Preparation And Basic Properties Of Foamed Phosphogypsum Lighweight Materials

Phosphogypsum is a by-product of phosphoric acid production. However, high influence of impurities on the performance and large fluctuations in composition lead to phosphogypsum stockpiling in the form of industrial waste. This phenomenon results in a waste of resources, causes a burden on the emission enterprises, and also causes serious environment pollution. Aiming at the high efficiency utilization of phosphorus gypsum, in this paper, the flowability and setting property are regulated by adding alkaline substances, mineral admixtures, superplasticizer and retarder, and the mechanical strength and water resistance are improved by adding cement. Finally, lightweight phosphorus gypsum materials are produced by means of foaming and its microstructure is also discussed.Mineral admixtures can improve the fluidity and setting property of the phosphorus gypsum paste. The mechanical strength of hardened specimen decreases with the increasing amount of mineral admixture, and the strength of hardened specimen with slag is higher than that of fly ash. But cracking usually occurs when the higher content of slag.is used, as a result, the optimum proportion of gypsum and fly ash is 8:2, and the ratio of gypsum to slag is 9:1. Addition of alkaline materials can activate the mineral materials, and the activating effect of hydrated lime is better than that of cement under the same conditions. The optimal dosage of hydrated lime is 6% of the total content of mineral admixtures and gypsum.The water reducing rate of 0.3% polycarboxylate superplasticizer on modification gypsum is approximate 60%, and the fluidity of paste is greatly improved. However, high content of polycarboxylate superplasticizer could cause the strength loss. Citric acid can significantly prolong the setting time of gypsum and cause strength loss, and the strength loss becomes more evident as the extension of setting time increases. Addition of 35% cement improves the 28 d strength of the hardened paste for 97.9% and the softening coefficient increases from 0.36 to 0.46.When the content of foam increases from 0% to 60%, the compressive strength decreases from 17.9 MPa to 1.7 MPa, the bulk density reduces from 1404.9 kg/m3 to 521.7 kg/m3, and the thermal conductivity reduces from 0.4246 W/(m·K) to 0.0724 W/(m·K). For foaming plaster surface spray treatment with organosilicone can offer a great water-proofing effect. Addition of fly ash increases the porosity and lowers the most probable aperture; and cement particles can reduce porosity, decrease the most probable aperture, and increase the amount of small holes.