NDTnet - April 1997, Vol.2 No.04

Detection of Thickness, Voids, Honeycombs and Tendon Ducts Utilising Ultrasonic ImpuIse-Echo-Technique

R. Jansohn, O. Kroggel (kroggel@hrz1.hrz.th-darmstadt.de), M. Ratmann Technische Hochschule Darmstadt, Darmstadt (D)

Keywords: Concrete, Coupling, Matched Filtering, Transducer Array, Ultrasound
This paper was presented at the International Symposium Non-DestructiveTesting in Civil Engineering (NDT-CE) 26.-28.09.1995 in Berlin. NDT-CE, Full Program or the Ultrasound Part


1 INTRODUCTION

2 DEVICES

3 SIGNAL ANALYSIS

4 DETECTION OF TARGETS OF INTEREST

5 EXPERIMENTAL WORK

6 CONCLUSIONS AND REMARKS ON IMPROPER FILLED DUCTS

    It is possible to measure the thickness of concrete structures and to detect tendon ducts, voids and honeycombs with the ultrasound impulse echo technique.

    The question wether a duct is properlly filled or not can only be answered by spatial averaging utilizing a larger amount of single measurements. Echoes caused at ducts where the mortar lost the bond to the ducts inner surface are not to distinguish from those generated at completly unfilled ones. Figure 7 shows four stages of imperfect filling. Because ultrasound is sensitive against interfaces in all stages an ultrasonic test would yield in nearly the same result. It is obvious that only the last stage becomes harmful for the tendons corrosion protection.


figure 7:
different stages of imperfect filling

REFERENCES

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    © Copyright 1. April 1997 Rolf Diederichs, info@ndt.net
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