- Email: [email protected]
Identification of corrosion in a prestressed concrete pipe utilizing acoustic emission technique
Construction and Building Materials 242 (2020) 118053
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Identification of corrosion in a prestressed concrete pipe utilizing acoustic emission technique Reza Goldaran a,⇑, Ahmet Turer b, Mehdi Kouhdaragh c, Kezban Ozlutas a a
Civil Engineering Department, Faculty of Engineering, Girne American University, Girne, N. Cyprus Via Mersin 10, Turkey Civil Engineering Department, Faculty of Engineering, Middle East Technical University, Ankara, Turkey c Civil Engineering Department, Malekan Branch, Islamic Azad University, Malekan, Iran b
h i g h l i g h t s It is simplified to identify both active and passive damages caused by corrosion. Misleading information caused be concrete water absorption could be recognized. Cathodic protection plate as a wave collector is a best place for bonding sensors. The strength and amplitude of AE signals are more in the dried reinforced concrete.
a r t i c l e
i n f o
Article history: Received 17 July 2019 Received in revised form 21 December 2019 Accepted 2 January 2020
Keywords: Acoustic emission Corrosion identification Prestressed concrete Accelerated corrosion Health monitoring
a b s t r a c t One of the significant imperfections of prestressed cylinder concrete pipe (PCCP) which leads to fatal failure is corrosion in spiral rebars. The use of PCCP is very widespread, but most often, their instantaneous failures are experienced. In this paper, acoustic emission (AE) technique was employed to detect corrosion in PCCP. To achieve this object three experimental specimens were made in the laboratory of Middle East Technical University. Each specimen was built for the specific aim in which the third one was the almost full-scale sample of PCCP. The pipe was loaded internally by water pressure and accelerated corrosion test was conducted on the specimens. For detecting the corrosion, especially for identifying the passive damages, water pressure was fluctuated during the experiment in both dry and wet conditions along with using the Kaiser Effect phenomenon in both conditions. It was observed that significant changes in some captured AE parameters occur as the pipe pressure exceeds the previous level by which the condition assessment is made feasible. Results indicated that the proposed technique is an efficient procedure for evaluating both active and passive damage types in PCCP. Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction Prestressed concrete has been extensively used in many structures such as bridges, concrete pipes, pressure vessels, dams, protective shells of nuclear reactors, rail traverses, and piles. The main purpose of using prestressed concrete is to improve the tensile strength of concrete which leads to tensile cracks minimization under service loads. High-strength steel used in prestressed concrete has a specific strength of nearly five times that of mild steel tendons. Many studies indicate that corrosion phenomenon is the reason for prestressed concrete pipes failure that takes place in a relatively short period of time after construction. Presence of cover concrete can increase the service life of concrete structures for ⇑ Corresponding author. E-mail address: [email protected] (R. Goldaran). https://doi.org/10.1016/j.conbuildmat.2020.118053 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.
more than 50 years [1]. Nevertheless, the corrosion of reinforcing steel bars, which occurs due to chloride attack and carbonation phenomena, can reduce the structural lifetime significantly [2]. The total length of 50-year-old prestressed concrete pipes in North America, which have been used for drinking water conveyance and sewage transmission, exceeds 35,000 km [3]. Also, about 4000 m of prestressed concrete pipes (PCCP) with 4 m of internal diameter have been used in the Great Man-Made River (GMMR) project in Libya in order to transmit water from the Sahara Desert to coastal areas [4]. In addition, these kinds of pipes have been widely used to transmit water from the north of China to the south recently [5]. Although many factors cause failure in prestressed pipes, main failure reasons for prestressed concrete pipes can be classified into corrosion, hydrogen embrittlement and high internal and external pressure [6,7]. Similarly, Prestressed reinforced concrete pipelines with 2000 mm diameter and 110-kilometer-length were used in
2
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
one of the drinking waters pipelines in Iran. However, corrosion led to major cracks and catastrophic damage in these pipes in a short period time of service. Therefore, because of these structures’ importance, the adverse consequences of failures and also economic considerations, health monitoring of these structures is inevitable especially in cases where the pipes are buried underground. The aim of this paper is to find a way of detecting corrosion at early stage as well as identifying the passive corrosion and cracks. In this study, an experimental specimen of a prestressed pipe was made as close as to real scale in accordance with the technical specification for PCCP manufacturing used in Iran by the Regional Water Company of East-Azerbaijan. Damage detection was performed on the specimen under accelerated corrosion conditions during internal loading–unloading processes. All generated signals were recorded by the acoustic emission (AE) technique over the time and various AE parameters were analyzed. Kaiser effect has been assessed at both dry and wet condition of pipe for detecting any type of damages. This technique is being spread in various industries to identify damage in different types of structures, especially in composites. Since the AE signals are generated by materials due to their damage and defeat, the most important advantage of the system can be defined as real-time detection and monitoring which is possible to be done online.
