Long-term mechanical and durability properties of recycled aggregate concrete prepared with the incorporation of fly ash

doi:10.1016/j.cemconcomp.2012.12.011

Cement and Concrete Composites

Volume 37, March 2013, Pages 12-19

https://doi.org/10.1016/j.cemconcomp.2012.12.011 Get rights and content

Abstract

This paper presents the findings of a long-term study on the mechanical and durability properties of concrete prepared with 0%, 50% and 100% recycled concrete aggregate that were cured in water or outdoor exposure conditions for 10 years. The recycled aggregate concrete (RAC) was prepared by using 25%, 35% and 55% class-F fly ash, as cement replacements. It was found that, after 10 years, the compressive strength and modulus of elasticity of the concrete prepared with 100% recycled concrete aggregate was still lower than that of the control concrete. Over this period, the highest gain in compressive strength and modulus of elasticity was recorded for the concrete mixture prepared with 55% fly ash. Fly ash improved the resistance to chloride ion penetration but it also increased the carbonation depth of the concrete.

Introduction

The use of recycled aggregates (RAs) in structural concrete production is still limited probably because of the limited knowledge of the long-term and durability performance of recycled aggregate concrete (RAC). Much data are available on the short to medium-term (up to 90 days) mechanical properties of RAC [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. The use of recycled aggregate generally increases the drying shrinkage, creep and water sorptivity and decreases the compressive strength and modulus of elasticity of recycled aggregate concrete compared to those of natural aggregate concrete [9], [10], [11], [12]. It is known that when using the same water to cement ratio, as RA percentages increase, the mechanical properties of the RAC deteriorate. However, reducing the effective water–cement ratio in concrete production or adding fly ash (FA) as a supplementary binder material can improve the mechanical and durability properties such as compressive and tensile splitting strength, modulus of elasticity, drying shrinkage and resistance to chloride ion penetration of RAC prepared with recycled concrete aggregate [13], [14], [15].

There is a need to obtain more information on the long-term properties of RAC, including RAC incorporating fly ash. This paper presents the long-term experimental results of the use of fly ash as a cement replacement in proportion to the RAC. The effects of fly ash on the long-term mechanical and durability properties, such as compressive strength, tensile splitting strength, static modulus of elasticity, carbonation depth and resistance to chloride ion penetration, of RAC that were cured in water or outdoor exposure conditions for 10 years were investigated.

Section snippets

Binders

The cementitious materials used in this study were Portland cement (PC) equivalent to ASTM Type I, ASTM Class-F fly ash (FA) obtained from a local coal-fired power plant. The chemical composition and physical properties of the cement and FA are listed in Table 1.

Aggregates

Natural and recycled aggregates were used as the coarse aggregate in the concrete mixtures. In this study, crushed granite was used as the natural aggregate. The recycled aggregate contained almost entirely of crushed concrete rubbles

Compressive strength

The results of the compressive strength of the concrete under both curing conditions at the ages of up to 10 years are shown in Table 5. Each presented value is the average of three measurements. It can be seen that at all the test ages the compressive strength of the water cured RAC was lower than that of the NAC. The compressive strength decreased with increase in recycled aggregate content. At 28 days, The strength of the concretes was reduced by 12.6% and 21.6%, respectively, in comparison to

Conclusion

In this paper, the effect of fly ash on the properties of 10-year-old concrete made with recycled aggregate was investigated. Based on the results and discussion, the following conclusions can be drawn:

1.
Due to pozzolanic reaction between fly ash and Ca(OH)₂ in the RAC, the long-term mechanical and durability properties of the concrete were significantly improved.
2.
After 10 years, the compressive strength of recycled aggregate concrete was still lower than that of corresponding natural aggregate

Acknowledgements

The authors would like to thank Sun Hung Kei Properties Ltd. and The Hong Kong Polytechnic University for funding support.

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Long-term mechanical and durability properties of recycled aggregate concrete prepared with the incorporation of fly ash

Abstract

Introduction

Section snippets

Binders

Aggregates

Compressive strength

Conclusion

Acknowledgements

Recycled concrete aggregates

Cem Concr Compos

RILEM REPORT 6, recycling of demolished concrete and masonry

The use of recycled aggregates in concrete, BRE information paper IP 5/94

Performance of concrete made with commercially produced coarse recycled concrete aggregate

Cem Conr Res

Influence of moisture states of natural and recycled aggregates on the properties of fresh and hardened concrete

Cem Conr Res

Drying shrinkage and durability of concrete made from recycled concrete aggregates

Trans Jpn Concr Inst, Tokyo

Elasticity and drying shrinkage of recycled aggregate concrete

J Am Concr Inst