Research On Preparation And Performance Of Phosphogypsum Foamed Concrete And Block

With the increasing demand for human settlements and the strong support of national policies,green wall materials are developing rapidly and have broad prospects.As a by-product of the phosphoric acid industry,phosphogypsum is the largest mass of gypsum waste residues.The environmental problems caused by the increase in the stock of phosphogypsum have become increasingly prominent,and the utilization rate of phosphogypsum is low worldwide.The development of phosphogypsum large-scale treatment technology and its use in green wall materials is in line with the needs of the era of sustainable development.This paper focuses on the research of phosphogypsum-Portland cement foamed concrete and its block technology,and consequently to provide technical support for the application of phosphogypsum in green wall materials.This paper studied the heat treatment process of converting phosphogypsum into CaSO4·0.5H2O;Using fluidity,setting time,and mechanical properties as the main evaluation indicators,the influence of the main constituent materials on the performance of phosphogypsum paste was studied,and the composition of the phosphogypsum paste with better performance was determined;The phosphogypsum foamed concrete with density grades A03,A05,A07,A09(dry density grades 300kg/m3、500kg/m3、700kg/m3、900kg/m3)was prepared by chemical foaming and investigated the influence of ingredients on concrete;A09 grade phosphogypsum foamed concrete was used to prepare the blocks,and the basic properties of the foamed concrete blocks were analyzed,and the block properties met the specification requirements.The cementitious property of phosphogypsum depends on the amount of CaSO4·0.5H2O produced after heat treatment(heat treatment includes dehydration and standing).The main factors affecting the cementitious property of phosphogypsum are dehydration temperature,dehydration time and indoor standing time.Thermal analysis and cementitious property test results show that the dehydration reaction of phosphogypsum begins at about 110℃,and CaSO4·0.5H2O with a dehydration temperature of 130℃ at the same dehydration time produces the most,that is,the highest cementitious property;When the dehydration time is 30-60min,the gelation of phosphogypsum increases with the extension of the dehydration time.When the dehydration time is 60-90min,the gelation decreases;when it is standed indoors for 6d,the cementitious property of phosphogypsum is higher.A longer standing time reduces the cementitious property.Based on the experimental results,the optimal heat treatment process for phosphogypsum was determined to be 130℃ for 60 to 70 minutes of heating and dehydration,and then to stand indoors for 4 to 6 days.For the main constituent materials of gypsum paste,mineral admixtures(slag,fly ash),alkaline materials(Ca(OH)2,cement),chemical admixtures(water reducers,retarders),research shows that the mineral admixtures are beneficial to improve the fluidity of the phosphogypsum paste and prolong the setting time.When the content of mineral admixtures is 0.0%-40.0%,the strength of the hardened paste decreases with the increase of the admixture content.When the content of mineral admixtures is the same,the strength of phosphogypsum paste mixed with slag is higher than that of fly ash;When the content of alkaline materials is 0.0%～10.0%,the activation effect of Ca(OH)2 is better than that of cement;when the content of cement is 0.0%～40.0%,the mechanical properties and water resistance of phosphogypsum paste increase with the increase of cement content;The mechanical properties and water resistance of the phosphogypsum-cement system are better than that of the phosphogypsum-mineral admixture system,so the phosphogypsum-cement system is used to prepare foamed concrete and blocks;when the water-reducing agent content is 0.00%～0.18%,the phosphorus The water reduction rate and fluidity of the gypsum-cement system increase with the increase of the water reducing agent content.When the retarder content is 0.00%～0.18%,the paste setting time increases with the increase of the retarder content,but the mechanics performance is reduced.Using phosphogypsum-cement as the matrix material,foamed concrete and blocks are prepared by chemical foaming.When the cement content is 0.0%-40.0%,the cement content increases,the foamed concrete mechanical properties and softening coefficient increase,the water absorption rate decreases and shrinkage increases.The phosphogypsum foamed concrete block meets class one requirements of JC/T 1062-2007 "Foamed concrete Block"standard:first-class quality,dry apparent density 880～912kg/m3,compressive strength 3.55MPa,The drying shrinkage value is 0.78mm/m,the thermal conductivity is 0.225 W/m·K,the freeze-thaw cycle strength loss rate is 14.2%,and the mass loss rate is 3.2%,carbonization coefficient 1.05;the blocks meet the radioactivity standards of class A decoration materials.