An analysis of the impact of chloride-induced corrosion on reinforced concrete structures in the port of Cape Town
Corrosion of steel reinforcement is a main deterioration mechanism for reinforced concrete structures in the marine environment, where chloride ingress causes severe and widespread damage. These structures make up a substantial proportion of infrastructure globally and are costly to construct and require constant maintenance throughout their service life. For infrastructure owners such as the Transnet National Ports Authority, whose infrastructure is mostly civil in nature and is exposed to severe marine exposure conditions, an improved understanding of each port's environment can lead to the design of more durable structures, or the improved maintenance of existing structures, both leading to more effective investment decisions. The aim of this research is therefore to understand the relationship between marine exposure conditions, cover depths, age, and deterioration due to chloride-induced corrosion in the port of Cape Town through the investigation of select structures. As-built data collection, visual condition assessments, and cover measurements were performed on various components of seventeen reinforced concrete structures in the port of Cape Town. These structures varied in terms of type, age, distance from the sea and marine exposure. The condition assessments focused on deterioration related to corrosion namely rust staining and spalling, and damage ratings were ascribed based on the classification scheme provided in the RILEM technical committee 104-DDC 1994. Further, the predominant wind direction affecting the structural component (either South Easterly or North Westerly) and the marine exposure class were noted. These assessments were supplemented by cover readings on the structural components, with a focus on average and minimum cover depth per component. Findings from the visual condition assessments confirmed significant reinforcement corrosion damage on twelve of the seventeen structures. This would imply that these structures are in the propagation phase of the two-phase corrosion model, or at the end of the maintenance free period in service life models. In addition, the average cover depth was found to be above 50 mm in most of the structural components (27 out of 38), however, the minimum cover was found to be below 40 mm in 55% of the structural components and below 30mm in 26% of the components. The distance from the sea was found to significantly affect the damage ratings of structures, particularly for those further than 100 m from the sea, where ratings showed minimal damage. Further, the predominant wind direction was found to have a significant influence, damage ratings being higher for structures exposed to South Easterly winds compared to those exposed to North Westerly winds. Minimum cover, or localised low cover depth, and average cover were found to have no significant influence on the degree of deterioration as no trend could be identified. In addition, deterioration compared to the age of structures, particularly for structures in the age ranges of 40-50 and 50-60 years showed an increase in damage ratings with an increase in age. Anomalies in the data can be attributed to the limitation of performing single parameter analysis since it is likely that multiple parameters influence the deterioration ratings. The findings from this study can be used to inform the design and maintenance of structures in severe marine environments while quality controls can be put in place during construction to ensure the design cover is met and that localised low cover areas are prevented as much as possible. In addition, the findings from the visual condition assessment can be used to inform repair strategies for damaged structural components. The incorporation of cover meter readings in condition assessments, as well as other tests such as chloride concentration tests, can be used to inform preventative repair methodologies for existing structures at a high risk of corrosion damage, but with little to no visual damage.
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