A risk-cost optimised approach to managing structures affected by corrosion

Reinforcement corrosion is the main cause of premature deterioration of concrete structures in coastal environments, with the structural effects varying during the different stages of the corrosion process. As a consequence, much of the maintenance of such structures during their service life relates

Although extensive research on reinforcement corrosion in concrete has been undertaken, the whole-life behaviour of corrosion-- affected structures has not been investigated. With the increasing scarcity of resources, any maintenance of corrosion-affected structures needs to be evaluated cost-effectively, taking into account economic constraints. One solution could be to prolong the service life of corroded structures, providing their safety is not compromised. Establishing the whole-life behaviour of corroded structures will help achieve this.

The whole-life behaviour of coastal concrete structures is being examined in an EPSRC-funded project in the Department of Civil Engineering, University of Dundee, worth 213,000. This encompasses:

corrosion initiation

corrosion-induced cracking and spalling that result in unserviceability

the ultimate reduction of structural strength, which may result in an unsafe structure.

The outcome of the project should close the gap between 'unserviceable' and 'unsafe' structures and provide necessary guidance on the possible extension of service life.

Key objectives of the project include the development of:

a risk-based maintenance strategy for coastal concrete structures

a method to benchmark and measure the integrity of coastal structures

a database on strength deterioration, corrosion-induced surface cracking and delamination of coastal structures.

Two aspects of the project are of particular relevance to practical engineers. One is the application of time-dependent reliability theory, coupled with risk-cost optimisation in determining life cycles of corrosion-affected structures. The other is the production of hard data on the formation of reinforcement corrosion in concrete and, importantly, its effect on the reduction of structural capacity. A testing method has been developed to simulate the coastal environment in a large corrosive environmental chamber in which full-size specimens can be tested under service loading. The chamber is 3m wide X 7m long X 2.8m high. The specimens are represented by 2000 X 1000 x 150mm concrete walls with various test variables. Corrosion is accelerated by intensifying the drying period of six-hour wetting and drying cycles. A method of calibration and interpretation of test data acquired under accelerated conditions has also been developed. The project is being executed by a multi-disciplinary team with a close academic and industry partnership.

While the initiative has been taken at the University of Dundee, it is desirable that a cohesive research strategy into whole-life behaviour of corrosion-affected structures be brought together at a national level. The limited funding and resources will then be optimised.

If readers would like to participate, contact Chun Li on +44 (0)1382 344 345; e-mail c.q.li@dundee.ac.uk.