Scholarly article on topic 'Recycled Aggregate Concrete for Transportation Infrastructure'

Recycled Aggregate Concrete for Transportation Infrastructure Academic research paper on "Civil engineering"

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Abstract of research paper on Civil engineering, author of scientific article — M. Surya, Kanta Rao VVL, P. Lakshmy

Abstract With rapid urbanization and development in the field of construction the demand for natural aggregates is increasing day by day with a corresponding increase in concrete production. Extraction of natural aggregates from mother earth leads to destruction of environment. Also, in the process of urbanization, the buildings and other structures which no-longer serve the intended purpose are often demolished. However, the disposal of this construction debris is becoming a major concern in the current era. The solution for these concerns are interdependent and inter connected. The use of the construction and demolition waste in concrete as a replacement of the natural aggregates is recognized as a viable way to effectively utilize this waste. These aggregates are known as recycled concrete aggregates. Though the idea of using construction and demolition waste in concrete in infrastructure projects has been in practice for a long time around the world, its use in India is limited till date. This paper reports the results of a laboratory based exploratory study aimed at characterizing the properties of recycled aggregate and recycled aggregate concrete, to verify their utilization in civil infrastructure. Recycled aggregates used in this study were generated by crushing of concrete cubes tested in the laboratory. Five different concrete mixes were produced; three recycled aggregate concrete viz with 50%, 75% and 100% recycled aggregates with fly ash, and two natural aggregate concrete mixes with and without fly ash, respectively. Triple mixing method was adopted for making of recycled aggregate concrete. Compressive strength, split tensile strength, flexural strength, modulus of elasticity, water absorption and resistivity of the concrete were determined. It was observed that there was no significant variation in compressive strength, split tensile strength and flexural strength of concrete, while the modulus of elasticity and resistivity decreased and water absorption increased with increase in percentage of recycled aggregates. The findings from the study show that the recycled concrete aggregate may be useful for construction of transportation infrastructure such as pavements and bridges. However, further research is needed particularly on the long term field performance of the recycled aggregate concrete before it can be used with confidence.

Academic research paper on topic "Recycled Aggregate Concrete for Transportation Infrastructure"

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Social and Behavioral Sciences

Procedia - Social and Behavioral Sciences 104 (2013) 1158 - 1167 —

2nd Conference of Transportation Research Group of India (2nd CTRG)

Recycled aggregate concrete for Transportation Infrastructure

Surya, M.a , Kanta Rao, VVL.ba*1 , Lakshmy, P.ca

aAcademy of Scientific and Innovative Research, New Delhi bPrincipal Scientist, Bridges and Structures Division, CSIR-CRRI, New Delhi cChief Scientist, Bridges and Structures Division, CSIR-CRRI, New Delhi

Abstract

With rapid urbanization and development in the field of construction the demand for natural aggregates is increasing day by day with a corresponding increase in concrete production. Extraction of natural aggregates from mother earth leads to destruction of environment. Also, in the process of urbanization, the buildings and other structures which no-longer serve the intended purpose are often demolished. However, the disposal of this construction debris is becoming a major concern in the current era. The solution for these concerns are interdependent and inter connected. The use of the construction and demolition waste in concrete as a replacement of the natural aggregates is recognized as a viable way to effectively utilize this waste. These aggregates are known as recycled concrete aggregates. Though the idea of using construction and demolition waste in concrete in infrastructure projects has been in practice for a long time around the world, its use in India is limited till

This paper reports the results of a laboratory based exploratory study aimed at characterizing the properties of recycled aggregate and recycled aggregate concrete, to verify their utilization in civil infrastructure. Recycled aggregates used in this study were generated by crushing of concrete cubes tested in the laboratory. Five different concrete mixes were produced; three recycled aggregate concrete viz with 50%, 75% and 100% recycled aggregates with fly ash, and two natural aggregate concrete mixes with and without fly ash, respectively. Triple mixing method was adopted for making of recycled aggregate concrete. Compressive strength, split tensile strength, flexural strength, modulus of elasticity, water absorption and resistivity of the concrete were determined. It was observed that there was no significant variation in compressive strength, split tensile strength and flexural strength of concrete, while the modulus of elasticity and resistivity decreased and water absorption increased with increase in percentage of recycled aggregates. The findings from the study show that the recycled concrete aggregate may be useful for construction of transportation infrastructure such as pavements and bridges. However, further research is needed particularly on the long term field performance of the recycled aggregate concrete before it can be used with confidence.

