High-volume coal gasification fly ash–cement systems: Experimental and thermodynamic investigation

Coal gasification fly ash (CGFA) as a silica-rich material can be potentially used as a supplementary cementitious material (SCM) in concrete. In this study, the cements prepared by CGFA and ordinary Portland cement (OPC) mixtures were systematically investigated to explore the possibility of large-volume utilization of CGFA in cement industry. The hardened cements were subjected to experimental and thermodynamic investigation. The selective dissolution tests suggested that the CGFA had a generally low reaction degree in the CGFA-OPC reaction systems, although the XRD pattern indicated it was a highly amorphous material. The mechanical property tests suggested that the incorporation of 10% CGFA into OPC did not significantly influence the material properties, and the CW-1 mixture (10% CGFA) achieved the compressive strength of 33.8 MPa and the flexural strength of 8.2 MPa. In addition, the drying shrinkage increased with increasing CGFA content in the mixtures. The phase assemblages generated by thermodynamic simulation show that the CGFA always causes reduction in the amount of C-S-H in the hydration products, although the pozzolanic reaction of CGFA can contribute to the formation of secondary C-S-H. The volume of simulated free water is higher in CGFA-rich mixtures, which explains the larger drying shrinkage strains in those mixtures. This study can provide a preliminary guideline for the beneficial utilization of CGFA in OPC and contribute to the recycling and reuse of the waste solid from coal gasification.