Subsurface water path detection in concrete structures using active thermography: Fid-Bau Portal

Subsurface water path detection in concrete structures using active thermography

Sham, F.C. / Lo, Y. / Chen, Y.S. / Hung, Y.Y.

This paper presents a novel technique using active thermography for subsurface water path detection in concrete structures. Active thermography allows full field and noncontact qualitative observation and quantitative measurement of thermal radiation from the surface of a test object. During testing, the structure's surface is radiated with a heat pulse of short duration, and a series of thermograms (the image of surface radiation of the object) is subsequently recorded. Processing the thermograms allows the rate of temperature change of the surface to be determined. The presence of water underneath the surface will exhibit anomalous temperature change; hence, the water seepage path can be traced. Unlike traditional moisture content measurement, which requires contact and paint by point measurement, active thermography is a full field and noncontact technique for detecting water seepage paths. This technique is applied in the examination of water paths with different depths and diameters. Preliminary experimental results illustrated the detectability of various subsurface water paths. In this study, three concrete samples (A, B and C), with artificial subsurface water paths having different depths, are pulsed by flash lamps and tested. Surface temperature time evolution of the concrete is recorded with an infrared camera and processed. Preliminary results show that the subsurface air path can be obtained more easily than the subsurface water path, and further processing techniques such as time derivation are required for tracing the water path successfully. Depth evaluation of subsurface water paths has also been done, and the results show that the depth of a subsurface water path can be determined while the diffusivity of wet concrete is known in advance.