Acoustic Emission Characterization of the Onset of Corrosion in Reinforced Concrete M. Di Benedetti *a , E. De Cais a , Z. Karim a , G. Loreto a , F. Presuel b , A. Nanni a a Department of Civil, Architectural & Environmental Engineering, University of Miami, McArthur Engineering Building, Coral Gables, FL, USA, 33124 b Department of Ocean and Mechanical Engineering, Florida Atlantic University, Ocean and Mechanical Engineering, Dania Beach, FL, USA, 33004 ABSTRACT The development of techniques capable of evaluating deterioration of reinforced concrete (RC) is instrumental to the advancement of the structural health monitoring (SHM) and service life estimate for constructed facilities. One of the main causes leading to degradation of RC is the corrosion of the steel reinforcement. This process can be modeled phenomenologically, while laboratory tests aimed at studying durability responses are typically accelerated in order to provide useful results within a realistic period of time. Among nondestructive methods, acoustic emission (AE) is emerging as a tool to detect the onset and progression of deterioration mechanisms. In this paper, the development of accelerated corrosion and continuous AE monitoring test set-up for RC specimens are presented. Relevant information are provided with regard to the characteristics of the corrosion circuit, continuous measurement and acquisition of corrosion potential, selection of AE sensors and AE parameter setting. Results from small-scale pre-notched RC specimens aim to isolate the frequency spectrum where the corrosion first takes place. Waveform analysis critical in the definition of a prognosis model will extend the AE dataset for the onset of corrosion. Key words: acoustic emission, corrosion, reinforced concrete, accelerated test, steel reinforcement, service life 1. INTRODUCTION The majority of the US transportation infrastructure (highways and bridges) was constructed in the 1950-70’s with a 50- year design life. The American Society of Civil engineers estimates that more than 26% of the nation’s bridges are either structurally deficient or functionally obsolete. While some progress has been made in recent years to reduce the number of deficient and obsolete bridges in rural areas, the number in urban areas is rising 1 . One of the main causes leading to degradation of reinforced concrete (RC) is the corrosion of the steel reinforcement. Once the alkalinity of concrete is reduced (typically because of carbonation due to CO2) and/or depassivating anions (typically chloride ions) reach the steel reinforcement and exceed a critical threshold concentration then corrosion occurs. Once corrosion has initiated, then corrosion propagation stage initiates. During this stage there is a build-up of corrosion products (occupy about 3 times the volume of the parent steel) that cause tensile stress. Depending on the environmental conditions this might lead to rust staining of the concrete or cracks with eventual spalling of the cover. Corrosion occurs at the anode where the metal oxidizes, and simultaneously, reduction occurs at the cathode. The electrons produced during this process are conducted through the steel while the ions are transported via the pore water which acts as an electrolyte 2 . The deterioration becomes even more detrimental for structures exposed to environment rich of chloride ions 3-5 and carbon dioxide such as coastal areas and regions where de-icing salts are regularly used. The corrosion process in marine environment can be modeled phenomenologically 6 , while laboratory tests aimed at studying durability responses are typically accelerated in order to provide useful results within a realistic period of time. Acoustic Emission (AE) has been proven as an effective technique to the detection of localized corrosion. The chemical and petrochemical industry, for example, has already implemented this technology to detect stress corrosion cracking 7 , pitting 8 and crevice 9 of stainless steel. Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2012, edited by Masayoshi Tomizuka, Chung-Bang Yun, Jerome P. Lynch, Proc. of SPIE Vol. 8345, 83453Y · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.915197 Proc. of SPIE Vol. 8345 83453Y-1 Downloaded From: http://spiedigitallibrary.org/ on 09/04/2014 Terms of Use: http://spiedl.org/terms