| Phosphogypsum(PG) is an industrial byproduct of manufacturing phosphoric acid by wet process. Usually when 1 ton phosphate acid is produced, about 5 tons of PG is generated. At present the utilization rate of PG is only about 15%, the cumulative stock has more than 1 million tons. Most of the PG is stored in the open land, so that it not only occupies a lot of land resources, but also easy to penetrate into the groundwater system under the rain water, causing environmental problem and pollution. Therefore how to realize the high efficient and clean utilization of the PG is the main research direction of the utilization of the PG resources in the future.In this paper, using PG as main raw materials, mixing slag powder, cement and lime to prepare composite cementitious material(CCM). This material belongs to a new type of building material, which can satisfy the needs of the strength of most wall building materials. On the basis of the former, the aerated concrete block was prepared by adding the powder of aluminum powder. It has the advantages of light weight, sound insulation, sound absorption and good heat resistance and so on. It belongs to a kind of new green environmental protection material. The production of concrete block, not only can be extensive use PG, slag and other industrial solid waste, in line with the strategic development of circular economy, but also itself conforms to the national policy to encourage the development of new wall materials. It will become a new type of high rise building wall of green energy saving material.The preparation of CCM, the effects of additive and modified phosphogypsum on CCM and the preparation of aerated concrete block are studied. The following conclusions are obtained:(1) Through single factor experiments, the effects of the amount of PG. the content of cement clinker and lime on the CCM were investigated. Finally, the best compound ratio of CCM was determined. According to the quality, the ratio is PG:50%, slag powder:30%. cement clinker:15% and lime:5%. The ratio of water to material (W/G) was 0.28; the compressive strength of 3 d was about 29 MPa.7 d was about 32 MPa and 28 d was about 37 MPa.(2) The XRD and SEM micro analysis showed that, the main hydration products of CCM are ettringite and C-S-H gel. The more hydration products are produced, the more closly of the hydration system structure, the higher of the compressive strength.(3) The effects of the content of CaCl2, NaSO4, water-glass and NaF on the CCM were researed.The results of orthogonal optimization experiment showed that when the content of CaCl2 is 0.6%, NaSO4 is 0.2%, water-glass is 0.6%, NaF is 0.3%, the 3 d and 28 d compressive strength can reach maximum values of 35.96 MPa,42.88 MPa and the strength were increased by 19.27%.20.89%.(4) In the experiment, the CCM prepared by replacing the dehydrate gypsum with β-hemihydrate gypsum was studied. The experimental results showed that with the content of β-hemihydrate gypsum increased, the setting time of CCM decreased, the standard consistency water increased. And it can slightly improve the compressive strength of CCM.(5) The micro analysis of XRD and SEM showed that, the addition of β-hemihydrate gypsum can accelerate the hydration reaction rate. After 7 days of hydration, the hydration reaction of the system has been basically completed, the structure of the system has been basically stable. The compressive strength of the CCM was little difference between 28 d and 7 d.(6) Through single factor experiments, the effects of the amount of aluminum powder, the W/G, the ratio of sodium hydroxide to aluminum powder, the foam stabilizing agent/Al ratios and the different mixing water temperature on the dry density and compressive strength of aerated concrete block were investigated.(7) The effects of other experimental conditions on the performance of the aerated block were also studied, such as the additive compound proportion of orthogonal experimental. CMC and surfactant compound and the β-hemihydrate gypsum instead of dehydrate gypsum to prepare aerated concrete block.(8) Through the above experimental studies, the following conclusions are obtained. When the the amount of aluminum powder is 0.75%o. the W/G is 0.31. the ratio of sodium bydroxide to aluminum powder is 2. the CMC/A1 ratio is 0.75. the mixing water temperature is 20 degree centigrade and the ratio of CMC to surfactant equal to 1. the dry density of aerated concrete block is about 720 kg/m3～760 kg/m3 and compressive strength is about 5.25 MPa～5.65 MPa. The drying shrinkage value is less than 0.8 mm/m, and the mass loss is less than 5% when the frost resistance is tested. It nearly satisfy 11968-2006 GB/T "autoclave aerated concrete block" in the requirements of qualified products B07.(9) The XR.D and SEM micro analysis showed that, the main hydration products of aerated concrete block are also ettringite and C-S-H gel. However, compared with the hydration products of the CCM, the hydration products of aerated concrete block samples are reduced a lot, and the structure of the system is not so tight as a whole. It mainifests in a substantial reduction in compressive strength.(10) Based on the calculation of the production of 500 thousand tons of CCM and 200 thousand cubic meter aerated concrete blocks, the technical and economic analysis is carried out. Analysis results show that these two projects have good environmental and social benefits, in line with China’s comprehensive utilization of resources, ecological environment and sustainable development of a virtuous circle of economic industry oriented. It has strong competitive advantage, wide application prospect and great market potential.
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