Scholarly article on topic 'Mechanical Properties of Concretes with Recycled Aggregates and Waste Brick Powder as Cement Replacement'

Mechanical Properties of Concretes with Recycled Aggregates and Waste Brick Powder as Cement Replacement Academic research paper on "Civil engineering"

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{"Recycled aggregates" / "waste brick powder" / "replacement of cement" / "mechanical behaviour of recycled concrete"}

Abstract of research paper on Civil engineering, author of scientific article — Viviana Letelier, Ester Tarela, Giacomo Moriconi

Abstract The cement industry is responsible for around a 5% of the CO2 emissions worldwide and considering that concrete is one of the most used materials in construction its total effect is significant. An alternative to reduce the environmental impact of concrete production is to incorporate certain amount of residuals in the dosing, limiting the replacement percentages to avoid significant losses in the mechanical properties of the final material. This study analyses the variation in the mechanical properties of structural concretes with recycled aggregates and waste brick powder as cement replacement to test the effect of the simultaneous use of different residuals in the same material. All concretes are dosed for a compressive strength of 30MPa. The recycled aggregates are obtained from prefabricated pipe debris with a compressive strength of 20MPa. The waste bricks are obtained from construction demolitions. Four levels of replaced cement by waste brick powder are considered: 0%, 5%, 10% and 15%. Also, two kinds of samples are studied regarding the amount of recycled aggregates: 0% and 30%. All these levels are combined to analyze the effect of both residuals in the mechanical properties of the concrete through compressive strength tests, flexural strength tests and elasticity modulus tests, all of them after 28 curing days. Results show that when no recycled aggregates are used, the cement can be replaced up to a 15% by waste brick powder. But when both residuals are combined the amount of waste brick powder recommended without significant losses in the final material properties is limited to a 5%. Replacing a 30% of the aggregates together with a 5% of the cement can considerably reduce the environmental impact of the final material.

Academic research paper on topic "Mechanical Properties of Concretes with Recycled Aggregates and Waste Brick Powder as Cement Replacement"

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Procedía Engineering 171 (2017) 627 - 632

Procedía Engineering

www.elsevier.com/locate/procedia

Sustainable Civil Engineering Structures and Construction Materials, SCESCM 2016

Mechanical properties of concretes with recycled aggregates and waste brick powder as cement replacement

Viviana Leteliera'*? Ester Tarelaa, Giacomo Moriconib

aDepartment of Civil Engineering. Universidad de la Frontera, Av. Fco. Salazar 01145, Temuco-Chile bUniversita Politécnica delle Marche, ViaBrecceBianche - 60131 Ancona - Italy

Abstract

The cement industry is responsible for around a 5 % of the CO2 emissions worldwide and considering that concrete is one of the most used materials in construction its total effect is significant. An alternative to reduce the environmental impact of concrete production is to incorporate certain amount of residuals in the dosing, limiting the replacement percentages to avoid significant losses in the mechanical properties of the final material. This study analyses the variation in the mechanical properties of structural concretes with recycled aggregates and waste brick powder as cement replacement to test the effect of the simultaneous use of different residuals in the same material. All concretes are dosed for a compressive strength of 30 MPa. The recycled aggregates are obtained from prefabricated pipe debris with a compressive strength of 20 MPa. The waste bricks are obtained from construction demolitions. Four levels of replaced cement by waste brick powder are considered: 0 %, 5 %, 10 % and 15 %. Also, two kinds of samples are studied regarding the amount of recycled aggregates: 0 % and 30 %. All these levels are combined to analyze the effect of both residuals in the mechanical properties of the concrete through compressive strength tests, flexural strength tests and elasticity modulus tests, all of them after 28 curing days. Results show that when no recycled aggregates are used, the cement can be replaced up to a 15 % by waste brick powder. But when both residuals are combined the amount of waste brick powder recommended without significant losses in the final material properties is limited to a 5 %. Replacing a 30 % of the aggregates together with a 5 % of the cement can considerably reduce the environmental impact of the final material.

©2017 The Authors.PublishedbyElsevierLtd. Thisis an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of SCESCM 2016.

