The Effect of Colloidal Nano-Silica on the Initial Hydration of High-Volume Fly Ash Cement.

High-volume fly ash cement exhibits drawbacks such as delayed hydration and reduced early-age compressive strength due to the replacement of large amounts of cement with fly ash. In recent years, various studies have been conducted to overcome these limitations by incorporating nanomaterials, such as nano-silica, to promote the hydration of cementitious systems. This study aims to investigate the effect of colloidal nano-silica on the hydration behavior of cement. Cement paste specimens were prepared with varying dosages of colloidal nano-silica to evaluate its influence. To examine the hydration characteristics and mechanical performance, compressive strength tests, isothermal calorimetry, and thermo-gravimetric analyses were conducted. Furthermore, the effect of colloidal nano-silica on the hydration of cement blended with fly ash was also examined. The experimental results revealed that the incorporation of colloidal nano-silica accelerated the hydration reactions in both ordinary and fly ash-blended cement pastes and significantly improved early-age compressive strength. In particular, the 7-day compressive strength of fly ash-blended cement mortar improved by 22.2% compared to the control specimen when 2% colloidal nano-silica was incorporated. The use of colloidal nano-silica appears to be a practical approach for enhancing the early strength of high-volume fly ash concrete, and its broader application and target expansion could contribute to the advancement of a low-carbon construction industry.