Severity of Rain-Induced Wetting–Drying Conditions and the Associated Risk of Concrete Carbonation in the Tropics

Assessing the probability of failure of typically adopted cover depths to resist the onset of carbonation-induced corrosion under the influence of seasonal rains is important for the durability design of reinforced concrete elements. The exposure scenario commonly manifests in the tropics, wherein the majority of monsoonal rainfall remains confined to location-specific annual wet-spells. The study aimed to develop an improved methodology for the identification of annual wet-spell and proposed an index based on the judicious combination of wet-spell characteristics to enable the mapping of its severity over a region of interest and facilitate the selection of Moisture Reference Years (MRYs). The developed paradigm was implemented using gridded meteorological data sets to map the severity of annual wet-spell at 1° resolution for India. The map provides an improved severity classification compared to rainfall amount over regions of scanty rain but considerable wet-spell duration. The estimates of time conducive for carbonation over a period of 100 successive MRYs, as deduced from the simulated moisture distribution data for the five climatic zones of India, were also found to correlate well with the corresponding index values. Finally, the √t modeling of the carbonation depth using the derived estimates of conducive duration and assessment of failure probabilities of typical cover depths suggested that a nominal depth of 45 mm is able to resist carbonation at a safety level of 90% for all the five climatic zones.