NDTnet 1998 Aug, Vol.3 No.8

Abstract

Post tensioned concrete has historically been a popular choice for road bridges. The form of construction, consisting of tendons passing through ducts which are later backfilled with cement grout, is illustrated in the Figure. A problem with this form of construction is that it is currently very difficult to detect corrosion of the tendons and it is widely recognised in the UK and elsewhere that there is a need to develop improved inspection techniques.

Figure: Post-tensioned concrete, showing test configuration

The paper presents results of an investigation which is being conducted by the authors to determine the feasibility of using ultrasonic waves which are guided along the tendons for the inspection. The primary test configuration is essentially pulse-echo, employing a transducer which is attached to the free ends of the tendons at their anchor points.

It is to be expected that guided wave modes in the tendons may lose their energy very quickly by leakage into the surrounding grout. However, model studies of the wave properties of this system have revealed that there are several modes whose leakage loss is moderate and which could therefore be used to inspect the integrity of useful lengths of the tendons adjacent to the anchors. This is a region of the structures where there is a relatively high risk of corrosion and where it is particularly difficult to inspect at present. The phenomena predicted by the model studies have been validated experimentally and preliminary tests on realistic structural configurations have also been performed. These indicate very positively the viability of the proposed technique.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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