Study On Utilization Of Phosphogypsum For Construction And Building Materials Production

Phosphogypsum is one kind of industry waste, the emission and accumulationof which has seriously polluted the surrounding and damaged people’s health. Ithas greatly drawn the attention of enterprises and government departments toenhance the multi-utilization research of phosphogypsum, which is extremelyurgent. This work investigates the feasibility of multi-utilization ofphosphogypsum for construction and building materials from four parts:(1)High-belite ferroaluminum cement was prepared by the utilization ofphosphogypsum and pyrite cinder. The burning process of clinker, effect ofnatural gypsum content on the performances of cement and the hydration ofcement were studied.(2) Non-autoclaved load-bearing wall bricks weremanufactured by the use of original phosphogypsum, which was untreated in anyway. The basic mix proportions of raw materials and technological parameterwere investigated, and the various properties of bricks were also tested.(3)Non-autoclaved aerated concrete was manufactured by the use of originalphosphogypsum. The basic mix proportions of raw materials and technologicalparameter were investigated basing on the dry density and compressive strengthof specimens, and the various performances of products were also tested.(4) Thepreparation of self-leveling floor mortar was explored by the use of originalphosphogypsum as filler. The mix proportions of raw materials were investigatedbasing on the performances of the mortar, and the mechanism was also explored.High-belite ferroaluminum cement clinker with excellent performances couldbe prepared at1250℃for60min in the laboratory. The setting time was shortenedobviously when the cements were made of clinker and natural gypsum, which wasless than25min when natural gypsum content was5%~15%. Natural gypsumcould promote the early hydration of ferroaluminum cement, besides, with naturalgypsum content increasing, the acceleration was more and more obvious and thehydration heat was lower and lower. Effects of natural gypsum content oncompressive strength with different curing time were various; the compressivestrength of1d,3d and28d was39.3MPa,43.2MPa,53.9MPa respectively. Effectof natural gypsum content on expansion ratio of cement cured for different timewas nearly same, it reduced with natural gypsum content increasing from0%to 10%, however, which increased again when natural gypsum content came up to15%. Natural gypsum content was an important influence factor of the hydrationof ferroaluminum cement, which not only affected the hydration products, butalso affected the microstructure of hydration products.Non-autoclaved wall bricks were manufactured utilizing originalphosphogypsum, and the effect of hemihydrate gypsum, fly ash and slag on theperformances of bricks was compared. The results showed that fly ash was goodfor improving later compressive strength and frost-resistance of bricks comparingwith hemihydrate gypsum, nevertheless, when compared with slag, althoughlater compressive strength were closed to each other, the frost-resistance of brickscontaining slag was better. The best mix proportion of raw materials was asfollows: cement: phosphogypsum: slag: sand=10:65:10:15, the press for moldingwas20MPa.The compressive strength of bricks, which were cured in room for28d after curing in80℃steam for8hours, was larger than35MPa, besides, thebricks had excellent frost-resistance and water-resistance.Non-autoclaved aerated concrete was prepared by the utilization of originalphosphogypsum; the optimum mix proportion of raw materials was as follows:cement15%, phosphogypsum55%(dry basis), slag30%, quick lime7%,Na2SO41.6%, aluminum powder0.074%. Water to raw materials ratio was0.47.The best gas-forming conditions were40℃water and50℃pre-curing, and thebest curing condition was cured in90℃steam for24hours. The dry density ofproducts was686Kg/m3and the compressive strength was6.3MPa. After15freezing and thrawing cycles, the loss of dry weight and compressive strength was1.5%and12.7%, separately. The thermal conductivity of product was0.15W/(m·K). All the above performances met the requirements ofGB11968-2006《Autoclaved aerated concrete blocks》(grade B07), except the dryshrinkage overstepped the demand and which will be a great challenge in thefuture research.It was feasible to prepare cementitious self-leveling mortar utilizing untreatedoriginal phosphogypsum. The self-leveling mortar that meet the requirements ofJC/T985-2005《Cementitious self-leveling floor mortar》could be prepared byadding sulfoaluminum cement12%, portland cement8%, phosphogypsum40%~55%and sand25%~40%. The analysis of mechanism showed that phosphogypsum not only played the role of filler but also took part in thehydration of cement.