Crack Depth Determination using Advanced Impact-Echo Techniques

Concrete cracking resulting in stiffness loss and also corrosion of the steel reinforcement is an important aspect in reinforced concrete structures. Normally the concrete cover will protect the steel from corrosion. However, if cracks occur and become large the corrosion protection is not given anymore. The corrosion rate strongly depends on the crack width and the crack depth so there is the need to measure and to characterize its dimensions. Only if the crack dimensions exceed a certain level, a repair is necessary. To increase the lifetime of the structure and to optimize the repair this deterioration level has to be known. One way to do this is with the Impact-Echo method. The impact-echo technique is a useful tool for the de- tection of different faults in concrete structures. Unfortunately, the existing instru- ments and analysis tools designed for measurements were lacking of several features in the past detaining the extensive use. For many applications as for inspections of large structures, it is essential that the equipment for Impact-Echo measurements along profiles uses a scanning technique and a fast and reliable data acquisition. A new concept for Impact-Echo testing systems is presented in this paper. Therefore, a new device was developed, which is small and easy to handle, robust and unproblematic regarding transportation. The system utilizes advanced impact generation for fast scanning techniques and reproducible impacts. The data acquisi- tion, filtering and visualization of data are optimized for the inspection of large structures obtaining data at many measurement points. A new option is the auto- matic estimation of crack parameters like crack depth. The crack depth determina- tion is a combination of the well known time-of-flight method with new analysis methods that were made in the time domain. Therefore the acoustic wave and the energy content will be further analysed. In this paper fundamental principles of the different measurement techniques as well as details of the hardware and software functionality of the measurement system are described.