Regulations on the hydration, morphology, and sulfate-attack resistivity of C₃A with micro/nano-silica particles

Micro- and nano-sized SiO₂ particles, i.e., silica fume (SF) and nanosilica (NS) have been extensively documented of improving the durability of concrete, but rare investigation on their specific effects on tri-calcium aluminate (3CaO·Al₂O₃, C₃A) reactions/performances in harsh environment has been reported. This work determined the effects of SF and NS on the hydration and hardening properties of C₃A-gypsum systems, and their performances under sulfate attack. Results showed that NS and SF can effectively improve the sulfate attack resistivity of the C₃A-gypsum systems due to the filling effect and the reduction of crystal size/morphology-induced expansion: a significant reduction of the aspect ratio (length/diameter) can be observed in the NS-added sample comparing the pure C₃A-gypsum system. Comparatively, SF can hardly change the morphology of ettringite (AFt), which could be due to that its bigger particle size cannot effectively block the ion migration. It is expected that these findings could contribute to the utilization of fine/ultra-fine SCMs in cementitious materials systems, especially those with high amount of aluminate phases.