Effect of MgSO4·7H2O on the hydration of Portland cement

Abstract

MgSO4 is usually found in the groundwater or seawater and can influence the early hydration of Portland cement. In this paper, the reaction kinetics of the early hydration of the MgSO4·7H2O + Portland cement clinker (MPC) was revealed compared with the CaSO4·2H2O + Portland cement clinker (OPC) by means of isothermal calorimetry, chemical shrinkage and solid–liquid phase analysis. The test results indicated that MgSO4·7H2O had more pronounced retarding effect on Portland cement clinker hydration than CaSO4·2H2O. The MPC system had longer initial time and final time than OPC system. In the initial period and induction period of MPC system, Mg(OH)2 and CaSO4·2H2O precipitated on not only the C3A partials but also on the C3S partials, and prevented the flash-set of clinker. The early hydration of C3A and C3S were both retrained by the combined retardation of Mg(OH)2, CaSO4·2H2O and hydration products, which resulted to a slower hydration rate of MPC than OPC before the deceleration period. The intense hydration of C3A and C3S were postponed and appeared in the deceleration period of MPC compared with OPC, which ultimately caused a deeper hydration of MPC than OPC.