Corrosion depth of concrete can reflect the damage state of the load-carrying capacity and durability of the concrete structures servicing in severe environment. Ultrasonic technology was studied to evaluate the corrosion depth quantitatively. Three acidic environments with the pH level of 3.5, 2.5, and 1.5 were simulated by the mixture of sulfate and nitric acid solutions in the laboratory. 354 prism specimens with the dimension of 150？mm × 150？mm × 300？mm were prepared. The prepared specimens were first immersed in the acidic mixture for certain periods, followed by physical, mechanical, computerized tomography (CT) and ultrasonic test. Damage depths of the concrete specimen under different corrosion states were obtained from both CT and ultrasonic test. Based on the ultrasonic test, a bilinear regression model is proposed to estimate the corrosion depth. It is shown that the results achieved by ultrasonic and CT test are in good agreement with each other. Relation between the corrosion depth of concrete specimen and the mechanical indices such as mass loss, compressive strength, and elastic modulus is discussed in detail. It can be drawn that the ultrasonic test is a reliable nondestructive way to measure the damage depth of concrete exposed to acidic environment. 1. Introduction Since 1940s, pollution of acid rain has become to be a significant environmental problem confronting the environmentalists. In the past two decades, it is reported that acid rain falls have become more and more serious worldwide [1–6]. It is well known that concrete has become and will continue to be the most widely used construction material in civil engineering. However, when concrete is subject to acid rain, physical and chemical reactions occurred. The complex reactions will alter the internal structure of concrete, which will result in the change of its material property. Many famous buildings, such as Emei Mountain, Leshan Grand Buddha, Acropolis monument in Greece, and the Statue of Liberty in the United States, have been strongly damaged by acid rain in the previous decades. The damage effect of acid rain on concrete structures has attracted more and more attention of civil engineers gradually. A better understanding of the material properties of concrete exposed to acidic environment can help to discover the damage process of the in-service structures. Some experimental studies have been performed to discover the corrosion mechanism of acid rain attacking concrete, and simulation test of the acid rain attacking concrete was analyzed [7–12]. However, it is still
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