Utilization of fine recycled aggregates in concrete with fly ash and steel slag

An experimental program was carried out in order to investigate the possibility of producing concrete incorporating large volumes of industrial by-products and secondary materials. The alternative materials tested were fly ash as binder for cement replacement, recycled fine aggregate originating from mixed construction and demolition waste and steel slag as coarse aggregate. Several mortar and concrete mixtures were prepared using different aggregate and binder combinations in order to identify the feasibility of producing concrete with maximum use of alternative materials. The different mixtures were tested for mechanical strength at different ages, while durability measurements such as chloride ion penetration and freeze–thaw resistance were also carried out. The results showed that the use of fine construction and demolition waste aggregate increases porosity in concrete and also reduces strength and durability, while its combination with steel slag aggregate partly recovers strength and durability loss. Concrete with mixed construction and demolition waste as fine aggregate and steel slag as coarse aggregate reached 30 MPa 28-day compressive strength and showed adequate durability for low grade applications. Also, 50% cement replacement with high calcium fly ash and use only of steel slag and recycled aggregates resulted in concrete of adequate strength and considerable environmental gains.