Optimisation of mortar properties through the combined use of crushed limestone sand and silica fume

The aim of this work was to optimise mortar properties through the combined use of local byproducts, specifically silica fume (SF) and crushed limestone sand (CLS). The optimisation process involved examining the effects of SF and CLS, both separately and in combination, on the mortar’s rheology, mechanical strength and porosity. Three levels of SF replacement (5%, 10% and 15% by cement weight) and three levels of CLS replacement (16.67%, 33.34% and 50% by sand weight) were examined. The workability of fresh mortars was measured using an LCPC workability meter, and the superplasticiser (SP) demand was also quantified. The hardened-state tests included the mass at 28 days, compressive and flexural strengths at 7 and 28 days of curing, and porosity at 28 days. The optimal mix, containing 10% SF and 50% CLS, demonstrated excellent performance: compared with the control mix, the 28-day compressive strength was increased by 70% to 45.9 MPa and the porosity was reduced by 61% to 1.8%. This was achieved while maintaining good workability (15 s flow time) with only 1.2% SP. In addition to optimising the mortar formulation and improving its performance, this study significantly contributes to the understanding of how local byproducts (SF and CLS) can be effectively used in cementitious materials.