Development of low content phosphogypsum waste composites modified by lime-fly ash-basic oxygen furnace slag

Abstract

Abstract: The generation and disposal of phosphogypsum (PG) is a worldwide challenge, due to the environmental pollution posed by the material. The contaminants laden in the material are the major limitations for the utilisation of PG. Other materials considered as wastes such as fly ash (FA) and basic oxygen furnace slag (BOF slag) are generated by numerous industrial activities and disposed into environment. This study investigated the use of three wastes materials for the development of a composite applicable for road construction. Two types of PG were investigated, namely citric acid treated PG (TPG), for the removal of the contaminants and raw PG (RPG). Lower content PG containing 20% and 30% were investigated and modified with FA, Lime (L) and BOF slag. The effect of particle size distribution (PSD) on unconfined compressive strength development, durability of the composites and hydration products contributing to strength development were studied. Modification of PG with FA-L-BOF slag significantly improved the unconfined compressive strength of PG. The PG content of 20% for the RPG and TPG yielded the highest strengths of 7.4 MPa and 5.4 MPa, respectively when cure at elevated temperatures. Normal curing of the composites over 7 days and 28 also showed an increase in strength development. Particle size played a significant role in the unconfined compressive strength development. Kieserite, calcium aluminium sulphate and calcite were the predominant hydration products formed during the curing process