Desulfurized gypsum regulates the hydration and hardening process of all-solid-waste-based belite sulphoaluminate cement paste

Using solid waste instead of natural raw materials to prepare cement is an effective solution to reduce carbon emissions. An in-depth understanding of the hydration and hardening process of all solid waste cement is helpful for its promotion and application. In this paper, coal gangue, carbide slag and desulfurized gypsum (DG) were used as raw materials to calcine the all-solid-waste-based belite sulphoaluminate cement (BSAC), and the hydration and hardening process of BSAC with different DG content was studied. Through the test of XRD, TG-DSC, FTIR, hydration heat, SEM and compressive strength, the phase change, hydration heat, microstructure and strength change of BSAC hydration and hardening process were obtained, and the regulation mechanism of DG on the hydration and hardening of BSAC was revealed. The results show that the incorporation of DG makes it easier to cover a hydration layer on the surface of cement particles after dissolution, and the hydration reaction of BSAC changes from phase boundary reaction process to diffusion reaction process, which slows down the early hydration rate, reduces the number and size of hydration products, and reduces the compressive strength. With the progress of hydration, sufficient DG reacts with aluminum glue to continuously generate AFt, which prolongs the hydration cycle and improves the compressive strength. The optimal content of DG is 10 %, and the compressive strength of BSAC slurry at 28 d is the highest, which is 84.36 MPa.