The Performance of Concrete in Bridges: a Survey of 200 Highway Bridges

This report describes a study undertaken to ascertain the level of concrete deterioration in British bridges. A representative sample of bridges across the country was selected from the Department of Transport's bridge data base in 1985. In all, 200 bridges were studied in the following categories: overbridge, underbridge, elevated road, and underpass for major road. Six main causes of deterioration were investigated, namely, chloride attack, alkali silica reaction (ASR), carbonation, frost action, sulphate attack, and high alumina cement. The following measurements were taken during site investigation: a) visual inspection, to determine defects such as spalling, rust, cracks, efflorescence, or water runs; b) depth of concrete cover to the reinforcement using a Fe covermeter; c) the half cell potential using a copper/copper sulphate half cell; d) carbonation; e) chloride ion concentration; f) cement content; g) sulphate content; h) petrographic examination to identify signs of ASR. Other information used included test data already obtained by maintenance authorities, details of maintenance and repair already carried out, and traffic flows. The results show that the most serious and widespread form of deterioration is reinforcement corrosion arising from contamination by chlorides from deicing salts. Recommendations for construction and maintenance are provided, and the costs of such maintenance estimated.