Application investigation of high-phosphorus steel slag in cementitious material and ordinary concrete

Abstract It is essential to utilize high-phosphorus steel slag (SS) effectively. The retarding effect of phosphate on the setting time is investigated, the retarding mechanism of high-phosphorus SS is concluded. The hydration activation of high-phosphorus SS in cementitious material are studied with additives of calcium oxide and sodium sulfate. The application of high-phosphorus SS with composite admixture of blast furnace slags (BFS) or BFS + fly ash (FA) is investigated. The main properties such as setting time, flexural strength (FS), unconfined compressive strength (UCS), hydration mineral, microstructure, etc., are investigated. The results show that the soluble phosphate would be generated during the depolymerization and dissolution processes of vitreous bodies in high-phosphorus SS, the retardation effect of soluble phosphate is greater than that of insoluble phosphate. The approximate amounts of calcium oxide and sodium sulfate for the hydration activation are 4% and 1%. To ensure sufficient later UCS of concrete, the high-phosphorus SS content is suggested not to be over 35%. To ensure optimal mechanical performance, the range of blended mixture is recommended as 30–40%. The blended proportion of high-phosphorus SS, slag and fly ash is recommended as 1:2:1. This investigation is new at present and important to the recycling of high-phosphorus SS.