Industrial By-product Gypsum In Building Materials

People pay more attention to the utilization of industry by-product gypsum. Citric acid residue, titanium gypsum and FGD gypsum, the three kinds of industry by-product gypsum took the object of study in this paper, analysed their composition and structure by chemical composition analysis, thermal analysis, XRD analysis and so on, researched the application of them in cement and wall material.By using the citric acid residue, titanium gypsum and FGD gypsum instead of natural gypsum for the retarder of cement, the content of SO₃ in cement was 1.25%-2.75%, compared with the same SO₃ content of cement added with natural gypsum. The results show that each performance of cement specimen added with industry by-product gypsum conforms to the national standards. The citric acid residue replaces natural gypsum as the cement retarder, its strength character is higher, the optimal mixing quantity of citric acid residue is 4.9%; when the titanium gypsum replaces the natural gypsum as the cement retarder, its early strength is higher than that added with natural gypsum specimen, the 28d compressive strength is slightly lower than the natural gypsum specimen, the optimal mixing quantity of titanium gypsum is 6.7%; The FGD gypsum replaces the natural gypsum as the cement retarder, its strength character is slightly lower than the natural gypsum specimen, the optimal mixing quantity of FGD gypsum is 4.78%.Took the industry by-product gypsum, slag, specific surface area of slag as factors, and each of them had three levels, selected L9(34) orthogonal test table. The three levels of industry by-product gypsum were 3%, 4%, 5%; the three levels of specific surface area of slag were 353.8m²/kg, 367.9m²/kg, 392.3m²/kg; the three levels of slag were 15%, 20%, 25%. Explored the feasibility of the industry by-product gypsum replacing the natural gypsum as the slag cement retarder, the results show that when the citric acid residue content is 4%, slag content is 25%, specific surface area of slag is 353.8m²/kg, when the titanium gypsum content is 4%, slag content is 25%, specific surface area of slag is 371.9m²/kg, when the FGD gypsum content is 5%, slag content is 20%, specific surface area of slag is 371.9m²/kg, the slag cement performance achieves the optimal separately. Took the industry by-product gypsum as main raw material to prepare wall material, and took relevant performance test. Respectively tested and analysed the fineness of obtained building gypsum, set time, 2h mechanical strength. After the citric acid residue being took off the free water, stir-frying it for 2h to obtain the building gypsum at 130℃, 140℃, 150℃, 155℃, 160℃. The results show that when the citric acid residue stir-fry at 140℃ 160℃for 2h the qualified building gypsum can be obtained. While at 150℃ 160℃for 2h, the properties of citric acid residue specimen is superior to the purchased building gypsum specimen. While at 155℃for 2h, its performance meets the superior product requirements. The optimal water consumption of the stir-fried building gypsum is 60%. Took the citric acid residue stir-fried at 155℃for 2h as main raw materials, added with proper amount of cement, fly ash, slag and expanded perlite to prepare composite blocks. The results show that apparent density and strength of composite blocks are decreased with the increasing addition of expanded perlite. The building gypsum could be obtained from the titanium gypsum stir-fried 3h at 130℃, 145℃, 160℃, the results show that the building gypsum stir-fried from titanium gypsum is unqualified. Took the obtained building gypsum at 145℃for 3h as main raw materials, added with proper amount of citric acid, cement, lime, and calcium lignosulfonate to improve the performance of titanium gypsum blocks. The results show that it is difficult to improve its strength character greatly because of large amount of water requirement. Stir-fried the FGD gypsum at 135℃, 145℃, 155℃, 165℃for 2.5h, 3.5h separately to obtain the building gypsum. The results show that the fineness of the obtained FGD gypsum meets the superior product requirements. Water requirement of normal consistency is between 70% and 74%. Stir-fries between 135℃and 165℃for 3.5h are able to obtain high quality building gypsum; and the performance of the obtained building gypsum which is stir-fried 3.5h at 165℃is optimal. Took the FGD gypsum at 145℃for 3.5h as main raw materials, and took cement, slag, fly ash and curing age as factors to prepare composite blocks. The results show that the content of cement, slag, fly ash and curing age are 10%, 16%, 10%, 3d separately, the performance of composite blocks achieves the optimal.