Over the past several years the posttensioned concrete bridge industry in America has experienced several tendon failures because of corrosion. These isolated failures resulted in the conduct of additional investigations in Florida as well as several other states. Those investigations have determined that several structures have shown grouting deficiencies. Some of the areas with grouting deficiencies had voids with no corrosion present, but others showed corroded ducts and posttensioning strands. As a result, the owners and the industry have evaluated the process of grouting and have developed a course of action to improve the grouting and thus the long-term durabilities of these structures. The Post-Tensioning Institute Specification for Grouting of Post-Tensioned Structures, The Concrete Society Technical Report 47, as well as the American Segmental Bridge Institute (ASBI) Interim Statement on Grouting Practices address several areas in which the grouting process can be improved. First, several design details have been changed to improve the recharge characteristics and performance of the posttensioning systems. Second, several changes to the grout material have been recommended. The use of antibleed or no-bleed grouts is recommended, and in Florida the use of such grouts is required. Third, improvement of the grout equipment will provide a consistent mix and density for the grout. Fourth, it was recommended that training and certification for grouting technicians and inspectors be required. ASBI and the Florida Department of Transportation have created training and certification programs for inspectors and grouting technicians. Although no structural deficiencies on segmental posttensioned bridges in America have been noted to date, the industry has mobilized to address the grout problems to further enhance the durabilities of these structures.
Samenvatting