Performances of highly insulated compact zinc roofs under a humid-moderate climate - part II: corrosion behavior

Abstract

In the first paper (Zheng et al., 2010), the hygrothermal performance of highly insulated flat compact zinc roofs was assessed. This article evaluates the zinc sheeting corrosion behavior of the roofs. After an exposure of 28 months, little corrosion occurred at the sheeting upside. However, serious pitting corrosion developed at the sheeting underside. The maximum pit depths measured in the samples (0.5 × 0.7 m2) collected from each roof were between 124 and 209 μm. The main corrosion products identified were Zn5(CO3) 2(OH)6 and ZnO. It was found that less condensation deposit at the sheeting underside did not guarantee a reduction in underside corrosion. The wetting/drying cycling at the sheeting underside played a very important role in the corrosion process. The results show that, in addition to the reduction of the sheeting underside TOW (time of wetness), the number of wetting/drying cycles should also be decreased.