1752

the highest toughness. Liu et al. (2013) partially replaces 1753

natural sand (maximum size 5 mm) in concretes with recy- 1754

cled tyre rubber (grain size 2 mm) at levels of 0%, 5%, 10% 1755

and 15%, by volume. They reported that concrete toughness 1756

increased with increasing rubber sand content. The ratio of 1757

the flexural strength to the compressive strength of rubber 1758

concretes with 5%, 10% and 15% rubber was 1.08, 1.16 1759

and 1.26 times greater than the plain concrete, respectively. 1760

This indicated that rubber concrete is better in anti-cracking 1761

performance than the plain concrete. Balaha et al. (2007) 1762

reported that concrete containing ground waste tyre rubber 1763

(size < 4 mm) as a partial replacement of natural sand had 1764

much more toughness than concrete without rubber sand. 1765

The damping ratio of the rubberised concrete containing 1766

20% rubber sand was much higher than that of normal con- 1767

crete by approximately 63.2%. Taha et al. (2008) replaced 1768

natural sand in concrete with crumb rubber (size 5-1 mm) 1769

at levels of 25%, 50%, 75% and 100%, by volume. They 1770

reported that fracture toughness of concretes increased with 1771

the inclusion of rubber sand. 1772

Khaloo et al. (2008) reported a maximum increase in the 1773

toughness with the inclusion of 25% rubber (maximum size 1774

4.75 mm), by total aggregate volume. Beyond this level, the 1775

toughness decreased due to the systematic reduction in 1776

strength (Fig. 13). Guo et al. (2014) partially replaced nat- 1777

ural sand in concretes, containing recycled coarse aggre- 1778

gate, with crumb rubber (size 1.4-0.85 mm) at levels of 1779

0%, 4%, 8%, 12% and 16%, by volume. Results showed that 1780

as the rubber sand content increased from 4% to 16%, the 1781

fracture toughness first increased and then decreased with 1782

increasing rubber sand content. The inclusion of 4% and 1783

8% rubber sand exhibited the highest fracture toughness. 1784

On the other hand, Huang et al. (2013) partially replaced 1785

iron ore tailings (IOTs) that used as aggregates in ECC 1786

with rubber (average size 0.135 mm) at levels of 0%, 10%, 1787

20%, 30% and 40%, by volume. They reported that the rub- 1788

ber particles led to a substantial reduction in fracture 1789

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1800 1801 1802

1810 1811 1812

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Figure 13. Effect of rubber aggregate content on the toughness index values (Khaloo et al., 2008).

toughness by about 50% compared to the control. This reduction may be related to increasing porosity of ECC with tyre rubber content which weakens the matrix. The weak interfacial bond between tyre rubber particles and surrounding cement paste allowed a crack to easily develop around the tyre rubber particles. Table 5 summarises the mentioned studies about the effect of rubber sand on the toughness of mortars and concretes.

From the above review of the literature in this section, it can be noted that the inclusion of rubber sand in the mixture increased the toughness of concrete as reported by many studies. The increase of the fracture toughness of concrete with the inclusion of rubber particles can be explained by the ability of the rubber to add a few toughening mechanisms to the conventional concrete including crack bringing by rubber particles and rubber particles' bending, compressing and twisting. The tyre rubber particles absorb part of the energy the matrix is subjected to, and therefore the composite material can absorb more energy before fracturing compared to the bare concrete matrix (Taha et al., 2008). The enhancement in the toughness of concrete with the inclusion of rubber sand is one advantage of using this recycled material.

7. Ductility and strain capacity

Guo et al. (2014) reported that appropriate rubber content increased the ductility of the concrete mixtures, but

Table 5

Effect of rubber sand on the toughness of mortars and concretes.

too much rubber may have a negative effect on the ductil- 1816

ity. Jingfu and Yongqi (2008) reported that rubberised 1817

mortar and concrete specimens exhibited ductile failure 1818

and significant deformation before fracture. The ultimate 1819

deformations of both rubberised mortar and concrete spec- 1820

imens increased more than 2-4 times that of control spec- 1821

imens. Grdic et al. (2014) reported an increase in the 1822

concrete ductility by partially replacing natural sand with 1823

crumb rubber (size 4-0.5 mm) at levels of 10%, 20% and 1824

30%, by volume. The ductility index increased with increas- 1825

ing rubber sand content. The increment in the ductility 1826

index was 25%, 81.25% and 93.75% with the inclusion of 1827

10%, 20% and 30% rubber sand, respectively. Hilal (2011) 1828

report that foamed concretes containing 20% and 30% 1829

crumb rubber (size 5-0.7 mm) as natural sand replacement, 1830

by weight, showed a cohesive behaviour at failure than the 1831

control. Vadivel et al. (2014) reported an improvement in 1832

the ductility of concrete by partially replacing natural sand 1833

with 6% rubber (size ^4.75-0.1 mm), by weight. Lijuan 1834

et al. (2014) partially replaced natural sand in concretes 1835

with rubber at levels of 0%, 2%, 4%, 6%, 8% and 10%, 1836

by cement mass. They used different rubber sizes (4, 2, 1837

0.864, 0.535, 0.381, 0.221 and 0.173 mm). They reported 1838

that the inclusion of rubber in the concrete specimens can 1839

improve the deformability. Thus, the ultimate strain of 1840

normal concrete increased. The ultimate strain of rub- 1841

berised concretes increased as rubber content enlarged 1842

and particle size dwindled. Issa and Salem (2013) reported 1843

that the inclusion of rubber as natural sand replacement in 1844

concrete enhanced its ductility and damping properties. 1845

Mohammed, 2010) partially replaced natural sand in con- 1846

crete slabs with crumb rubber (size 0.6 mm) at levels of 1847

0% and 10%, by volume. Results showed that the rub- 1848

berised slabs achieved the ductility requirements of the 1849

Eurocode 4, whilst the conventional concrete slabs were 1850

considered as brittle composite slabs. Ganesan et al. 1851

(2013) partially replaced natural sand in concrete of 1852

beam-column joints with rubber (maximum size 4.75 mm) 1853

at levels of 0% and 15%, by volume. They reported that 1854

the addition of shredded rubber sand could bring about 1855

improvement in the beam-column joint behaviour under 1856

cyclic loads in term of ductility. They also showed that 1857

the brittleness values index of rubber concrete specimens 1858

reduced by 16% compared to the control. Najim and 1859

Hall (2012) reported higher ductility and energy absorption 1860

References

Rubber content (%)

Size (mm)

Increased toughness

Najim and Hall (2012) Liu et al. (2013) Balaha et al. (2007) Taha et al. (2008) Khaloo et al. (2008) Khaloo et al. (2008) Guo et al. (2014) Guo et al. (2014) Huang et al. (2013)

5, 10 and 15 5, 10 and 15 20

25, 50, 75 and 100 25

75 and 100 4 and 8 16

10, 20, 30 and 40

Maximum 5

Maximum 4.75 Maximum 4.75 1.4-0.85 1.4-0.85 Average 0.135

24 December 2015

A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

1861 of SCCs containing crumb rubber (size 6-2 mm) as natural

1862 sand replacement at levels of 5%, 10% and 15%, by weight.

1863 Raj et al. (2011) reported lower value of brittleness index of

1864 SCCs containing rubber (maximum size 4.75 mm) as par-

1865 tial replacement of natural sand at levels of 5%, 10%,

1866 15% and 20%, by volume.

1867 Ling (2012) reported that concretes containing 10%,

1868 20% and 30% rubber as natural sand replacement, by vol-

1869 ume, did not demonstrate brittle failure, but ductile failure.

