Energy saving and applicability of gypsum?

China is rich in phosphate rock resources, and phosphorus chemical enterprises discharge a large amount of phosphogypsum every year, and the annual discharge of Guizhou Wengfu Phosphorus Industry Group alone reaches 5.5 million tons. The construction investment of phosphogypsum storage yard is large, the operation cost is high, it occupies a lot of land and causes great pollution to the environment. At present, only a small amount of phosphogypsum is used as soil improver, and the development and utilization ways are mainly concentrated in the fields of chemical industry and building materials. In chemical industry, it is mainly used to make sulfuric acid products such as potassium sulfate and ammonium sulfate and cement retarder, and in building materials, it is mainly used to make gypsum board, wires, adhesives, mortar ingredients and blocks. The utilization rate of phosphogypsum is low. Based on the abundant phosphate rock resources in Guizhou Province, Cao Jianxin of Guizhou University and others started a series of research work on the resource utilization of phosphogypsum in 2000 [12, 13]. In terms of building engineering, Ma Kejian of Guizhou University and others carried out the comprehensive application research of phosphogypsum in large bay flexible partition residential buildings from 2005 to 2007, and made feasibility analysis from structural forms, structural measures, construction technology, thermal insulation, energy saving and industrialization prospect, and made preliminary theoretical analysis and experimental research, and concluded that phosphogypsum has great development value in energy saving and structural integration [14]. Then a new residential structure with energy saving and structural integration is proposed [15- 17]. The load-bearing wall of this structure adopts concrete grid as the load-bearing skeleton, and the floor adopts concrete ribs, both of which use phosphogypsum as precast formwork. The experimental study shows that when the formwork wall is too thin, the site loss is large and it is not convenient for construction, so the future research idea is changed from phosphogypsum prefabrication to cast-in-place In 2007-2008, Cao Jianxin and others carried out the research on the water resistance of phosphogypsum and the modification of wall-forming materials (patent application number: 2009 1030 1656.6), which prolonged the initial setting time of phosphogypsum, shortened the final setting time of wall, and solved the problems of slow evaporation of residual water in natural state of phosphogypsum, and low water resistance of walls, walls and decoration.

Cast-in-place phosphogypsum load-bearing wall

After the implementation of the national land-saving policy, all localities began to use other blocks instead of clay bricks [18], or adopt frame structures in low-rise houses, with masonry only as filler walls. The structural type has a great influence on the project cost. In the future, especially in rural areas, mixed structure will still be the main structural type of low-rise residential buildings. Modified cast-in-place phosphogypsum has the characteristics of fast initial setting time and high strength, and can be used in low-rise small-bay houses. The wall is changed from traditional block masonry to cast-in-place phosphogypsum. For example, the two-story residential building shown in Figure 3 is made of mortar mixed with phosphogypsum and additives after shuttering on both sides of vertical and horizontal walls. The wall pouring method is shown in Figure 4, with low construction technology and convenient operation. The initial setting time of cast-in-place phosphogypsum wall is about 30 minutes, so the formwork removal time is fast, which greatly shortens the construction period and does not need additional structural insulation. In order to apply phosphogypsum to a greater extent, precast phosphogypsum modules can be used as low-ribbed concrete grid plates with bottom formwork. Its structural arrangement is shown in Figure 5(a), and the precast phosphogypsum module shown in Figure 5(d) is supported on the attachment beam ear of the rib beam. After the floor reinforcement binding is completed, the concrete is embedded into the phosphogypsum module. As shown in Figure 5(c), the use of precast phosphogypsum modules not only reduces the concrete consumption of the floor, but also provides sound insulation and sound insulation between the upper and lower floors.

Cast-in-place phosphogypsum-concrete grid frame composite wall

There are two construction methods of composite wall: one is to pour concrete grid frame first, and then pour phosphogypsum, that is, after each layer of concrete grid frame is molded and demoulded, phosphogypsum grouting material is poured on both sides of the frame. This construction method is faster, and the pouring of concrete and phosphogypsum does not affect each other, which is convenient for the division of vertical construction sections; Secondly, as shown in fig. 6(c), concrete and phosphogypsum are poured in the vertical part of each floor. The wall is vertically divided into three sections. At the bottom, the phosphogypsum grouting material is poured on both sides of the wall. After the phosphogypsum is initially set, the steel bars of the sandwich beam are bound, and then the concrete of the sandwich beam is poured into the side formwork according to the thickness of phosphogypsum required on both sides of the sandwich beam. After the initial setting of concrete, the construction of the middle wall can be carried out, and the construction of the whole wall can be completed in this way. There are many cross procedures on this road. However, the initial setting time of cast-in-place phosphogypsum is short, which has little effect on the wall construction period. The disadvantage is that the concrete grid is completely wrapped by cast-in-place phosphogypsum, which is not convenient for the appearance inspection of concrete members. The composite wall structure is mainly used for the peripheral wall of small high-rise residential buildings and the household wall of each household. Every household's room partition wall is a non-load-bearing wall, which makes each household's floor span larger. Therefore, the floor of cast-in-place phosphogypsum-concrete grid frame composite wall can adopt box-shaped multi-ribbed floor as shown in Figure 7. The floor is composed of ribbed beams and upper and lower panels, and its construction sequence is as follows: after the ribbed beams and lower panel reinforcement are bound, the lower panel concrete is poured, the precast phosphogypsum formwork is placed, the upper panel reinforcement is bound, and then the ribbed beams and upper panel concrete are poured. This kind of floor provides a structural basis for the re-partition of the rooms in the house, thus realizing the flexible partition function of the large width room of the house.

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The resource utilization of industrial waste residue mainly involves environmental protection, utilization rate and added value of products. In order to improve the added value of products, industrial treatment of waste residue will bring new environmental problems and new waste residue. The cast-in-place phosphogypsum load-bearing wall and cast-in-place phosphogypsum-concrete grid frame composite wall structure discussed in this paper are based on the direct consumption of phosphogypsum discharged by enterprises, and the operation is simple, without special machinery and excessive technological requirements. The engineering practice shows that the structural rigidity is high, the amount of steel used is less, and the amount of phosphogypsum is equivalent to that of concrete, which makes phosphogypsum the main building material of cast-in-place method, conforms to the requirements of national land-saving and energy-saving policies, and has great popularization and application value. The follow-up work will carry out the research on the mechanical properties and calculation methods of the structure, such as strength and stiffness, as well as the seismic performance of the structure.

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