Characterization and valorization of fly ash and phosphogypsum into a binary composite for construction

The limited comprehensive laboratory and analytical studies on the physico-mechanical properties of fly ash (FA) and phosphogypsum (PG) hinder the extensive valorization of these readily available waste materials. This study aimed to conduct a comprehensive laboratory and analytical investigation of the physico-mechanical properties of FA, PG, and a developed FA-PG composite in relation to their mineralogy and morphology. The significance of the study is in lowering environmental pollution by valorizing FA and PG into an FA-PG composite for use as a construction material. Various physical and mechanical tests were conducted based on ASTM standards. The chemical composition, morphology, and mineralogy were analyzed using X-ray fluorescence, scanning electron microscopy, and X-ray diffraction. The results showed that the addition of PG activated the FA in the presence of water, thereby increasing its strength such that the developed FA-PG composite gave an optimal strength of 0.66 MPa at a 70 wt% FA:30 wt% PG mix proportion, making it applicable for soil stabilization and lightly trafficked road pavements. The hydraulic conductivities of FA, PG, and FA-PG composite were found to be 7.72667 * 10⁻⁴, 5.281002 * 10⁻³, and 1.972907 * 10⁻⁵, respectively. The practical implication of this study comprises landfill solid waste management and high-volume valorization of FA and PG waste materials for construction applications, reducing virgin raw materials extraction and promoting circularity and sustainable development goals.