Acoustic Emission Intensity Analysis Research Articles

Experimental investigation on the deterioration process and spatial variation of corrosion damage of RC segmental specimens under sustained load

• Early deterioration damage of a bearing segment is investigated via AE technique. • Effect of sustained load on spatial variability of steel corrosion is studied. • Spatial correlation between steel corrosion and surface corrosion cracks is studied. For the reinforced concrete (RC) shield tunnel in coastal regions, premature corrosion damages are always investigated after construction because of the combined effects of sustained earth and water pressures and marine chloride attacks. To evaluate the performance of these deteriorated shield tunnels, the effect of sustained load on structural performance degradation must be considered. In this paper, an experiment was conducted using the corrosion-accelerated specimens of a tunnel segment. The deteriorating damage processes of the RC segmental specimens were illustrated via acoustic emission (AE) with an emphasis on the influence of sustained load. Based on AE intensity analysis, intensive cracking damages for a bearing segment were identified when the average steel cross-section area losses increased from 0.5% to 2%. Meanwhile, the spatial variations of corrosion damage were discussed incorporating the impact of tensile load. The effect of tensile load on spatial correlation of distribution between steel cross-section area loss and surface corrosion cracks was experimentally verified. The experimental outcomings can help in modelling a random field-based probabilistic model associated with non-uniform steel corrosion in the bearing segmental linings.

Effect of grouting material strength on bond strength of sleeve and acoustic emission characterization of bond failure damage process

The grouted sleeve connection is widely used in fabricated structures, and the bonding performance is a vital indicator to evaluate its property. Total of 24 grouted sleeves specimens were designed to study the effect of grouting material strength on bond strength of two forms of sleeves under monotonic tensile loading. The qualitative and quantitative evaluation of the bond failure damage process of the grouted sleeves was carried out relying on acoustic emission (AE) technology. Results demonstrated that the relative displacement between the rebar and grouting material was generated after the hardening stage of the tensile process. More importantly, the relationship between grouting material strength and bonding strength was revealed. Compared with Carbon steel sleeves, ductile iron sleeves exhibited better bonding properties in the tensile process. Moreover, a designing method was proposed to prevent bond failure of the ductile iron sleeves and carbon steel sleeves. The trends of AE ringing count and energy with the variation of load could better characterize the bonding failure damage process, which corresponded well to the five stages of the tensile process. The rapid increase of the ringing count and energy level could be a precursor to the occurrence of bond failure of the grouted sleeve. The safety zone to avoid the bond failure of the grouted sleeves was established based on the AE intensity analysis. The emergence of the AE signal corresponding to the bond failure should be vigilant in engineering practice.

Assessment of bond-slip behavior of hybrid fiber reinforced engineered cementitious composites (ECC) and deformed rebar via AE monitoring

This paper investigates the efficiency of acoustic emission (AE) technique for monitoring and assessing the bond-slip behavior and damage characteristics of deformed rebar embedded in hybrid fiber reinforced engineered cementitious composites (ECC). A series of pull-out tests were conducted on 48 prism samples with variable rebar diameters (14 mm, 20 mm, and 25 mm), embedded length (3d, 4d and 5d), and cover thickness (2.5d, 4d, 5d and 6d). Two AE sensors, attached on ECC surface and rebar surface respectively, were utilized to critically monitor the AE activity emitted from the ECC matrix and the interface between ECC and rebar throughout the tests. The bond-slip behavior of ECC-rebar presented a more ductile performance than conventional concrete (CC)-rebar because of fiber bridging effect. The damage classification and damage characteristics were clarified by measuring AE activity. The debonding process of ECC-rebar could be divided into four main stages based on the slope changes of cumulative AE hits, and further refined into several substages based on the sudden rises of AE energy. Besides AE cumulative parameters, the Ib-values calculated from AE signals of ECC matrix and ECC-rebar interface were analyzed and compared, which behaved more effectively in identifying the development of cracks and distinguishing the maximum bond stress. Also, the AE intensity analysis was implemented to identify the micro-mechanism transformation during different bonding stages. Moreover, the AE intensity results of CC-rebar obtained from previous research and ECC-rebar in this study were compared.

