| The industrial by-product gypsum stockpiling outside, both take up a large area of land, and wasted a lot of resources. It’s easy to cause pollution to the surrounding environment because of the contains of acid and other harmful substances. However, the emissions of industrial by-product gypsum in our province was more than 12 million tons very year, and still increased year by year. The comprehensive utilization of industrial by-product gypsum problem need to be solved right now. Using the industrial waste gypsum to produce gypsum blocks widely, from the chemical enterprise or the power plant, saved the natural gypsum resource, reduced the secondary pollution of industrial waste, and was conducive to the sustainable development of local economy. Therefore, the research and development for high waterproof performance of gypsum block, whether from the aspects of resource development and energy saving, or from the development of new building materials and so on, all had important economic and social benefits.The biggest disadvantages of gypsum products were low strength, poor waterproof performance and bad humidity resistance. The bibulous rate of ordinary gypsum products was in commonly 50% above, and the softening coefficient was only 0.2 ~ 0.3. Gypsum products would be prone to deformation after affected with damp, causing the phenomenon of soft building wall and rotted roots, thus affected its usability. In parts of anhui province, the annual average relative humidity was above 60%, as a result, the gypsum products often occurred the phenomenon of moisture absorbing, damping and bending deformation, etc., even in dry areas, it also appeared this kind of phenomenon. Gypsum products that their own shortcomings, greatly hindered the development and the usability of it. Therefore, in this article, the mineral composition and structure were analyzed embarking from the huainan coal plant solid wastes, the desulfurization gypsum. Then the suitable retarder was selected according to the different types of building gypsum retarder, and its retarding mechanism was analyzed. Through a series of experiments, a conform to the requirements of the organic silicon waterproof agent was developed, and the waterproof mechanism was analyzed. Finally, both the silicone water-proofing agent and the inorganic waterproof materials were used to further improve the waterproof performance of blocks. All the above work would be promoting the development of gypsum blocks with high strength, high softening coefficient and good waterproof performance.First of all, the desulfurization gypsum was studied by thermogravimetric analysis to make sure it mineral composition and structure, and its chemical composition was also studied by the X-ray fluorescence spectrum analysis. The results showed that the β- semi-hydrated gypsum content was over 71.4%, conforming to the GB9776-2008 standard.Secondly, the effect of hydrolyzed wheat protein retarder, citric acid retarder and sodium hexametaphosphate on the setting time and the strength loss of FGD gypsum was investigated, and the retarding action on the setting and hardening characteristics at different pH was also discussed. Furthermore, the retarding mechanism and the influence of various properties on the hardened gypsum plaster was investigated in detail by SEM and XRD. By contrast, the results indicated that the hydrolyzed wheat protein retarder for plaster had better retarding effect, low strength loss and less influence on the crystal morphology of dihydrate gypsum.In this article, the influence of a hydrolyzed wheat protein retarder on the hydration process, ion concentration in liquid phase, degree of supersaturation, and crystal morphology of plaster was mainly investigated. Furthermore, the retarding mechanism and the strength loss of gypsum were also studied by scanning electron microscopy(SEM). The results indicated that the use of the hydrolyzed wheat protein retarder for plaster achieved a better retarding effect and lower strength loss. The combination of gypsum plaster with the retarder not only decreased the plaster’s early hydration rate and prolonged its setting time efficiently, but also militated against the crystal morphology of dihydrate gypsum. For example, the crystal dimensions changed little, but the proportion of needle-shaped crystals decreased. Combination with calcium ions on the surface of dihydrate gypsum crystal nuclei may form a chemisorbed layer, reduce the surface energy of the crystal nuclei, and inhibit the growth of the crystal nuclei of dihydrate gypsum. Consequently, the hydration process of building gypsum becomes greatly extended and is slowed down significantly.Again, in order to improve the waterproof performance of gypsum products, the study of two kinds of building gypsum was synthesized using organosilicon waterproofing agent. For example, the amino functional silane coupling agent and the emulsifying agent was compounded with methyl silicon alkoxide at some radio to improve the performance of the traditional organosilicon water-proofing agent(eg. methyl silicon alkoxide), and a new type of the excellent gypsum water-proofing additive was producted. Furthermore, the waterproof mechanism and the influence of various properties on the hardened gypsum plaster was analyzed in detail. The results show that organic silicon monomer molecules formed a layer of silicon resin network in the substrate surface. The emulsifier of alcohol carboxylate introduced RCOO— to form coordination compound with Al3+ and Ca2+ and formed a layer of film that enhanced combination with the substrate surface and further improved the water resistance ability of gypsum. This new type of gypsum water-proofing additive was suitable for gypsum plaster and would not produce adverse effects on the strength of it. The softening coefficient of gypsum increased and the bibulous rate decreased significantly, compared with the common organosilicon water-proofing agent(eg. methyl silicon alkoxide).At last, the suitable inorganic waterproof material was chose to further improve the waterproof performance of blocks. All the above work would provide the theoretical basis to develop high strength, high softening coefficient, good waterproof performance of gypsum blocks. |
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