The effect of slag and natural pozzolan on the rheological and compressive strength properties of recycled self-compacting mortar

Cement replacement materials are used in self-compacting concrete mixes to reduce the cement content and hence its environmental effect. This article examined the effects of ground granulated blast-furnace slag (S) and natural pozzolan (NP) powder on the rheological and mechanical properties of recycled self-compacting mortar (RSCM). Natural sand was replaced by 100% of recycled sand (RS) by volume; while cement was replaced by slag and NP up to 40% by weight of cement. The slump flow, V-funnel time, yield stress and plastic viscosity and compressive strength of RSCM are investigated and compared with natural self-compacting mortar. The results showed that fresh properties of RSCM meet the requirements of self-compacting mortar if slag and NP contents are limited to 35%. The increase in slag content increases the yield stress and the plastic viscosity of fresh mortars whereas a decrease in the rheological properties is noticed when NP content is increased. Increasing slag and NP content leads to a reduction in compressive strength of RSCM at early ages, but enhances compressive strength at later age. The cement substitution levels by 25% of slag and 15% of NP are the optimum for attaining the desired strength that compensate for strength loss due to the use of RS.