Study On The Composite Activation Of Coal Gangue

Coal gangue is an industrial solid residues raised from the excavation of coal ore and the floatation process. Coal gangue is known as one of the largest industrial waste materials in our country, the accumulated deposit of which is estimated about 4 thousand million ton and about 10 thousand hectare farmland is occupied. Such vast amount of coal gangue not only occupies the farmland but also causes severe pollution to the surrounding environment. Therefore, the effective reutilization of coal gangue became big problem to be solved. A series of experiments related to the activation of coal gangue to be used as a property modifying mineral admixture for high performance cement were conducted in this paper.The activity of coal gangue calcined at different temperatures was examined by means of cement mortar test, and results showed that original coal gangue did not produce pozzolanic reactivity when blended with Portland cement. Whereas, those thermally activated coal gangue showed better pozzolanic reactivity, producing improved mortar strength properties. It was believed due to the formation of amorphous silica and alumina from the decomposition of kaolin in calcined coal gangue. Furthermore, the so called composite activation with the addition of Glauber's salt or water glass into calcined coal gangue was proved to be beneficial to the development of cement mortar strength, especially for those at early curing ages, the activation effect with the addition of water glass being better than that with Glauber's salt. Therefore, the most appropriate condition of so called thermal and chemical composite activation for the activation of coal gangue is calcination temperature from 600℃to 800℃and water glass addition 4%.The activity of coal gangue calcined at 800℃and followed by so called mechanical and chemical activation was also examined by means of cement mortar test, which showed a remarkable activation effect. The most appropriate condition of so called mechanical and chemical composite activation for the activation of coal gangue is the simultaneous addition of 6% water glass and 5% slaked lime with its grinding duration of 60min, the 28d compressive strength of cement mortar blended with 30% coal gangue reached 50.2MPa, that is 86% of the compressive strength of P?52.5 cement at the same curing age. Meanwhile, the amount of combined water and Ca(OH)2 formation in hardened cement paste blended with coal gangue at different curing ages was determined by means of chemical analysis. The results revealed that...