A study of the permeability and related microstructure of refractory concrete

De-watering of refractory concrete is greatly influenced by the permeability of the concrete, which in turn is a complex property determined by gradation of the aggregate in the mixture, water/cement ratio of the mixture, additives, curing condition of the concrete, and composition of the cement. The permeability of concrete is known to be related to the porosity of the mixture. Permeability of a commercial refractory castable product measured by rapid determination of chloride ion permeability was related to its microstructure. This technique was utilized as a screening method for low permeability and low porosity monolithics. The theory and methodology of rapid determination of chloride ion permeability are appended; the testing method is also evaluated. Scanning Electron Microscopic analysis of a typical CA cement-based castable is included. BEI and SEI imaging techniques were applied to provide qualitative information on pore structure. The types of pores observed in this study confirmed results reported by other investigators. Atomic Force Microscopy was also conducted and allowed imaging of the finest gel and capillary pores in the structure, providing useful information on the pore structure. Another commercial product was exposed to a temperature gradient and analyzed by SEM. The impact of the type of heat treatment on the microstructure of the castable was also investigated. A complete literature review on the permeability measurement and related properties of construction concrete is appended --Abstract, page iv