1870 Aules (2011) reported that the inclusion of rubber (maxi-

1871 mum size 4.75 mm) in mortar as natural sand replacement

1872 up to 30% increased its ductility. Li et al. (2011) partially

1873 replaced natural sand in concretes encased by FRP with

1874 crumb rubber (size 160 im) at levels of 0%, 15% and

1875 30%, by volume. They reported that the FRP encased rub-

1876 berised concretes had higher confinement effectiveness and

1877 higher ductility than FRP confined conventional plain con-

1878 crete. FRP tube encased rubberised concrete cylinders

1879 might be a viable alternative for energy absorbing cylin-

1880 ders. Ho et al. (2012) partially replaced natural sand (size

1881 4-0 mm) in concretes with rubber (size 4-0 mm) at levels

1882 of 0%, 20%, 30% and 40%, by volume. Fixed w/c ratio

1883 and various dosages of SP were used. Results showed a

1884 reduction in the brittleness and damage with increasing

1885 rubber sand content (Fig. 14). The rubberised concretes

1886 exhibited elastic quality index values within acceptable lim-

1887 its for the design of cement-based pavements. Mohammadi

1888 et al. (2014) partially replaced natural sand in concrete with

crumb rubber (after treatment in water-soaking). They reported that the failure of rubberised concrete samples was found to be gradual without a total sudden collapse or a major crack. Rubberised concrete samples could hold themselves even after the occurrence of failure cracks without shattering to pieces (Fig. 15). Topcu (1995) replaced natural sand in concretes with rubber (size 1-0 and 41 mm) at levels ranging from 0% to 45%, by volume. They reported that the ductility of concrete improved with the inclusion of rubber sand. Pierce and Blackwell (2003) reported an improvement in the ductility of mortars by replacing natural fine aggregate with crumb rubber (size 0.6 mm) at levels ranging from 32% to 57%, by volume. Khaloo et al. (2008) replaced natural sand (maximum size 4.75 mm) in concretes with rubber at levels of 25%, 50%, 75% and 100%, by volume. They found more ductile behaviour in rubberised concretes compared to the plain concrete under compression.

Turatsinze et al. (2006) reported that the inclusion of shredded non-reusable tyres (maximum size 4 mm) in mortars as natural sand replacement at levels of 0%, 20% and 30%, by volume, limited the cement-based mortars brittle-ness and increased their strain capacity. Nguyen et al. (2010) reported that the strain capacity before macro-cracking location was improved by partially replacing natural sand in mortars with rubber at levels of 20% and 30%, by volumes. Huang et al. (2013) reported that the tensile strain capacity of ECC containing rubber as partial replacement of iron ore tailings that were used as aggregate, by volume, increased with increasing rubber content. The increase in the tensile strain capacity was 11.11%, 16.67%, 44.44% and 66.67% with the inclusion of 10%, 20%, 30% and 40% rubber sand, respectively. This means that the incorporation of tyre rubber aggregate is beneficial to the performance of ECC in terms of tensile ductility.

From the above review of the literature in this section, it can be noted that the inclusion of rubber sand in the mixture increased its ductility. The failure state in rubberised concretes did not occur quickly and did not cause any detachment in the specimens compared to the control (Khaloo et al., 2008). As reported by Raj et al. (2011) the addition of rubber sand in concretes reduced the brittleness index value and improved the ductility of concretes, thus

IJSBE 96 ARTICLE IN PRESS No. of Pages 37

24 December 2015

24 A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

enabling a transition from a brittle material to a ductile one. This is due to the better energy absorption capacity of rubber, which led to plastic deformations at the time of fracture. Li et al. (2011) related the enhancement in the ductility of rubberized concrete to the incorporation of small ductile particles into concrete. At the same line, the inclusion of rubber aggregate in the matrix increased its strain capacity as reported by Turatsinze et al. (2006), Nguyen et al. (2010) and Huang et al. (2013). The enhancement in the ductility of concrete with the inclusion of rubber sand is one advantage of using this recycled material.

8. Shrinkage

Jingfu et al. (2009) partially replace natural sand in concretes with rubber (size 1.5 mm) at levels of 50, 80, 100 and 120 kg/m3. The tyre rubber particles were incorporated by replacing the same volume of natural sand. Results showed higher drying shrinkage with the inclusion of rubber sand. The drying shrinkage increased with increasing rubber sand content. Turatsinze et al. (2006) reported that the inclusion of shredded non-reusable tyers (maximum size 4 mm) in mortars at levels of 20% and 30%, by volume, increased the free shrinkage. Bravo and de Brito (2012) found an increase in the shrinkage by partially replacing natural sand in concretes with rubber (with the same size of the natural sand) made from used tyres at levels of 0%, 5%, 10% and 15%, by volume. The shrinkage increased by 43% at 15% rubber sand content. Pedro et al. (2013) reported an increase in the shrinkage of mortar specimens by partially replacing natural sand with 15% shredded rubber (size 4.75-0.15 mm), by volume. Yung et al. (2013) measured the change in the length of concrete prisms containing waste tyre rubber as natural sand replacement. Natural sand was partially replaced with rubber at levels of 0%, 5%, 10% and 20%, by volume. Fixed w/c ratio and fixed dosage of binding agent were used. There are three different particle sizes of rubber (0.6, 0.3 and 0.6 + 0.3 mm). Results showed an increase in the shrinkage with increasing rubber sand content and rubber fineness. The change in the length at 28 days was —0.0183% for the control, whilst it was — 0.0294%, —0.0298% and —0.0308% for the specimens containing 5% rubber sand with particle size of 0.6, 0.3 and 0.6 + 0.3 mm, respectively. The average change in the length of the rubber specimens was —0.0248%, which was 35% higher than that of the control. When 20% waste tyre rubber powder was added, the change was the largest, and the average change in the length of rubber specimens was 95% higher than that of the control.

Sukontasukkul and Tiamlom (2012) partially replaced natural sand in concretes with two different particle sizes of rubber at levels of 0%, 10%, 20% and 30%, by volume. The sizes of crumb rubber were No. 6 (passing sieve No. 6) and No. 26 (passing sieve No. 26). Results showed an increase in the drying (free) shrinkage with increasing rubber sand content. Specimens containing a small size of rubber sand showed higher free shrinkage than those

containing large size. Turatsinze et al. (2007, 2005) found an increase in the free shrinkage by partially replacing natural sand in mortars with 20% and 30%, by volume, with rubber (maximum size 4 mm) obtained from shredded non-reusable (Fig. 16). Huang et al. (2013) reported an increase in the drying shrinkage of ECC by partially replacing iron ore tailings (average size 0.135 mm), that were used as aggregate, with tyre rubber (size 0.15-0 mm) at levels of 10%, 20%, 30% and 40%, by volume. The drying shrinkage increased as the rubber sand content increased. The drying shrinkage increased about 1.5 times for specimens containing 40% tyre rubber aggregate compared to the control.

Uygunoglu and Topcu (2010) reported an increase in the drying shrinkage of self-consolidating mortars by partially replacing natural sand with tyre rubber (size 4-1 mm) at levels of 10%, 20%, 30%, 40% and 50%, by weight, when w/c ratio was 0.4. At w/c ratio of 0.51, the inclusion of rubber at levels of 10%, 20% and 30% reduced the drying shrinkage, whilst levels of 40% and 50% significantly increased it. Aules (2011) reported a reduction in the length change of mortars by partially replacing natural sand with rubber (maximum size 4.75 mm) up to 30%, by volume. This reduction increased as the rubber sand content decreased. Chunlin et al. (2011) reported lower shrinkage of concretes by partially replacing natural sand with 10% crumb rubber (size 5-1 mm), by volume. Table 6 summarises the mentioned studies about the effect of rubber sand on the shrinkage of mortars and concretes.

From the above review of the literature in this section, it can be noted that the inclusion of rubber sand in the mixture increased the shrinkage as reported by several studies. The higher shrinkage of rubberised mortar/concrete is partly due to the lower compressive strength and elastic modulus. At the same line, Turatsinze et al. (2006) reported that the benefit of the higher straining capacity of rubberised cement-based composites could be offset by their higher shrinkage length change. However, the shrinkage of rubberised mortar/concrete seemed to be depending on the particle size and the content of rubber sand in the mix-

»--•-- 20°«

' h > O-1-

o loo :oo 300 400

Curing time (day)

Figure 16. Effect of rubber sand content on the free shrinkage of mortar specimens (Turatsinze et al., 2007).

24 December 2015

A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx 25

Table 6

Effect of rubber sand on the shrinkage of mortars and concretes.