well as fracture failure process of asphalt mixtures [21,22]. Damage of reinforced concrete due to bars corrosion was evaluated using this method in 2017 [23] and it used for monitoring and classification of signals in cement composites during early-age hydration [24]. The AE method is also used to monitor crack growth caused by corrosion in reinforced concrete structures [25] and for damage monitoring of masonry structures [26]. The reliability of this technique for monitoring of PCCPs has been proved [27,28]. Attempts were made to localize and characterize acoustic emission sources just using a single sensor in plate-like structures [29,30]. Along with the AE method, Kaiser effect phenomenon was also used in this study. The Kaiser effect was proposed by Joseph Kaiser in 1953 in a metal tensile test [31]. As shown in Fig. 1, when a substance is placed under mild cyclic loading, the AE signals are not significant unless the stress exceeds previously applied maximum stress (point B). From point A to B, the AE signals are released continuously, but after unloading up to point C and reloading until point B, no signal can be observed unless it exceeds point B. This phenomenon is called irreversibility and is known as the Kaiser effect. As long as the loading continues, the AE signals are emitted. When the loading cycles reach higher stress in point D, the material enters an unstable phase in which the previous microcircuits expand significantly and serious damage occurs. AE signals can be seen even before reaching point D, which means that the Kaiser effect at the higher stress level tends to decrease [32].
2. Non-destructive testing (NDT) in identification of corrosion Recently, several methods have been used in corrosion evaluation of reinforced concrete structures, which can be classified into six distinct categories: visual inspection (VI), electrochemical methods, electromagnetic methods (EM), optical sensing methods, infrared thermography (IRT) and elastic waves methods. In the elastic waves methods category, there are three major techniques; Ultrasonic Pulse Velocity (UPV), Impact Echo (IE) and Acoustic Emission (AE) which are used for corrosion monitoring in RC structures [8]. In this study, AE technique is employed. The AE method refers to the released elastic energy from materials under deformation or generated transient elastic wave by the rapid release of energy from certain sources in a material [9]. 2.1. Kaiser effect and the AE data analysis method For the analysis of AE data there are two different forms of analysis, (i) the classical and qualitative or the AE parameter-based analysis, and (ii) a quantitative or the signal-based analysis [8]. The parameter-based analysis is useful for better source characteristic of AE [8]. In this study, a parameter-based analysis has been used. The first application of the AE method in corrosion monitoring was proposed by Devon in 1984, it was indicated that AE is corrosion sensitive and a suitable monitoring method for concrete structures [10]. Indeed, the main AE application for concrete began in late 70s in which AE was used in metals and then it was developed for heterogeneous materials by applying some changes [11]. The most important factors causing damage in prestressed pipes reinforcement are pitting corrosion [12], stress corrosion cracking [13], and hydrogen embrittlement [14]. The sensitivity and capability of the acoustic emission method in various kinds of corrosion, such as stress corrosion cracking [15], cavitation corrosion [16], crevice corrosion [17], and uniform acidic corrosion [18] have been proved. This method has been used to identify the cracks caused by stress corrosion in hollow and stainless-steel sections [19] and industrial structures during operation and maintenance [20]. Acoustic emission technique was employed for characterization of damage in concrete beams under bending as
3. Experimental study Three specimens were made for implementing specific tests, which are described separately in the following sections. The first and second tests conducted as a preliminary experiment in which the first one implemented for evaluating the attenuation caused by the connection between rebars and plate as well as the effect of distance between sources and sensor on attenuation, and assessment of the feasibility of installing the sensor on the plate. The second one carried out for identifying the signals due to the water absorption of concrete along with finding a way for filtering corresponding signals. The last one was the core experiment of the present study. The prestressed concrete pipes that are produced in Iran, as shown in Fig. 2, are made up of a concrete core with 28day cylinder compressive strength of 50 MPa, high-tensile spiral bars with 7 mm diameter and ultimate strength of 1670 MPa,
Fig. 1. Kaiser effect [32].
