Effects of Decarbonized Coal Gasification Coarse Slag and Fine Ash on Properties of Cement Paste as Supplementary Cementitious Materials

Abstract

Coal gasification coarse slag (CGCS) and coal gasification fine ash (CGFA), both of which are composed of inorganic oxides and unburned carbon, are the two solid wastes produced in the process of coal gasification. However, the utilization of CGCS and CGFA in cement and concrete is greatly limited due to the existence of unburned carbon. After the unburned carbon is removed, CGCS and CGFA can be used in cement-based materials as supplementary cementitious materials on a large scale. This paper studied the influence of decarbonized CGCS and CGFA on hydration heat, setting time, and compressive strength of cement paste. The experimental results show that replacement of cement by CGFA delayed the time of the maximum exothermic peak, and replacement of cement by CGCS greatly reduced the peak value of the maximum exothermic peak; hence, it is revealed that both CGFA and CGCS had a retarding effect on the setting time of cement paste. Moreover, the pozzolanic activity of CGCS was lower than that of CGFA according to the dissolution property in the alkaline solution and compressive strength of cement mortar. Furthermore, the fineness of CGFA particles showed a harmful effect on the fluidity of fresh cement binders, but the fineness of CGFA particles had a positive effect on the pozzolanic activity and thus is beneficial to the strength of cement mortar.