Understanding the impact of ultrafine phosphorus slag on the workability of cement paste

Phosphorus slag is a potential high-valued mineral admixture of concrete, which can be ground into ultrafine powder to increase utilization efficiency. However, little is known about the impact of phosphorus slag fineness on the workability of cement paste. In this work, the influence of ultrafine phosphorus slag (UPS) on the workability of cement paste was in-depth investigated. Results show that with addition of UPS, the delay of hydration exothermic peak and the extension of setting time are more obvious than those with ordinary phosphorus slag (OPS). However, the fluidity and rheological properties show reverse trends. UPS paste exhibits a faster fluidity loss and a more rapid increase in yield stress compared with OPS paste. It reflected that in OPS paste, the chemical retarding effect of OPS on cement hydration is the primary factor driving the workability, while in UPS paste, it is the physical flocculation effect of UPS that plays an important role.