Micro-silica, an ultrafine byproduct from the silicon and ferrosilicon alloy industry, offers significant potential as a supplementary cementitious material for sustainable concrete. The purpose of this study is to investigate the mechanical performance and water absorption properties of concrete that contains micro-silica as a partial replacement for cement at five different percentages: 5%, 10%, 15%, 20%, and 25%. A total of 108 concrete cylinders (4ʺ×8ʺ) were made and subsequently tested for compressive and splitting tensile strengths at 7, 14, and 28 days, following ASTM C39 and C496 standards. Eighteen concrete cylinders (4″×8″) were also made and tested for water absorption according to standard procedures. The results demonstrated that after 28 days of curing, concrete incorporating 20% micro-silica as a partial cement replacement exhibited the highest compressive strength of 31.38 MPa, representing a 56.6% enhancement compared to the control mix (19.99 MPa). Similarly, the splitting tensile strength improved by approximately 38% at the same 20% substitution level. Furthermore, micro-silica addition reduced water absorption by up to 42%, indicating enhanced impermeability and resistance to chemical ingress. This research establishes a practical balance between environmental benefits and performance improvements in concrete production and the findings confirm that incorporating micro-silica up to an optimal 20% substitution significantly enhances concrete’s strength and durability while contributing to a lower carbon footprint and sustainable material utilization.
