Effect of desulfurization gypsum on alternating-current impedance characteristics of all-solid-waste belite sulphoaluminate cement mortar

The utilization of solid waste to prepare low-carbon footprint sulfoaluminate-based cementitious materials is considered an effective solution to replace Ordinary Portland cement. In this work, coal gangue, carbide slag, and desulfurization gypsum were used to prepare all-solid-waste belite sulphoaluminate cement (BSAC). The phase change, pore structure evolution, strength development and alternating-current (AC) impedance characteristics of BSAC mortar with different desulfurized gypsum content were characterized by X-ray diffraction, scanning electron microscopy, nuclear magnetic resonance, compressive strength and AC impedance. It was demonstrated that the desulfurization gypsum slows down the hydration rate of BSAC mortar in the early stage, prolongs the hydration period, and improves the compressive strength in the later stage. The compressive strength of the sample with 10 % content is the highest at 28 d, which is 84.6 MPa. In 28d of hydration, with the increase of desulfurized gypsum content, the pore size of mortar decreases, so that the porosity decreases from 3.09% to 1.52%. This also makes the diameter of Nyquist curve of mortar gradually increase, and the volume resistance increases continuously. The volume resistance of mortar with 20 % desulfurization gypsum is the largest. which is 28317 Ohms. As the hydration age increased, the conductive path of mortar transitions led to the formation of a continuous conductive path to an insulated conductive path. The AC impedance parameters of R 1 yielded the highest correlation with compressive strength, showing a linear correlation, which provides an effective method for predicting the change of compressive strength.