Ground-penetrating radar (GPR) is a nondestructive test method that involves the transmission and reflection of electromagnetic waves into a structure or material. GPR testing detects the arrival time and energy level of a reflected electromagnetic pulse. Electromagnetic energy is affected by changes in the dielectric properties of the materials, thus variations in the condition and configuration of the structure will cause changes in the received signal. Information is obtained by evaluating the return time, amplitude, shape, velocity variations, attenuation and polarity of the signal
GPR testing is commonly used to estimate the thickness of concrete and multi-layer systems, to locate embedded reinforcement in concrete, to locate wall anchors and underground utilities, to measure concrete cover thickness, to locate moisture variations, to locate voids and identify their lateral dimensions, to locate honeycombing, cracking and delaminations in concrete, and to assess the degree of concrete deterioration due to corrosion of embedded reinforcement.
GPR is also used to investigate other construction materials such as stone, masonry and soils. GPR is very effective in determining if CMU wall systems are grouted and what the condition of the grout is.