The ratio optimization and hydration mechanism of multi source solid waste cementitious materials

In order to design a novel environmentally friendly cementitious material, in this paper, different ratios of fly ash (FA), desulfurized gypsum (DG) and shell powder (SP) were designed as multi-source solid waste cementitious materials by response surface method (RSM). Uniaxial compression strength (UCS), scanning electron microscope (SEM) and low-field nuclear magnetic resonance (Lf-NMR) tests were performed to study the mechanical properties, microscope structures and hydration process. In the interaction, DG and SP have the greatest effect on strength, while FA and DG have the least; FA seriously affects strength; DG mainly affects the ductility, elastic modulus; SP can appropriately weaken the adverse effects caused by FA and DG. The optimal ratio of solid waste cementitious material is FA14.13%, DG3.36%, SP7.48%. Solid waste cementitious slurry (SW) has bigger internal pore size, lower initial hydration rate, but higher hydration degree than pure white cement slurry (PW). Meanwhile, based on fractal theory, the total structural complexity of SW is greater than that of PW, and the spatial structure is mainly on the meso-pores and macro-pores, while the PW is on micro-pores, meso-pores and macro-pores. The 3 d and 28 d flexural strength of solid waste cementitious material is greater than 3.5 MPa and 6.5 MPa. The chemical composition content, initial and final setting time meet the requirements of ordinary Portland cement.