One of the main aspects for the development of refractories castables is to master the knowledge regarding calcium aluminate cement (CAC), as this binder is the most applied in these products. The objective of this work was to analyze the available information in the literature in order to explain the understanding regarding the actions of retarder and accelerator additives in the setting mechanisms of CACs. The analysis of the compiled information pointed out that the retarder additives, in a general way, act in two ways: 1) inhibiting the process of cement dissolution, by the build up of insoluble barriers around the cement particles, and 2) enhancing the formation of more soluble hydrates, which increase the time necessary for the hardening beginning. On the other hand, the accelerators can induce the formation of less soluble hydrates, diminishing the time necessary for the setting or speeding up the beginning of the hydrate nucleation. The overall analysis pointed out that the action of some retarder and accelerators additives takes place in different periods of the setting time of the CACs. This aspect allows the combination of additives confering a good workability associated to a short demolding time.
calcium aluminate cement; hydration; retarding and accelerating additives
