Utilization of Nanosilica in M50-grade Concrete: Mechanical and Microstructural Performance for Sustainable Construction

The growing demand for green building materials has spurred the development of strategies to partially replace
cement with nanoengineered additives, thereby minimizing the ecological footprint. This study evaluates the properties of
M50-grade high-strength concrete with nanosilica (NS) as a partial replacement for cement, which can also assist in the
reduction of CO2 emissions into the atmosphere. Due to its high reactivity and small particle size, nanosilica was used as a
partial replacement for cement at 0%, 5%, 10%, and 15% by weight. Mechanical properties, including compressive strength,
split tensile strength, and flexural strength, were evaluated at various curing ages to identify the optimal replacement level.
For microstructural characterization, separate experiments were carried out using Scanning Electron Microscopy (SEM) and
X-ray Diffraction (XRD) techniques to examine the formation of calcium silicate hydrate (C–S–H) gel and the refinement
of the pore structure. The test results show that the addition of nanosilica improves the strength properties of the mix up to
an optimum replacement level of 15%. At 28 days, the mix with 15% NS exhibited superior properties compared with all
other mixes. The mix with 15% NS replacement exhibited a compressive strength of 58.21 N/mm², a split tensile strength of 8.83 N/mm², and a flexural strength of 5.34 N/mm². Thus, a 15% NS replacement level is optimal for producing high-strength M50-grade concrete suitable for environmentally friendly construction. The study further demonstrates that nanosilica iseffective in developing sustainable concrete mixes through its use as a supplementary cementitious material.