References Rubber content (%) Size (mm) Increased shrinkage

Turatsinze et al. (2006) 20 and 30 Maximum 4 P

Bravo and de Brito (2012) 5, 10 and 15 Same sand size P

Pedro et al. (2013) 15 4.75-0.15 P

Yung et al. (2013) 5, 10 and 20 0.6, 0.3 and 0.6 + 0.3 P

Sukontasukkul and Tiamlom (2012) 10, 20 and 30 Sieve No. 6 and No. 26 P

Turatsinze et al. (2007, 2005) 20 and 30 Maximum 4 P

Huang et al. (2013) 10, 20, 30 and 40 0.15-0 P

Uygunoglu and Topcu (2010) 10, 20, 30, 40 and 50 4-1 P

(w/c = 0.4)

Uygunoglu and Topcu (2010) 10, 20 and 30 4-1 P

(w/c = 0.51)

Uygunoglu and Topcu (2010) 40 and 50 4-1 X

(w/c = 0.51)

Aules (2011) Up to 30 Maximum 4.75 X

Chunlin et al. (2011) 10 5-1 X

2027 ture. In terms of rubber sand content, the shrinkage

2028 increased with increasing rubber sand content in which

2029 rubber sand is weaker and highly flexible than natural

2030 sand. As the replacement rate increased, the lack of fine

2031 aggregate caused a greater decrease of internal restraints

2032 and led to higher shrinkage (Sukontasukkul and

2033 Tiamlom, 2012). In terms of rubber sand particle size, the

2034 smaller size appeared to shrink much more than the larger

2035 size (Sukontasukkul and Tiamlom, 2012). Sukontasukkul

2036 and Tiamlom (2012) reported that large shrinkage might

2037 come from two combined effects: (1) the lower internal

2038 restraint (from lack of sand) and (2) the increase of more

2039 flexible material. Uygunoglu and Topcu (2010) reported

2040 that the increase in the total shrinkage with the inclusion

2041 of rubber sand is a consequence of the increase of open

2042 porosity and thus shrinkage increases. The enhancement

2043 in the drying shrinkage of mortar/concrete with the inclu-

2044 sion of rubber sand is one of disadvantages of using this

2045 recycled material.

2046 9. Abrasion resistance

2047 Ozbay et al. (2011) reported a reduction in the abrasion

2048 resistance of concretes by partially replacing natural sand

2049 with crumb rubber (size 3-0 mm) at levels of 5%, 15%

2050 and 25%, by volume. The abrasion resistance decreased

2051 with increasing rubber sand content. The increase in the

2052 depth of wear was approximately 11.59%, 17.39% and

2053 23.19% with the inclusion of 5%, 15% and 25% rubber,

2054 respectively. Sukontasukkul and Chaikaew (2006) partially

2055 replaced natural fine and coarse aggregates in concrete

2056 blocks with crumb rubber at levels of 0%, 10% and 20%,

2057 by weight. They reported that skid resistance increased

2058 with the inclusion of rubber aggregate. The skid resistance

2059 increased with increasing rubber aggregate content.

2060 Ganesan et al. (2012) reported 20% increase in the abrasion

2061 resistance of concrete by partially replacing natural sand

2062 with 15% rubber (size < 4.75 mm), by weight. Thomas

2063 et al. (2014) partially replaced natural sand in concretes

with discarded tyre rubber (40% powder from mesh 30, 2064

35% size 2-0.8 mm and 25% size 4-2 mm) upto 20% at dif- 2065

ferent w/c ratios. They reported that the rubberised con- 2066

crete exhibited better resistance to abrasion than the 2067

control when w/c ratios were 0.4 and 0.5. At w/c ratio of 2068

0.45, the inclusion of rubber up to 7.5% showed less abra- 2069

sion resistance than the control, whilst better abrasion 2070

resistance was obtained for the remaining mixtures (i.e. 2071

rubber sand > 7.5%). Grdic et al. (2014) reported an 2072

increase in the abrasion resistance of concrete by partially 2073

replacing natural sand with crumb rubber (size 4- 2074

0.5 mm) at a level of 10%, by volume. On the other hand, 2075

the inclusion of 20% and 30% rubber sand decreased it. 2076

Valadares et al. (2012) reported an increase in the abrasion 2077

resistance of concretes containing 12.5%, 24.15% and 2078

35.77% shredded rubber (size 4 mm) as natural sand 2079

replacement, by volume. The abrasion resistance increased 2080

with increasing rubber sand content. The abrasion wear 2081

depth of the control was 2.6 mm, whilst it was 2.0, 1.5 2082

and 1.1mm with the inclusion of 12.5%, 24.15% and 2083

35.77% rubber sand, respectively. 2084

From the mentioned studies in this section, it can be 2085

noted that the abrasion resistance of concrete with the 2086

inclusion of rubber sand still needs more investigations. 2087

Although there are contradictory reports about the effect 2088

of rubber sand on abrasion resistance, it can be concluded 2089

that rubber sand can increase the abrasion resistance if 2090

appropriate rubber sand content and suitable w/c ratio 2091

were used. 2092

10. Freeze/thaw and ageing resistance 2093

Paine et al. (2012) studied the performance of rubberised 2094

concrete aggregate under freeze/thaw cycles. They found 2095

that the incorporation of rubber aggregate improved the 2096

resistance of freeze/thaw cycles. Paine and Dhir (2010) 2097

reported that concrete containing 4% rubber with different 2098

particle sizes of 1.5-0.5, 8-2 and 25-5 mm as natural sand 2099

replacement provided good resistance to freeze-thaw. Al- 2100

IJSBE 96 ARTICLE IN PRESS No. of Pages 37

24 December 2015

A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

2101 2102

2110 2111 2112

2120 2121 2122

"olOO E

> 60 4-*

1 1 1 1 1

—■—Control -5%TRA —*—10%TRA

— < 1 >

V • ►

50 100 150 200 250 Number of freezing/thaw cycles

Figure 17. Effect of rubber ash content on the variation of relative dynamic modulus with a number of freezing and thawing cycles (Al-Akhras and Samadi, 2004).

Akhras and Samadi (2004) reported higher freeze/thaw resistance of mortars containing rubber ash (size 0.15 mm) as natural sand replacement at levels of 5% and 10%, by weight. Increasing rubber ash sand content led to increasing freeze/thaw resistance (Fig. 17). Topcu and Demir (2007) exposed concrete specimens containing rubber (size 4-1 mm) as natural sand replacement at levels of 10%, 20% and 30%, by volume, with 30 freeze-thaw cycles according to ASTM C 666. Results showed that the damage as a result of freeze-thaw in concrete containing 10% rubber sand was less than the damage in the control. In spite of the reduction in concrete strength because of the increase in rubber ratio, an increase was observed in durability against freeze-thaw of the 10% rubber concrete. Karahan et al. (2012) partially replaced natural sand in SCCs with rubber (size 4.75-0.15 mm) at levels of 0%, 10%, 20% and 30%, by volume. They exposed concrete specimens to 300 freeze/thaw cycles. Results showed a slight reduction in the flexural strength after freeze/thaw cycles with the inclusion of 10% rubber sand compared to the control. The reduction in the flexural strength was 6.78% and 5.56% with the inclusion of 0% and 10% rubber sand, respectively. On the other hand, the inclusion of 20% and 30% rubber sand led to a significant reduction in the flexural strength after freeze/thaw cycles. This reduction reached 12.5% and 13.16% with the inclusion of 20% and 30% rubber sand, respectively. Turgut and Yesilata (2008) reported higher freeze-thaw resistance of concrete blocks containing crumb rubber (size 4.75-0.075 mm) as natural sand replacement at levels exceeding 50%, by volume. Pedro et al. (2013) partially replaced natural sand in mortars with 15% shredded rubber (size 4.75-0.15 mm), by volume. They tested the specimens under accelerated ageing at 112 days according to En 1015-21. They reported that mortar specimens containing rubber sand are not particularly susceptible to weathering.

