Drying behavior optimization of dense refractory castables by adding a permeability enhancing active compound

Abstract New challenges have been identified over recent decades regarding the increasing complexity of the dry out step of refractory castables, mainly due to the advances on the particle size distribution design (and consequent reduction in the ceramic linings' permeability) and growing demand for shorter equipment maintenance time, which generally results in pressures to speed up the drying. Some efforts focused on the design of novel permeability enhancing active compounds (PEAC) have been receiving great attention, as such products may be an interesting alternative for producers and end-users. This work evaluates the addition of a permeability enhancing active compound (AC) to high-alumina based castables and also analyzes the effect of different parameters (i.e., particle packing models, hydraulic binders, drying temperature, etc.) which could affect the dry out behavior of such refractories. Initially AC-containing castables, additive-free and mixtures with a polymeric fiber with low melting point were analyzed. Further investigations of the selected AC action mechanism were carried out in a second moment, where novel castables containing distinct binders (Secar 51, Secar 71 or Alphabond 300) and with or without this drying agent were characterized regarding their flexural strength, apparent porosity, permeability and explosion resistance at different temperatures and heating rates. The obtained results indicated that adding this active compound into the alumina-based castables favored a change in the cement hydration path, giving rise to gel-like hydrates (instead of AH 3 and C 3 AH 6 phases) that underwent decomposition at low temperatures (100–140 °C). Consequently, such transformations resulted in the samples' permeability increase, which inhibited their explosion during the heating up step. However, other important properties such as flowability, setting time and green mechanical strength of the AC-containing compositions were also affected, due to the interaction of this additive with water and the fine refractories' raw materials and the generation of a CAH-gel phase in the castables’ microstructure.