Detection of air blisters and crack propagation in FRP strengthened concrete elements using infrared thermography

This paper explores the possibility of (i) detecting the extents of air-voids between the bond-line of advanced composite materials (FRPs) and concrete substrate and (ii) predicating crack initiation and propagation in a reinforced concrete (RC) beam at early stage of failure. Both studies have been carried out successfully using Infrared (IR) thermography. The artificial blisters (air-voids) with controlled sizes, embedded between the interface of FRP and concrete, were detected by the IR thermography remotely up to 20 metres away. The RC beam, which was initially at pristine condition, was subject to continuously static or cyclic loading tests. The preliminary results show that the damaged region of the RC beam, partially strengthened by glass fibre reinforced polymer (GFRP), which was covering the cracks, was clearly identified using an IR thermal imaging system. The anticipated failure plane was proven to be identical to the actual failure of the test beam.