No abstract

Guided longitudinal modes in both low (<200 kHz) and high (2–8 MHz) frequency ranges were invoked to monitor damage in reinforced mortar specimens undergoing accelerated uniform corrosion. The fundamental longitudinal mode, i.e. L(0, 1), and the L(0, 9) mode were invoked for low- and high-frequency testing, respectively. Because of the significant amount of axial displacement at the steel/mortar interface, the L(0, 1) mode was so appreciably attenuated for the particular specimen size used that it is was not detected until after corrosion had initiated and corrosion product accumulation caused mortar cracking. Once detected, the L(0, 1) mode was sensitive to the combined effects of bond deterioration and mortar stiffness reduction. The L(0, 9) mode has negligible radial and axial displacement at the steel/mortar interface. As a result, the L(0, 9) mode is relatively insensitive to the surrounding interface conditions at high frequencies. This allows for changes in the steel cross-sectional area and bar topography to be isolated and monitored from the onset of corrosion up to severe pitting.

Corrosion of reinforced concrete is a chronic infrastructure problem, particularly in areas with deicing salt and marine exposure. To maintain structural integrity, a testing method is needed to identify areas of corroding reinforcement. For purposes of rehabilitation, the method must also be able to evaluate the degree, rate, and location of damage. Toward the development of a wireless embedded sensor system to monitor and assess corrosion damage in reinforced concrete, reinforced mortar specimens were manufactured with seeded defects to simulate corrosion damage. Taking advantage of waveguide effects of the reinforcing bars, these specimens were then tested using an ultrasonic approach. Using the same ultrasonic approach, specimens without seeded defects were also monitored during accelerated corrosion tests. Both the ultrasonic sending and the receiving transducers were mounted on the steel rebar. Advantage was taken of the lower frequency (<250kHz) fundamental flexural propagation mode because of its relatively large displacements at the interface between the reinforcing steel and the surrounding mortar. Waveform energy (indicative of attenuation) is presented and discussed in terms of corrosion damage. Current results indicate that the loss of bond strength between the reinforcing steel and the surrounding concrete can be detected and evaluated.

No abstract