Study On Strength Properties Of Gypsum Block Prepared By Phosphogypsum

Phosphogypsum is a side-product from the wet process production of phosphoric acid in phosphate fertilizer industry, with its constituents of dehydrate calcium sulphate accounting for 90%. Every year, phosphogypsum is of high yield in China, whose bulk deposition exerts an effect on the environment. The gypsum block is bound to become the new-type wall materials in China. Fewer studies on the gypsum block made of phosphogypsum has been carried out. Therefore, the thesis will open a new chapter for the comprehensive utilization of phosphogyp-sum, and bring new vitality for the development of new-type wall materials.The thesis focuses on phosphogypsum, phosphogypsum and product were characterized by particle-size analyzer, XRD and SEM. The seting calcination temperature was set between 120℃ and 180℃, researching the calcined process of making phosphogypsum into β-hemihydrate gypsum including the water-reducing rate, calcination time and three-phase components under the different calcination temperature. After different calcination temperature, measuring the initial setting and final setting time and compressive strength value of β-hemihydrate gypsum, which was calcined from phosphogypsum. The optimum conditions of using phosphogypsum to calcinate into β-hemihydrate gypsum has been concluded that temperature was 170℃, the best calcinations time was7 hours, with 4 days’aging time.Adding the additives in the hydration and hardening process of β-hemihydrate gypsum powder to analyze the influence of additives on the physical properties of β-hemihydrate gypsum,such as water-reducing rate,compressive strength, etc.Using SEM to analyze the internal micro-structure of the sample block after blending additives. The experimental results have indicated as follows:(1) In the range of dosage (0.1 to 0.3%), Sephadex (G-50), comb polycarboxylate(HC),FDN superplasticizer,lignin (MZS) water reduction respectively had a significant positive correlation on β-hemihydrate gypsum. Meanwhile, the optimal dosage of four kinds water reducer was 0.3%. Among them,0.3% of the G-50 Water Reducer had the best water-reducing effect, water reducing rate reaching 25%, corresponding compressive strength of Gypsum block reaching 15MPa. Comparing with the control group, its compressive strength had increased by 36%. The influence of the water-reducing rate and compressive strength on P-hemihydrate gypsum had no proportional linear relationship in the condition of superplasticizer double mixing. Double Mixture of G-50 and FDN water reducer had the best water-reducing effect on β-hemihydrate gypsum, reaching 33.3%, of which the compressive strength was 14.5MPa. The intensity value was slightly lower than the other groups such as MZS and FDN superplasticizer double-mixing. Double mixture of MZS and FDN water reducer had the best compressive strength effect on β-hemihydrate gypsum, reaching 15.2 MPa, of which the water-reducing rate was 20%. Comparing with G-50 and FDN superplasticizer double mixing and G-50 single-doped, it had the worst water-reducing effect.(2)The initial and final setting time of the Slurry had different degree of shortening in the experiment of singe-added four kind of alkali-activator CaO、 Al(OH)3、KOH、NaOH and four kind of Sulfate Activator Al2(SO4)3、K2SO4、Na2SO4 CaSO4,. In the experiment of alkaline activators single-added, the sample of CaO with 0.5% had the highest compressive strength, reaching 18.2MPa. In the experiment of sulfate activators single-added, the sample of Al2(SO4)3 with 0.5% had the highest compressive strength, reaching 18MPa. In the experiment of between alkaline activators and sulfate activators pair combination, the sample of CaO with 0.3% and Al2(SO4)3 with 0.5% double-added had the higher compressive strength,maximizing 18.5MPa.(3)In the hydration process of β-hemihydrate gypsum, mixing superplasticizer of G-50, FDN and activator of CaO, Al2(SO4)3, of which the content was 0.3%,0.3%,0.3%,0.5% respectively, compressive strength of generating gypsum block maximizing 22MPa, which has improved 46% comparing with desulfurization gypsum block in industrial production.The crystal structure of its internal distribution in gypsum block had the most dense structure.