Effects of amorphous AH3 phase on mechanical properties and hydration process of C4A3S¯-CS¯H2-CH-H2O system

Calcium sulfoaluminate cement (CSA) is promoted as one of the most promising cements, which requires less energy for its production and leads to lower CO2 emissions. AH3 phase is the main amorphous hydration product of CSA. This study explored the effect of AH3 phase on mechanical property and hydration process. Calcium sulfoaluminate (C4A3S¯) was synthesized by laboratory reagents with different phase compositions. Afterwards, C4A3S¯ was incorporated with specific quantities of gypsum and calcium hydroxide, which determined the ratio of AH3 phase to ettringite in the final products. The compressive strength was investigated and hydration products were characterized with XRD and TGA. The microstructure and morphology were followed with SEM and MIP. The findings showed that the hydration process proceeds rapidly and there only exists ettringite and amorphous AH3 phase in hydration products. AH3 phase has great influence on the mechanical strength and fills empty spaces thus improving the compacity of the cement paste, meanwhile this increase in compacity seems to reduce the dissolution of anhydrous phases leading to a decrease of the hydration degree.