Use of phosphogypsum in cementitious systems containing spent equilibrium catalyst (Ecat) as a supplementary cementitious material (SCM)

Abstract

Ecat, generated by the petroleum industry, shows potential for use as a Supplementary cementitious material (SCM) due to its rich composition of Al2O3 and SiO2. Phosphogypsum (PG) can be applied as a residual source of calcium sulfate in cements, but its application as a setting regulator in systems containing Ecat is unexplored. This study investigates the influence of PG on the hydration and mechanical performance of cementitious pastes, as well as its viability in composite cements with Ecat. PGs from different origins (SP and MG) were evaluated at levels of 0, 4, 8, and 12%, replacing natural gypsum; the level with the best performance was selected for the formulation with Ecat. Isothermal calorimetry, compressive strength, and XRD tests were performed. The addition of 4% PG provided balanced hydration and greater mechanical strength, while higher levels reduced the maximum heat flow and mechanical performance. The absence of sulfate accelerated hydration and increased the initial heat release. Systems with 50% Ecat exhibited a longer induction period, lower heat flux, and reduced resistance, with greater ettringite formation and portlandite consumption. Thus, performance depends on the balance between sulfate and SCM, making it feasible to incorporate optimized levels.