| Gypsum plaster is a new type of plastering material,which has the characteristics of green environment protection.Different from traditional cement-based plastering materials,gypsum based plastering materials avoid the problems of hollow drum cracking and construction expansion.Gypsum plaster not only has the characteristics of low cost,low consumption and easy construction,but also has the characteristics of low bulk density and low load on the wall.These advantages of gypsum plaster make it widely concerned and applied.Under the green economy requirement of the national"14th Five-Year Plan",lightweight gypsum plaster instead of traditional plastering materials will become the development direction of the construction field.First,desulfurized gypsum was calcined into desulfurized building gypsum,supplemented by retarding agent,water retaining agent,light aggregate and other admixtures,adding fly ash,mineral powder,silica fume and other admixtures to prepare lightweight gypsum plaster.In order to improve the performance of desulphurized building gypsum,ZnO crystal modifier was added during the calcination of desulphurized gypsum.By XRD,SEM and three-phase test,the influence of ZnO additive on the crystalline quality and content of calcined building gypsum（β-Ca SO4·0.5H2O）was analyzed,and the appropriate added amount was determined.According to GB/T 9776-2008,the influences of calcination temperature,calcination time and additive content on slurry properties and hydration and hardening properties of desulfurized building gypsum were studied to determine the best calcination system.By adding different retarding agents,water retaining agents and sawdust as lightweight aggregate,according to the national standard GB/T28627-2012,the influence on the properties of gypsum plaster slurry（setting time,water retention rate）and hardening properties（strength,bulk density）were explored,and the appropriate amount of addition was determined.Through orthogonal design optimization,the optimal ratio of fly ash,mineral powder,silica fume and other mineral admixtures was determined.The results show that:（1）The desulfurized building gypsum prepared by adding 0.6%ZnO to the desulfurized gypsum and calcining at 160～180℃for 2 h has good crystallinity,the content of hemihydrate gypsum is between 82.11%～87.32%,and the slurry performance and strength are good.The standard consistency water consumption of desulfurized building gypsum prepared at 180℃is 68%,the initial setting time is 18 min,the final setting time is27 min,the 2 h flexural strength and compressive strength are 3.5 MPa and 10.3 MPa,and the 28 d flexural strength and compressive strength are 6.7 MPa and 18.03 MPa,respectively.The bulk density of hardened body is 1156 kg/m3.（2）The combination of 0.1%sodium citrate and 0.1%sodium glutamate as retarding agent,0.1%100000 cpi HPMC as water retaining agent,the prepared gypsum plaster has the most appropriate setting time and strength.The initial setting time is 78 min,and the final setting time is 88 min.The modified sawdust can obviously reduce the density of gypsum plaster and ensure a certain strength.At this time,the flexural strength of gypsum plaster is 1.39 MPa,the compressive strength is 2.68 MPa,and the bulk density is 894kg/m3.（3）The strength of gypsum plaster decreases and the setting time increases slightly when different admixtures are mixed separately under neutral condition.The orthogonal test under alkaline condition（adding 10%CaO）shows that the optimal ratio is A3B3C2,that is,10%of fly ash,15%of ore powder and 10%of silica fume.The modified lightweight gypsum plaster is obtained by adding 55%lightweight gypsum plaster with the optimal ratio of admixtures,and its flexural strength is 5.74 MPa,compressive strength is 8.85 MPa and bulk density is 885.16 kg/m3.By observing the morphology of gypsum after hydration,it is found that the hydration reaction of the admixtures takes place under alkaline condition,and the ettringite that can enhance the strength of gypsum is formed. |
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