Permeability to water of sintered clay ceramics

The microstructural characteristics of sintered clay ceramics depend mainly on the clay type and thermal transformations. Different pore morphology and connectivity change the liquid water flow process through the material, as in the case of roof tiles which are progressively saturated with water during rain. In this study, 2 clays mined in Burkina Faso are used for manufacturing roof tiles. The major phases detected by X-ray diffraction in the two clays are kaolinite, illite, smectite, quartz and feldspar. The thermal behavior of clays by DTA and TG between 25 degrees C and 1100 degrees C is mainly related to individual roles of clay minerals. During sintering, dilatometry curves show successive densification stages in variable temperature ranges, as a function of clay mineral fractions in compositions. It explains differences in microstrutural characteristics and pore structure. The simulation of the capillary absorption of water uses the Sharp Front model. The interesting feature of this approach is that measurement of the data for the model requires no complex equipment. Only the Darcy permeability of the material and the steady state capillary pressure are necessary. Results evidence the strong difference of water absorption rates in the 2 clay ceramics, whereas they present similar porosity. It confirms the importance of pore morphology and connectivity in ceramics, induced mostly by the clay type and the sintering process. (C) 2009 Elsevier B.V. All rights reserved.