Setting behavior of ultra-low cement refractory castables in the presence of citrate and polymethacrylate salts

The effect of citrate and polymethacrylate salts on the setting behavior of ultra-low cement (ULC) refractory castables was addressed in this paper, with special attention to the interactions of such chemical additives with the cement particles in the aqueous medium. Rheological experiments, electrical conductivimetry, temperature measurements, SEM, X-ray diffractometry and mechanical tests were performed to characterize the cement-based compositions prepared in this work. In spite of its strong inhibiting effect on the precipitation of cement hydrated phases, sodium citrate was found to induce the earlier setting of ULC refractory castables, due most likely to the formation of a gelled phase between the citrate anions and the ions originated from the dissolution of cement particles. The most probable reasons for the formation of this unexpected gelled phase are discussed in this paper.