From the above review of the literature in this section, it can be noted that the inclusion of rubber sand in the mixture increased its freeze/thaw resistance. The freeze/thaw

resistance increased with increasing rubber sand content. 2140

The rubberised concrete had better resistance to freeze/ 2141

thaw cycles than the control due to the incorporation of 2142

air in the matrix caused by the addition of rubber. The 2143

enhancement in the freezing/thaw of concrete with the 2144

inclusion of rubber sand is one advantage of using this 2145

recycled material. 2146

11. Fire resistance and thermal insulation 2147

Topcu and Demir (2007) reported a reduction in the 2148

residual compressive strength after firing at 150, 300 and 2149

400 °C for 3 h of mortars containing rubber (size 4- 2150

1 mm) as natural sand replacement at levels of 10%, 20% 2151

and 30%, by volume. The reduction in the residual com- 2152

pressive strength increased with increasing rubber sand 2153

content. Guo et al. (2014) reported a reduction in the resid- 2154

ual compressive strength and Young's modulus of con- 2155

cretes by partially replacing natural sand with crumb 2156

rubber (1.4-0.85 mm) at levels of 4%, 8%, 14% and 16%, 2157

by volume, after firing at 200, 400 and 600 °C for 2 h. 2158

The residual compressive strength decreased with increas- 2159

ing rubber sand content. On the other hand, the inclusion 2160

of rubber sand reduced the micro-crack results by elevated 2161

temperatures. The number of micro-cracks decreased with 2162

increasing rubber sand content. In fact, crumb rubber 2163

helped to alleviate the initiation and development of cracks 2164

in concrete under the effect of elevated temperatures. This 2165

may be due to the fact that the rubber is melted under 2166

approximately 170 °C, providing space for the evaporated 2167

water in concrete to escape from the concrete, thus signif- 2168

icantly reducing the pore pressure caused by the water 2169

vapour, one of the main reasons leading to the cracking 2170

of concrete under higher temperature (Netinger et al., 2171

2011). On the same line, the inclusion of an appropriate 2172

amount of rubber sand in concrete improved its energy 2173

absorption capacity (toughness) after exposure to elevated 2174

temperatures. 2175

Marques et al. (2013) partially replaced natural aggre- 2176

gates in concretes with shredded rubber at levels of 0%, 2177

5%, 10% and 15%, by volume. The specimens were exposed 2178

to 400, 600 and 800 °C for 1 h accordance with ISO 834. 2179

Results showed a reduction in the residual compressive 2180

strength and residual splitting tensile strength after expo- 2181

sure to elevated temperatures. This reduction increased 2182

with increasing rubber aggregate content. At 400 °C, the 2183

reduction in the compressive strength was 24%, 39.8% 2184

and 54.8% with the inclusion of 5%, 10% and 15% rubber 2185

aggregate, respectively, compared to the control specimen 2186

heated at the same temperature. At 800 °C, the reduction 2187

in the compressive strength was 37.3%, 55.4% and 69.5% 2188

with the inclusion of 5%, 10% and 15% rubber aggregate, 2189

respectively. The reduction in the splitting tensile strength 2190

at 400 °C was 5.7%, 20.9% and 37.7% with the inclusion 2191

of 5%, 10% and 15% rubber aggregate, respectively, com- 2192

pared to the control specimen heated at the same tempera- 2193

ture. At 800 °C, the reduction in the splitting tensile 2194

IJSBE 96 ARTICLE IN PRESS No. of Pages 37

24 December 2015

A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

strength was 47.9%, 57.1% and 63.6% with the inclusion of 5%, 10% and 15% rubber aggregate, respectively. They also reported that the relative reduction in the rubberised concrete should not prevent it from being used in structural applications. Correia et al. (2012) partially replaced natural aggregates in concretes with shredded rubber at levels of 0%, 5%, 10% and 15%, by volume. They reported that higher rubber content and increasing heat flux led to a worse fire reaction response particularly in terms of ignition time, heat release rate and smoke production.

Paine et al. (2012) reported that the inclusion of rubber in concrete as natural sand replacement decreased its thermal conductivity. Issa and Salem (2013) reported that the inclusion of crumb rubber (size 2.54-0.075 mm) as natural sand replacement in concrete enhanced its insulation properties. As the rubber sand content in the concrete increased, the conductivity decreased. Paine and Dhir (2010) reported lower thermal conductivity, and that lower U-value of concrete containing rubber (sizes of 1.5-0.5, 8-2 and 25-5 mm) as natural sand replacement. Mohammed et al. (2012) reported lower thermal conductivity of rubberised hollow concrete blocks compared to normal hollow blocks in which the thermal conductivity of crumb rubber (size 0.6 mm) particles (0.16 W/m K) is lower than that of natural sand (1.5 W/m K) (Fig. 18). Hall et al. (2012) partially replaced natural sand (size 5 mm) in concretes with crumb rubber (size 6-2 mm) at levels of 0%, 10%, 20% and 30%, by weight. They reported that the substitution of natural sand with rubber appeared to cause a significant reduction in thermal conductivity. Sukontasukkul (2009) reported 20-50% reduction in the thermal conductivity of concretes by partially replacing sand with 10-30% crumb rubber, by volume. The sizes of crumb rubber were No. 6 (passing sieve No. 6) and No. 26 (passing sieve No. 26). Results showed that the crumb rubber concretes exhibited lower heat transfer rate and higher heat resistivity than the plain concrete. The reduction in the heat transfer was 16.58%, 44.45% and 54.62% with the inclusion of 10%, 20% and 30% rubber sand with large size (passing sieve No. 6), respectively, whilst it was 45.38%, 48.22% and 49.73%, respectively, with the inclusion of small size rubber sand

§ 1.1

« 3 0.9

c 0 0.8

<D 0.6

< )rdin iryco ncrel e

» 1.1:

-l.Oi 1 tr V

---SF0FA1S ---SF5FA15 ---SF10FA15 ■flli) -__

' ' — frjjj

IS 20 25 30 35 40 Rubber content (%)

45 50 55

Figure 18. Effect of rubber sand content on the thermal conductivity of concrete block specimens at 28 days air curing (Mohammed et al., 2012).

Figure 19. Effect of rubber content and fineness of the thermal conductivity of concretes (Sukontasukkul, 2009).

(passing sieve No. 26). In addition, crumb rubber concretes showed lower thermal conductivity compared to the control. The thermal conductivity of the plain concrete was 0.531 W/m K, the K-values of crumb rubber concretes were lower by approximately 20-50% and in the range of 0.2410.443 W/m K (Fig. 19). Pelisser et al. (2012) reported 13.8% reduction in the thermal conductivity of mortar containing 40% recycled tyre rubber (maximum size 2.4 mm) as natural sand replacement, by volume, compared to the control. Fadiel et al. (2014) reported 13.1%, 15.2%, 17% and 21.2% reduction in the thermal conductivity of mortar specimens containing 10%, 20%, 30% and 40% crumb rubber (size 0.6-0 mm), respectively, as natural sand replacement, by weight. 18.2%, 24.6%, 26% and 27.8% reduction in the thermal conductivity was obtained with the inclusion of 10%, 20%, 30% and 40% crumb rubber (size 0.20.84 mm), respectively. Eiras et al. (2014) reported lower thermal conductivity of mortars containing 40%, 50% and 60% crumb rubber (size ^0.08-1.3 mm) as natural sand replacement, by volume. The thermal conductivity decreased with increasing rubber sand content. Pierce and Blackwell (2003) concluded that mortars containing crumb rubber (size 0.6 mm) as natural fine aggregate replacement at levels ranging from 32% to 57%, by volume, showed higher thermal insulation.

From the above review of the literature in this section, it can be noted that the inclusion of rubber sand in the mixture decreased its thermal conductivity. This means that the inclusion of rubber sand in the mixture increased its thermal insulation. The thermal insulation increased with increasing rubber sand content. Theoretically, the thermal conductivity is proportional inversely to the density of the material. Since crumb rubber concrete is lower in density, it should be expected to exhibit a lower value of thermal conductivity (Sukontasukkul, 2009). The reduction in the thermal conductivity of the rubberised matrix could be partly attributed to increasing air entrapment caused by non-wetting rubber particles during mixing and partly to the lower thermal conductivity of the crumb rubber par-

IJSBE 96

24 December 2015

28 A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

2275 ticles. As the addition of crumb rubber increased, there was

2276 a greater moisture-dependent effect on the saturated state

2277 thermal conductivity due to the increase apparent porosity

2278 caused by air entrapment (Hall et al., 2012). Increasing

2279 thermal insulation of mortar/concrete with the inclusion

2280 of rubber sand is one advantage of using this recycled

2281 material. It can be used as construction material where

2282 thermal insulation is required. On the other hand, the

2283 inclusion of rubber sand in the mixture decreased its fire

2284 resistance, but decreased the risk of spalling caused by

2285 exposure to elevated temperatures.

2286 12. Carbonation resistance

2287 Bravo and de Brito (2012) reported a reduction in the

2288 carbonation resistance of concrete specimens containing

2289 rubber aggregate made from used tyres (with the same size

2290 of the natural sand) as natural sand replacement at levels of

2291 5%, 10% and 15%, by volume. The carbonation depth

2292 slightly increased with increasing rubber sand content.

2293 The increase in the carbonation depth may be due to the

2294 greater void volume between rubber aggregate and the

2295 cement paste.

