Synergistic regulation of sulphoaluminate cement hydration by polyaluminum sulfate and calcium carbide slag: Hydration kinetics, phase assemblage and microstructure

The hydration behavior and performance of sulphoaluminate cement (SAC) are highly influenced by the availability of sulfate, aluminate, and calcium bearing species and the hydration environment, highlighting the need for effective hydration regulators. This study investigates the individual and synergistic effects of polyaluminum sulfate (PAS) and calcium carbide slag (CCS) on the hydration kinetics, phase evolution, microstructure, and mechanical properties of SAC. PAS acts as a source of aluminum and sulfate species, while CCS can contribute alkaline and calcium-bearing conditions to the hydration system. A small amount of PAS promotes early-age strength development, whereas relatively high PAS dosages result in pronounced late-age strength retrogression, accompanied by delayed hydration and continued formation of AFt-related hydration products at later ages. CCS can alter the hydration pathway of SAC and modify the composition of hydration products. The combined PAS-CCS system produces a more concentrated early-age heat-release response and promotes favorable pore-size redistribution. In particular, the PC-5 mixture containing 0.8% PAS and 5% CCS achieves a 28-day compressive strength of 100.5 MPa, with harmless and less harmful pores accounting for 82%. A preliminary cradle-to-gate material-level assessment shows that, compared with the reference mixture, PC-5 reduces the global warming potential and production cost by approximately 4.4% and 3.5%, respectively, while substantially improving compressive strength. Overall, the combined incorporation of PAS and CCS can regulate the hydration kinetics, hydrate assemblage, and pore structure of SAC, providing a potential approach for improving the performance of SAC-based materials and promoting the utilization of CCS.