Study On Preparation And Properties Of Desulfurization Gypsum Based Self-Leveling Mortar

Desulfurized gypsum is a solid waste produced by removing SO₂ gas produced by coal combustion in thermal power plants.At present,desulphurized gypsum emissions have exceeded 100 million tons in China.Massive accumulation and storage of desulphurized gypsum has become an important factor restricting the development of thermal power generation in China.Gypsum based self-leveling material has the characteristics of high flatness,good heat preservation and excellent stability,and is widely used in indoor leveling layer.Today,natural gypsum resources have shortage in China,the government has taken measures to limit exploitation.Using desulfurized gypsum as base material for self-leveling material is not only a reasonable way to realize high dosage and reuse of desulfurized gypsum,but also promote the sustainable development of Chinese economy and society.This topic is based on desulfurization building plaster as a base material,and selects P·O 42.5 cement,fly ash,limestone powder as mineral admixtures.The effects of three mineral admixtures on the performance of gypsum based cementitious system were studied by orthogonal experiment.Further,the effects of water reducer,retarder,HPMC,re-dispersible latex powder,defoamer and aggregate（ISO sand,quartz sand,limestone sand）on the performance of mortar were studied.The hydration products and microstructure were analyzed by X-ray diffraction and scanning electron microscopy（SEM）.The results showed that:1.The mixing ratio of gypsum based cementitious system is determined as follows:desulphurized building gypsum 80%,P·O 42.5 cement 5%,fly ash 10%,lime powder 5%.Gypsum-cement-fly ash-limestone powder composite cementitious materials can improve the physical and mechanical properties of hardened bodies,and the C-S-H and AFt generated after hydration play a key role.2.Polycarboxylate superplasticizer has less impact on mechanical properties of mortar under the premise of reducing water consumption and improving mortar fluidity.Retarding agent can greatly improve the constructability of mortar,and increase the strength of mortar and show a steady trend in a certain dosage range.HPMC can effectively solve the problem of bleeding of mortar.Re-dispersible latex powder can improve the absolute dry strength and flexibility of mortar,but reduce the 24 h strength of mortar.Defoamer can eliminate bubbles in mortar so as to improve the performance of mortar.3.Get a compound ratio of gypsum base self-flowing mortar（sand）:desulfurization building plaster 80%,P·O 42.5 cement 5%,fly ash 10%,limestone powder 5%,water reducer 0.23%,laminator 0.15%,HPMC 0.08%,can be scattered by 1.0%of latex powder,and 4.1%of the defoaming agent.On this basis,the optimal amount of three kinds of aggregate（ISO sand,quartz sand,limestone sand）are obtained from 20%to 30%,which can be used in mortar instead of natural sand.The main performance indicators prepared by the experiment（sandless,sand）have met the standard requirements.