Effect of aluminum sulfate on the hydration of tricalcium silicate

Abstract In order to obtain a deep understanding of the hydration of sprayed concrete, C 3 S pastes with and without aluminum sulfate (AS) were comparatively investigated. The results showed that AS significantly accelerated the hydration of C 3 S and refined the pore structure of the hardened C 3 S paste, by reacting with the calcium ions to produce ettringite; this acted as nucleation seeds to induce the formation of C S H gel. Differing from C S H based nucleation seeds, the ettringite-based nucleation seeds were formed in bulk solution where was away from rather than inside the rich silicate layer, thereby inducing the formation of C S H gel in the interspace among C 3 S particles. Furthermore, the formation of ettringite consumed a large amount of calcium ions, which not only expedited the dissolution of C 3 S to release the calcium ions into solution, but also perturbed the crystallization of calcium hydroxide (CH), resulting in formation of amorphous CH.