Utilization of Coal gasification fine ash for construction material: From physical and chemical properties to the hydration activity of thermally modified CGFA

Coal gasification technology is the core of clean and efficient utilization of coal, while coal gasification fine ash (CGFA) is the solid waste inevitably produced in the coal gasification process. Due to the high residual carbon content and water retention of CGFA, the solubility of its silica-aluminium-calcium-containing minerals is poor, which affects its potential cementing properties in construction materials. In this paper, the basic physicochemical properties were investigated, and it was found that small particles of CGFA (CGFA-S) had more active mineral components, lower residual carbon content (17.17%) and weaker water retention (6.91%), which facilitated the removal of impurities and water. In addition, the best effects were achieved at a heat treatment temperature of 650 degrees C, which exposed the minerals and increased the solution solubility, and the leaching concentrations of Si4+, Al3+, and Ca2+ increased by 21.2%, 44.6%, and 97.8%, respectively. However, when the temperature was too high (815 degrees C), the minerals recrystallized, leading to structural instability and dissolution difficulties, and the concentrations of the three major ions were reduced by 84.4%, 82.0%, and 42.2%, respectively, compared with the control.Finally, the optimal heat treatment temperature was 650 degrees C, with the highest exothermic hydration rate (11.92 mW/g) and the highest cumulative exothermic heat (199.81 J/g). The hydration products were tightly bound, and the cement mortar specimens had the highest compressive strength, with a 28d strength of 45.4 MPa.