Keywords: Recycled aggregates; waste brick powder; replacement ofcement; mechanical behaviour ofrecycled concrete.

* Corresponding author. Tel.: +56-45-2596533. E-mail address: viviana.letelier@ufrontera.cl

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of SCESCM 2016.

doi:10.1016/j.proeng.2017.01.396

1. Introduction

Concrete is one of the most used materials in construction and, at the same time, one of the materials with higher contribution to the amount of construction and demolition waste (CDW) generation. In concrete production the main responsible for CO2 production is the use of ordinary Portland cement with a contribution rate roughly equivalent to 80-90 % [1]. Hence, an effective way to reduce the environmental impact of concrete production is to minimize the CO2 emission related to cement.

Viera et al. [2] studied the effect of adding fine aggregates from waste bricks and ceramic sanitary ware in concretes, concluding that these fine aggregates contribute to the pozzolanic activity. They found that the use of these residuals increased the strength of the concretes compared to a traditional control one. Puertas et al [3] found that ceramic materials, used as cement replacement, have pozzolanic activity after at least 8 curing days. Kulovana et al [4] study the replacement of up to a 60 % of brick residuals as cement, with a 0.4 water/cement ratio, concluding that the use of up to a 20 % does not compromise the mechanical properties of the concrete and it enhances up to a 50 % its heat conductivity. On the other hand, Katzer [5] analyzes mortars with 10 % and 50 % brick waste replacements, finding that these residuals can be used in materials with low mechanical requirements (over 0.6 water/cement ratios). This disparity in the results can be attributed to the particle size distribution of the residual, while Katzer [5] uses material with particles under 8 mm, Kulovana et al [4] mainly replace material under 100 microns.

Moreover, the use of ceramic brick residuals enhances the durability due to a refinement in the pore structure. Bignozzi and Bondua [6] found that the use of a 25 % of ceramic residuals as cement supplement increases the cement durability compared to ordinary Portland cements. Similar results are obtained by Pacheco and Jalali [7,8] using 20 % of brick and sanitary ware ceramic waste. On their behalf, Toledo et al [9] and Vejmelkova et al. [10] conclude that the use of up to a 20 % of ceramic brick has no influence in the compressive strength and elasticity modulus of the mortar, and Lavat et al. [11] establish that 20 % to 30 % of the cement can be replaced by adequately grinded ceramic roof tile.

Besides, the replacement of up to a 25 % of cement by brick waste has been tested along with the use of waste glass as sand replacement. Results have proven that the brick powder is able to counteract the negative effects of the use of glass in the alkali-silica expansive reaction responsible of the production of fissures in the concrete [12].

An alternative to reduce even more the CO2 emissions and the amount of CDW from concrete production is to replace, not only some amount of cement but also other of the raw materials, such as coarse aggregates. Several studies [13-23] have proven the feasibility of the use of recycled aggregates (RA) if the percentage of replacement is limited [16-23]. Differences between the mechanical properties of traditional concrete and concretes with RA have been mainly attributed to the old mortar adhered to the surfaces of the RA. Two interfaces have to be considered when using RA rather than one, the old interface, between the old mortar and the RA, and the new one, between the RA and the new cement mixture [14]. The quality of these interfaces, given by the quantity and quality of the old adhered mortar, is a key factor influencing the mechanical behavior of recycled concrete [15,24].

Despite the use of RA and waste brick powder (WBP) has been studied in construction materials, there is still a lack of information about the mechanical behavior of concretes produced with both residuals simultaneously. Therefore, the goal of this research is to analyze the effects of the simultaneous replacement of WBP as cement and RA as natural coarse aggregates, in particular, in the mechanical properties (compressive strength and flexural strength) of concrete mixtures, to efficiently maximize the reuse of concrete waste. The aim of this study is to optimize the mixture combining the considered parameters, maximizing the amount of WBP and RA reused.

2. Methods and materials

2.1. Cement and bricks

Pozzolanic cement, equivalent to ASTM type P cement, was used. The targeted 28-days-compressive concrete strength was set at 30 MPa.

