Defying Time: Durability of DYWIDAG DCP Bar Tendons After 30 Years

Project Background

During the 1990s, DYWIDAG designed, supplied, and installed an external strengthening system for a new stadium expansion in northeastern USA, extending the original structure constructed in the 1960s.

Over 150 double corrosion protection (DCP) DYWIDAG THREADBAR® tendons were integrated across the stadium's reinforced concrete bents, forming the principal load-bearing components of the concourse areas and access ramps.

Crafted in a temperature-controlled environment at a DYWIDAG facility, these GR 150 DCP THREADBAR® tendons employed a groundbreaking technique that embedded an epoxy-coated bar tendon within a corrugated polyethylene duct.  This duct was positioned within a secondary, high-density polyethylene duct, and the bar tendon was centrally aligned before undergoing a pressure grouting process using cementitious grout.

Over its lifespan, DYWIDAG has performed multiple rounds of lift-off testing, indicating force verification is in line with engineered criteria.  These tests show that DYWIDAG THREADBAR® exhibits low relaxation properties.  

After thirty years in service, a representative amount of tendons were selected from the outer bents' most exposed exterior surfaces, extracted for examination, and replaced with new tendons. Each selected tendon was meticulously labeled and transferred to a secure facility. Here, they underwent a detailed dissection and visual inspection to identify any indications of corrosion, wear, abrasion, or other surface irregularities. Subsequently, the THREADBARS® were dispatched to an independent third-party laboratory for testing of their tensile strength. 

Inspection and Results

The examination of the DYWIDAG DCP system, encompassing THREADBAR tendons and anchor nuts and couplers, involved a comprehensive evaluation of their state. Initially, visual analysis was performed to document the external condition of the materials. Subsequently, the bar tendons underwent dissection to unveil their cross-sectional profiles, providing insights into the status of the grout, corrugated plastic duct, smooth plastic duct, and THREADBAR®.  Among these, four bar samples had their ducts and grout removed for a detailed assessment of the bar tendons' condition. 

The yield and tensile strength of the examined THREADBAR® exceeded the minimum guaranteed strength specified in ASTM A722. The inspections and tests conducted affirmed that the overall structural soundness of the DYWIDAG DCP THREADBAR®, anchor nuts, and couplers had been effectively maintained throughout their three decades of service. This favorable outcome can be attributed to the layered safeguarding mechanisms of the DYWIDAG-designed DCP system, its inherent durability, and the diligent maintenance efforts carried out over the years by DYWIDAG.