© 2013 The Authors. Published by Elsevier Ltd.

Selectionandpeer-reviewunderresponsibilityof International ScientificCommittee. Keywords: recycled aggregate, recycled aggregate concrete, construction and demolition waste

* Corresponding author. Tel.: (m) 9899059885; fax: 011-26845943. E-mail address: vvlkrao.crri@nic.in, kantarao_vvl@yahoo.co.in

1877-0428 © 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of International Scientific Committee. doi: 10.1016/j.sbspro.2013.11.212

1. Introduction

A rapidly advancing economy and rising standards of living have spurred a phenomenal increase in infrastructure and construction activities, leading to an increase in demand and consumption of natural aggregates. During construction, a lot of waste concrete (construction waste) is often generated. Also in the process of urbanization, the old buildings which no longer serve the purpose are demolished and disposal of the demolition debris thus generated is becoming a major concern. The demolition waste is often disposed off in land-fills. However, with ever increasing demand for constructible land, use of land-fills for disposal of demolition waste is not a welcome option. The large scale depletion of natural resources for extraction of natural aggregates, accumulation of huge quantities of construction and demolition waste (CDW) led to search for a viable option for effective utilization of CDW. Crushing of CDW, and generation of particles of size of natural aggregate for use as replacement of natural aggregate in a concrete mix has been recognized as the most viable and sustainable solution for using the CDW. The particles thus generated are often called 'recycled aggregates'. When the recycled aggregate is generated primarily from crushed cement concrete, it is called recycled concrete aggregate (RCA). The concrete made using RCA is called 'Recycled Aggregate Concrete (RAC)".

The coarse recycled aggregate comprises of two phases, namely the original virgin aggregate and the adhered mortar. The quantity of adhered mortar influences to a large extent the engineering, mechanical and durability properties of the aggregate, and the RAC. The influence of using coarse recycled aggregate as a replacement of natural aggregate, on the properties of RAC, has been topic of research by many, from the results of which it was observed that the properties of the RAC were lower than those of the Natural Aggregate Concrete (NAC), which has been attributed primarily due to the adhered (porous) mortar. Chai (2004), and Adnan et al. (2007) reported that the compressive strength of RAC decreased by 4 to 37% with increase in percentage replacement of coarse RCA. Yong and Teo (2009) and Limbachiya (2012) observed that till 50 % replacement, there was no difference in split tensile and flexural strengths between the RAC and the NAC, but at 100% replacement the same was higher for RAC possibly due to better interlocking. For concretes with similar range of strength properties, the elastic modulus was found to decrease, by up to 30 %, with increase in percentage of RCA (Etxeberria et al, 2007, Limbachiya 2012). The water absorption of RAC depends on amount of RA and it increased with increase in percentage of RCA (Gomez- Soberon, 2002a; Casuccio et al, 2002). Kou et al (2007) reported that the chloride permeability (RCPT) of RAC was 1.53 times more than that for NAC. Also, RAC exhibited a higher depth of carbonation, by up to 1.3 - 3 times, than the NAC under similar exposure conditions (Katz 2003; Shayan and Xu, 2003).

Attempts were also made to improve the properties of RAC to bring them at par with NAC. The adoption of double mixing method and triple mixing method improved the micro structure of concrete and decreased the depth of Interfacial Transition Zone (ITZ) which in turn decreased the depth of chloride penetration and depth of carbonation and enhanced the overall durability of concrete (Otsuki et al, 2003; Smith, 2009; Tam et al 2005; Kong et al, 2010). The properties of ITZ improved more by triple mixing method than by the double mixing method.

