Utilization of coal gangue powder to improve the sustainability of ultra-high performance concrete

The application of coal gangue (CG) powder as cementitious material is significant for the sustainable man-agement of CG. However, concrete containing a small content of CG powder suffers from obvious strength degradation due to its low activity, limiting full-scale recycling. In this study, CG powder was introduced into the non-fibrous ultra-high performance concrete (UHPC) matrix. This strategy is anticipated to achieve a higher CG reuse rate without sacrificing the superior mechanical properties of UHPC, as the filling effect of particles dominates the performance of UHPC rather than the chemical activity. The results showed that replacing cement with CG powder extended V-funnel time and slump flow. In addition, the compressive strength at later ages of UHPC containing CG powder was improved due to the pozzolanic reaction, as evidenced by the results of XRD and DTG. Moreover, the introduction of CG powder brought benefits to the autogenous shrinkage and chloride ion permeability of UHPC. Compared to the CG powder, calcined CG (C-CG) powder contributed to the higher strength and dense pore structure due to the enhanced chemical activity; nevertheless, the slightly increase in strength (<5%) favored the use of unpretreated CG powder in view of energy expenditure.