2296 It can be clearly noted that there is a distinct lack in

2297 studying the effect of rubber sand on the carbonation resis-

2298 tance of mortar/concrete. Indeed the carbonation resis-

2299 tance of mortar/concrete containing rubber sand still

2300 needs more investigations. This can be a major topic for

2301 future investigations. However, according to the available

2302 study, it can be concluded that the inclusion of rubber sand

2303 in the matrix decreased its carbonation resistance. This one

2304 of the disadvantages of using this recycled material.

2305 13. Corrosion resistance

2306 Karahan et al. (2012) reported that reinforcing bar mass

2307 loss of concrete without rubber and concrete containing

2308 10% crumb rubber (size 4.75-0.15 mm) as natural sand

2309 replacement, by volume, was almost the same. On the other

2310 hand, when crumb rubber content reached 30%, the rein-

2311 forcing bar mass loss was approximately two times greater

2312 than the control concrete. Yung et al. (2013) reported that

2313 partially replacing natural sand in concretes with 5% rub-

2314 ber (size 0.6 or 0.3 mm), by volume, led to anti-sulphate

2315 corrosion resistance.

2316 It can be clearly noted that there is a distinct lack in

2317 studying the effect of rubber sand on the corrosion resis-

2318 tance. The corrosion resistance of bar imbedded in mor-

2319 tar/concrete containing rubber sand still needs more

2320 investigations. This can be a major topic for future

2321 investigations.

2322 14. Water absorption, porosity and chloride ion penetration

2323 Segre et al. (2004) studied the percentage of water

2324 absorption of mortars containing 10% rubber (size

2325 0.2 mm) as natural sand replacement, by weight. The

results showed lower percentage of water absorption with 2326

the inclusion of rubber sand. Marques et al. (2008) 2327

reported a reduction in the percentage of water absorption 2328

at ages of 7, 28, 56 and 90 days by partially replacing 12% 2329

natural sand with rubber (passed in sieve 0.8 mm), by vol- 2330

ume. The reduction in the percentage of water absorption 2331

with the inclusion of rubber sand was approximately 2332

5.55%, 7.4%, 23.43% and 6.34% at ages of 7, 28, 56 and 2333

90 days, respectively. Pedro et al. (2013) reported 8.9% 2334

reduction in the water absorption of mortar specimens, 2335

tested at age of 28 days, with the inclusion of 5% shredded 2336

rubber (size 4.75-0.15 mm) as natural sand replacement, by 2337

volume. On the other hand, it increased by 6.93% with the 2338

inclusion of 10% rubber sand. The inclusion of 15% rubber 2339

showed comparable water absorption to the control. They 2340

also reported that the inclusion of 15% rubber sand led to 2341

better permeability performance. Ganesan et al. (20 1 2) 2342

reported a reduction in the water permeability, percentage 2343

of water absorption and chloride ion penetration of con- 2344

crete by partially replacing natural sand with rubber 2345

(size < 4.75 mm), by weight. Gesoglu et al. (2014) reported 2346

a reduction in the permeability of concrete specimens with 2347

the inclusion of rubber (size either 4 mm or 2 mm) as nat- 2348

ural aggregate replacement at levels of 10% and 20%, by 2349

total aggregate volume. The inclusion of 10% and 20% rub- 2350

ber sand with particles of size 4 mm reduced the permeabil- 2351

ity coefficient by 43.75% and 67.46%, respectively, whilst 2352

the inclusion of rubber sand with a particle size of 2 mm 2353

reduced it by 40.73% and 43.1%, respectively. Ling (20 1 2) 2354

found a reduction in the concrete porosity by partially 2355

replacing natural sand with 10% rubber, by volume. On 2356

the other hand, replacing natural sand with 20% and 30% 2357 rubber, by volume, led to an increase in the porosity of 2358

concretes. Sukontasukkul and Tiamlom (2012) reported a 2359

reduction in the absorption of concrete specimens contain- 2360

ing small rubber size (passing sieve 26). The reduction in 2361

the absorption was 30.77%, 15.38% and 11.54% with the 2362

inclusion of 10%, 20% and 30% small size rubber sand, 2363

by volume, respectively. On the other hand, concrete spec- 2364

imens containing large rubber size (passing sieve 6) showed 2365

an increase in the absorption. The increase in the absorp- 2366

tion was approximately 11.54%, 21.15% and 34.62% with 2367

the inclusion of 10%, 20% and 30% large size rubber sand, 2368

by volume, respectively. Hilal (2011) reported an increase 2369

in the percentage of water absorption in foamed concretes 2370

by partially replacing natural sand with crumb rubber (size 2371

5-0.7 mm) at levels of 20% and 30%, by weight. The incre- 2372 ment in the percentage of water absorption at age of 2373 28 days was 10.32% and 22.15% with the inclusion of 2374

20% and 30% rubber sand, respectively. 2375

Azevedo et al. (2012) studied the capillary water absorp- 2376

tion coefficient of HPCs containing tyre waste rubber. They 2377

reported an increase in the capillary water absorption coef- 2378

ficient by partially replacing natural sand with tyre rubber 2379

(dimensions between 2.4 and 1 mm), by weight. The 2380

increase in the capillary water absorption coefficient was 2381

71.43%, 85.71% and 95.24% with the inclusion of 5%, 2382

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A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx

10% and 15% rubber sand, respectively. Bravo and de Brito (2012) reported an increase in the percentage of water absorption with the inclusion of rubber aggregate made from used tyres (with the same size of the natural sand) as natural sand replacement. The percentage of water absorption increased with increasing rubber sand content. The increment in the percentage of water absorption was approximately 2.86%, 12.99% and 14.29% with the inclusion of 5%, 10% and 15% rubber sand, respectively. The inclusion of 5% rubber sand led to a reduction in chloride diffusion, whilst an increase in the chloride diffusion coefficient occurred when the replacement ratio increased from 5% to 15%. Onuaguluchi and Panesar (2014) reported an increase in the water absorption and porosity of concrete mixtures by partially replacing natural sand with crumb rubber (size ^86% smaller than 2.3 mm) at levels of 5%, 10% and 15%, by volume. The water absorption and porosity increased with increasing rubber sand content. Thomas et al. (2014) reported an increase in the rate of water absorption of concrete mixtures by partially replacing natural sand with discarded tyre rubber (40% powder from mesh 30, 35% size 2-0.8 mm and 25% size 4-2 mm) up to 20%. Bignozzi and Sandrolini (2006) reported an increase in the percentage of water absorption of SCCs, at age of 28 days, containing rubber (size 55% 2-0.5 mm and 45% 0.7-0.5 mm) as natural sand replacement at levels of 22.2% and 33.3%, by volume. The increase in the percentage of water absorption was 4% and 10.67% with the inclusion of 22.2% and 33.3% rubber sand, respectively.

Karahan et al. (2012) reported an increase in the porosity and water absorption of SCCs containing 10%, 20% and 30% rubber (size 4.75-0.15 mm) as natural sand replacement, by volume. The increase in the porosity was 5%, 6% and 12% with the inclusion of 10%, 20% and 30% rubber sand, respectively, whilst the increase in the percentage of water absorption was 10%, 14% and 29%, respectively. Fadiel et al. (2014) reported 24% and 4% reduction in the water absorption of mortar specimens by replacing natural sand with crumb rubber (size 0.6-0 mm) at levels of 10% and 20%, by volume, respectively, whilst 30% and 40% rub-

Figure 20. Effect of rubber sand content on the water absorption of self-consolidating mortars (Uygunoglu and Topcu, 2010).

