Cement-Stabilized Phosphogypsum Synergistized with Curing Agent as Sustainable Pavement Base Materials

Abstract

Phosphogypsum (PG) is an industrial solid waste generated during the preparation of phosphoric acid, which is produced in large quantities and stockpiled or discharged into the sea. This study aims to design sustainable pavement base materials constituting significant PG content. The physical and chemical properties of the raw materials were first tested. The optimum moisture content and maximum dry density of specimens were determined by compaction tests. The unconfined compressive strength (UCS), split tensile strength (STS), freeze-thaw cycles, and shrinkage tests were used to evaluate the mechanical performance of phosphogypsum pavement base material (PPBM). Furthermore, the interaction mechanism was investigated by applying scanning electron microscope (SEM) and Fourier-transformed infrared (FTIR) tests. The results showed that the 7-day UCS of PPBM with cement content 8%–12% was greater than 3 MPa. The specimens retained 91.3% unconfined compressive strength over five freeze-thaw cycles. Unlike traditional semirigid base materials, the PPBM exhibited no shrinkage strain, which is manifested by the growth of expansion strain with increasing amounts of PG. Through microscopic observation, the PPBM produced ettringite (AFt) and calcium-silicate-hydrate (CSH) with the extension of curing time, which is consistent with the analysis of FTIR spectrums. The crystallized water in the PG participates in the hydration reaction.