Non-contact inspection of construction materials using 3-axis multifunctional imaging system with microwave and laser sensing techniques

Microwave imaging techniques have been applied in a wide variety of commercial and scientific applications such as non-destructive testing and evaluation, material characterization and medical applications [1]-[3]. Microwave non-contact techniques have demonstrated the ability to detect flaws in various dielectric and composite materials using relatively simple microwave reflectometers [3]-[8]. These materials include construction materials and composites such as cement-based materials and concrete structures strengthened by carbon fiber reinforced polymer (CFRP) laminates possessing delamination and debonds [3]-[7], and layered dielectric materials with a hidden crack [8]. The assessment of cracks in concrete structures is crucial for their safety and cost effective maintenance since they not only affect their appearance but also the load-carrying capacity and durability [9]-[11]. Several non-invasive testing techniques have been under investigation for the purpose of crack detection in concrete. They include acoustic testing, ultrasonic techniques, optical methods, and microwave techniques. However, if compared with non-invasive methods for metal structures, the non-invasive methods for concrete structures are at a relatively early stage of development [9]-[11].