Hydration and Mechanical Performance of Coal Gangue–Based Limestone Calcined Clay Cement

Coal gangue (CG) is a solid waste produced during coal mining that exhibits pozzolanic activity after calcination. Utilizing calcined coal gangue (CCG) to replace the calcined clay in limestone calcined clay cement ( LC 3 ) not only facilitates the resource utilization of industrial solid waste but also provides significant economic and environmental benefits. This study focuses on CCG–based LC 3 with 30% clinker content, using methods such as compressive strength testing, isothermal calorimetry, x-ray diffraction, and microstructural characterization to systematically investigate the effects of kaolinite content (20%, 40%, and 60%) and the addition of CH on hydration reactions and mechanical properties. The results indicate that CH significantly enhances the pozzolanic reactivity of CCG, particularly in the LC 3 system with high kaolinite content (60%), where the 28 day compressive strength increased from 24.0 to 36.9 MPa. Microstructural analyses revealed that CH addition promotes the formation of calcium (aluminate) silicate hydrate gels (C─(A)─S─H) and carboaluminate phases, while markedly refining the pore structure and reducing porosity. When the mass ratio of CCG:LS:CH was 2 ∶ 1 ∶ 1 , the system exhibited optimal overall performance. This study confirms the critical role of CH in improving the performance of low-CCG-based LC 3 cement and provides theoretical and practical guidance for the efficient utilization of CG with varying qualities.