Suitable Intervention Strategy for a Road Bridge Structure Affected by Alkali-Silica Reaction (ASR) and Chloride Induced Corrosion

摘要

The purpose of this paper is to provide a review of the issues facing the Maintenance Engineer in relation to repairing a bridge structure affected by alkali-silica reaction cracking and chloride induced corrosion. In addition, a discussion of appropriate remedial solutions and contract delivery mechanisms are provided. The bridge structure chosen consists of reinforced concrete piers supported on prestressed concrete piles. This bridge was built in 1977 and consists of 7/25.3 m spans of prestressed concrete I girders. Field inspection indicates the piers are suffering chloride induced corrosion distress and the piles are suffering significant alkali-silica reaction distress. This structure resides in a very aggressive environment in relation to concrete durability and the environment would be classified as type C in relation to the Austroads Bridge Code requirements. The associated river is tidal with mangroves growing on the banks. As a result of the work performed on this bridge, alkali-silica reaction (ASR) was determined as the primary mechanism causing the observed cracking in the prestressed piles with crack widths up to 15 mm. An approach to the rehabilitation of this structure is outlined which had a degree of urgency in relation to the satisfactory long-term performance of this structure. The vertical cracking was proven to have been initiated by ASR distress and most likely widened due to corrosion of the underlying reinforcement and prestressing strands. A new technique of fibre composite encasement was chosen to arrest the rapid deterioration of these major supporting elements of this structure. The corrosion in the piers was controlled using a cathodic protection system in the usual manner.