Salt Weathering in Residential Concrete Foundations Exposed to Sulfate-bearing Ground

When a residential concrete foundation is constructed on sulfate-bearing ground, scaling of the concrete surface often arises from the crystallization and hydration pressure of the sodium sulfate that crystallizes in the pores of the concrete. Similar deterioration has been confirmed in stones and rocks and so on. This deterioration phenomenon is called "salt weathering." We have confirmed several deterioration cases of residential concrete foundation and it is clear that such cases are widely distributed across Japan. This paper describes the results of field investigations and laboratory experiments on salt weathering of concrete. The laboratory experiment using mortar specimen shows the deterioration of mortar similar to residential concrete foundations was reproduced. We focused on the influences of the dry-wet cycle and the carbonation of the cement matrix, presuming that these are one of influential factors for salt weathering. With regard to the influence of the mix proportion of mortar, we established that low water-cement ratio has good resistance against salt weathering. However, additions to the mix proportion were not found to be effective, and the decrease in pH and the decomposition of C-S-H by carbonation are thought to affect the salt weathering resistance.