Research On Preparation Of Cements And Alkali-activated Cementitious Materials With Calcium Silicate Slag

Calcium silicate slag is the residue yielding from sintering of high-aluminum fly ash after extraction of alumina. The utilization of calcium silicate slag is one of the key points for the technology of extraction of alumina from high alumina fly ash to realize benefits maximization of economy, society and environment. Aiming at the utilization of calcium silicate slag, based on the study of dealkalization pretreatment of calcium silicate slag, dealkalized calcium silicate slag used to replace lime stone to produce cement clinker, used as admixture and alkali-activated cementitious materials were studied respectively. The results have important guiding significance for the utilization of calcium silicate slag.The factors affecting the dealkalization of calcium silicate slag under atmospheric conditions, and the dealkalization mechanism were discussed. The results show that the optimized process conditions of calcium silicate slag dealkalization is: reaction temperature 90~95℃, reaction time 40min~1.5h, dealkalizitor addition 6~10%, liquid-solid ratio 3.0~4.0, calcium silicate slag fineness 160~200 mesh beads. The optimized Na2 O content ranges from 0.5~1.0%. The composition of the liquid phases of calcium silicate slag slurry can greatly affect the dealkalization process, however, its effect could be eliminated by adding carbide slag or lime slurry.The effects of dealkalized calcium silicate slag on burnability of raw meals were studied. The mineral composition, microstructure and sintering kinetics of clinker were studied by XRD、TG-DSC、ESEM and optical microscope. The results show that it is feasible for dealkalized calcium silicate slag to partly replace limestone as raw material in cement production. With replacement of 30% dealkalized calcium silicate slag, the optimized factors for burnability are as follows: KH < 0.92, n = 2.60, p = 1.60. The addition of dealkalized calcium silicate slag could notably promote the sintering of clinker and the growth of minerals. The reason for this phenomenon is that there are a large amouts of β-C2 S in dealkalized calcium silicate slag, which reduces the activation energy and sintering temperature of clinker.The effects of dealkalized calcium silicate slag on cement performances were studied. The hydration products were studied by XRD、IR、ESEM. The results show that with 30% replacement of cement by dealkalized calcium silicate slag, the cement can meet the strength requirements of the standard PC 32.5 cement. Compared with Portland cement, β-C2 S in dealkalized calcium silicate slag has lower activaty. When it is used as admixture, the cements hydrate more slowly. Therefore, the amount of calcium silicate slag is positively correlated with the shrinkage decrease of cement paste.The alkali-activated cementitious materials were prepared with calcium silicate slag. The hydration products were investigated by XRD、IR、TG-DSC、ESEM. The results show that the optimization of waterglass-activated cementitious materials mixing ratio design is: 70% calcium silicage slag + 15% ultra fine slag(600 m2/kg) + 15% slag(400 m2/kg) + 5% waterglass(by the Na2 O content, with a module of 2.40). The hydration products are mainly C-S-H and C-A-S-H gel. The addition of sodium phosphate changes the morphology of C-S-H and C-A-S-H gel, which causes a decrease in the density and results in a reduction in the strength of specimen.