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
3
Fig. 2. Manufactured prestressed pipe.
and mortar coating sections. High length of spiral bars, about 3000 m, can cause a current attenuation in cathodic protection which can be overcome by installing a metal plate below the bars as shown in Fig. 2. In this study, a Physical Acoustic Corporation (PAC) system including a USB-AE Node, type 1283, with 4 channels, AEwin software package and piezoelectric sensors, PK-15I, with a resonant frequency of 150 kHz was employed to capture and record the AE signals. The AE sensor is of paramount importance for improving the performance of AE testing. Its effect on reliability and accuracy of test result is considerable, so calibration of sensitivity of AE sensors in frequency domain is essential to prevent misleading evaluations. To this end, before commencing experiments all sensors have been calibrated by MISTRAS Group as well as providing a printout results of the calibration response curve.
Fig. 3. A scheme of the experimental specimen for attenuation evaluation.
3.1. Feasibility of sensor installation on the cathodic protection plate The attenuation in the metal is much less than concrete [33]. On the other hand, due to the higher length of the spiral bars in the real pipes, a large number of piezoelectric transducers is required to be installed which is not economical. Therefore, a cathodic protection plate was used as an ultrasonic waves’ collector. However, due to the discontinuity between the bars and metal plate connection, a part of waves passes through and a part of them would return which cause wave amplitudes to drop and attenuate. To evaluate the attenuation value, a specimen was used as illustrated in Fig. 3. The experimental and prototype specimens are shown in Figs. 3 and 4, respectively. The experimental specimen was made up of a bar and a metal plate, which were tightened with metal fasteners using rubber strip between fastener and other members. The cathodic protection metal plate and prestressed spiral bar in the main pipe shown in Fig. 2. Represented by the metal plate and bar respectively, in this specimen. In this study, the attenuation was evaluated by using the Hsu-Nielsen source considering two S1 and S2 sensors which were mounted on the metal plate. Pencil Lead Break (PLB) test was performed at 8 distinct points of which 4 of them were on the bar (m1, m2, m3, and m4) and the rest (n1, n2, n3 and n4) were on the plate. The first set of AE sources were assumed on the bar for obtaining the attenuation caused by discontinuity between bars and cathodic protection plate, as waves travel from sources on the bar towards the platebonded sensors. Further set of AE sources on metal plate are for comprising of the AE hits amplitude of both sets of AE sources and determination of the attenuation due to the discontinuity. If the magnitude of amplitude drops (attenuation) is remarkable, plate-bonded sensors would not be able to detect and record the
Fig. 4. Experimental specimen for attenuation evaluation.
