Influence of a C12A7 mineral-based accelerator on the strength and durability of shotcrete

This study analyzed the long-term strength and durability of shotcrete when a C12A7-based accelerator is added to the mixture. Since an accelerator with a high alkali content causes a remarkable decrease in the long-term strength of shotcrete and is toxic to humans, this study evaluated the setting time, compressive strength, and resistance to permeability and repeated freeze–thaw cycles of an amorphous C12A7-based accelerator. The results showed that the C12A7 accelerator set quickly by forming a web structure from its initial setting state due to the presence of ettringite. In addition, the ettringite, with its characteristic acicular crystals, proved resistant to permeability and repeated freeze–thaw cycles. Ettringite has a structure that encouraged a smooth hydration reaction, maintaining the voids at the surface of the cement particles and resulting in the observed initial strength and decrease in the reduction of the long-term strength.