Corrosion Forecasting and Failure Projection of Post-Tensioned Tendons in Deficient Cementitious Grout

Post-tensioning has evolved to become the construction method of choice for many large structures, including bridges. However, instances of corrosion-induced fracture of wires and strands and resultant tendon failures have occurred as a consequence of either chemically or physically deficient grout (or a combination of these), where the former involves elevated levels of chlorides or free sulfates (or both) and the latter soft, chalky, separated, segregated grout with free water. In the extreme, there is the possibility of structure collapse. The present project builds on results from a recently completed in-house Federal Highway Administration study, termed “phase 1,” which determined the extent of localized wire and strand corrosion as a function of grout chloride concentration, presence of free sulfates, and physical deficiencies.(1) The objective of the present study was twofold: first, to present results from a phase 2 experimental study that extended what was accomplished in phase 1 and, second, to develop a methodology whereby the onset and subsequent rate of wire and strand fractures and tendon failures can be forecast given information regarding the extent of grout deficiency or deficiencies.(1) The former involved stressed, single-wire specimens that were exposed to deficient grouts. The latter was accomplished by relating occurrence of fractures and failures to the extent of localized wire corrosion and to the resultant rate of wire cross-section loss with time, as affected by the severity of a grout deficiency or deficiencies. Primary inputs to the model are the mean and standard deviation of, first, localized wire corrosion rate and, second, residual wire fracture strength. Results indicate an initiation period for fractures and failures during which corrosion progresses and that, once these commence, they do so initially at a progressively increasing rate up to a point beyond which this rate moderates. Other variables that were investigated include level of prestress, wire strength, number of tendons, tendon length, and fracture and failure rates subsequent to initial occurrence. Equations are presented whereby bridge engineers can forecast the onset of fractures and failures based on either localized wire corrosion wastage statistics or grout chloride concentration, and examples are provided.

Language

  • English

Media Info

  • Media Type: Web
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 240p

Subject/Index Terms

Filing Info

  • Accession Number: 01670152
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-HRT-17-074
  • Contract Numbers: DTFH61-14-D-00011
  • Files: TRIS, ATRI, USDOT
  • Created Date: May 21 2018 10:26AM