AE hits due to any damage on the bars. A scheme of the experiment is shown in Fig. 3. The recorded amplitudes are listed in Table 1. 3.2. Identification of the signals for water absorption of concrete Concrete is a porous material which can absorb water. A new specimen was built for identifying signals caused by water absorption shown in Fig. 5. In the new specimen, one end of the existing bar was covered by cube shaped concrete. The cathodic protection metal plates, prestressed spiral bars and cover concrete in the main pipes represented by the metal plate, bar and concrete, respectively, in this specimen. The dry concrete specimen was placed inside a water container for saturation. Two sensors, S1 and S2 were bonded on the metal plate and concrete, respectively, as shown in Fig. 5. Sensors settings were chosen differently depending on the installed materials so that the AE parameters settings are listed in Table 2. For both sensors, the threshold level, gain,
4
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
Table 1 Recorded amplitude in PLB test. Points number
n1
n2
n3
n4
m1
m2
m3
m4
Recorded amplitude by S2 sensor (dB)
76
75
75
77
66
64
65
65
Fig. 5. (a) A scheme of experimental specimen and (b) Experimental specimen; for signals detection due to water absorption of concrete.
Table 2 AE parameter setting.
1 2 3 4
Sensor
Sampling Rate (MSPS1)
HLTs2 (m)
HDTs3 (m)
PDTs4 (m)
S1 S2
5 5
2 2
800 100
400 50
Mega Sample Per Second. Hit Lockout Time. Hit Definition Time. Peak Definition Time.
hit length, and the band-pass filter was set to 23 dB, 40 dB, 1 k, and 20 kHz to 1 MHz, respectively. Both cumulative distribution of generated hits and the amplitude of them during water absorption are illustrated in Fig. 6 for sensor S1. It is observed that water absorption of concrete generates acoustic signals that are similar to the signals caused by blasting of hydrogen bubbles during corrosion.
Since this process can lead to significant errors in results, these signals must be identified and eliminated. The test result for sensor S2 indicates that by setting threshold magnitude, no signal was recorded. As a result, it is simply possible to filter unnecessary signals generated by the concrete water absorption just by setting the threshold line value.
Fig. 6. Amplitude distribution and Accumulated AE hits during water absorption of concrete.
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
3.3. Identification of corrosion in prestressed concrete pipe A specimen as detailed in Fig. 7 was built in the laboratory based on the instructions of the piping manufacturer of the East Azerbaijan Regional Water Company. Instead of an inner reinforced concrete core, a precast non-reinforced concrete pipe was employed. The inner and outer diameter of the concrete core was 300 mm and 420 mm, respectively. High tensile bars with 5 mm diameter and ultimate strength of 1670 MPa were posttensioned around the pipe with a tensile stress of 500 MPa. Finally, a mortar coating with 28-day cylinder compressive strength of 45 MPa and dimensions of 360 440 30 mm was concreted on the pipe as a cover concrete. According to Fig. 7, a container was conducted on the cover concrete to place the electrolyte and apply corrosion. Two sides of the pipe were closed with two metal plates, one of which had an air valve and the other end including a pump for applying the internal water pressure. Two AE sensors (S3 and S4) were mounted on the concrete and two sensors (S1 and S2) were bonded on the metal plate that acts as a cathodic protection plate in the main pipes. In the present study, among different means of coupling and various methods of fixing sensors to the structure, the glue has been used as coupling. Using glue allows the sensor to be in stationary state in addition to operating as a coupling. Thus, 4 AE sensors were glued to the surface of the specimen. FAL-5-11 strain gauges were installed on the bars to control both stress and strain as shown in Fig. 8. In this experiment, the accelerated corrosion technique was conducted. The conducted pool on cover concrete is filled with the 4% NaCl solution, as the electrolyte. A 340 300 3 mm metal plate was located on the concrete surface to act as a cathode. The 12-volt power supply was used and its negative and positive poles were connected to the metal plate (cathode) and circular bars, respectively. A current with a density of 2000 lA/cm2 was charged between the anode and the cathode. Fig. 9 shows the experimental specimens.
Fig. 8. Strain gauge used during the test.
