One of the main issues facing reinforced concrete structures, which are the largest category of infrastructure, is corrosion. Corrosion of metallic reinforcing in concrete is influenced by a variety of attributes of the concrete, including depth of cover and the porosity of the hardened or mature concrete. Ground penetrating radar (GPR) is a leading tool for determining and verifying cover depth and other physical features like delamination. It is an emerging tool for characterization of the concrete material itself, including applications to study hydration processes and early age properties. Recent work has identified relationships between GPR signals and mature concrete porosity measured using cold-water saturation. This work presents an initial study that compares GPR attributes and physical properties (cold water saturation porosity, compressive strength, and density) to new measurements of the porosity performed using the vacuum saturation method. This method is applied to a small set of mature samples and the results are compared across each measurement and sample characteristic. On average, all mixes except concrete paste (containing no coarse aggregate) have higher vacuum saturation porosity than cold water saturation porosity because the method captures smaller pore sizes. Basic GPR attributes (maximum amplitude, total energy, and average amplitude) have no strong direct linear correlation with either porosity measurement, but there are some promising relationships found in the average trends. This study gives insight into the porosity-controlled mechanisms of GPR signal propagation and how they may be used to evaluate mature in situ concrete without collecting or directly testing samples.
Concrete compressive strength is important, yet difficult to quantify without direct testing. In particular, it is difficult to obtain the mature concrete strength measurements which are necessary for safe and optimal use of existing structural capacity. Reliable measurements of mature strength using nondestructive testing methods (NDT) like ultrasonic pulse velocities depend on many factors, including the inherent material variability, sampling frequency, and quality of the NDT measurements. Methods like ground penetrating radar (GPR) and concrete maturity relationships are common for investigating the early-age properties of concrete but are rarely used for mature concrete. Using a case study of a concrete pedestrian bridge where both long term temperature data from structural health monitoring (SHM) and recent GPR surveys of the bridge are available, this work compares the predicted 8-year strength using two different indirect methods. The first uses a regression model trained on laboratory GPR attributes and material properties. The second uses the maturity method to predict strength based on 28-day cylinder tests and the temperature history recorded by the bridge's SHM system. The maturity method predicts the correct relative trends in strength between the two phases and overpredicts the cylinder 28-day strength by 12% 25%. The GPR predictions do not reliably capture the relative difference between the two phases, but have similar accuracy and underpredict cylinder strength by 4% 22%. These strength comparisons from noninvasive methods motivate further improvements in GPR attribute modeling and integrating these methods with other ultrasonic models to improve spatial resolution and reliability.
Conference Committee Involvement (4)
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2025
17 March 2025 | Vancouver, Canada
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2024
25 March 2024 | Long Beach, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2023
13 March 2023 | Long Beach, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
7 March 2022 | Long Beach, California, United States
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