This paper presents the results of a laboratory based exploratory study on the properties of RAC mixes of characteristic compressive strength of 40 MPa, The coarse RA for the study was generated in the laboratory. The study included investigation of some of the physical and mechanical properties namely compressive, split tensile and flexural strength, modulus of elasticity and, durability properties such as water absorption and resistivity of concrete. The RAC's were produced by triple mixing method with various percentage of RCA viz 0%, 50%, 75%, 100%, with fly ash.

2. Experimental Details

2.1 Materials

Ordinary Portland Cement (OPC) of grade 43 conforming to IS 8112, and Class F low calcium fly ash suitable for use in concrete as an admixture according to IS 3812 (Part 2) were used. Crushed granite natural aggregate (NA) of 20 mm size and 10 mm size available in Delhi region was used. The recycled aggregates used in this study were generated by crushing of concrete cubes which were cast and tested in CSIR-CRRI over a period of 2 to 3 years, and also those cast at various bridge construction sites near Delhi. Even though the minimum compressive strength of concrete adopted for construction of reinforced concrete and prestressed concrete bridges as per MOSRTH specifications (2001) is 35 MPa, the concrete cubes used for generation of RCA in the present study were having compressive strength in the range of 35 MPa to 45MPa. The cubes were first manually broken into pieces of size less than 100 mm and then were crushed using a mini jaw crusher. The crushed material retained between IS sieves 20 mm and 4.75 mm was used. The particle size distribution of both NA and RCA were within the margins as specified in IS 383. The physical and mechanical properties of coarse aggregates are given in Table 1. The recommended specifications of RCA, as per some of the International Standards, are also presented in Table 1 for comparison. It is seen from Table 1 that the RCA used in the present study is satisfying the acceptance criteria prescribed in JIS A 5021 for Class H and can be used for concrete structures and segments requiring a nominal strength of 45 MPa or less. According to JIS 5021, the RAC prepared with this aggregate can be subjected to any exposure condition without any limitations. From Table 1, it is seen that the impact and abrasion properties of the RCA are complying with the limits given in MOSRTH for aggregates used in base and sub-base of pavement and also for pavement concrete. Natural sand available in Delhi region conforming to Zone I of IS 383 was used as fine aggregate. Super plasticizer based on second generation poly carboxylic ether polymer was used. It was a light brown liquid with a relative density 1.1.

Table 1 Specifications and Observed Properties of Natural and Recycled Coarse Aggregates

RCA NA

Property Value obtained in present study Acceptance criteria Value obtained in present study Acceptance criteria

Class H Class M Class L

Specific Gravity 2.501 2.5 or more (JIS A 5021 -class H) 2.3 or more (JIS A 5022 -class M) (JIS A 5023 — class L) 2.675 2.30 - 2.90 (ACI E1-07)

Water Absorption (%) 2.76 3.0 or less (JIS A 5021 -class H) 5.0 or less (JIS A 5022 - class M) 7.0 or less (JIS A 5023 — class L) 0.42 <2.0 (IS 2386 - Part 5)

Abrasion Loss (%) 29.24 40 or less (KS F 2573) 26 < 30 (IS 383) < 40 (MOSRTH,2001)

Crushing value (%) 28.87 - 27.12 < 30 (IS 383)

Impact value (%) 16.04 - 21.77 < 30 (IS 383) <30 (MOSRTH, 2001)

Bulk Density kg/m3 1340 1200 (HB 155 : 2002) 1630 1280 -1920 (ACI E1-07)

