Effect of superplasticizer on mechanical and durability properties of recycled aggregate concrete

Abstract

Recycled concrete aggregate (RCA) may be an alternative to use for natural aggregate (NA) in concrete production. Recycling of demolished concrete into aggregate to produce recycled aggregate concrete (RAC) is environmentally beneficial by preserving natural resources, by waste reduction and by preserving landfill space. Usually the mechanical and durability properties of recycled aggregate concrete is inferior to natural aggregate concrete (NAC) prepared with the same concrete mix design. But various chemical admixtures have the ability to enhance these properties of concrete. This research presents the effect of superplasticizer on mechanical and durability properties of recycled aggregate concrete. A comprehensive experimental program was conducted having a series of RAC with various replacement ratios (0%, 25%, 50% and 100%) of natural stone coarse aggregates by recycled aggregates. Two types of recycled aggregates namely recycled stone aggregate (RSA) and recycled brick aggregate (RBA) have been used in the research. Half of the prepared concrete specimens were admixed with the superplasticizer to evaluate and compare different concrete properties. The obtained test results were encouraging to use superplasticizer for improving mechanical and durability properties of recycled aggregate concrete. In general, mechanical properties such as compressive strength, tensile strength, modulus of elasticity of concrete have been improved. Compressive strength has been increased by 28-35% and 25-31%, split tensile strength by 6-13% and 7-12%, and static modulus of elasticity by 21-22% and 22-36%, for stone and brick recycled aggregate concretes respectively. Durability property assessed by total charge passing through the specimens in RCPT test decreases by 5-30% and 11-17% for stone and brick recycled aggregate concretes respectively for the considered replacement of aggregates. It is also observed that natural stone aggregates in a concrete mix can be replaced with 50% recycled stone aggregates and 25% recycled brick aggregates with the addition of the superplasticizer without compromising the compressive strength and durability.