Monitoring of Thermally Damaged Concrete by Various Ultrasonic Methods

Monitoring of Thermally Damaged Concrete by Various Ultrasonic Methods

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The performance of concrete under elevated temperatures is very complicated and difficult to characterize. With increasing temperature there is a decrease (or change) of mechanical and physical properties such as compressive strength, tensile strength, modulus of elasticity, density, etc. In this paper we examine the interaction of thermal damage processes in concrete and parameters obtained by different nondestructive ultrasonic methods. We were focused on conventional and innovative ultrasonic methods. The conventional technique was Ultrasonic Pulse Velocity (UPV) method. The pulse velocity in a material depends on its density and its elastic properties which in turn are related to the quality and the compressive strength of the concrete. The innovative ultrasonic method is based on principles of Nonlinear Elastic Wave Spectroscopy. Material nonlinearities manifest themselves as resonant frequency shifts and harmonics or dumping coefficients changes. The procedure described and tested in this article uses broadband pulse-compression signal, with variable amplitude to measure the change of fundamental frequency.

The performance of concrete under elevated temperatures is very complicated and difficult to characterize. With increasing temperature there is a decrease (or change) of mechanical and physical properties such as compressive strength, tensile strength, modulus of elasticity, density, etc. In this paper we examine the interaction of thermal damage processes in concrete and parameters obtained by different nondestructive ultrasonic methods. We were focused on conventional and innovative ultrasonic methods. The conventional technique was Ultrasonic Pulse Velocity (UPV) method. The pulse velocity in a material depends on its density and its elastic properties which in turn are related to the quality and the compressive strength of the concrete. The innovative ultrasonic method is based on principles of Nonlinear Elastic Wave Spectroscopy. Material nonlinearities manifest themselves as resonant frequency shifts and harmonics or dumping coefficients changes. The procedure described and tested in this article uses broadband pulse-compression signal, with variable amplitude to measure the change of fundamental frequency.