2.2 Concrete Mixes

Five concrete mixes were made i.e. a) Control concrete with 100 % Natural aggregate without fly ash (NAC), b) 100 % Natural aggregate concrete with fly ash (NAF), c) Recycled aggregate concrete with 50% of recycled aggregate (R50), d) Recycled aggregate concrete with 75% of recycled aggregate (R75) and e) Recycled aggregate concrete with 100% of recycled aggregate (R100). The concrete mixes with recycled aggregates

contained fly ash as admixture. All the concrete mixes were designed as per IS 10262 to achieve a characteristic compressive strength of 40 MPa. But the specific gravity used for determining the weight of coarse aggregate is the specific gravity of NA (2.675) for NAC and NAF, specific gravity of RCA (2.501) for R100 and the specific gravity of the combination of NA and RCA (2.593 and 2.553) for R50 and R75 respectively. The details of mix proportions of the concrete mixes are given in Table 2.

Table 2 Details of mix proportions

Mix Designation Cement (kg/m3) Water (kg/m3) Fly Ash (kg/m3) Fine Aggregate (kg/m3) (SSD Condition) Coarse Aggregate (kg/m3) (SSD Condition) Super plasticizer (Percentage by weight of cement ) Slump (mm)

NA RCA

NAC 410 164 706 1172 0.6 65

NAF 410 164 82 706 1172 0.6 61

R50 410 164 82 706 568 568 0.6 63

R75 410 164 82 706 280 839 0.6 62

R100 410 164 82 706 - 1119 0.6 68

2.3 Casting and Curing

The concrete mixes were prepared in a drum mixer of capacity 300 kg. Triple mixing method, developed by Kong et al (2010), was adopted for the production of concrete. In conventional method dry mixing of aggregates and cement is carried out first and then the water is added, whereas in triple mixing water is added in two parts allowing less water near ITZ, making the same more compact contributing to better mechanical and durability properties. The steps involved are as follows: coarse (RCA and NA) and fine aggregates were initially mixed for 15 s. A part of water was then added to the aggregate mixture and mixed for 15 s, and to this wet aggregate the fly ash was added and further mixed for 15 s to facilitate coating of the surface of aggregate with fly ash. Cement was then added to the surface coated aggregate and the remaining water was added and the mixing was continued for further 60s. The oiled moulds were filled with concrete in layers and vibrated on a table vibrator. The details of test specimens prepared, their test age and the standards describing the test procedure are given in Table 3. The cast specimens were water cured till the date of test.

Table 3 Details of tests

Property Age at test (days) Specimen size (mm) Standard Prescribing the Test method

Compressive strength 7 IS 516

Split tensile strength 28 Cylinder - 150 ® X 300 IS 5816

Elastic Modulus 28 Cylinder - 150 ® X 300 IS 516

Flexural strength 56 Prism - 100x100x500 IS 516

Water absorption 56 cube - 150x150x150

Resistivity 56 Prism - 100x100x500 Werner's Probe

2.4 Testing of the concrete specimen

Concrete test specimens were tested for different properties as indicated in Table 3. Mean of test values of three test specimen was considered as suggested by respective standards cited in Table 3. In the present study a

standard deviation of 0.55 to 11.5 for compressive strength, 1.69 to 14.7 for split tensile strength and 0.87 to 14.5 for flexural strength were obtained for the test values which are below the acceptable standard deviation limit of 15 as per IS 456. IS 516 allows a variation upto 5% in the test value for the elastic modulus test and the same criteria have been adopted in this study for acceptance of the test results. Each specimen for resistivity was tested at four locations and the mean of three test specimen (12 readings) is reported.

3. Results and Discussion

3.1 Compressive strength

The test results of different concrete specimen are presented in Table 4. Fig.1 shows the variation of strength of various mixes with age. It may be seen that the compressive strength of all the samples increased with age. The strength of NAC was higher during the early days, but the strength of other mixes (containing fly ash) was higher at later days. It is clear that the fly ash exhibits its pozzolanic effect at later ages.

