Effect of fibers addition on mechanical properties of eco-friendly phosphogypsum-based composite at high temperatures

Abstract

In this study, the mechanical properties of an eco-friendly hemihydrate phosphogypsum-based composite (HPGC) added with basalt, glass, and PVA fibers upon exposure to high tempera-tures (250 degrees C, 450 degrees C, 650 degrees C, and 850 degrees C) were investigated. The fibers content (0%-1.35 vol%) did not have a significant effect on compressive strength at ambient temperature, while the flexural strength of HPGC was enhanced optimally at 1.0% fiber volume. For the investigation at high temperatures, the fiber inclusion could effectively reduce the cracks but increased the mass loss of HPGC. Compared to other fiber types, HPGC with PVA fiber, which did not melt at 250 degrees C, exhibited the highest compressive strength and flexural strength (32.59 MPa and 10.56 MPa, respectively) at the temperature of 250 degrees C but had a greater strength reduction between tem-peratures of 450 degrees C and 850 degrees C. At 850 degrees C, HPGC with basalt fiber exhibited higher flexural strength than HPGC added with other fibers, and with 133.3% higher flexural strength than HPGC without fiber. The microstructural investigation confirmed that the changes of calcium sulfate forms (dihydrate to hemihydrate and anhydrite) and ettringite in the matrix contributed to the strength loss of all HPGC mixtures at high temperatures, while the existence of basalt fiber-matrix bond allows the HPGC added with basalt fibers to have the best residual properties at 850 degrees C compared to the other mixes.