Effect of nano-SiO2 on early hydration of natural hydraulic lime

Abstract Natural hydraulic lime (NHL) containing both hydraulic and air-hardening contents is of an ideal alternative binder for mortars used in interior decoration, cultural relics repair and historic buildings maintenance. In this study, early hydration and hardening properties of NHL2 with nano-SiO 2 (NS) were researched. Hydration exothermic rate firstly decreased within 5 h of hydration and then increased after 5 h of hydration with the increase of NS, which could be attributed to the C 2 S hydration and the additional pozzolanic reaction between Ca(OH) 2 and NS. It is noted that the initial hydration of C 2 S would be restrained by the increase content of NS in NHL2 due to the delayed exothermic peak occurring time within 5 h of hydration. A decreased porosity of hardened NHL pastes with the increase of NS at each curing age were observed, which might be also caused by the pozzolanic reaction between Ca(OH) 2 and NS. Meanwhile, an increased capacity for the pores about 50 nm and decreased capacity for the pores about 1 μm with the increase of NS were also observed. In addition, mechanical level of NHL could be improved from NHL2 to NHL3.5 when more than 2% NS were added.