Dynamic permeability behavior during drying of refractory castables based on calcium-free alumina binders

Considerable efforts have been made to understand the dewatering behavior o f refractory castables, Modeling of this process must be based on realistic heat and mass transfer data; hence, consistent values of castable properti es are required, particularly permeability values, since these are the most important parameters that govern the process. Permeability values, however , are usually obtained at room temperature and therefore may not reflect th e remarkable microstructural changes that take place during water removal, The problem has become more critical for castable compositions based on cal cium-free binders, in which the dehydration process is still unclear and ex plosive spalling is more likely to occur, This study has investigated the b ehavior of the dynamic permeability of high-alumina calcium-free refractory castables subjected to a drying process up to 700 degreesC, Samples were p reviously treated at temperatures ranging from 110 degrees to 1650 degreesC to provide information on the castables' reversible and irreversible micro structural changes. The results revealed fluctuations and a dramatic decrea se in the permeability level near 200 degreesC, which may help to explain t he occurrence of explosive spalling in this class of castables.