Research On The Preparation Of Paint Plaster Based On Gypsum

Most of China’s emissions of chemical gypsum, estimated higher than 100,000,000 tons annualy, are stacked and abandoned. Thus not only occupies vast land, also pollutes the enviroment seriously. Therefore, comprehensive utilization of industrial by-product gypsum is of great significance for the protection of ecological environment. In the current recycling of the industrial solid waste, the field of building materials accounts for more than 90% , which therefore enjoys a special status to build a conservation-oriented society and develop sustainable economy. Utilization of chemical gypsum to produce gypsum-based building materials has proved to be effective. In addition, compared with cement-based building materials, the gypsum-based building materials are charactrized by energy-saving, enviormentally friendness and good thermal insulation. Due to the considerable improvement of both quality and fuction of buildings by the use of gypsum-based building materials, it is a type of eco-friendly building materials.For the purpose of utilization of the wasted industrial gypsum and energy reduction, two innovative methods to make wall plaster were put forward in this thesis. Dihydrate gypsum and dihydrate–anhydrite composite, were blended with a certain amount of blast slag,ordinary cement,addtives to make wall plaster,respectively. This is beyond the traditional method of production of wall plaster, which always experiences a process of calcining of dihydrate gypsum to obtain anhydrate or hemihydrate gypsum. Systematic investigation on influence of sulphoaluminate cement,composite setting accelerator,water-retaining agent(etc.) and pretreatment of gypsum on properties of wall plaster were conducted. The hydration mechanism of gypsum,blast slag and cement were also discussed.Based on the experimental results, some important findings were obtained and showed in the following:(1) Phosphogypsum must be neutralized with lime prior to use due to the existence of free acid. The slaking time affects the properties of the manufatured composite wall plaster radically and at least seven days of slaking proved to be needed.(2) The dosage of sulphoaluminate cement and composite setting accelerator influences the setting time and early strength of the wall plaster considerably. The setting time reduces and the strength improves with the increase of the dosage of sulphoaluminate cement and composite setting accelerator. However, the strength decreases if excessive sulphoaluminate cement and composite setting accelerator were added.(3) When phosphogypsum is involved to make wall plaster,the optimum mix proportion can be expressed as phosphogypsum: slag: ordinary cement (mass percent)= 60:30:10. In addition, 10% sulphoaluminate cement,1.5% lime,2.5% composite setting accelerator, 0.1%methyl cellulose(MC),0.5% polyvinyl alcohol(PVA) were added. The flexural ,compressive strength at the age of 3 days and the bonding strength at the age of 28 days achieved 3.1MPa,12.7MPa,and 1.0MPa,respectively. The flexural strength can meet the technical requirement specified in the gypsum specification. The bonding strength and compressive strength is considerably higher than the indexes required.(4) When desulfogypsum-fluorogypsum is involved to make wall plaster,the optimum mix proportion can be expressed as desulfogypsum:fluorogypsum slag: ordinary cement(mass percent) = 35:35:20:10. In addition, 5% sulphoaluminate cement,2% lime,2% composite setting accelerator, 0.1% MC, 0.3% PVA were added. The flexural ,compressive strength at the age of 3 days and the bonding strength at the age of 28 days achieved 3.6MPa,12.2MPa,and 1.1MPa,respectively.