Influence of Environmental Parameters upon Permeation in Concrete

Abstract

This report is largely concerned with the effects of moisture, temperature, and carbonation upon gas permeation and water absorption in concrete, particularly in the zone adjacent to an exposed surface. Permeation of substances through this surface zone (cover concrete) is often a critical factor for concrete durability. Gas permeability and water absorption are significantly increased as the capillary pores in the concrete are emptied by drying and the channels available for gas flow increase in volume and connectivity. An additional increase of permeability and absorption can be observed with severe drying, depending upon the temperature and duration of treatment. This is probably due to changes in the microstructure of the cement paste matrix. The effect of test temperature upon gas permeation is small, but water absorption is significantly affected. The increase in water absorption with temperature is predictable in terms of changes in the viscosity and surface tension of water. Carbonation can significantly affect the permeability of cover concrete because the reaction modifies the pore structure of the cement paste matrix. Supplementary measurements relating to moisture conditions in the concrete and the depth of carbonation are desirable when interpreting in situ permeability data. Laboratory test methods for gas permeability and water absorption should standardize the moisture conditions of the concrete and preferably simulate in situ conditions. Severe drying does not realistically simulate practical conditions and can alter the pore structure of the concrete.