| Phosphogypsum is a kind of industrial waste generated in industrial production.Due to the huge annual discharge and high disposal cost,most of the phosphogypsum can only be stacked in the storage yard and can not be effectively used,resulting in serious ecological environment problems and resource waste.In this paper,phosphogypsum is mainly used as the main raw material.Acid phosphogypsum is modified by lime neutralization method and applied to building products.Two material systems,phosphogypsum precast concrete and phosphogypsum cement stabilized material for pavement base,are designed respectively.The main research results are as follows:（1）The main component of phosphogypsum used in this paper is calcium sulfate dihydrate,which contains some phosphoric acid,eutectic phosphorus and other impurities.Before putting into use,lime is used to pretreat the acid phosphogypsum to reduce the harmful impurities in the acid phosphogypsum.The results show that the dosage of lime should not be too large.When the dosage is 0.5%,the impurity content in phosphogypsum can be reduced to a low level,and will not affect the later use.（2）Design and study of phosphogypsum precast concrete block with pretreated phosphogypsum.The effect of cement and mineral admixtures on the solidification of phosphogypsum particles is studied and discussed,and the experimental mix proportion is optimized according to the experimental results.The results show that phosphogypsum exists in excess in the block system,and curing with cement alone will hinder the hydration of cement,and its strength will increase slowly.However,with the help of mineral admixtures,the curing effect of phosphogypsum can be improved,and the strength of the material system can be enhanced.Moreover,adding activator can improve the compressive strength of the block,making the effect of mineral admixture more obvious.This kind of block can increase the use ratio of phosphogypsum to 40%,among which the best quality ratio is pretreatment phosphogypsum: cement: metakaolin: fly ash: gravel aggregate: water reducer: activator =40: 10: 4.32: 3.68: 42: 0.18: 0.18.The 28 d compressive strength can reach 30.71 MPa,which can reach the grade standard of Cc30.The water-soluble phosphorus dissolution test was carried out on the crushed sample,and the impurity phosphorus was rarely dissolved,so it can be used safely.（3）Cement stabilized material for phosphogypsum pavement base is designed and studied with the pretreated phosphogypsum.Phosphogypsum and graded gravel are used as the stabilized material,and cement and fly ash are used as the binder.The results show that the mechanical strength and water stability of the mixture are significantly affected by the change of phosphogypsum proportion in the mixture.Moreover,sodium silicate can obviously improve the performance of the material system and promote the curing of phosphogypsum,but the dosage should not be too large.Without the addition of additives,the maximum content of phosphogypsum can reach 60%.At this time,it can only meet the use requirements of the lowest grade highway.After the addition of activator,the cement stabilized material can meet the use requirements of class II and above highways.Among them,the best performance ratio is pretreated phosphogypsum: cement: fly ash: graded gravel: water: admixture =50: 6: 5: 39: 11: 0.33.The water-soluble phosphorus dissolution experiment was carried out on the samples of phosphogypsum cement stabilized material for pavement base with different content.The phosphorus element dissolution was very little and would not cause secondary pollution to the environment. |
PDF Full Text Request