Classification of damage in self-consolidating rubberized concrete using acoustic emission intensity analysis

This article presents the results from an experimental study on the application of acoustic emission (AE) analysis to assess the damage progression of self-consolidating rubberized concrete (SCRC) mixtures under four-point flexural tests. Self-consolidating concrete (SCC) mixtures incorporating four variable replacements of crumb rubber (CR) including 0, 10, 20, and 30% were examined to study the effect of CR content on the AE damage detection and quantification capability. Normal concrete (NC) and normal rubberized concrete (NRC) mixtures, with 0 and 40% CR respectively, were also tested for the comparison. Two prism samples were tested from each mixture under monotonic loading conditions, while being constantly monitored via two attached AE sensors until failure. The acoustic emissions obtained from these sensors were related to the damage evolution of the tested prisms from all mixtures. The effects of variable mixture types and CR content on different AE parameters were highlighted. The considered AE parameters included signal characteristics (in terms of signal amplitude) as well as number of AE hits and cumulative signal strength (CSS). In addition, AE b-value and intensity analyses were further performed on the amplitude and signal strength of all AE signals to evaluate the extent of damage by means of three additional AE parameters including b-value, historic index, H (t), and severity, Sr. The outcomes of the AE analysis indicated the usefulness of the considered AE parameters in the detection of two early damage stages including micro- and macro-cracking before failure, irrespective of the CR content. Eventually, the intensity analysis parameters (H (t) and Sr) were correlated to the stages of micro- and macro-cracking in all mixtures for the purpose of damage classification via developed chart.

Characterisation of damage due to abrasion in SCC by acoustic emission analysis

This investigation evaluates and compares the abrasion resistance of various concrete types by means of acoustic emission (AE) analysis. Normal concrete, self-consolidating concrete (SCC) and SCC with variable supplementary cementing materials (SCMs) were tested under the rotating cutter method for abrasion resistance. The effect of using different SCMs in SCC mixtures including fly ash, metakaolin (MK), silica fume and slag on the abrasion resistance of SCC was examined. In conjunction with the abrasion testing, AE monitoring was simultaneously conducted on all mixtures using AE attached sensors. AE parameters such as signal amplitude, signal strength, number of hits, duration and cumulative signal strength (CSS) were collected during the abrasion tests. Three additional parameters were determined through further analyses: b-value, severity (Sr) and historic index (H(t)). Results from the abrasion tests indicated that the SCC mixture containing MK had the highest abrasion resistance among all tested mixtures. The studied AE parameters including CSS, number of hits, b-value, H(t) and Sr were well correlated to the extent of abrasion damage in all tested specimens. The progression of abrasion damage was associated with increased AE activities indicated by high fluctuations in the b-value and H(t) along with ever-increasing values of CSS, number of hits and Sr. The AE intensity analysis quantified which ranges for H(t) and Sr would indicate the extent and severity of the damage due to abrasion by means of developed damage classification charts.

Assessing abrasion performance of self-consolidating concrete containing synthetic fibers using acoustic emission analysis

The key objective of this investigation was to evaluate the abrasion resistance of self-consolidating concrete (SCC) with and without synthetic fibers (SynFs). The abrasion resistance of normal concrete was also investigated in this study for comparison. The abrasion test was performed on concrete specimens according to the rotating-cutter method along with continuous monitoring of acoustic emission (AE) using attached AE sensors. The effects of changing concrete type and incorporating various types (flexible and semi-rigid) and lengths of SynFs on the abrasion behaviour were investigated with the aid of AE analysis. AE signal characteristics such as amplitude, signal strength, number of hits, and duration were gathered during testing. Furthermore, the collected AE data was used to complete b-value analysis as well as intensity analysis resulting in three additional parameters: b-value, severity (Sr), and historic index (H(t)). The results showed that the AE parameters were directly correlated with the abrasion damage in all tested mixtures. Adding SynFs to all SCC mixtures enhanced their abrasion resistance. The flexible fibers variety exhibited better abrasion performance on average than the semi-rigid fibers. Meanwhile, longer fibers showed lower abrasion resistance than the shorter ones with the same type. The results also indicated that AE intensity analysis was able to determine the ranges for H(t) and Sr that identify the extent of damage due to abrasion of SynF-reinforced SCC.

