Synergistic effects of nano-silica and fly ash on properties of cement-based composites

Abstract The combined utilization of mineral admixtures and nano-materials in cement-based composites is an inevitable trend based on the purpose of improving the durability. However, synergistic effect of mineral admixtures with nano-materials and their formation mechanism remains poorly understand. Therein, synergistic effect of nano-silica and fly ash on mechanical property, hydration process, non-evaporative water content, pozzolanic activity were investigated, the pore size distribution of hardened paste were tested and synergetic effect formation mechanism was analyzed. The results indicate that nano-silica improved compressive strength in the early stage and high content of fly ash with moderate fineness contributed to the strength growth in the later stage. In addition, nano-silica promotes cement hydration in early stage and provides favorable hydration conditions for later hydration of fly ash. Synergistic effect of nano-silica and fly ash increases content of non-evaporative water and improves pozzolanic activity. Moreover, synergistic effect of nano-silica and fly ash significantly optimizes pore structure in hardened paste. The suggested synergistic effect mechanism is attributed to the optimization of hydration process, mixing ratio matching and fineness matching among cement, nano-silica and fly ash.