Study On Preparation Technology And Resource Utilization Of Recycled Gypsum

Gypsum is a kind of green building material, It is widely used in architecture. China's gypsum is rich in resources, but the distribution of resources is not balanced, and the proportion of high quality gypsum resources is small. As gypsum is widely used, resulting in a large number of waste gypsum.These gypsum not only occupy a lot of farmland, pollute the environment, but also is a waste of resources.In theory, gypsum can be recycled.But at present, the research on gypsum is mainly aimed at the primary gypsum and industrial by-product gypsum.Well less research on the waste gypsum.With the resource crisis is more and more serious, the re-use of materials is even more important.So it is necessary to research the recycled gypsum, which provides theoretical guidance for the utilization of waste gypsum.Ourgroup have made some basic research on recycled gypsum.The difference between natural and recycled gypsum has been revealed from the aspects of phase composition, thermal properties, microstructure and so on.On this basis, this paper explores the best preparation technology of recycled gypsum, and explores the ways of resource utilization of recycled gypsum.The thermal performance of recycled gypsum is different from that of primary gypsum. So,the production process of the original gypsum can not be copied to be used in the recycled gypsum.In this paper,we changing the grinding time, calcination temperature, calcination time three conditions to explore the best preparation technology of recycled gypsum.Water-reducer and cement is often added to the gypsum to improve its performance.And the building gypsum is sometimes difficult to separate from the cement mortar. So,In this paper, the effect of water reducing agent and Portland cement on the properties of primary and recycled gypsum was studied..The setting time of recycled gypsum is longer, and the strength is lower, well plastering gypsum requires a long setting time and low strength.So it is suitable for use recycled gypsum to prepare plastering gypsum.In this paper, we modified the setting time, water retention property, bond strength and strength of recycled gypsum.Based on the influence of several additives on the performance of recycled gypsum,determine the best volume of admixture, and formulate recycled plastering gypsum with good performance.Research results show that,the best preparation technology of recycled gypsum is different from that of primary gypsum. Prepare recycled building gypsum need longer grinding time, lower calcination temperature.Analysis shows that,This is due to the increase in the specific surface area of recycled gypsum plaster to a certain extent, its grain is fine,surface is smooth and easy to flow, cause the reduce of standard water requirement.And the thermal stability of recycled gypsum decreased,dehydration temperature decreased.Recycled gypsum prepared according to the best process, The initial setting time is 8min,final setting time is 12 min,2h flexural strength is 2.33 MPa,compressiom strength is 4.45 MPa,propertiesmeet the gypsum standard GBT9776-2008,2 rate of building gypsum.The more water reducing capacity was possessed by recycled gypsum at the same dosages with primary gypsum.The performance of recycled gypsum was continuously enhanced under the content of 0.20%.Portland cement can improve the strength of recycled gypsum.Analysis shows that,this is due to the large surface area of recycled gypsum, so the water reducer can easily play a role of disperse.The mixed growth of cement hydration product and gypsum crystalcan improve the performance of gypsum.The water reducing agent of primary gypsum still has the function of reducing water in recycled gypsum.And the cement in the primary gypsum has a negative effect on the recycled gypsum.Analysis shows that,this is due to the calcination temperature is not enough to make poly carboxylic acid water reducing agent to produce thermal decomposition and desorption. And cement in the recycle process is nonreversible. After regeneration, it become inert power, have disadvantage to gypsum strength.It presence critical volume(0.4%) when adjusting the setting time of recycled gypsum with sodium phosphate retarder.Above this amount,the setting time was significantly increased, and the strength deteriorated seriously.To improve the water retention of recycled gypsum with hydroxypropyl methyl cellulose ether,it improves the water retention property of gypsum and it is disadvantageous to the strength of gypsum,selection 0.15%content.To improve the performance of recycled gypsum bonded with rubber powder,below the critical volume(1.5%),it is favorable to bond performance,above the critical volume have disadvantage.The strength of recycled gypsum increases with the increase of the content of water reducing agent and desulfurization gypsum.Selection of 0.05% water reducing agent or 20% desulfurization gypsum.Several kinds of admixture prepared recycled plastering gypsum to meet the requirements of GB/T 28627-2012 standard.For the bottom plastering gypsum,20-40 purpose sand should be selected, and selectsand binder ratio of 1:0.5,The bottom plastering gypsum prepared can meet the standard requirements.