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原文传递 Investigation of Protection Systems for Bridge Stay Cables

题名：	Investigation of Protection Systems for Bridge Stay Cables
作者：	H. R. Hamilton III, J. E. Breen and K. H. Frank
关键词：	stays, cables, corrosion protection, strands, grouting, cement, grout, corrosion inhibitors. durability testing, galvanized strand, epoxy-coated strand, greased and sheathed strand, design recommendations
摘要：	The use of cable-stayed bridges in medium- and long-span applications in the United States has increased significantly in the past ten years. Of paramount importance with this type of bridge is die protection of the stay cables from corrosive elements. An extensive survey, reported herein, showed a general concern over the adequacy of the corrosion protection of the most widely used cement System. In this study, the popular two-barrier system (prestressing strand inside polyethylene injected with Portland cement grout) was examined expermentally. The effectiveness of the grout in providing secondary corrosion protection in die event of a cot or break in the extranal sheathing was a major focus of the experimental work. Such breaks have been documented on a US bridge. Small-scale experimental studies were conducted to develop a low-bleed grout for use in the large-scale stay tests. In addition. Smallscale accelerated corrosion tests were conducted on grouts containing corrosion inhibiting admixtures. The major portion of the experimental program involved accelerated durability testing of eight large-scale stay cable specimens. Each stay specimen was 9.5-m long and was composed of 12 12.7-mm diameter 7-wire prestressing strand. The inclined stay specimens were stressed to bridge dead load levels and then injected with the low-bleed Portland cement grout. Additional axial and lateral loads were then applied to most specimens to simulate field loading conditions. Selected small areas of the sheathing were removed to simulate breaks in the exterior barrier. The exposed grout in these locations was then subjected to altemate wet and dry cycles with salt solution. Variables included use of temporary corrosion protection, galvanized strand, epoxy-coated strand, and greased and sheathed strand. One important finding was that when the sheathing was breached for die accelerated corrosion tests, the grout would shrink and crack at that location. As a result of die cracking, corrosion of the underlying unprotected strand occurred soon after the application of the salt solution. Anodira imfxiftant finding was that significant air pockets formed in the grout in all specimens except one. Undamaged epoxy-coated, greased and sheathed, and galvanized strand provided significant improvement over grouted bare strand in corrosion protection along die free length. However, corrosion occurred on all of the strands in varying degrees at the anchor head. Based on the extensive survey of the state-of-die-art and on the experimental findings, a rational basis for selecting a stay cable protective system is proposed in the form of suggested additions to the Post-Tensioning Institute’s Recommendations for Stay Cable Design, Testing and Installation.
报告类型：	科技报告