Effects of nano-silica modification on early age hydration process in winter construction of tunnel engineering

Fast hardening and high early strength are crucial factors for concrete used in tunnel construction in cold regions. The incorporation of nano-silicate has been found to be an effective method for improving the properties of cement-based materials at an early age. Thus, the objective of this paper is to investigate the nano-modification effects of different nano-silica contents on the hydration process, mechanical properties, and hydration products of cement cured in a low-temperature environment. The effects of various nano-silica concentrations, including 1%, 2%, 3%, and a high dose of 6%, on the properties of the concrete were investigated. According to the test results, the optimal quantity of nano-silica plays a crucial role in determining the properties of concrete. The effects of nano-silica on the hydration of C3A were found to dominate the cement hydration process at an early age. The incorporation of nano-silica led to a significant improvement in the dissolution rate of anhydrite and the reaction rate of the C3A renewal, which may be responsible for the gain in early strength of concrete. However, an excessive amount of nano-silica could negatively affect the hydration process of the alite and C3A, as evidenced by the total heat generated during the silica and aluminate reactions. The XRD patterns further confirmed these results.