An FHWA Special Study: Post-Tensioning Tendon Grout Chloride Thresholds

CHAPTER 2. OBJECTIVE AND SCOPE OF WORK

The objective of this study was to determine chloride threshold values of PT strands exposed to chloride-contaminated grout. For this, a comprehensive investigation has been conducted over 12 months to complete the following two tasks:

• Task 1: Literature review on chloride threshold for prestressed strands.
• Task 2: Accelerated corrosion testing to determine chloride threshold values to initiate corrosion and critical threshold values for recognizable corrosion-induced damage. This task had three subtasks employing three types of specimens as follows:
• Task 2.1: Single-wire specimens.
• Task 2.2: Single-strand specimens.
• Task 2.3: Multi-strand specimens.

TASK 1: LITERATURE REVIEW ON CHLORIDE THRESHOLD FOR PRESTRESSING STRANDS

A thorough literature review was conducted as far back as the 1950s to disseminate historical chloride limit data applicable to the prestressed strand. Also, the PT tendon corrosion failure reports were gathered and analyzed to extract pertinent information for this study. The complete literature review report was published as an FHWA summary report.⁽³⁾

TASK 2: ACCELERATED LABORATORY CORROSION TESTING

Accelerated laboratory corrosion testing was performed to determine chloride threshold values for the prestressed strands through investigating interacting effects among multiple parameters including chloride concentration, presence of voids, stress level, temperature, relative humidity (RH), and pH using new 0.6-inch, 270-ksi low-relaxation grade strands. The strands employed in this research study were handled in the same way as delivered without additional cleaning and installed in the actual bridges. After they were delivered to the laboratory, they were stored in a clean and dry condition to prevent atmospheric corrosion.