Time and spatially dependent transient competitive antagonism during the 2-D diffusion-reaction of combined chloride-sulphate attack upon concrete

The long-term impact of competitive antagonism of the combined chloride-sulphate attack upon structural concrete is difficult to determine experimentally. In this study, a pair of time and spatially dependent models is proposed to study the diffusion-reaction of the combined chloride-sulphate attack. The competitive antagonism is quantified as Delta C-cl and Delta strain respectively, for the chloride and sulphate induced attacks. The results reveal that the competitive antagonism clearly shows both a time- and a spatial-dependence. The competition between them is minimal in the early stages of exposure and also, at depths closer to the surface. It increases and reaches a peak with an increase in the duration of exposure and the depth inside the specimen, before decaying gradually. The proposed models, therefore, predict a transient competitive antagonism. A sensitivity analysis was carried out, which shows that the combined chloride-sulphate attack itself and the ensuing competitive antagonism are both most sensitive to the water-to-cement ratio and, to a lesser extent, to the instantaneous calcium aluminate content in the binder.

Automated summary

This study proposes models to study the diffusion-reaction of combined chloride-sulphate attack and finds that the competitive antagonism is time- and spatial-dependent. The competition between chloride and sulphate attacks is minimal in the early stages and closer to the surface, but increases with longer exposure and deeper depth before gradually decaying.