# Detection of Impact Damage on PVA-ECC Beam Using Infrared Thermography
## 1 Introduction  
Polyvinyl alcohol fiber reinforced engineering cementitious composite (PVA-ECC) is a class of ultra-ductile fiber reinforced cementitious composite, which has been widely adopted in the large material volume usage and cost sensitive construction industry [1]. PVA-ECC material has been demonstrated as an important structural material due to its excellent performance, such as high strength, high temperature resistance and corrosion resistance [2; 3]. It is best suited for engineering applications that require large ductility, such as earthquake-resistant bridges. It also has been widely utilized in applications that require high durability, such as bridge piers, pavements and other infrastructure exposed to harsh environmental conditions [4]. In the past few decades, a large numbers of bridges spanning great rivers were built both at home and abroad. For the structures constructed in navigable waters, they constitute a hazard that is vulnerable to damage or destruction in the event of vessel collision. Among the most significant structures exposed to this hazard are bridges that cross coastal or inland waterways. According to relevant reports, impact accidents due to ship-bridge collision are increasingly common, and are a major cause of traffic disruption and economic loss. The records indicate an average of one seriousship-bridge collision accident per year worldwide [5]. However, impact-induced structural damage is a major concern and has not been fully characterized for PVA-ECC structures. Accidental impacts can severely reduce the structural strength and stability, which can lead to severe consequences due to the degradation of the mechanical properties. After impacts, there may be subsurface cracks or buried cracks under the surface, which will significantly reduce the bearing capacity of the structure. It is essential to develop an effective detection technique to monitor and study the impact damage, to provide early warning of possible faults. In recent decades, different types of instruments and techniques have been utilized for structural damage detection and health monitoring. These techniques can be classified into acoustic emission [6; 7; 8; 9; 10; 11; 12; 13], electromagnetic techniques [14; 15], ultrasonic inspection [16; 17; 18], microscopy [19], sensors [20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30] and thermography [31; 32; 33; 34; 35; 36; 37]. For example, [PERSON] monitored the impact damage on fiberglass composite plates based on surface lava wave propagation [38]. [PERSON] et al. detected the impact damage on bridges due to high-speed vehicle collision using embedded piezoceramic transducers [39]. [PERSON] et al. studied the low velocity impact and delamination buckling behavior of composite laminates with embedded optical fibers [40]. [PERSON] and [PERSON] investigated the impact process based on the spectral analysis of acoustic emission signals [41]. Each monitoring technique has its own limitation and disadvantage. Most of them require an experienced technician to analyze the information, which leads to a significant decrease in effectiveness. Among the various new techniques developed recently, infrared thermography is a well-known non-destructive evaluation (NDE) technique, which has attracted considerable interests in a wide variety of industries. It can transform the thermal energy emitted by objects in the infrared band of the electromagnetic spectrum into a visible image [42; 43]. It allows fast inspection of large surfaces [44; 45; 46; 47]. The active thermography method is fast and can provide full-field information of defects. It measures the surface heat-transfer response due to thermal excitation. Thermography is a surface thermal radiation measurement technique, which can be used to detect spatial variations of the surface temperature pattern [48; 49]. The crack or flaw can be detected by searching anomalous hot-spots after thermal excitation.