ber sand increased it by 4.5% and 67%, respectively. They also reported that the inclusion of 10%, 20% and 30% rubber (size 2-0.84 mm) in mortar specimens as natural sand replacement decreased the water absorption by 32.5%, 25% and 6%, respectively, whilst the inclusion of 40% rubber (size 2-0.84) increased it by 10%. Mohammed et al. (2012) reported an increase in the water absorption by partially replacing natural sand in hollow concrete blocks with crumb rubber (size 0.6 mm) at levels of 10%, 25% and 50%, by volume. The water absorption increased with increasing rubber sand content. Eiras et al. (2014) reported higher percentage of absorption by partially replacing natural sand in mortars with crumb rubber (size ^ 1.3-0.08 mm) at levels of 40%, 50% and 60%, by volume. Turgut and Yesilata (2008) reported a reduction in the water absorption and porosity of concrete blocks containing crumb rubber (size 4.75-0.075 mm) as natural sand replacement at different levels, by volume. The increment in the water absorption was 24.92%, 52.13%, 63.93%, 95.1%, 112.46%, 121, 97% and 142.95% with the inclusion of 10%, 20%, 30%, 40%, 50%, 60% and 70% rubber sand, respectively, whilst the increment in the porosity was 21.21%, 42.42%, 46.97%, 65.15%, 69.79%, 65.15% and 72.73%, respectively. Turki et al. (2009) partially replaced natural sand (size 2-0 mm) with rubber made from shredded worm tyres (size 4-1 mm) upto 50%, by volume. They reported an increase in the porosity with the inclusion of rubber sand. The porosity increased with increasing rubber sand content. The increase in the total porosity (by pycnometer method) was 76.51%, 262.12% and 471.21% with the inclusion of 10%, 30% and 50% rubber sand, respectively, whilst it was 12.89%, 24.32% and 87.18% (by an image analysis), respectively. Uygunoglu and Topcu (2010) reported higher percentage of apparent porosity and water absorption in self-consolidating mortars containing scrap tyre rubber (size 4-1 mm) as natural sand (size 4-0 mm) replacement, by weight. Natural sand was partially replaced with rubber sand at levels ranging from 10% to 50%. Various w/c ratios were used. The percentage of apparent porosity and water absorption increased with the inclusion of rubber sand. They increased with increasing rubber sand content (Fig. 20). At a w/b ratio of 0.4, the inclusion of 50% rubber increased the percentage of water absorption by 71.4% compared to the control.

Gesoglu and Guneyisi (2011) partially replaced natural fine aggregate in SCCs with crumb rubber (size < 4 mm) at levels of 0%, 5%, 15% and 25%, by volume. Results showed that the percentage of water absorption and chloride ion permeability of SCCs increased with the inclusion of rubber sand. As the rubber sand content increased from 0% to 25%, the chloride ion penetration increased from 2491 to 3460 C and from 2131-3139 C at ages of 28 and 90 days, respectively. The increase in the percentage of water absorption at age of 28 days was approximately 5.81%, 15.32% and 35.77% with the inclusion of 5%, 15% and 25% rubber sand, respectively. They also reported that these values of chloride ion permeability and percentage of

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Table 7

Effect of rubber sand on the water absorption, porosity and chloride ion penetration of mortars and concretes.

References

Rubber content (%)

Size (mm)

Effect

Segre et al. (2004) Marques et al. (2008) Pedro et al. (2013)

Ganesan et al. (2012)

Gesoglu et al. (2014) Ling (2012)

Sukontasukkul and Tiamlom (2012) Sukontasukkul and Tiamlom (2012) Hilal, (2011) Azevedo et al. (2012) Bravo and de Brito (2012) Onuaguluchi and Panesar (2014) Thomas et al. (2014) (Bignozzi and Sandrolini (2006) Karahan et al. (2012) Fadiel et al. (2014)

Fadiel et al. (2014)

Mohammed et al. (2012) Eiras et al. (2014) Turgut and Yesilata (2008) Turki et al. (2009) Uygunoglu and Topcu (2010) Gesoglu and Güneyisi (2011) Al-Akhras and Samadi (2004) Oikonomou and Mavridou, (2009) Onuaguluchi and Panesar (2014) Gesoglu and Güneyisi (2007)

5, 10 and 15

10 and 20 10, 20 and 30

10, 20 and 30 10, 20 and 30 10 and 20 5, 10 and 15 5, 10 and 15 5, 10 and 15 2.5-20% 22.2 and 33.3 10, 20 and 30 10, 20, 30 and 40

10, 20, 30 and 40

10, 25 and 50 40, 50 and 60 10-70

10, 30 and 50 10-50

5, 15 and 25 5 and 10 2.5, 5, 7.5, 10, 5, 10 and 15 5, 15 and 25

12.5 and 15

Passing sieve 0.8 4.75-0.15

4 and 2

3-31 and 5-1

Passing sieve No. 26 Passing sieve No. 6 5-0.7 2.4-1

Similar to sand gradation ~86% smaller than 2.3 mm Mesh 30, 2-0.8 mm, 4-2 mm 55% 2-0.5 and 45% 0.7-0.5 4.75-0.15 0.6-0

2-0.84

~1.3-0.08 4.75-0.075

4-1 4-1 <4 0.15

1.18-0.75

~86% smaller than 2.3 mm Similar to sand gradation

- Reduced water absorption

- Reduced water absorption

- 5% reduced water absorption

- 10% increased water absorption

- 15% better permeability

- Reduced water permeability, water absorption and chloride ion penetration

- Reduced permeability coefficient

- 10% reduced porosity

- 20% and 30% increased porosity

- Reduced water absorption

- Increased water absorption

- Increased water absorption

- Increased capillary water absorption

- Increased water absorption

- Increased water absorption and porosity

- Increased water absorption

- Increased water absorption

- Increased porosity

- 10%, 20% decreased water absorption

- 30%, 40% increased water absorption

- 10%, 20%, 30% decreased water absorption

- 40% increased water absorption

- Increased water absorption

- Increased water absorption

- Increased water absorption and porosity

- Increased porosity

- Increased water absorption and porosity

- Increased chloride ion permeability

- Reduced chloride ion penetration

- Reduced chloride ion penetration depth

- Reduced RCPT

- Increased chloride ion penetration depth

2480 water absorption can be lowered by replacing part of

2481 cement with fly ash (FA). Al-Akhras and Samadi (2004)

2482 measured the resistance to chloride ion penetration of mor-

2483 tars in terms of the electrical charge passed through the

2484 specimens in Coulombs according to ASTM C1202-97.

2485 Natural sand was partially replaced with rubber ash (size

2486 0.15 mm) at levels of 0%, 5% and 10%, by weight. The

2487 control mortar showed the highest value of electrical

2488 charge. The electrical charge passed through the specimens

2489 containing 5% and 10% rubber ash sand reduced by

2490 27.18% and 86.88%, respectively. Oikonomou and

2491 Mavridou (2009) reported a reduction in the chloride ion

2492 penetration depth by partially replacing natural sand in

2493 mortars with worn automobile tyre rubber (size

2494 1.18-0.75 mm) at different levels, by weight. This reduction

2495 was 14.22%, 16.76%, 25.43%, 30.25%, 35.18% and 35.85%

2496 with the inclusion of 2.5%, 5%, 7.5%, 10%, 12.5% and 15%

2497 rubber, respectively. Onuaguluchi and Panesar (2014)

2498 reported a reduction in the rapid chloride permeability

2499 (RCPT) of concrete specimens by partially replacing 5%,

2500 10% and 15% of natural fine aggregate with crumb rubber

2501 (size ~86%> smaller 2.3 mm), by volume. Gesoglu and

2502 Guneyisi (2007) reported an increased in the chloride pen-

2503 etration depth of concretes containing crumb rubber (grad-

ing close to the natural fine aggregate) and tyre chips as 2504

replacement of natural fine and coarse aggregate, respec- 2505

tively, at levels of 5%, 15% and 25%, by total aggregate vol- 2506

ume. The increment in the chloride depth increased as the 2507

content of rubber aggregate increased. They also reported 2508

that the chloride penetration depth can be reduced by 2509

replacing 10% cement with SF. Table 7 summarises the 2510

mentioned studies about the effect of rubber sand on the 2511

water absorption, porosity and chloride ion penetration 2512

of mortars and concretes. 2513

From the above review of the literature in this section, it 2514

can be noted that the inclusion of rubber sand in the mix- 2515

ture increased its percentage of water absorption and 2516

porosity, as reported by several studies, but it mainly 2517

depended on the rubber particle size and its content in 2518

the matrix. In general, the cause of high absorption could 2519

be the result of the formation of porosity during mixing 2520

process. As known, rubber particles are non-polar by nat- 2521

ure (water insolvable), during mixing, they are able to trap 2522

air bubbles at the particle surfaces (Fig. 21). This phe- 2523

nomenon causes the interface between cement paste and 2524

rubber to be porous and highly absorptive. On the other 2525

hand, small particle size of rubber (size < 0.5 mm) reduced 2526

the absorption. This is because the smaller particles of rub- 2527

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A.M. Rashad/International Journal of Sustainable Built Environment xxx (2015) xxx-xxx 31

Figure 21. trapped air bubbles at rubber passing sieve No. 6 (Sukontasukkul and Tiamlom, 2012).