Acoustic emission monitoring for bond integrity evaluation of reinforced concrete under pull-out tests

This article presents the results of an experimental investigation on the application of acoustic emission technique for monitoring the steel-to-concrete bond integrity of reinforced concrete structures. A series of direct pull-out tests were performed on 54 reinforced concrete unconfined prism samples with variable rebar diameter (10, 20, and 35 mm), embedded length (50, 100, and 200 mm), and concrete cover (20, 30, and 40 mm). The samples were tested under incrementally increasing monotonic loading while being continuously monitored via attached acoustic emission sensors. These sensors were utilized to acquire different acoustic emission signal parameters emitted throughout the tests until failure. Also, an acoustic emission intensity analysis was implemented on acoustic emission signal strength data to quantify the damage resulting from loss of bond in all tested specimens. This analysis employed the signal strength of all recorded acoustic emission hits to develop two additional parameters: historic index ( H ( t)) and severity ( Sr). The results of bond behavior, mode of failure, and free end slip were compared with the recorded acoustic emission data. The results showed that the cumulative number of hits, cumulative signal strength, H ( t), and Sr had a good correlation with different stages of bond damage from de-bonding/micro-cracking until bond splitting failure and bar slippage, which caused cover cracking or delamination. The analysis of cumulative signal strength and H ( t) curves enabled early identification of two progressive stages of bond degradation (micro-cracking and macro-cracking) and recognized the various modes of failure of the tested specimens. The variations of bar diameter, concrete cover, and embedded length yielded significant impacts on both the bond behavior and acoustic emission activities. The results also presented developed intensity classification charts, based on H ( t) and Sr, to assess the bond integrity and to quantify the bond deterioration (micro-cracking, macro-cracking, and rebar slip) in reinforced concrete structures.

The Use of Acoustic Emission Intensity Analysis for the Assessment of Cover Crack Growth in Corroded Concrete Structures

In this paper, acoustic emission (AE) intensity analysis was utilized to assess the concrete cover cracking due to steel corrosion in reinforced concrete structures. A total of 30 reinforced concrete prism samples were tested under an accelerated corrosion test coupled with continuous AE monitoring using attached AE sensors. The samples were cast with three concrete cover thicknesses (20, 30 and 40 mm) around steel bars and were exposed to five percentages of steel mass loss: 1, 2, 3, 4, and 5 %. The cover cracking was monitored daily by visual inspection to detect and measure crack widths. Different AE signal parameters were continuously recorded during the tests, including number of hits, signal strength, energy, and amplitude. The acquired AE events were subjected to an intensity analysis of signal strength to estimate historic index (H (t)) and severity (\(S_r)\). In addition, a b value analysis was conducted on all AE data and the results were compared to those obtained from the intensity analysis. The results showed that increasing the cover thickness had no significant impact on AE parameters (number of hits, cumulative signal strength, cumulative energy, amplitude, H (t), and \(S_{r})\) at similar values of crack growth. Nonetheless, varying the cover thickness from 20 to 40 mm resulted in lower crack widths and slightly higher b values at the same levels of steel mass loss. It was also found that both H (t) and \(S_r\) showed a more evident correlation with the values of crack growth than did b values, regardless of cover thickness or percentage of steel mass loss. Finally, an intensity classification chart was developed to quantify the cover crack growth based on the values of H (t) and \(S_{r}\).

Detection of bond failure in the anchorage zone of reinforced concrete beams via acoustic emission monitoring

In this study, acoustic emission (AE) monitoring was utilised to identify the onset of bond failure in reinforced concrete beams. Beam anchorage specimens were designed and tested to fail in bond in the anchorage zone. The specimens included four 250 × 250 × 1500 mm beams with four variable bonded lengths (100, 200, 300, and 400 mm). Meanwhile, an additional 250 × 250 × 2440 mm beam, with 200 mm bonded length, was tested to investigate the influence of sensor location on the identification of bond damage. All beams were tested under four-point loading setup and continuously monitored using three distributed AE sensors. These attached sensors were exploited to record AE signals resulting from both cracking and bond deterioration until failure. The variations in the number of AE hits and cumulative signal strength (CSS) versus test time were evaluated to achieve early detection of crack growth and bar slippage. In addition, AE intensity analysis was performed on signal strength of collected AE signals to develop two additional parameters: historic index (H (t)) and severity (Sr). The analysis of these AE parameters enabled an early detection of both first cracks (at almost the mid-span of the beam) and bar slip in either of the anchorage zones at the beams’ end before their visual observation, regardless of sensor location. The results also demonstrated a clear correlation between the damage level in terms of crack development/measured free end bar slip and AE parameters (number of hits, CSS, H(t), and Sr).

