<p>This study investigated the effects of water-to-binder ratios (w/b) and calcined kaolinite content on the hydration properties of the ternary limestone calcined coal gangue cements. Two types of coal gangue (CG) with the kaolinite content of 11.7% and 40.6%, and three w/b ratios of 0.4, 0.45 and 0.5 were considered. Compressive strength tests, isothermal calorimetry, X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and scanning electron microscope (SEM) analysis were conducted over a period of 28 days to evaluate the compressive strength of the mortar, and the hydration properties and microstructure of the pastes. The results indicated that although increasing w/b ratio promoted early cement hydration and earlier onset of calcined coal gangue (CCG) reaction, the compressive strength of the mortars was adversely affected due to the excessive water. Conversely, at all w/b ratios, higher calcined kaolinite content resulted in an enhanced reaction of CCG and a more rapid consumption of CH from 7 to 28 days. This led to the generation of more hydrates and a corresponding positive development in compressive strength. Furthermore, the 28-day compressive strength of the mortar prepared with a higher calcined kaolinite content of 40.6% was found to be 1.4, 2.6 and 0.8&#xa0;MPa higher than that of the reference OPC mortar at w/b ratios of 0.4, 0.45 and 0.5, respectively.</p>