Recovery and reuse of phosphogypsum: Effect of ternary cementitious materials on the performance of phosphogypsum pavement base layers

Abstract

In this paper, the performance of a new type of phosphogypsum (PG) pavement material is studied under the joint action of ternary cementitious materials (cement, mineral powder, and fly ash), CaCl2 and gravel. The experimental results of mechanical properties and durability of the material system, including compressive strength, splitting strength, dry and wet cycle, freeze-thaw cycle, etc., confirm that the material system can meet the design standards for road base material design standards for highways and primary highway sub-base. The test results of SEM, XRD, EDS, contact angle, and solubility of trace elements show that the material system does not cause secondary pollution to the environment, and its strength mainly comes from the C-S-H gel and calcium alumina (AFt) generated by the reaction of the reactive substances in the cementitious materials with PG in an alkaline environment. Finally, the optimal ratio of modified PG: mineral powder: cement: fly ash: gravel: water: CaCl2 was 50:8:3:0:39:11:0.22, and its 7d compressive strength, splitting strength, loss of strength in dry and wet cycles, loss of strength in freezing and thawing cycles, and water absorption were 6.41 MPa, 6.84 MPa, 3.01%, 16.22%, and 8.87%, respectively.