Carbonisation and calcium leaching-induced deterioration of concrete in dams: field inspection and microstructural investigation

Abstract

The durability of dam concrete is considerably affected by environmental effects. Although great progress was achieved on environment-induced deterioration mechanism of concrete, there still seems that a gap exists between researches of the concrete durability in natural and standardised laboratory conditions. This article is concerned with carbonisation and calcium leaching-induced deterioration of concrete in dams in service. Field inspections and analyses of dozens of investigated dams in China are presented. The results show that the carbonation speed is closely related to the age of construction and its location. The carbonisation depth of the upstream surface is generally smaller than that of the downstream surface for the same dam. The calcium leaching degree of dam concrete is affected by several factors, such as reservoir water chemistry, type, height, construction age and quality of the dam. Calcium leaching of dam concrete is common in China because the reservoir water is usually soft and has medium soluble corrosivity. These deteriorating processes and characteristics are consistent with the previous laboratory results. A masonry gravity dam due to 17 years of exposure to natural environment was taken as a case study on concrete alteration mechanisms. Concrete cylinders drilled out at four vertically different locations on the upstream concrete-faced slab were analysed by compressive strength test and mercury intrusion porosimetry test. The deterioration process controlling the concrete near the waterline varies according to its location, resulting in the variation of micropore structures at various depths from the upstream surface. Long-term exposure to natural environment has led to chemical and mineralogical zonation of the concrete. The results of this study can be used to compare the similar results from the short-term laboratory investigations.