The effect of gyrolite substituted with cadmium ions on the hydration kinetics of OPC at early stages

This study examined the effect of gyrolite substituted with cadmium ions on the kinetics of the hydration of ordinary Portland cement (OPC) at early stages of hydration. Gyrolite was synthesised after 48 h at 200°C from a stoichiometric composition (calcium oxide/silica dioxide = 0·66) of calcium oxide and a hydrated silica mixture. Calcium silicate hydrate substituted with cadmium ions (97 mg cadmium ions/g) was added as a partial replacement of the OPC at levels of 0%, 2·5%, 5% and 7·5% by weight of the total cementitious material. Therefore, the water-to-cement ratio of all OPC samples was 0·5. It was found that the additive of a synthetic contaminated with cadmium ions (∼97 mg cadmium ions/g) retained very good adsorption properties for the alkaline and alkaline earth ions that penetrated into the gyrolite structure. It was estimated that this additive accelerates the early stage (5–7 h) of hydration of OPC and its individual compounds. It was found that during the main reaction of calcium silicate, the additive of gyrolite contaminated with cadmium ions had no influence on the apparent reaction rate (W_app) of the hydration process (7–12 h): in all samples, the increase in the degree of hydration (∆α) was almost the same: ∆α = 15%.