Study On Preparation Of Phosphogypsum-based Aggregate And Properties

Phosphogypsum is a bulk solid waste residue produced in the process of wet preparation of phosphoric acid.It has high annual output,large stock and serious pollution.It is expected to consume a large amount of phosphogypsum when it is used as aggregate in roadbed and pavement.Although there have been relevant attempts,there are still many problems,such as aggregate strength and water stability.In this paper,the method of preparing artificial aggregate by using unmodified phosphogypsum powder and its application in concrete are explored.The following work is mainly carried out : Firstly,the preparation process of phosphogypsum based aggregate is determined by disc granulation method,and the influence of disc inclination angle,rotation speed and water spray rate on aggregate forming is explored.Then the artificial aggregate is prepared by phosphogypsum powder and the influence of material composition on the mechanical properties,water absorption and water stability of the aggregate is explored and optimized to obtain the best ratio.The mechanism of aggregate strength enhancement is revealed from the perspective of hydration products and micro morphology.Finally,gravel,shale ceramsite and phosphogypsum based aggregate are applied to concrete respectively.The mechanical properties,shrinkage properties,thermal insulation properties and interfacial transition zone were studied.The results show that :(1)The preparation method of two centrifugations can effectively improve the particle shape coefficient of the aggregate,and the tilt angle of the turntable and the amount of water spray have a direct and huge impact on the size of the aggregate.When the disc inclination angle is 80 °,the disc speed is 100 r / min,and the water spray rate is 20 %,the formed aggregate particle size is relatively uniform,and the particle size is mainly distributed between 5-20 mm.(2)On the basis of 25 % cement content,the effect of admixture J and B is better.When1 % admixture J is added,the strength of aggregate is 4.33 MPa and the water absorption is12.17 %.The aggregate strength prepared by the 1 : 2 diluted admixture B emulsion is4.88 MPa,and the water absorption rate is 13.10 %.The combined use of admixtures J and B can increase the aggregate strength to 6.22 MPa,which is 43.6 % and 40.7 % higher than that of single admixture J and admixture B emulsion,respectively,and the water absorption rate is reduced to 10.58 %.Further optimization of the ratio,adding 20 % slag instead of cement can improve the aggregate strength to 10.24 MPa,and the water absorption rate is only 6.60 %.The softening coefficient of phosphogypsum-based aggregate under the optimum ratio is 0.73,and the mass loss rate under long-term saturated environment and dry-wet cycle is 1.64 % and0.46 % respectively.(3)The mechanical properties of phosphogypsum-based aggregate concrete are close to those of shale ceramsite concrete,which is about 65 % of gravel concrete,and it has great application potential in low-grade concrete.At the same time,phosphogypsum-based aggregate concrete has good shrinkage performance and thermal insulation performance.The hydration products around the interface transition zone are very dense,the transition zone is relatively smooth,and the bite force and glue force at the interface are weak.These research results provide a theoretical reference for the practical application of phosphogypsum-based aggregates,and provide a new choice for the resource utilization of phosphogypsum.