An evaluation of highly insulated cold zinc roofs in a moderate humid region―part Ⅱ: corrosion behavior of zinc sheeting

摘要

In a previous paper [Zheng et al., Hygrothermal Performance, Part Ⅰ; Const Building Mater, Vol. 18, Issue 1, pp. 49-59], the hygrothermal performances of four well-insulated cold zinc roofs were evaluated. This paper investigates the corrosion behavior of the zinc sheeting used in the roofs. The main corrosion products identified are Zn_5(CO_3)_2(OH)_6 and ZnO. Little corrosion occurred at the upside of the zinc sheeting. However, serious pitting corrosion developed at the underside. The maximum pit depths measured in the collected samples with an area of 0.35 m~2 were between 167 and 273 μm. The traditional measures to minimize condensation deposit, i.e. low air exfiltration and good roof cavity ventilation, clearly did not work effectively in reducing the underside corrosion of the zinc sheeting. The results show that new techniques and roofing systems should be developed and implemented.