Durability of marine concrete structures - field investigations and modelling

This article presents a series of investigations on six concrete structures along the North Sea coast in The Netherlands. They had ages between 18 and 41 years and most of them were made using Blast Furnace Slag cement. Visual inspections showed corrosion damage in only one structure, related to relatively low cover depths. All structures showed considerable chloride ingress with a large scatter within the relatively small tested areas. The interpretation was based on the DuraCrete model for chloride ingress. Curve fitting to chloride profiles produced chloride surface contents and apparent diffusion coefficients. Comparison was made to previously published data on chloride ingress and electrical resistivity of similar concretes. It was found that a single mean value and standard deviation applied to all concrete up to 7 m above mean sea level for the chloride surface content. Above 7 m, the local microclimate had a decisive influence, either increasing or reducing the chloride surface content. Apparent chloride diffusion coefficients did not depend on height above sea level. Their age dependency was expressed in a single value for the exponential aging coefficient. A simplified environmental factor was adopted from literature. A probabilistic model for corrosion initiation in Blast Furnace Slag Cement concrete in marine environment was proposed, the DuMaCon version of the DuraCrete model. Its application is explained for design of new structures and for assessment of existing structures. Issues for further research are the critical chloride content and the target failure probability for corrosion initiation, the effect of drying out on chloride transport in the marine splash zone and the nature and influence of spatial variation of chloride ingress.

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