ber acts as fillers to fill up capillary pores in the matrix that lead the absorption to be lower (Sukontasukkul and Tiamlom, 2012). Karahan et al. (2012) reported that the reason behind the increased capacity could be that higher amounts of air were trapped during mixing (Bignozzi and Sandrolini, 2006), a factor that may have occurred due to the tendency of rubber particles to entrap air in their rough surfaces because of their nonpolar nature (Turatsinze and Garros, 2008; Benazzouk et al., 2007) and/or because the hydrophobic nature of rubber increases air content when rubber particles are added. Uygunoglu and Topcu (2010) related the reduction in the absorption to the entrapment of air by the rubber particles at the particle-paste and particle-particle interfaces. Gesoglu and Guneyisi, 2011) related the increase in the absorption with increasing rubber content to the increase in porosity of rubber in mixtures and probably due to some deviations of rubber particles from sand grain size distribution and/or a significant higher air amount trapped during mixing procedure of rubberised mixtures. The increase in the water absorption of the mortar/concrete with the inclusion of rubber sand is one of the disadvantages of using this recycled material. On the other hand, Ling (2012) reported that as a small proportion (~10%) of rubber was distorted and filled the voids between the solid particles (natural aggregate) under a compression force of a plant-made machine. This filling mechanism was found to reduce the porosity by filling up the free pore volume in the concrete mixture. The chloride ion penetration depth increased with increasing rubber sand content. However, the magnitudes of the chloride penetration depth can be reduced by replacing 10% cement with SF (Gesoglu and Guneyisi, 2007) or by replacing part of cement with FA (Gesoglu and Guneyisi, 2011, 2011).

15. Resistance to aggressive environmental

Segre et al. (2004) studied the durability of mortar containing 10% rubber (size 0.2 mm) as natural sand replacement, by weight, exposed to 5% HCl for 6 days. Results showed higher resistance of rubber mortar against HCl compared to the control. Topcu and Demir (2007) pre-

Figure 22. Effect of rubber sand content on the mass loss after sulfuric acid attack of concretes (Azevedo et al., 2012).

pared mortar specimens by partially replacing natural sand with crumb rubber (size 1-0 mm or 4-1 mm) at levels of 10%, 20%, 30% and 40%, by volume. Some specimens were cured in NaCl solution simulating the effect of seawater. Other specimens were kept in normal curing for 28 days. Results showed a reduction in the dynamic elasticity modulus with the inclusion of rubber. The reduction in the dynamic elasticity modulus was 35%, 50%, 60% and 74% with the inclusion 10%, 20%, 30% and 40% rubber sand (size 1-0 mm), respectively, whilst it was 20%, 31%, 50% and 63%, respectively, with the inclusion of rubber sand with a particle size of 4-1 mm. Azevedo et al. (2012) studied the resistance of HPCs containing tyre waste rubber as natural sand replacement at levels of 0%, 5%, 10% and 15%, by weight, against sulphuric acid attack. After curing for 56 days, the specimens were exposed to sulphuric acid for a period of 28 days. Results showed that increasing rubber sand content led to higher mass loss degree (Fig. 22). Ganesan et al. (2012) reported that the weight loss of concrete specimens containing 15% rubber sand (size < 4.75 mm) after exposure to seawater or acidic solution (H2SO4) or sulfuric acid for 90 days was less than the control.

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Figure 23. Effect of rubber aggregate content on the average energy transferred at maximum load of concretes (Atahan and Yiice, 2012).

Figure 24. Effect of rubber sand content on the sound reduction coefficient of concretes (Mohammed et al., 2012).

2590 From the above mentioned studies in this section, it can

2591 be clearly noted that there is a distinct lack of studying the

2592 effect of aggressive environmental resistance on mortar/2593 concrete containing rubber sand. The aggressive environ-

2594 mental resistance of mortar/concrete containing rubber

2595 sand still needs more investigations. This can be a major

2596 topic for future investigations. However, according to the

2597 available studies, it can be noted that the inclusion of rub-

2598 ber sand in the matrix increased its resistance against HCl

2599 and seawater.

2600 16. Energy absorption

2601 Ganesan et al. (2013) partially replaced natural sand in

2602 concrete of beam-column joints with rubber (maximum size

2603 4.75 mm) at levels of 0% and 15%, by volume. They

2604 reported that the addition of shredded rubber sand could

2605 bring about improvement in the beam-column joint beha-

2606 viour under cyclic loads in term of the energy absorption

2607 capacity. Ozbay et al. (2011) reported an enhancement in

2608 the energy absorption of concretes by partially replacing

2609 natural sand with crumb rubber (size 3-0 mm) at levels of

2610 5%, 15% and 25%, by volume. The energy absorption

2611 increased with increasing rubber sand content. The

2612 enhancement in the energy absorption was approximately

2613 3.42%, 11.98% and 25.66% with the inclusion of 5%, 15%

2614 and 25% rubber sand, respectively. Atahan and Yiice

2615 (2012) replaced natural fine aggregate and coarse aggregate

2616 in concretes with crumb rubber at levels of 0%, 20%, 40%,

2617 60%, 80% and 100%, by volume. The small rubber particles

2618 that were used to replace natural sand passed mesh sizes of

2619 10 and 20, whilst large particles passed through a 13 mm

2620 screen that was used to replace the natural coarse aggregate.

2621 They reported that the energy dissipated by the rubber con-

2622 crete specimens at maximum load increased drastically as

2623 rubber aggregate content increased (Fig. 23). A maximum

2624 of 160.8% increment was measured between the control

2625 specimen and the 100% rubber specimen.

2626 From the above mentioned studies in this section, it can

2627 be concluded that the inclusion of rubber sand in the

matrix increased its energy absorption. The improvement 2628

of the energy absorption with the inclusion of rubber sand 2629

is one advantages of using this recycled material. 2630

17. Sound absorption 2631

Sukontasukkul (2009) partially replaced natural sand in 2632

concretes with two different particle sizes of crumb rubber 2633

at levels of 0%, 10%, 20% and 30%, by volume. The sizes of 2634

crumb rubber were No. 6 (passing sieve No. 6) and No. 26 2635

(passing sieve No. 26). Results showed an increase in the 2636

noise reduction coefficient with the inclusion of rubber 2637

sand. The increment in the noise reduction coefficient was 2638

40%, 40.57% and 22.72% with the inclusion of 10%, 20% 2639

and 30% rubber sand with large size, respectively, whilst 2640

it was approximately 41%, 25.58% and 46.37%, respec- 2641

tively, with the inclusion of small size rubber sand 2642

(Khaloo et al., 2008) replaced natural sand in concretes 2643

with rubber (maximum size 4.75 mm) at levels of 25%, 2644

59%, 75% and 100%, by volume. They reported that the 2645

sound absorption by concrete increased with increasing 2646

rubber sand content in which the velocity of ultrasonic 2647

waves reduced significantly with increasing rubber sand 2648

content. Mohammed et al. (2012) reported better sound 2649

absorption of concretes containing rubber (size 0.6 mm) 2650

as natural sand replacement compared to the conventional 2651

concrete. The noise reduction coefficient increased as the 2652

rubber sand content increased (Fig. 24). Najim and Hall 2653

(2012) reported that SCCs containing crumb rubber (size 2654

6-2 mm) as natural sand replacement at levels of 5%, 2655

10% and 15%, by weight, exhibited superior vibration 2656

damping behaviour compared to the control. Bowland 2657

et al. (2012) reported that ground rubber (maximum size 2658

of 0.25 mm) mixed with latex which replaced natural sand 2659

at levels of 5%, 10% and 15%, by volume, in concrete mix- 2660

tures improved damping characteristics. Eiras et al. (2014) 2661

reported an increase in the damping properties of mortars 2662

by partially replacing natural sand with crumb rubber (size 2663

-0.08-1.3 mm) at levels of 40%, 50% and 60%, by volume. 2664

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The damping properties increased with increasing rubber sand content. Gisbert et al. (2014) reported that mortars containing crumb rubber as natural sand replacement at levels of 10%, 20%, 30% and 40%, by weight, exhibited superior damping behaviour compared to the control. The damping increased with increasing the rubber sand content. They also reported that if the percentage of crumb rubber is higher, the presence of rubber can cause sound absorption if a finer granulometry is involved (size 0.25 mm).

From the above discussion in this section, it is safe to conclude that the inclusion of rubber sand in the matrix increased its sound insulation. The increment in the noise reduction coefficient of the matrix with the inclusion of rubber sand is one advantage of using this waste material. Because of this advantage, rubberised concrete can be used as sound barriers. The rubber sand in this case cannot be considered as waste material, but can be considered as valuable material.

