  Despite the continuous evolution on the performance of refractory ceramic
products, monolithic materials still require special attention during their
processing steps as various phase transformations may take place during the
curing, drying and firing stages. Drying is usually the longest and the most
critical process observed during the first heating cycle of refractory linings,
as the enhanced particle packing and reduced permeability of the resulting
microstructure may lead to recurrent explosive spalling and mechanical damage
associated with dewatering and the development of high steam pressure at the
inner regions of such dense materials. In this context, this review article
mainly addresses (i) the theoretical aspects related to the drying process of
dense refractories, (ii) the influence of the phase transformations derived
from the binder additives, and (iii) the usual and advanced experimental
techniques to assess the water removal from consolidated castable pieces. Many
studies have pointed out that due to the complex nature of this phenomenon
(i.e., considering combined thermal stresses and pore pressure, heterogeneous
microstructure, evolving pore structure with temperature, etc.), the mechanisms
behind the water withdrawal and castables explosive spalling are lacking
further understanding and, consequently, it has been difficult to save time and
energy during the first heating of industrial equipment lined with ceramic
materials. On the other hand, different methods are used for refractory
spalling assessment and many efforts have been carried out in applying in situ
imaging techniques (such as NMR and neutron tomography) to follow the moisture
evolution during such thermal treatments.
