Polyethylene Duct Cracking on Posttensioning Tendons in Florida Segmented Bridges

Abstract

During the past 20-plus years, designs based on the post-tension segmental concrete box concept have evolved to become prominent in bridge construction. Critical to the safety and longevity of such structures is the integrity of post-tensioning tendons. However, during the past five years, several Florida bridges have suffered tendon deterioration and failure because of strand corrosion at grout voids in which bleed water had accumulated. In some cases, the high-density polyethylene (HDPE) ducts within which the grouted strands reside had cracked. Although none of the tendon failures to date have been related to the HDPE duct cracking, left unaddressed moisture, chlorides, and oxygen will invariably corrode strands in the long-term. In order to assess the cause(s) and mechanism(s) of HDPE duct cracking, fatigue tests were performed upon duct samples retrieved from representative bridges and the results were compared with those from (1) material property determinations of the corresponding ducts, (2) experiments on simulated tendons that were subjected to thermal cycling, and (3) finite element analyses. Based on the outcomes, a mechanism is proposed for the duct cracking and time-to-cracking projections are made for ducts that are still sound.