Moisture uptake in concrete under freezing-thawing exposure

Freezing-thawing (F-T) exposure produces higher absorption in concrete than an isothermal condition. This work investigated the moisture absorption characteristics in different air-entrained concrete mixtures under two exposure conditions (water and a 3% salt solution) by simultaneously monitoring the weight change, mass loss and internal damage of 100 x 100 x 70 mm concrete blocks subjected to repetitive F-T cycles. The results indicate that permanent bulk moisture uptake is primarily a result of the accelerated saturation of poorly connected capillary pores, the slow filling of entrained air voids in concrete mixes with sufficient air entrainment, or the re-saturation of newly generated cracks in concrete with poor frost resistance. No detectable discrepancy was observed in moisture uptake between water and salt exposures, but the mass loss difference was found to be substantial. The measured bulk absorption is not a reliable predictor for salt frost scaling resistance, since it reflects the universal moisture condition in the specimen while scaling deterioration is dominated by the degree of saturation in a thin surface region.