Details:

Creators:
Hamilton, H.R. ; Patil, Satyajeet R ; Torres, Eduardo
Hamilton, H.R. ; Patil, Satyajeet R ; Torres, Eduardo Less -
Corporate Creators:
University of Florida. Dept. of Civil and Coastal Engineering
Corporate Contributors:
Florida. Department of Transportation
Subject/TRT Terms:
[+]
Bridges Corrosion Defective Grout Defects Drying Hydrodemolition Moisture Content Post-tensioning Tendons Soft Grout Tendon Corrosion Tendons (Materials) Tensioning
Resource Type:
Tech Report
Geographical Coverage:
United States
Edition:
Final Report, May 2016 – Feb 2020
Corporate Publisher:
University of Florida. Department of Civil and Coastal Engineering
Abstract:
Bridge girders in the U.S. are commonly constructed using multistrand post-tensioned (PT) tendons. Defective grout has been found in some of recently constructed bridges in the form of soft grout, which consists of segregated and unhardened grout with free moisture and is often the cause of corrosion of prestressing strands. To address this problem, two techniques of remediation were tested and evaluated: hydrodemolition removal of the defective grout and drying of the defective grout. Hydrodemolition involved use of a high-pressure water jet to break up and remove soft grout from inside the PT duct, but it did not completely remove grout from any one section of the mockup and was deemed unsuitable for use in the removal of grout. To evaluate drying as a means to remediate soft grout, two types of PT tendon mockup specimens were fabricated and filled with multiple layers of grout with varying quality. Grout was dried in place by passing dehumidified air through the tendon to remove moisture. Mockup specimens containing normal grout required 167 days to dry and the specimen containing only soft grout dried in 117 days. Moisture content measurements on dried layers of soft grout were consistently below 1%, which indicated that drying had effectively removed moisture from the soft grout. Dried specimens, however, exhibited strand corrosion in several locations, which did not occur in the control specimens. To better understand the corrosion behavior discovered in the mockup testing, a series of small-scale corrosion tests were conducted using specimens consisting of a 1.5-in. diameter PVC pipe and a single prestressing strand. Forty-eight of the seventy-two specimens were fabricated and dried. Drying was terminated when the difference in RH between the inlet and outlet was indistinguishable. During and after drying, corrosion potential was measured in specimens containing two strands, macrocell current was measured between strand pairs after drying. After monitoring corrosion for a designated time, corrosion specimens were dissected to evaluate grout moisture content and strand corrosion. Moderate corrosion was found on the prestressing strands when the specimens were dissected, with the majority of the corrosion occurring in chloride-contaminated specimens. Given the unknowns in the field application of this method and the fact that corrosion occurred during drying in laboratory conditions, it is advisable to combine the grout drying with the use of a corrosion inhibitor injected into the tendon immediately following drying. For PT tendons with chloride-contaminated grout, it is advisable to use an inert gas for drying followed by injection with a corrosion inhibitor effective in high-chloride environments.
Format:
PDF
Funding:
BDV31-977-58
Collection(s):
US Transportation Collection
Main Document Checksum:
[+]
urn:sha256:dcb1e243da4bcbc4f8c1700f208fd6660029b2b8b8bff98516ee83206dc8913c
Download URL:
https://rosap.ntl.bts.gov/view/dot/54625/dot_54625_DS1.pdf
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