Use of Higher-Harmonic and Intermodulation Generation of Ultrasonic Waves to Detecting Cracks due to Steel Corrosion in
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020) 14:52
International Journal of Concrete Structures and Materials Open Access
RESEARCH
Use of Higher‑Harmonic and Intermodulation Generation of Ultrasonic Waves to Detecting Cracks due to Steel Corrosion in Reinforced Cement Mortar Miguel Ángel Climent‑Llorca1* , Marina Miró‑Oca1 , Pedro Poveda‑Martínez2 and Jaime Ramis‑Soriano2
Abstract The aim of this work was to provide further confirmation of the possible use of non-linear ultrasonic techniques for detecting the cracking due to corrosion of steel reinforcements in concrete. To this end accelerated steel corrosion tests have been conducted on model reinforced cement mortar specimens, while monitoring the appearance and width evolution of visible surface cracks, and performing non-linear ultrasonic measurements based on the phenom‑ ena of harmonic distortion and intermodulation. A new parameter, based on the difference between the amplitude of the fundamental frequency and the sum of the amplitudes of all the first-order and second-order intermodulation products, has been proposed in this work. The results confirm that the appearance of visible surface micro-cracks are preceded and accompanied by the observation of strong non-linear features in the received signal. Furthermore, the new parameter proposed in this work is as efficient as the relative non-linearity parameters, classically used in har‑ monic distortion non-linear ultrasonic studies, for detecting the non-linear features associated with the critical events of the cracking of cement mortar due to embedded steel corrosion. A hypothesis has been developed considering the possible effect of the filling of the void space by liquid containing rust products after the formation of new cracks or the enlargement of its width. This filling process, which might be particularly enhanced by net convective transport of liquid, would explain the evolution of the values of all the parameters used for putting in evidence the non-linear elastic features after the critical events of the cracking process. Keywords: reinforced concrete, steel corrosion, cracking, non-linear ultrasonic test, non-destructive detection 1 Introduction Corrosion of steel rebar in reinforced concrete or cement mortar constructive elements is a problem of major concern in both the exploitation and maintenance of building and civil engineering structures (American Concrete Institute 1996). Usually, when this kind of structures are subjected to harmful environmental agents (e.g., *Correspondence: [email protected] 1 Civil Engineering Department, University of Alicante, Sant Vicent del Raspeig, 03690 Alicante, Spain Full list of author information is available at the end of the article Journal information: ISSN 1976-0485 / eISSN 2234-1315
seawater, rain, high humidity, drastic thermal changes, etc.) continuously over time, steel corrosion products are generated, which leads to stress cracking phenomena of the cementitious matrix, and the unexpected sudden failure of the structure (Bertolini et al. 2013). For this reason, the development
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