Corrosion induced loss of capacity of post-tensioned seven wire strand cable used in multistrand anchor systems installed at Corps projects

Abstract : Over the past five decades, the U.S. Army Corps of Engineers has been upgrading its projects by installing high-capacity, post-tensioned foundation anchors, typically with seven-wire strand cables. The purpose of these anchors has been to achieve structural stability for Corps hydraulic concrete structures (e.g., locks, dams, approach walls) and/or to remediate cracked concrete monoliths. Substantial improvements to protect multistrand anchor systems from corrosion have been made in the past five decades, but the corrosion of older multistrand anchorage systems is still a major concern. This report discusses a laboratory-testing program for the estimation of post-tensioning (PT), seven-wire strand cable strength as a function of corroded cross-sectional material loss. Pull tests were performed to gather reduced cable strength measurements. An innovative morphological procedure using digital photography was developed by U.S. Army Engineer Research and Development Center (ERDC) researchers for quantifying the cross-section geometrical properties of cables near their failure locations. The laboratory-testing program also included a successful series pull test to failure on pristine specimens for a control set of data, and the issues encountered are detailed. A statistical assessment of pull-test data to failure of pristine and corroded cables is used to establish a correlation between cross-section properties, corroded and pristine, and the cable strength. An overview of the corrosion process and the variables, ranked by contribution in Corps structures, which determine corrosion rate at each of the multistrand cables, is provided. Further, methods for estimating cable capacity under load were developed using the provided best-fit curves from the laboratory pull tests.