WBP, used as cement replacement, was obtained from industrial brick residuals from demolition debris.

2.2. Natural and recycled aggregates

RA were obtained from precast concrete debris and their nominal sizes are 19.3 mm, 12.5 mm and 9.5 mm. The amount of mortar adhered to the surface of RA has been mechanically reduced by applying a 300 rev abrasion using a Los Angeles machine. This way the effect of the double interface problem is minimized.

The physical properties of the coarse aggregates were obtained following the ASTM C127-15 and ASTM C128-15. The results are shown in Table 1. Natural sand was used in all of the concretes. Natural aggregates (NA) present higher values of density than recycled ones. This decrease, of around 6 %, in the density is caused by the presence of remaining adhered mortar in RA. This has been proven measuring the density and the water absorption both before and after the abrasion treatment. On the other hand, the water absorption is around 2.5 times bigger in RA than in NA.

Table 1: Physical properties of the coarse aggregates

Aggregates Size pRsss prs pn Absorption

NA (Natural Aggregates) 6.3-9.5 2678 2629 2765 1.9%

9.5-12.5 2687 2642 2767 1.7%

12.5-19 2699 2661 2765 1.4%

RA (Recycled Aggregates) 6.3-9.5 2510 2390 2720 5.0 %

9.5-12.5 2530 2430 2720 4.4 %

12.5-19 2530 2440 2700 4.0 %

2.3. Sample preparation

In order to assess the effects of WBP as partial replacement of cement on the behavior of concrete, a constant water/binder (cement + fine addition) ratio of 0.42 was used for all samples.

The experimental phase consisted in analyzing the differences in the mechanical properties between concrete made with different amounts of WBP (0 %, 5 %, 10 % and 15 %) and NA, and concretes with the same amounts of WBP and 30 % of RA. This way not only the effect of the WBP can be assessed but also the combined effect of both residuals.

The manufactured samples and series are shown in Table 2.

Table 2: Concrete dosages

Natural Aggregate RA Cement WBP Sand Water

(2.36-19 mm) (6.3-19 mm)

kg kg kg kg kg Lt

B0-R0 1266.00 - 382.00 - 542.00 192.63

B5-R0 1266.00 - 362.90 19.10 542.00 192.63

B10-R0 1266.00 - 343.80 38.20 542.00 192.63

B15-R0 1266.00 - 324.70 57.30 542.00 192.63

B5-R30 886.2 379.8 362.90 19.10 542.00 192.63

B10-R30 886.2 379.8 343.80 38.20 542.00 192.63

B15-R30 886.2 379.8 324.70 57.30 542.00 192.63

Compressive strengths, flexural strengths and static modulus of elasticity were tested after 28 curing days. The compressive strength was tested using a hydraulic press with a maximum capacity of 3000 KN and was determined using the standard ASTM C39/C39 on three 150^*300 mm cylindrical specimens. The flexural strength was

measured following the ASTM C78 specifications on three 150x150x530 mm prism specimens. The static modulus of elasticity was determined on three 150^*300 mm cylindrical specimens according to ASTM C469 for each type of concrete produced.

3. Results and discussion

The results obtained for the compressive strength, flexural strength and static elasticity modulus after 28 curing days are shown in Fig. 1. The samples a named following the code: B(% ofWBP)-R(% ofRA).

Most of the series without RA present no significant negative effects, even when a 15 % of WBP is used, agreeing with several authors that conclude that up to a 20 % of the cement can be replaced by ceramic materials with almost no effect in the mechanical properties of the concretes [4,7,8]. Only when the WBP replacement exceeds a5% and is combined with the use of RA a slight decrease in the mechanical properties is observed.

_ s _

BORO B5-R0 BIO-RO B15-R0 B5-R30 BIOMO B15-R30

35000 30000 ï 25000

5 20000 j

5 15000 )

> 10000 '1

3-RO BS-RÛ Hin KG B1S-R0 B5-R30 B10-R30 B15-R30

4,00 3,50 là 3'00

£ 2,50 I £ 2,00 vi

I 1,50 —

1,00 0,50 0,00

— —

BO RO B5-R0 B10-R0 B15-R0 B5-R30 B10R30 B15-R30

■ Relative Compressive Stre right

■ Relative Flexural Stre right

a Relative Static Modulus Elasticity

j> J> j> # <$> ^

* ^ 4> J* ¿f

Fig. 1: (a) Compressive strength, (b) Flexural strength, (c) Static elasticity modulus, (d) Compressive strength, flexural strength an elasticity

modulus related to CC (B0-R0) values.

