THE COMBINED DETERIORATION OF PRESTRESSED CONCRETE BRIDGE GIRDERS CAUSED BY ALKALI-SILICA REACTION AND CHLORIDE INDUCED STEEL CORROSION

摘要

There exist large numbers of ASR-affected prestressed concrete bridge girders (PC) in the Hokuriku district in Japan. In some cases of serious ASR, the PC girders show a significant cracking and/or a large deformation due to the strong longitudinal confinement by prestressing steel strand (PS) and the relatively low steel reinforcement ratio by other supplementary steel reinforcement. This paper describes the deterioration characteristics of cracking and/or deformation in ASR-affected PC girders based on the recent survey of about 30 bridges. Furthermore, the repair and strengthing methods applied to them are discussed in the relation to their effectiveness of controlling ASR expantion for a long term service especially in a severe environment influenced by the sea water or deicing salt. As a specifically repair and strengthing method, the authors suggest that the effectiveness of the CFRP sheet bonding method or cathodic protection method has been no problem in the actual application. Particularly, in a saline environment, the authors propose that the applicaion of cathodic protection in ASR-affected girders has not accelerated ASR cracking at all.