0 7 14 21 28 35 42 49 56

Age in days

Fig. 1 Variation of strength of mixes with age

Fig. 2 shows the concrete cubes failed in compression and it may be seen that both natural aggregate and recycled aggregate concretes exhibited similar pattern of failure. The bar chart for variation of compressive strength concrete mixes with age is presented in Fig.3, and it can be seen that all the mixes had similar compressive strength range. This is may be because of the triple mixing method adopted for concrete mixing during which, the RA gets coated with a thin layer of fly ash. This fly ash layer during hardening of concrete improves the interfacial transition zones through the filler effect and pozzolanic effect (Kong et al, 2010). Thus, the transition zone of RAC is improved by fly ash making its strength similar to or marginally greater than NAC mix without fly ash.

Fig. 2 Failure pattern of various mixes in compression

Table 4 Strength properties of various mixes of concrete used in present

Mix Designation Compressive strength Split tensile strength Flexural strength Elastic Modulus

MPa MPa MPa GPa

3 days 7 days 28 days 56 days 28 days 56 days 56 Days 28 days 56 days

NAC 33.85 43.85 45.63 53.19 3.49 3.96 5.35 28.55 30.15

NAF 33.33 41.03 47.25 57.77 3.74 4.15 5.46 29.15 35.20

R50 28.89 37.49 47.40 54.02 3.49 3.53 4.78 24.07 27.17

R75 30.67 34.96 46.61 54.22 3.11 3.63 4.77 21.54 26.28

R100 30.15 43.11 48.89 57.33 3.68 4.15 5.72 19.38 25.03

££ 60 I S

3.2 Split tensile strength

NAC NAF R 50 R 75 R 100 Fig. 3 Compressive strength of various mixes

□ 3 days

□ 7 days ¡."J 28 days ■ 56 days

The split tensile strength of concrete with different percentages of RA increased with age and there was not much variation between the split tensile strength of NAC and the RAC (Table 4). However, it was noted from Fig. 4 that the split tensile strength of R100 mixes were found to exhibit a better split tension strength. This could be because of the rough texture and absorption capacity of the adhered mortar in RA which provides better bonding and interlocking between the cement mortar and the RA (Etxeberria, 2004).

-O— 28 days 56 days

NAC NAF R 50 R 75 R 100

Fig. 4 Variation in Split tensile strength with respect to percentage of recycled aggregates

The concrete cylinders failed in split tension are shown in Fig. 5. Visual observation of split tension specimen after failure shows that in of NAC and NAF (i.e.) natural aggregate concrete mixes the surface of failure is rough and uneven and the specimen failed through the ITZ. In case of RAC mixes surface of the failure was not only through the ITZ but also through the recycled aggregate. From the failed specimens it is found that the roughness of the failure surface decreased with increase in percentage of recycled aggregate, and the failure surface became nearly planar for R100 mixes.

3.3 Flexural strength

The results of flexural strength tests, given in Table 4 and Fig. 6, indicate that the flexural strength of R100 mixes is higher as compared to other mixes. The higher flexural strength of R 100 mix could be attributed to the improved interfacial transition zone due to the addition of fly ash, and improved pore size distribution of RAC mix due to the pozzolanic action of fly ash which exhibits its effect at longer ages. It is seen that all five mixes used in the study have a flexural strength value greater than 4.15 MPa, which is the minimum flexural strength specified by MOSRTH for pavement quality concrete.

CO Ph ? §

NAC NAF R 50 R 75 R 100

Fig. 6 Variation in flexural strength with respect to percentage of recycled aggregates

s 30 Ph Ü

...........

• ••

,.A ------28 days

""if" 56 days

Fig. 7 Variation in elastic modulus with respect to percentag e of recycled aggregates

3.4 Elastic Modulus

The elastic modulus was found to decrease with increase in percentage of RCA as seen from Table 1 and Fig. 7. Similar results were observed by Rao et al (2011), Etxeberria (2007), Kou et al (2007). This is primarily because the recycled aggregates are more prone to deformation than natural aggregates and the modulus of elasticity of recycled aggregate is lesser than modulus of elasticity of natural aggregate (Etxeberria, 2007). Thus, it can be inferred that the actual deformation of a structural member with recycled aggregate will be greater than the deformation of member with natural aggregate.

