Relationships between the strength, hydrate process, structure and porosity of hydrated supersulfated cement with the addition of gypsum, anhydrite and phosphogypsum

Abstract

Supersulfated cement (SSC) is a novel green cementitious binder characterized by greater solid waste, lower hydration heat and lower carbon emission, but its poor early strength presents a challenge for the construction field. The influences of the mineral composition of SSC on the compressive strength, heat of hydration, hydrates, pore structure, and microscopic characteristics are examined in this study. The reaction mechanism of gypsum, anhydrite and phosphogypsum (PG) in SSC is investigated. The results indicate that the compressive strength of the S95‒SSC system is significantly greater than that of the S105‒SSC system, and P6 in the S95‒SSC system has the highest strength of 51.8 MPa at 28 d. An increase in the dosage of anhydrite accelerates the early periods of hydration for SSC, which promotes more ettringite (AFt) and improves the mechanical performance at early ages. Early hydration is inhibited by the addition of PG to SSC, which increases the fraction of pores less than 50 nm in size. This work confirms that anhydrite and PG have a synergistic effect on SSC. To improve the early strength of SSC, the most effective research approach is to optimize the mineral composition.