Effect of nano-calcium carbonate on early-age properties of ultra-high-performance concrete

In this study, the effects of nano-calcium carbonate (CaCO3) addition on the early-age properties of ultra-high-performance concrete cured at simulated cold and normal field conditions were investigated. The nano-CaCO3 was added at rates of 0, 2.5, 5, 10 and 15% as a partial volume replacement for cement. Similar mixtures incorporating chloride-and non-chloride-based accelerating admixtures were also tested for comparison. Results indicate the high potential of nano-CaCO3 to accelerate the setting and hardening process of ultra-high-performance concrete through providing nucleation sites, increasing contact points and increasing the effective water-to-cement ratio. Although nano-CaCO3 exhibited a comparable or slightly lower accelerating effect to that of the chloride-and non-chloride-based accelerating admixtures, it brings a number of benefits to concrete production. These include the development of low-maintenance structures through eliminating the risk of steel corrosion induced by chloride-based accelerating admixtures, as well as a more environmentally friendly concrete through reducing the cement factor of ultra-high-performance concrete.