Effects of nanosilica on the hydration and hardening properties of blended cement-based materials under heat curing

The slow property gains of cement-based materials blended with industrial by-products such as fly ash (FA) and ground granulated blast-furnace slag (GGBS), especially at a high dosage, have been ascribed to be the main obstacle of increasing the sustainability of cement concrete industry. In this work, the effects of 1 mass% nanosilica on the properties of heat-cured cement-based materials blended with FA and GGBS were investigated. Three different percentages of FA or GGBS (15, 30 or 40 mass%) and four different curing temperatures (20, 60, 70 and 80 °C) were studied. The mechanical properties, hydration heat, mineralogy phase, calcium hydroxide content, and morphology were measured and analyzed after 1, 3, 7, and 28 days. The increase in 1-day compressive strength of 37.75% and 38.65% could be seen for samples blended with 30 mass% FA and 30 mass% GGBS and cured at 70 °C, respectively. More calcium hydroxide was consumed due to the acceleration effect of nanosilica on the pozzolanic reactivity of added FA and GGBS. More hydrates and a denser microstructure were observed in samples mixed with nanosilica compared with samples without nanosilica. This work showed the feasibility of using a small dosage of nanosilica to improve the properties of heat curing blended cement-based materials while improving greenability.