Compressive strength (Fig.la) varies between an increase of 9 % and a reduction of 6 % compared to the B0-R0 sample or the control concrete (CC). Series B5-R0 and B5-R30 present the highest values. Both series contain a 5 % WBP replacement. Agreeing with the conclusions presented by Ergun [5], the fineness and the amount of residue improved the initial porosity of the mix due to the obstruction of pores as a filler effect. This effect would improve the simultaneous behavior of RA and WBP. Nassar and Soroushian [26] studied the use of glass powder as cement replacement together with RA, concluding that a pozzolanic reaction occurs between the silicates in the glass powder and the calcium hydroxide (Ca(OH)2) in the cement of the mortar of RA, forming hydrated calcium silicate (CSH), enhancing the quality of the interface.

Flexural strength (Fig. lb) ranges between an increase of 1 % and a decrease of 16 %. Here the amount of RA seems to have low influence on the results. The most significant reduction is obtained for series B15-R30, with al6 "/ loss in relation to CC. Fig. Id shows the relative compressive and flexural strength related to CC. The use WBP and RA has more effects in the flexural strength than in the compressive strength.

Static modulus of elasticity (Fig. lc) decreases between a 1 % and a 12 %. The amount of RA seems to have low influence on these results. The most significant reduction is obtained for series B5-R30, with a 12 % loss respect to CC. Fig. Id shows the relative static modulus of elasticity related to CC. As it happened with flexural strength, the static elasticity modulus suffers the effect of the use of WBP and RA more significantly than the compressive strength.

ACI 318-11 proposes Eq. 1 to calculate the ultimate tensile strength or flexural strength and Eq. 2 to calculate the static modulus of elasticity:

fr = Q.GlJTc (1)

Where fr is the ultimate flexural strength (MPa) and fc the cylindrical compressive strength (MPa).

Ec = 4700JTc (2)

Where Ec is the static elasticity modulus (MPa) and fc is the cylindrical compressive strength (MPa).

The experimental results and those obtained using Eq. 1 and Eq. 2 for the studied specimens are shown in Fig. 2. Almost all of the specimens show higher values than the ones specified by ACI 318, except for the flexural strength in series B15-R30. As the values established by ACI 318 are quite conservative it is possible to state that concretes with recycled aggregates exceed expected resistances.

■ Experimenta! values

O-RO B5-R0 B1D-RO HIS KO 85-R30 B10-R30 B1S-R30

35000 -

1530000 a.

«5000 -220000 -

■ Experimental values

210000 ï

5000 0 -

B0-RÛ B5-RQ B1D-RÜ B1&-R0 BS-R30 B10-R30 B1S-R30

Fig. 2. (a) Flexural strength: experimental and ACI values, (b) Static elasticity modulus: experimental and ACI values.

4. Conclusions

• The best compressive strength results are obtained using 30 % ofRA, and 5 % of WBP.

• Low percentages of replaced cement by WBP were found to be beneficial, compensating the strength losses due to the use of RA because of the filler effect.

• Flexural strength and static elasticity modulus are slightly more affected than compressive strength by the use of recycled materials. However, most of the series obey theoretical strength values provided by ACI-318.

• Further studies are needed to establish and quantify the combined effects of WBP and RA on the durability of recycled concretes.

Acknowledgements

This analysis is part of the Project CORFO 15IPPID-45706 'Áridos reciclados de alta calidad a partir de escombros de hormigones'-'Evaluación de metodología para la eliminación de mortero por abrasión en áridos reciclados' (High quality recycled aggregates from concrete debris-Evaluation of the methodology to reduce mortar through abrasion in recycled aggregates), funded by CORFO-CHILE.

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