Hydration of CAC cement in a castable refractory matrix containing processing additives

A growing demand for refractory castables with a particular behavior has been inducing a continuous technological evolution, where one of the most important aspects, is an in-depth knowledge of hydraulic binders. These materials greatly influence the rheological properties and mechanical strength evolution of castables, defining their workability range and demolding time, respectively. The hydration process of hydraulic binders is influenced by the presence of matrix and additives (dispersants and accelerators), which affect the setting and demolding time of shaped bodies. In this work, the influence of these variables on the hydration process of calcium aluminate cement was studied by means of temperature measurements, oscillatory rheometry and normal force measurement. These techniques were able to evaluate the setting behavior of different binders, either in plain water or in matrix-representative suspensions. In both cases, the dispersants presented a retarding effect on the hydration process, which was more significant for citric acid and diammonium citrate. The combination of these additives with an accelerator (Li₂CO₃) was shown to be an efficient tool to control the setting time of castables.