Elemental zonation in marine concrete

This paper presents a large collection of microstructural studies on concretes exposed to marine environments for periods between 2 and 34 years. The phase changes were studied using optical as well as scanning electron microscopy. A total of 21 concretes, taken from 9 different locations along the Norwegian and Danish coastlines, were investigated. Chemical zonation and mineralogical zonation were observed in the surface regions of marine-exposed concrete. Three zones were found irrespective of the age, location or binder composition: a magnesium-rich zone, a sulfur-rich zone, and a chlorine-rich zone. The absence of major damage indicates that the observed phase changes led only to minor scaling. This suggests that, rather than sulfate attack, sea water merely causes sulfur enrichment.