Investigating the effect of using three pozzolans separately and in combination on the properties of self-compacting concrete

Today, the tendency to use self-compacting concrete (SCC) is expanding because of its significant benefits. In this study, SCC was made by using native materials and then different pozzolans were replaced instead of a part of cement and the rheological and mechanical properties and microstructure of the concrete were investigated. The pozzolans containing of metakaolin (15%, 25% and 35%), silica fume (6%, 12% and 18%) and fly ash (20%, 35% and 50%) were replaced instead of a part of cement separately or simultaneously. Self-compaction tests including slump flow, T500, L-box, U-box, and J-ring as well as mechanical tests including compressive strength, splitting tensile strength, and static modulus of elasticity were performed on the specimens. The results showed that the pozzolans improved the microstructure of the SCC and the secondary reactions improved the mechanical properties of the concrete containing the pozzolans at older ages than the reference concrete. At 15% replacement, metakaolin increased the 180-day compressive strength up to 106 MPa that was about 18% more than reference concrete. In ternary mixtures the maximum and minimum rate were 29% and 19%, respectively, and in quaternary mixtures the rates were significant and increased up to 46%, while the rate for reference concrete was 20%. This significant growth was probably due to the secondary reaction of pozzolans with calcium hydroxide residue from cement hydration.