Thermo-Mechanical Investigations of Reinforced Concrete Structures Using Coda Wave Interferometry

Civil engineering structures are aging. Ultrasonic coda waves offer an auspicious opportunity to monitor this deterioration. Current approaches with coda wave-based monitoring of concrete (structures) focus on specimens that are only a few centimeters small or on detecting cracks in reinforced concrete. The empirical model introduced in this thesis enables evaluating the load-bearing capacity of reinforced concrete structures subjected to bending using coda waves. The model involves the complex material behavior of reinforced concrete, from the linear-elastic range to the range of cracking and completed cracking. The underlying methodology is based on mechanical, thermal, and thermo-mechanical experiments on reinforced concrete beams. Ultrasonic measurements are evaluated using coda wave interferometry. This method yields the relative velocity change. The strain of the component is used as a reference. Investigations into the application, assembly and accuracy of strain measurement techniques reveal fiber optics as a suitable technique. The relative velocity change is correlated with the measured strain. The idea is based on the volume-like collection of influences by coda waves. The correlation of the two respective quantities (relative velocity change and average steel strain) exhibits a linear relationship. This gives a first-order approach. Using this approach, the strain of the beam can be accurately calculated via the relative velocity change. Statistically, the model is of high quality (R^2 = 0.99) and low error (RMSE = 0.09 ‰). Consequently, it becomes feasible to monitor reinforced concrete structures by means of ultrasonic measurements and to accurately indicate the load-bearing capacity even under progressive cracking.