Research On The Technology Of Modified Cement Material By Ultrafine Gypsum

Currently, the quantity of the industrial by-product gypsum of our home country is increasing gradually, but the number of high-quality gypsum that is decreasing. In order to improve the use efficiency of the industrial by-product gypsum and the physical properties of the cement base material, it is necessary to develop a kind new utilization technology of industrial by-product gypsum.In this paper, we processed the calcined gypsum, the FGD gypsum from a coal-fired power plant in Inner Mongolia and the phosphogypsum from a fertilizer plant in guanxi province into tiny sizes by adopting the superheated steam powered jet mill, which is designed by our university. These particles were collected from different classifiers, which is in 20Hz,35Hz, and 45Hz frequency. Then we analyzed the particles'size distribution by the LPSA, the mineral composition by XRD, the micro structure by SEM. We also tested the particles' moisture content. Based on the above analysis, different gypsum particles were used in clinker. Then by comparing the water consumption of standard consistency, the setting time and the gelling properties, we explored the most appropriate classifier frequency for processing gypsum particles and the most appropriate ratio of gypsum particles in clinker. Finally, the most appropriate ratio of three kind's gypsum particles'the hydration reaction mechanism was analysed by the SEM, XRD, and Hydration heat tester.According to the results of research, (1) After been processed by the superheated steam powered jet mill, the range of gypsum varied from D5o<2.5?m, D9o<10?m. Its ratio of adhesive water and crystal water decreased, and its structure transforms to hemihydrates and anhydrite. (2) In terms of those experiments, considering the powder production capacity and the mechanical strength of the cement composite material, it is proved that the most appropriate grade frequency separation of gypsum ultrafine powder is 35Hz. Use gypsum plaster powder, which is collected by 35Hz frequency of classifier, to make into composite cement of superfine gypsum. The most appropriate ratios of gypsum particles in clinker are as following:The superfine calcined gypsum is 6wt%, the superfine phosphogypsum is 4wt%, and the superfine FGD gypsum is 5wt% in clinker respectively. (3) It was proved that the ultrafine gypsum powder can improve the hydration properties of cement gel, and generate more pointed needle hydration products, which are stable in age 28 days. However, without the ultrafine gypsum powder, the cement gel would primarily generate lamellar or block hydration products and only a small number of apex acicular hydration products, which are difficult to be kept in the original form within age of 28 days. On the contrary, after mixed with superfine gypsum powder, more apex acicular hydration products can be produced and they can stay stable in age 28 days.From the perspective of essential safety, this study used the method of material science to recycle the industrial by-product gypsum resource and to reduce the hidden safety dangers of the industrial by-product gypsum occupation of land, the harmful ingredients diffused and the dust in the process of traditional disposal. At the same time, the ultrafine gypsum powder can make the hydration reaction process more sufficient, and optimize the working performance, and strengthen the security in the process of engineering construction.