Use of High Fineness of Fly Ash to Improve Properties of Recycled Aggregate Concrete

Abstract

This study used high fineness of fly ash as a cement replacement to improve recycled aggregate concrete properties. The mixture proportions of recycled aggregate concretes were first prepared using 100% recycled coarse aggregate, and then river sand was replaced with recycled fine aggregate at 0, 50, and 100% by weight of the fine aggregate (river sand plus recycled fine aggregate). Results indicated that use of 35–50% fly ash (with respect to total cementitious content) of high fineness could improve slump loss behavior in recycled aggregate concretes. Greater proportions of recycled fine aggregates decreased the compressive strength of concrete. However, use of high fineness of fly ash (1.2% retained on a No. 325 sieve) in recycled aggregate concrete could produce greater compressive strength than that of the recycled aggregate concrete alone. The splitting tensile strength of the recycled aggregate concretes containing high fineness of fly ash was 8.2% of its compressive strength, slightly lower than that of the normal aggregate concrete. The modulus of elasticity of recycled aggregate concrete, with or without high fineness of fly ash, was lower than that of the normal aggregate concrete and about 5.9% lower than the value predicted by ACI 318. The results suggest that high fineness of fly ash can be used to improve various properties of recycled aggregate concrete.