01042132

Monograph

http://onlinepubs.trb.org...y/NCHRP98_Final_Report.pdf

This Innovations Deserving Exploratory Analysis (IDEA) project developed and evaluated a nondestructive method, based on time domain reflectometry (TDR), to determine the presence of voids in post-tensioned ducts in highway structures. The voids were detectable using a single sensor wire in conjunction with an existing tensioning cable to form the two-wire transmission line. The voids could also be detected by using commercially available transmission lines such as lamp cord or 300 ohm TV cable. Factors affecting the void detection signal were identified and their effects quantified. The presence of sand, water, or moisture tended to decrease the positive amplitude of the reflected TDR signal but the void was still detectable. Work on using external sensors for void detection showed much weaker signals as compared to internal sensors indicating a need for a more powerful pulse generator and pulses of high magnitude and short rise time. While higher output voltage with high rise time did not lead to any improvement, a rise time of 40-100 ps appeared satisfactory. Parameters for TDR meters for field application with external sensor detection were identified and several commercial portable TDR meters were evaluated. Further refinement and evaluation of the technique is necessary before it can be implemented for field applications.

This NCHRP-IDEA investigation was conducted by the University of Delaware, Newark. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved

TRB-NCHRP-98

English

27p

2006-10

NCHRP-IDEA Program Project Final Report

Final Report

August 2003 - July 2005

Print

Figures (19) ; Glossary; Photos (1) ; References (6) ; Tables (1)

Air voids; Ducts; Highway bridges; Nondestructive tests; Technological innovations; Time domain reflectometers

Innovations Deserving Exploratory Analysis (IDEA) (Program)

Void detection

Bridges and other structures; Design; Highways; I24: Design of Bridges and Retaining Walls

TRIS, TRB

Feb 14 2007 7:28AM