Influence of nano-silica on the performances of concrete under the negative-temperature curing condition

In previous studies, nano-silica (NS) can improve the concrete performances under the conventional curing condition (about 20 degrees C). However, because more and more engineering projects are constructed in cold regions, it is very important to study the performances of concrete, which is cured under the negative-temperature condition. In order to explore whether NS still has the positive effect on concrete cured under the negativetemperature condition, multi-scale experiments were conducted to investigate the influence of NS on the performances (mechanics, resistance to chloride ion penetration (RCP) ability, pore characteristics, microstructure, and hydration products) of the concrete cured under the condition of -3 degrees C. The results indicate that the negative-temperature curing condition is not conducive to the formation of compressive strength for concrete. Under the curing condition of -3 degrees C, the cement paste and the interface transition zone are deteriorated by the addition of NS, which reduces the compressive strength of concrete. In addition, as the increase of the NS content added into the concrete under the curing condition of -3 degrees C, the compressive strength, the RCP ability, and the amount of calcium hydroxide generated decrease, and the coarsening of pore structure increases.