Synergic performance of low-kaolinite calcined coal gangue blended with limestone in cement mortars

Abstract Utilization of calcined coal gangue (CCG) as cement replacement has the potential to relieve the environmental burden and reduce clinker consumption. However, typical coal gangue in China usually contains low kaolinite content and exhibits poor pozzolanic reactivity even after calcination. This study aims to enhance the performance of CCG blended cement by coupled use of limestone. To further understand the pozzolanic and synergic effect of CCG (with kaolinite content of ~ 28.4%) and limestone, comparative studies were also conducted by replacing cement with CCG or inert quartz powder from 0 up to 60%. From the results of the experiment, it was clear that the co-utilization of CCG and limestone (2:1 wt ratio) enhances the later strength by 5 ~ 12% as compared with corresponding CCG mortars. Microstructure studies also reveal that limestone facilitates low-kaolinite CCG to form hemi- and mono-carboaluminates which refine the pore structure and improve the mechanical performance. In addition, the toxicity characteristic leaching procedure (TCLP) test was performed and no leached toxic element was detected for all blended cements containing CCG.