Feasibility study on the preparation of ternary blended cements with low-kaolinite calcined coal gangue and limestone.

This paper presents a feasibility study on the production of ternary blended cements with low-kaolinite calcined coal gangue (CCG) and limestone, considering kaolinite contents varying from 11.7 % to 40.6 % in coal gangue (CG). The ternary systems were designed with 15 %, 30 %, 45 % and 60 % by mass of cement replaced by CCG and limestone with a fixed mass ratio of 2:1. The fluidity and compressive strength of the mortars were measured, followed by the strength efficiency analysis combined with CO 2 emission. The potential hydration mechanism was revealed by analysing the hydration kinetics, hydrates and microstructural evolution of these ternary pastes. The results showed that it is possible to use low-kaolinite CCG and limestone to prepare ternary blended cements with adequate mechanical strength that can fulfill the 28-day strength requirement of 32.5 or 42.5 grade cement. In addition, Increasing the kaolinite content in CG can increase the substitution of cement up to 60 %. Microstructural studies indicated that the compressive strength of these ternary mortars at 3 and 7 days was mainly dominated by cement hydration and the pozzolanic reaction between CCG and portlandite (CH), respectively. The precipitation of carboaluminates from the synergy of CCG and limestone significantly reduced critical pore size and increased the volume fraction of fine capillary pores from 7 days, well supporting the strength development of the ternary mortar. The findings of this work underscores the potential of using low-kaolinite CCG as a supplementary cementitious material (SCM) to reduce carbon footprint in the field of construction, and also in contributing to a high-value green utilization of solid waste. • Good linear correlations are obtained between the strength of ternary mortars and the kaolinite content in CCG. • The pozzolanic reaction between CCG and portlandite supports the strength development of ternary mortars before 7 days. • The synergistic addition of CCG together with limestone enhances the precipitation of carboaluminates. • CCG20LS10 has a higher promising for engineering application with considering CO 2 emission and strength development. [ABSTRACT FROM AUTHOR]