Assessing the Synergistic Role of Nanosilica in the Performance of Concrete with Natural Pozzolans

With the diminishing availability of traditional supplementary cementitious materials, alternative options such as natural pozzolans (NPs) are emerging as promising alternatives. While NPs can significantly enhance the durability of concrete, their use often results in reduced early-age strength. Existing technical literature shows that when used in concrete, nanosilica (nS) provides nucleation sites for deposition of the hydrates, thus accelerating the hydration process and enhancing early-age strength development. Consequently, combining nS with NPs offers a promising, yet largely unexplored, pathway toward more sustainable and practical solutions for concrete construction. This study evaluates the combined effects of using NPs and nS in portland cement concrete for pavement applications. Two types of nS and three NPs (one calcined clay and two of volcanic ashes) were used. Concrete mixtures were prepared both with and without nS, incorporating NPs as a 25% weight replacement for cement. All concrete mixtures were evaluated for fresh properties, early and long-term compressive strength, and durability characteristics, including rate of water absorption, formation factor, and parameters of the air void system in hardened concrete. Additionally, pastes with the same compositions as those in corresponding concrete mixtures were subjected thermogravimetric (TG) analysis to quantify the calcium hydroxide content, providing insight into the extent of the pozzolanic reaction. The presentation will showcase both the benefits and challenges associated with the combined use of nS and NPs in concrete, offering insights related to performance and practical applications.