18. Electrical resistance

Yung et al. (2013) reported higher electrical resistance of rubberised concrete in comparison with the plain concrete. The electrical resistance increased as the rubber sand content increased. The inclusion of rubber (size 0.6 mm) increased the surface resistance by 17%. Mohammed et al. (2012) reported an increase in the electrical resistivity of hollow concrete blocks manufactured by partially replacing natural sand with crumb rubber (size 0.6 mm) at levels of 10%, 25% and 50%, by volume, compared to the control. The electrical resistance increased with increasing rubber sand content.

From the above mentioned studies in this section, it can be clearly noted that there is a distinct lack of studying the effect of rubber sand on the electrical resistance ofmortar/-concrete. The electrical resistance of mortar/concrete containing rubber sand still needs more investigations. According to the available earlier studies, it can be concluded that the electrical resistance increased with the inclusion of rubber sand.

19. Cracking resistance

Jingfu and Yongqi (2008) reported that the inclusion of 20% rubber (average size 1.5 mm), by volume, as natural sand replacement retarded the cracking time about 24 h in comparison with the plain mortar. Huang et al. (2013) studied the cracking resistance of ECC mixtures containing tyre rubber as partially replacement of iron ore tailings that were used as aggregate at levels of 0%, 10%, 20%, 30% and 40%, by volume. Results showed that the ECC containing rubber sand exhibited higher cracking resistance than the control (Fig. 25), implying that the inclusion of rubber sand led to lower cracking tendency under restrained drying shrinkage. They also concluded that higher tyre rubber aggregate content led to reduce the crack width, crack length and crack number in the matrix. Ganesan et al. (2013) partially replaced natural sand in concrete of beam-column joints with rubber (maximum size 4.75 mm) at levels of 0% and 15%, by volume. They reported that the addition of shredded rubber could bring about improvement in the beam-column joint behaviour under cyclic loads in terms of crack resistance. Nguyen et al. (2012) partially replaced natural sand in mortars containing 40 kg/m3 fibres with rubber (size 1.4-0.65 mm) at levels of 0%, 20% and 30%, by volume. Results showed a reduction in the width of shrinkage cracks with the inclusion of rubber sand. The shrinkage cracks width was reduced by 30.23% and 51.2% with the inclusion of 20% and 30% rubber sand, whilst the increment in crack time was 20% and 60%, respectively. Khaloo et al. (2008) replaced natural sand in concretes with crumb rubber (maximum size 4.75 mm) at levels of 0%, 25%, 50%, 75% and 100%, by volume. They reported that cracking width in rubberised concretes was smaller than that of the plain concrete and the propagation of failure symptoms was more gradual and uniform.

20. Usability of rubberised mortar/concrete

In general view, using rubber as fine aggregate in mortar and concrete showed some advantages, in which some properties are improved, and some disadvantages, in which some properties are defected. The advantages of using rubber sand are decreasing density, improving impact energy, improving impact load, increasing toughness, increasing ductility, increasing freeze/thaw resistance, increasing thermal insulation, increasing sound insulation, increasing damping capacity, increasing strain capacity, reducing micro-cracks after firing, increasing abrasion resistance (according to rubber sand content and w/c ratio) increasing resistance against HCl attack, improving energy absorption, increasing electrical resistance and increasing cracking resistance. On the other hand, the disadvantages of using rubber sand are decreasing workability, increasing bleeding, decreasing mechanical strength, increasing drying shrinkage, decreasing carbonation resistance, decreasing corrosion resistance (rubber sand content P 10%), increas-

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2758 ing water absorption, increasing chloride ion penetration

2759 depth and decreasing sulfuric acid resistance.

2760 It is safe to conclude that rubber sand can be used for

2761 manufacturing lightweight concrete; non-structural works;

2762 decreasing the risk of spalling caused by exposure to ele-

2763 vated temperatures; as safety barriers with improved resis-

2764 tance to traffic noise, as sound barriers, as a sound

2765 absorber; in highway construction as a shock absorber; in

2766 buildings as an earthquake shock-wave absorber (Topcu

2767 and Avcular, 1997); as construction material where thermal

2768 insulation, sound insulation, and acoustic anti-vibration

2769 properties are required; and as construction material where

2770 high resistance for impact load is required (rail founda-

2771 tions, tram-rail beds). Furthermore, rubberised concrete

2772 can be used in foundation pads for machinery and in the

2773 railway station where vibration damping is required; in

2774 railway buffers, jersey barriers, bridge abutment fill and

2775 bunkers where resistance to impact or explosion is

2776 required, for pipe bedding and trench filling, in artificial

2777 reef construction, for pile heads and as paving slabs.

2778 21. Remarks

2779 The current review paper aims to review the previous

2780 works that were carried out on the fresh properties,

2781 mechanical properties, impact energy, impact load, tough-

2782 ness, ductility, shrinkage, abrasion resistance, freeze/thaw

2783 resistance, carbonation resistance, corrosion resistance,

2784 water absorption, porosity, chloride ion penetration, resis-

2785 tance to aggressive environmental, thermal insulation,

2786 energy absorption, sound absorption, electrical resistance

2787 and cracking resistance of mortar/concrete based on PC

2788 containing rubber as fine aggregate replacement. The

2789 remarks of this literature review can be summarised as

2790 follows:

2791 1. Most of the previous studies believed that the inclu-

2792 sion of rubber sand in the mixture reduced workabil-

2793 ity. On the other hand, a few other studies believed

2794 the positive effect of rubber sand on workability.

2795 The inclusion of rubber sand in the mixture increased

2796 bleeding and setting time.

2797 2. The inclusion of rubber sand in the mixture reduced

2798 fresh and dry density. This reduction increased with

2799 increasing rubber sand content.

2800 3. The inclusion of rubber sand in the mixture reduced

2801 the mechanical strength. This reduction increased

2802 with increasing rubber sand content. This can be mit-

2803 igated by replacing a suitable part of cement with SF

2804 or treating rubber particles with NaOH aqueous solu-

2805 tion or in water-soaking. Also, mixing rubber parti-

2806 cles with latex before they are added to the matrix

2807 was recommended to improve the strength.

2808 4. The inclusion of rubber sand in the mixture, upto

2809 50%, improved impact energy. Rubber sand, upto

2810 20% improved impact load behaviour.

5. Most of the previous studies believed higher tough- 2811 ness with the inclusion of rubber sand. The inclusion 2812 of rubber sand in the mixture increased its ductility 2813 and strain capacity. 2814

6. The inclusion of rubber sand in the matrix increased 2815 its shrinkage. The shrinkage increased with increasing 2816 rubber sand content. 2817

7. Rubber sand increased the abrasion resistance of con- 2818 crete if appropriate rubber sand content and suitable 2819 w/c ratio were used. The inclusion of 5% rubber sand 2820 in concrete led to anti-sulphate corrosion resistance. 2821 More than 10% rubber sand in concrete increased 2822 the reinforcing bar mass loss. Rubber sand increased 2823 the resistance of freeze/thaw of the concrete. The 2824 freeze/thaw resistance increased with increasing rub- 2825 ber sand content. 2826

8. In general, the inclusion of rubber sand in the mixture 2827 increased its percentage of water absorption and 2828 porosity, but it is mainly dependent on the rubber 2829 particle size and rubber sand content. 2830

9. Rubber sand increased the chloride ion penetration. 2831 This can be mitigated by replacing 10% of cement 2832 with SF or replacing part of cement with FA. 2833

10. Rubber sand reduced the carbonation resistance of 2834 concrete. The reduction in the carbonation resistance 2835 slightly increased with increasing rubber sand 2836 content. 2837

11. The inclusion of rubber sand in the mixture increased 2838 its resistance against HCl. On the other hand, the 2839 inclusion of rubber sand led to a higher mass loss 2840

t degree after exposure to sulphuric acid. This reduc- 2841

tion increased with increasing rubber sand content. 2842

12. The inclusion of rubber sand in the mixture increased 2843 its thermal insulation, sound absorption, energy 2844 absorption and electrical resistance. These properties 2845 increased with increasing rubber sand content. On the 2846 other hand, the inclusion of rubber sand in the mix- 2847 ture reduced its fire resistance. 2848

13. The inclusion of the rubber sand in the matrix exhib- 2849 ited higher cracking resistance and retarded the 2850 cracking time. 2851

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