Use of performance specification and predictive model for concretes exposed to a marine environment

Paper in proceeding, 2010

The factors affecting longevity of concrete structures can be taken into account whilst designing appropriate concrete mixtures. Existing guidelines in BS 8500 allow design of concrete mixtures for different exposure classes mainly based on the severity of the surrounding environment and service life. These guidelines specify the variables such as compressive strength, maximum water to binder ratio, minimum cement content and minimum cover thickness. Due to the very prescriptive nature of these guidelines they do not take into account concrete performance in any given environment. This can be overcome by giving emphasis to durability based designs that supplement the existing guidelines in BS 8500, by specifying the required performance of concrete in terms of measurable properties such as resistance to environmental penetrations. This paper reports an approach for developing performance-based specifications for concretes exposed to marine environments. Firstly, a critical review of the test methods for assessing the chloride penetration resistance of concrete is given. The repeatability of the different test results is also included. In addition to the test methods, a numerical simulation model is used to explore the test data further to obtain long-term chloride ingress trends. The combined use of testing and modelling is validated with the help of long-term data from a North Sea exposure site. Based on the results presented, an approach for developing performance specifications is outlined.