Acoustic emission based structural health monitoring of corroded/un-corroded concrete structures

Structural health monitoring (SHM) is a continuous nondestructive evaluation system used for both damage prognosis and diagnosis of civil structures. Acoustic emission (AE) technique is defined as a passive SHM method that enables the detection of any possible damage. AE technique has been exploited for condition assessment and long-term monitoring of civil infrastructure systems. AE sensors are sensitive to the micro-cracking stage of damage, therefore showed a great potential for early detection of different forms of deteriorations in reinforced concrete (RC) structures. The rate of deterioration in RC structures greatly increases due to reinforcing steel corrosion embedded in concrete. Corrosion results in both expansion and mass loss of steel, thus causing concrete cover cracking and delamination. Moreover, corrosion causes reduction of bond between concrete and steel, which reduces the overall strength of RC structures. The objectives of this research were to: a) utilize AE monitoring for early corrosion detection and concrete cover/steel damage quantification of small-scale RC specimens, b) evaluate and localize corrosion activity using distributed AE sensors in full-scale RC beams, c) attain an early detection of loss of bond between corroded steel and concrete at different corrosion levels, d) identify and assess bond degradation of corroded/un-corroded bars in both small- and full-scale RC beams, and e) develop relationships between the collected AE data and variable levels of corrosion, corrosion-induced cover crack growth, and bond deterioration in RC structures. Four extensive experimental investigations have been conducted both on small- and fullscale RC elements to accomplish these aforementioned research objectives. AE monitoring was implemented in these studies on RC elements including a total of 30 prisms, 114 pull-out samples, and 10 beam anchorage specimens under accelerated corrosion, direct pull-out, and four-point load tests, respectively. The analysis of AE data obtained from these tests was performed and compared to the results of half-cell potentials (HCP) standard tests, visual detection of corrosion-induced cracks, crack width measurements, and overall bond behaviour of all tested pull-out samples/beams. The results showed that the analysis of AE signal parameters acquired during corrosion tests enabled the detection of both corrosion and cover crack onset earlier than HCP readings and prior to any visible cracking in both small- and full-scale RC beams, regardless of cover thickness or sensor location. Analyzing the AE signals attained from the pull-out tests permitted the characterization of two early stages of bond degradation (micro- and macro-cracking) in both corroded and un-corroded specimens at all values of bar diameter, corrosion level, cover thickness, and embedded length. The AE analysis also allowed an early identification of three stages of bond damage in full-scale corroded/uncorroded RC beams namely; first crack, initial slip, and anchorage cracking, before their visual observation, irrespective of corrosion level, embedded length, or sensor location. The results of AE intensity analysis on AE signal strength data were exploited to develop damage classification charts to assess the extent of corrosion damage as well as to categorize different stages of bond deterioration in corroded/un-corroded small- and fullscale RC samples