Microstructure evolution and strength development of ultra rapid hardening cement modified with redispersible polymer powder

Abstract

Ultra rapid hardening (URH) cement is used where ultra high early strength is required in construction. This study investigated the age-dependent characteristics of calcium sulfoaluminate (CSA)-based URH cement modified by the addition of acrylic redispersible polymer powder. Specifically, the effects of polymer powder on the microstructure evolution and strength development were examined from an early age of 2 h up to 90 days. The macro- and microstructural properties of various cement paste, mortar, and concrete samples were characterized by compressive strength, rheology, mercury intrusion porosimetry, powder X-ray diffraction, and scanning electron microscopy with energy-dispersive spectroscopy. The test results revealed that increasing the polymer proportion up to 10% by mass of cement not only delayed the setting and hydration, but also refined the pore structures of the URH cement systems, which is considered the main cause of the long-term strength convergence of the mortars with different polymer ratios. The polymer addition induced the formation of more ordered and denser ITZs between the mortar and coarse aggregate. All findings support the favorable effects of the polymer powder on the long-term strength and durability of the URH cement systems.