Investigation on strength and pore structure of supersulfated cement paste

Abstract

The compressive strength and pore microstructure of supersulfated cement (SSC) pastes with different kinds of gypsum, different treatments on phosphogypsum and different fineness, and ordinary Portland cement, slag Portland cement were investigated. The results indicate that phosphogypsum SSC performs better compared to anhydrite and dihydrate gypsum SSC for strength development, especially at late hydration age. For long curing age, burned at 500 °C for phosphogypsum is better than neutralized with 4 % lime in SSC. The higher the fineness, the higher the cement hydration degree, especially at early age, more hydration products such as ettringite and C-S-H form, and the strength improves to some extent. Compared to ordinary Portland cement and slag Portland cement, phosphogypsum-based SSC has the lowest strength at early age, while the strength growth rate increases over curing time. The paste strength mainly depends on the average pore size but porosity. SSC paste contains more harmless pore, which is beneficial for pore structure and strength.