Assessing Corrosion Damage and Corrosion Progression in Multistrand Anchor Systems in Use at Corps Projects

Abstract

Stressed steel tendons have been used to strengthen hydraulic structures and to improve their serviceability and stability. Over the past three decades, the US Army Corps of Engineers has worked to upgrade its projects by installing high-capacity, post-tensioned foundation anchors. The goal has been to achieve structural stability for Corps hydraulic concrete structures and/or to remediate cracked concrete monoliths. Substantial improvements to protect multistrand anchor systems from corrosion have been made since they were first used at Corps projects more the 50 years ago. Corrosion of older multistrand units is of concern.Researchers at the US Army Engineer Research and Development Center (ERDC) are looking to develop engineering procedures to estimate the current state of load-carrying capacity of the ground anchorage, to estimate remaining life of the tendon, and to establish the deterioration of anchorage capacity (with time) so costly replacement of ground anchorage can be delayed until absolutely needed. Analytical, laboratory, and field-testing efforts will be used to develop a methodology and analytical models. Probabilistic procedures will be used to quantify uncertainties for the primary variables and will be carried into the analytical model. Procedures to extend the life of deteriorating multistrand tendons also will be investigated.A review of Corps projects using multistrand anchors and a literature review of corrosion of the anchors are summarized in this report. Also included are the history and performance of the multistrand anchors at the John Day Navigation Lock (Columbia River, Portland District), along with postinstallation lift-off test results. A summary of a review of nondestructive testing (NDT) to identify defects in the anchors is part of this report, too.

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

“…This interim report, along with Ebeling et al (2012Ebeling et al ( , 2013 and Haskins et al (2014), reflects the research progress made to date. In FY14, the authors were able to develop an extensive database of 183 pristine and corroded seven-wire strand cable pull-test specimens and reveal that their capacity relates to either the minimum wire area or the minimum wire diameter.…”

“…The forensic investigation of John Day Lock anchorage revealed the presence of mildew (Ebeling et al 2013), which can lead to microbiological corrosion. It was judged that this mildew was not likely to be a primary contributor for anchor corrosion at John Day.…”

“…For post-tensioned multistrand anchors placed at Corps lock structures, most anchor wires are surrounded by grout, but there are exceptions, such as John Day (Ebeling et al 2013). Encasing the wires in grout raises the pH, which leads to lower corrosion rates.…”

An investigation of corrosion mitigation strategies for aging post-tensioned cables

“…One example is John Day Lock and Dam, shown in Figure 1.1. Each John Day anchor head ( Figure 1.2) contains 37 seven-wire strand cables that were locked-off at approximately 1,518 kips, or 70% of the Specified Minimum Tensile Strength (SMTS) (Ebeling et al 2012(Ebeling et al , 2013. The goal has been to achieve structural stability for Corps hydraulic concrete structures and/or to remediate cracked concrete monoliths.…”

“…In 2012, ERDC was involved with the disassembly of two highly corroded John Day anchor heads that the results from the 2009 Cornforth Consultants lift-off tests had shown to be no longer effective for bearing loads (Ebeling et al 2013). Based on ERDC's field investigation, one speculative finding was that the two analyzed anchor heads might have stopped taking grout through the lower stage grout tubes during construction.…”