Effect of air-void system on frost expansion of highway concrete exposed to deicer salt

The net frost expansion (dilation) was determined by monitoring the change in length of air-entrained concrete specimens undergoing a freeze-thaw cycle between 20 degrees C and -20 degrees C. Two dilation processes were found during freezing: an initial dilation at the freezing point and a subsequent dilation which continues during the entire freezing period. The second dilation dominates when the surface is exposed to a deicer solution. For both exposure conditions, a good correlation was found between the dilation and the spacing factor, which fits well with the hydraulic pressure theory. The results show that a lower spacing factor is required for frost protection against salt frost attack, consistent with the current practice of recommending higher total air content as compared to freezing without salt exposure. Concretes that had excellent field durability had frost dilation values below the paste fracture strain of about 250 micro strains. The dilation results suggest that cryogenic suction of external liquid exacerbates internal hydraulic pressure development which in turn may explain the surface scaling phenomenon.