Performance Improvement of Cement-Based Materials Containing Coal Gasification Fine Ash by Using High-Calcium Solid Waste: Experimental, Hydration Kinetics, and Thermodynamic Modeling Investigation

Abstract

The addition of an appropriate content of calcium source into cement-based materials containing coal gasification fine ash (CGFA) is found to be a potential method to improve its mechanical properties. In this study, three high-calcium solid wastes, such as calcium carbide residue (CCR), blast furnace slag (BFS), and flue gas desulphurization gypsum (FGDG), were selected as calcium sources. The effects of these high-calcium wastes on the properties of cement-based materials containing 30% CGFA, such as setting time, flowability properties, and mechanical properties, were investigated. The hydration behavior and hydration products of the cement-based materials were analyzed using calorimetry, chemical bound water content, and x-ray diffraction. Finally, the hydration kinetics model of the paste was established, and the effect of the calcium source on the Ca/Si ratio of the CSH gel was investigated using the GMES model. The results indicated that CCR and BFS accelerated the setting of the cement paste, while FGDG delayed it. Both BFS and FGDG improved the flowability of the cement mortar, but CCR reduced it. The addition of the calcium source changed the content of calcium, sulphate, and aluminum ions in the system triggering different degrees of ettringite phase transitions. The addition of high-calcium solid wastes effectively increased the Ca/Si ratio of the CSH gel. The improvement of strength of cement-based materials containing CGFA via high-calcium solid wastes is a result of multiple effects acting synergistically.