Neutron tomography analysis of permeability‐enhancing additives in refractory castables

Polymeric fibers are often used as a drying additive for refractory castables because they can increase their permeability, reducing the risk of pressurization that is believed to trigger explosive spalling. Despite the potential of synthetic polymers to be engineered and obtain desired properties, the required parameters for inducing permeability enhancement remain unclear. This inhibits the development of novel designed drying additives and improvement of the numerical models. This work investigates the effect of polypropylene (PP), polyethylene (PE) and cellulose fibers on the water transport in refractory castables through rapid neutron tomography, enabling the in situ visualization of the water distribution, the drying front advance and the size, intensity and duration of moisture accumulation. PE and cellulose fibers accelerate drying fronts earlier than PP, in which PE exhibits larger moisture accumulation, residual moisture behind its drying front and a slower drying rate at higher temperatures despite the early water removal initiation. In contrast, cellulose emerged as a better candidate, due to a swelling–shrinkage based mechanism. The neutron tomography observations unveil the dynamic and intricate effect of fibers in the permeability, emphasizing that safer industrial processes require a deeper understanding of the underlying mechanisms to develop better fibers and accurate numerical models.