Reaction properties of coal gangue-calcium hydroxide system

A simplified CG-CH-gypsum-H2O system was simulated to further study the reaction of coal gangue (CG) with calcium hydroxide (CH) in cement hydration system. According to pH value, electrical conductivity and XRD spectra, the reactive CG materials have pozzolanic activities. The variations of CG and CH in reaction process were quantitatively analyzed by acid dissolve method and differential scanning calorimetry (DSC) analysis respectively. The results prove the possibility of secondary hydration effect of CG and show that it takes part in the hydration reactions fleetly during the early ages. Whereas, in the long run, the CG reaction is limited and CG is just consumed approximately 20% in total in 90 d ages. According to their different variation trends of CG and CH, the reactions between CG and CH have two stages: firstly, reactions of CG and CH are carried out and make some products in the early ages; secondly, CH continues to react with the products produced in the former step. SEM observations and compressive strength tests testified the conclusion.