  Drying is the most critical process of the first heating cycle of monolithic
dense refractories, as the reduced permeability of the resulting microstructure
may lead to explosive spalling and mechanical damage associated with
dewatering. The first part of this review series pointed out the various drying
stages, the role of the binder components and the techniques that can be used
to follow the water release in as-cast refractory materials, when they are
exposed to heat. Although defining a suitable heating schedule is a great
challenge, some tools can be applied to minimize the spalling risks associated
with steam pressurization. In this context, this second review article points
out (i) the main drying agents and how they affect the resulting castables'
microstructure (organic fibers, metallic powders, permeability enhancing active
compounds, silica-based additives and chelating agents), and (ii) the effects
related to the procedures commonly applied during the designing of heating
routine (i.e., the role of the heating rate, ramp versus holding time), as well
as the influence of the castable's dimension on the overall drying behavior.
Considering the recent advances regarding the design of refractory formulations
and their processing, one may expect that incorporating suitable drying
additives into the prepared composition should lead to a suitable and safer
water release in such dense consolidated structures. Besides that, novel
engineering opportunities, such as the use of in-situ based experimental
techniques (i.e., neutron and X-ray tomography) to obtain more accurate data
and the development of numerical models, might help in simulating and
predicting the steam pressure developed in refractory systems during their
first heating.
