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Portland cement concrete (PCC) is a versatile and widely used construction material renowned for its strength and durability. The mechanical properties of PCC, including compressive strength, flexural strength, and splitting tensile strength, play a pivotal role in ensuring the safety and sustainability of structures such as buildings, bridges, and dams. Traditionally, the determination of PCC's compressive strength involves destructive testing of standard-size concrete cylinders until they fail. While nondestructive evaluation (NDE) techniques are available for assessing these properties, they often require direct contact between the sensor and the concrete surface, making them less efficient and practical compared to remote sensing techniques. In this paper, we applied three NDE techniques for estimating the mechanical properties of concrete, including synthetic aperture radar (SAR), ultrasonic pulse velocity (UPV), and a rebound hammer. We manufactured a total of 48 laboratory concrete cylinders (diameter = 3", height = 6"). These cylinders were created with different water-to-cement ratios (0.4, 0.45, 0.5, and 0.55) with a mix design ratio of 1:2:3 for cement: sand: gravel (by mass). Four dates of compressive testing were considered (7-day, 14-day, 28-day, and 96-day). Before these cylinders were tested by destructive compression test, they were measured by three NDE techniques. A 10GHz SAR system with a 1.5 GHz bandwidth, a 54kHz UPV system, and a Schimdt rebound hammer were used to inspect those cylinders. Our experimental results reveal a discernible relationship between the compressive strength of concrete and the NDE data. The increase of cylinder age resulted in the increase of compressive strength of PCC cylinders. SAR image parameters, UPV curves, and rebound hammer curves showed correlated patterns. This technique has the potential to provide a nondestructive and efficient means of assessing concrete strength and durability, with significant implications for the construction industry in ensuring the safety and sustainability of various structures.
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