Investigation of the C─S─H─PCE Promotion Mechanism on Early Hydration of the C3S─C3A─Gypsum System

Abstract

C─S─H─PCE is an innovative early-strength agent that enhances the early-strength development of concrete; however, its promotion mechanism on the hydration of primary cement mineral phases, particularly the C 3 S ─ C 3 A ─ gypsum , remains insufficiently understood. In this study, the influence of synthesized C─S─H─PCE on the early hydration of the C 3 S ─ C 3 A ─ gypsum system was systematically investigated using isothermal calorimetry, scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP), electrical conductivity, and nucleation test. Experimental results show that C─S─H─PCE significantly increases and advances the hydration exothermic peaks of both aluminate and silicate, particularly at dosages below 2%. C─S─H─PCE addition accelerates the consumption of solid-phase gypsum and promotes the formation of ettringite (AFt) and Portlandite (CH). Meanwhile, it enhances the longitudinal growth and densification of C─S─H gels. C─S─H─PCE enhances the mineral dissolution within the C 3 S ─ C 3 A ─ gypsum system in a dosage-dependent manner. The initial concentrations of Ca 2+ , SiO 4 2− , SO 4 2− , and [ Al ( OH ) 4 ] − ions are increased by the influence of C─S─H─PCE. PCE enables uniform dispersion of nanoscale C─S─H seeds, providing abundant nucleation sites that effectively lower the critical free energy required for nucleation, accelerating C─S─H gel formation. Additionally, the C─S─H seed is beneficial to create a local concentration gradient of ions, thereby enhancing the dissolution of C 3 S . A synergistic relationship is established between the hydration of aluminate and silicate phases.