Influence of Fly Ash on Slump Loss and Strength of Concrete Fully Incorporating Recycled Concrete Aggregates

This paper investigates the effects of fineness and replacement of fly ash on the fresh and hardened properties of recycled aggregate concrete. Two groups of recycled aggregate concretes were studied and compared with that of conventional concrete (CON) in which crushed limestone and local river sand were used as aggregates. The first group was prepared using 100% coarse recycled concrete aggregate and local river sand. For the second group, crushed limestone and local river sand were fully replaced by both coarse and fine recycled concrete aggregates. The results indicate that the slump loss of the recycled aggregate concrete with fly ash was reduced to lower than that of the recycled aggregate concrete without fly ash when the fineness of the fly ash was increased, which increased the slump loss of the fresh concrete. Fly ash can be used to increase the compressive strength of recycled aggregate concrete, depending on its fineness and the degree of fly ash replacement. The addition of fly ash with different fineness in recycled aggregate concrete had no significant effect on the splitting tensile strength and the modulus of elasticity of the recycled aggregate concrete, which are related to its compressive strength.