Assessment of concrete-to-steel bond behaviour of reinforced concrete structures using acoustic emission intensity analysis

Abstract. An experimental study was performed to utilize acoustic emission (AE) intensity analysis for the assessment of the concrete-to-steel bond behaviour of reinforced concrete structures. A total of 18 reinforced concrete unconfined prism samples were tested in a direct pullout test setup under incrementally increasing monotonic loading as being constantly monitored with attached AE sensors. The samples were cast using variable bar diameter (10, 20, 35 mm) and bar embedded length (50, 100, 200 mm). Different AE signals parameters were recorded throughout the tests until failure including rise time, counts, number of hits, signal strength, energy, amplitude, duration, and frequency values. Moreover, an AE intensity analysis was applied on AE signal strength results to produce two additional AE parameters: historic index (H (t)) and severity (Sr). Results demonstrated that cumulative signal strength (CSS) correlated well with different degrees of loss of bond from micro-cracking till bond splitting failure, which resulted in cover cracking or delamination. The review of CSS, H (t), and Sr curves allowed the detection of two progressive stages of bond deterioration (micro-cracking and macro-cracking) in all tested specimens. Intensity analysis parameters (H (t) and Sr) were employed to create bond damage classification chart to evaluate the concrete-to-steel bond condition in reinforced concrete structures.

Acoustic emission monitoring of early corrosion in prestressed concrete piles

SUMMARY Prestressed concrete (PC) piles in marine environments are vulnerable to corrosion damage especially at their tidal zone because of the concurrent exposure of steel reinforcement to moisture, chlorides, and oxygen. Early detection of corrosion in prestressed strands is desirable to enable the effective planning and prioritizing of maintenance operations. This paper reports on experiments aimed at testing the hypothesis that acoustic emission (AE) monitoring is suitable to recognize and classify early corrosion damage in PC piles exposed to saltwater. In fact, AE is sensitive to the formation and growth of microcracks in both steel and concrete, which may develop upon depassivation of reinforcement and buildup of corrosion by-products. In addition, the influence of AE signals produced through flexural cracks in the concrete is of less concern for PC piles as such cracks are seldom produced under service loads. Five specimens representative of full-scale portions of PC piles were designed to accelerate corrosion and subjected for 1 year to wet/dry cycles in saltwater simulating tidal action. The specimens were monitored continuously with AE sensors. Benchmark electrochemical measurements were routinely performed to understand when depassivation of the steel strands occurred. Visual evidence of early corrosion was collected from strands removed from two decommissioned specimens. It is shown that AE intensity analysis is more effective than AE signal strength and cumulative signal strength analysis in recognizing corrosion damage. Intensity analysis-based criteria for the assessment of early corrosion damage are proposed, complementing previously developed criteria for more severe corrosion damage in steel strands. Copyright © 2014 John Wiley & Sons, Ltd. Received 22 May 2014; Revised 15 September 2014; Accepted 2 November 2014

Early Corrosion Detection in Prestressed Concrete Girders Using Acoustic Emission

AbstractLong-term corrosion tests were performed on prestressed T-girders measuring 4.98 m (16 ft, 4 in.). The test program was composed of four specimens, including one control. The specimens were subjected to wet/dry cycles using 3% NaCl solution to accelerate corrosion. Two of the specimens were precracked prior to conditioning to examine the effect of crack presence and/or width. The specimens were continuously monitored using acoustic emission (AE). Half-cell potential (HCP) measurements and linear polarization resistance (LPR) were performed daily to serve as a benchmark for corrosion detection. Acoustic emission can detect the onset of corrosion comparable in time to conventional electrochemical methods. Furthermore, AE intensity analysis has the ability to distinguish between different levels of corrosion. The specimens were load-tested to measure the residual capacity, which can give an indication of AE’s ability to detect corrosion damage before it affects the strength of prestressed structures.

Corrosion Damage Quantification of Prestressing Strands Using Acoustic Emission

AbstractSteel degradation due to corrosion in prestressed concrete bridges has been of major concern as it presents a threat to the integrity of structures adjacent to marine environments or where deicing salts are regularly used. To assess the potential for monitoring of the corrosion process, an accelerated corrosion testing program has been conducted. A series of specimens with dimensions 114×114×508 mm (4.5×4.5×20 in.) were subjected to constant potential application through the embedded steel strand while being continuously monitored with acoustic emission (AE). Depassivation of the strand was detected by monitoring the fluctuations in applied anodic current. Half-cell potential measurements assessed the probability of corrosion, and all results obtained were compared to acoustic emission data. The mass loss of the corroded strands was correlated to acoustic emission intensity analysis to quantify the degree of damage. Results show that acoustic emission is as sensitive as half-cell potential for d...