Effect of nanosilica on the compressive strength development and water absorption properties of cement paste and concrete containing Fly Ash

Fly Ash (FA) as a Supplementary Cementitious Material (SCM) increases the sustainability of concrete by decreasing CO₂ emissions from cement production. The present study investigated the effect of nanosilica (nS) on the properties of cement paste and concrete, especially those containing FA. Fifteen cement paste and concrete mixtures with 15% to 25% of the cement content replaced with FA and four replacement ratios of nS (1.5%, 3%, 5%, 7.5%) were examined. The compressive strength development was measured and water absorption properties were tested by immersion and capillary absorption to investigate their early-age and long-term properties. The results demonstrate that the addition of nS accelerated the reactivity of early-age FA-based concrete and increased the strength development of cement paste and concrete over those without nS. The use of optimal ratios of up to 5% nS with 15% FA significantly improved the ITZ in FA concrete and noticeably decreased water absorption and the sorptivity coefficient of the concrete specimens.