Mesoporous expansive ettringite binder from chemically-treated phosphogypsum waste: Physico-mechanical properties and phase composition

This study uses an eco-efficient approach for sustainable phosphogypsum (PG) waste disposal by creating a mesoporous AFt binder. The results reveal that mixing PG waste with a synthetic sodium aluminate can induce the formation of the AFt phase through a cationic exchange reaction at room temperature. The morphology, expansive property, mesopore volume, and mechanical performance of the AFt-binder strongly depend on the activator (as Na₂O) / PG weight ratio, the alumina modulus (M_A) value, the mixing water content, and the curing temperature. The curing time has no significant effect on the performance of the AFt binder, as the majority of physico-mechanical properties are achieved within the first 24 h. For instance, a sample fabricated at a Na₂O/PG weight ratio of 0.2 using SA with an MA of 1.0 recorded a 1-day compressive strength of 12.1 MPa. Increasing the curing time up to 28 days has no effect on strength development. Therefore, the AFt-based binder can be categorized as a rapid-hardening cementitious material. The proposed strategy mitigates the environmental issues caused by PG waste, contributes to the conservation of natural resources, and reduces the energy demand required to produce this type of cement.