3.5 Water Absorption

The test results for water absorption of various mixes is given in Fig. 8, from which it may be inferred that water absorption increases with increase in proportion of recycled aggregates. The water absorption increased by 57%, 62.3% and 78.5% for R50, R75 and R100 mixes, respectively when compared with NAC, and the same increased by 70.3%, 76%, 93.6% when compared with NAF. This may be attributed to higher water absorption of recycled aggregate when compared to natural aggregates. In the present case water absorption of RCA is about 6.5 times higher than that of NA.

.2 5 £ 4

I 25-33 24.613 24.575 111

Fig. 8 Variation of Water absorption with percentage recycled aggregates

Fig. 9 Variation of concrete resistivity with percentage of recycled aggregates

3.6 Concrete Resistivity

The variation of concrete resistivity in the concrete mixes is presented in Fig. 9. It is found that the resistivity of the R50, R75 and R100 mixes was lesser than that of the NAF sample and greater than that of NAC sample. The higher resistivity of concrete is useful in resisting the initiation of reinforcement corrosion. It is noted that the resistivity of the RAC mixes fit in the category of 'low chloride ion permeability", according to the criteria of Florida Method of Test FM 5-578 (2004) shown in Table 5.

Table 5: Chloride ion permeability based on surface resistivity of concrete FM 5-578 (2004)

Chloride ion permeability Resistivity kiî cm

High < 12

Moderate 12 - 21

Low 21 - 37

Very low 37 - 254

Negligible > 254

4. Applications of recycled aggregates

The examples for use of RCA in various transportation infrastructures are given in the Table 6. Though there are certain inferior properties still the use of RCA in concrete construction is encouraged due to the following reasons, exploitation of natural resources for of aggregates can be minimized, transportation costs of aggregates from quarries to site can be minimized, construction and demolition wastes to be dumped in landfill can be reduced thus reducing the demand for land, apart from environmental aspects it is also an economically viable solution to reduce the cost of concrete.

Table 6: Instances for use of RCA in transportation infrastructure

Sl. No Structure Location Year of construction Remarks

1 Concrete kerb and Gutter Lent hall street project, Sydney 1999 -

2 Footway paving blocks and slabs London Borough of Bexley 2001 -

Recycled concrete pavement section.

3 (Anderson et al, 2009) Near Mountain Home, Idaho 1990/1991 -

4 Recycled concrete pavements. (Anderson et al, 2009 Houston, Texas 1995 -

5 Recycled concrete pavements (Anderson et al, 2009) Illinois 2006 The pavement was made completely of recycled aggregates

Curb, gutter and valley gutter

6 (Anderson et al, 2009) Michigan 2009 -

7 Base and shoulder material Wisconsin 2009

5.Conclusions

Based on the results from the study, the following conclusions were drawn.

1. The recycled aggregate used in the present study fulfilled the codal requirements for RCA with respect the physical and mechanical properties, however the same were lower than those for natural aggregates.

2. The natural aggregate concrete mixes i.e. NAC, NAF and the RAC mixes R50, R75 and R100 exhibited similar behavior in compression, split tension and flexure.

3. The elastic modulus of RAC decreased with increase in percentage of RCA. It implies that the deformation of structure made with RAC could be higher than the one constructed with nA concrete.

4. The water absorption of RAC increased with increase in percentage of recycled aggregates. However, the RAC had a relatively higher resistivity as compared to that of NAC. The higher resistivity of RAC indicates lower permeability to chloride indicating lower possibility of reinforcement corrosion.

5. It may be suggested that the properties of RAC are satisfactory for use in concrete; however a detailed investigation on long term performance of RAC is needed before their actual use in transportation infrastructure.

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