Influence of Waste Fly Ash on the Rheological Properties of Fresh Cement Paste and the Following Electrical Performances and Mechanical Strengths of Hardened Specimens

Waste fly ash (WFA) is a kind of solid waste without reasonable disposition. The WFA with active substance can promote the cement hydration, therefore, WFA may enhance the mechanical strengths of cement-based materials. In this paper, the rheological properties (slump flow and plastic viscosity) of fresh cement paste with WFA ranging from 0% to 25% by mass ratio of cement were studied. The alternating current (AC) electrical resistance and direct current (DC) resistance time curves were determined. The AC impedance spectroscopy curves of the specimens cured for 1 day and 28 days were obtained. Finally, the mechanical strengths of hardened cement paste cured for 1 day, 3 days, 7 days, and 28 days were tested. The results showed that the slump flow was decreased and the plastic viscosity was increased by the addition of WFA and the increasing curing time. The AC electrical resistance increased in the form of the quadratic function with the cuing age. Meanwhile, the addition of WFA demonstrated an enhancing effect on the electrical conduction of cement paste. The variation rate of DC electrical resistance during the testing time increased with the increasing dosages of WFA and the curing age. The mechanical strengths increased with the addition of curing time and the content of WFA. The increasing rate of mechanical strengths increased with the addition of WFA (0~15%) and decreased with curing time. However, when the dosage of WFA increased from 15% to 25%, the increasing rate decreased.