4. Discussion of results The results of the first test, as listed in Table 1, indicate that the attenuation of the AE waves caused by the discontinuity at the connection between the spiral bars and the cathodic protection plate is about 10 dB, which is not a significant attenuation for receiving the corrosion signal. Therefore, the cathodic protection plate can be considered as the location of bonding piezoelectric sensors which are of great importance due to the capability of the plate in receiving the damage signals at any point of the entire length and cross
Fig. 9. Prestressed pipe made in the laboratory.
Fig. 7. Schematic overview of experimental set up.
5
6
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
hits during the test. For evaluating the effect of pressure increment before the commencement of applying accelerated corrosion, cyclic pressure loading–unloading process up to 9 bars was carried out between 500 and 700 s. As shown in Fig. 10, graph slope is approximately constant over the entire time interval between 0 and 900 s, which indicates that no additional signal occurs by pressure increment between 500 and 700 s. On the other hand, in Fig. 11, the distribution of points over time is almost uniform which represents that the magnitude of amplitude and absolute energy are not fluctuated due to applying pressure load and unloading.
section of the pipe. According to Fig. 6, the results of the second experiment show that water absorption of concrete generates ultrasonic signals. On the other hand, due to the blasting of hydrogen bubbles which occurs during corrosion process, separation of their AE waves from each other is an issue of great complexity. In this study, pipe internal water pressure decrement and increment method were used for passive corrosion detection. The third experiment was performed to identify corrosion and damage in the main pipe. The changes in the pipe internal pressure were made in essential steps: the first stage (before the corrosion), the second stage (during the corrosion with the saturated cover concrete (filled pool), and the third stage (dried concrete). The AE parameters settings for the pipe installed sensors are listed in Table 3. Also, for sensors S1 and S2, the threshold level was set to 23 dB, while it was 33 dB for sensors S3 and S4. The gain and the hit length were chosen as 40 dB and 1 k respectively and the band-pass filter (20 kHz to 1 MHz) was used. At the beginning of the experiment, the Kaiser effect was employed to eliminate the construction related signals and the signals that were not caused by the pipe damage. For this purpose, the inside pressure of the pipe increased gradually up to 9 bar and then reduced to zero. As the pipe experienced a 9 bars pressure in leakage test for a while and all additional signals not related to damage and corrosion had been omitted, AE hits were not observed at this stage.
4.2. Phase II For the second phase, accelerated corrosion was applied for a week, then the inside pressure of the pipe was increased in 4 steps. For this purpose, the water pressure was increased to 2, 4, 6, and 8 bars respectively as shown in Fig. 12. The distribution of magnitude of amplitude and absolute energy, corresponding to above mentioned 4 steps of loading–unloading during corrosion are illustrated in Fig. 13. When the pressure was increased from zero to 2 bars, zone 1 in Fig. 13 formed a peak which indicates that the pressure increment produces both amplitude and absolute energy increments. In the next step, the pressure was reduced to zero and increased from zero to 4 bars. It was observed that no additional signal was generated up to 2 bars. According to Fig. 13, after exceeding 2 bars a peak in the amplitude and absolute energy were formed in zone 2. The same process was repeated by reducing the pressure to zero and increasing to 6 bars. The process was also repeated for 8 bars pressure. The same peaks in the amplitude and absolute energy were observed in zones 3 and 4 as the load exceeded 4 and 6 bars. During the water pressure loading–unloading in the mentioned four phases, Kaiser effect was observed in all cycles of loading as shown in Fig. 12. Significant changes in the magnitude of energy
4.1. Phase I For this phase, after 3 days of experiment that starts with filling up the container with electrolyte and not connecting the power supply, the inside pressure of the pipe was increased up to 9 bars and reduced to zero. The signals generated due to the electrolyte absorption of concrete were captured for 3 days that 900 s of which is plotted in Fig. 10. The mentioned figure represents the number of AE hits and the cumulative of them, and Fig. 11 shows distribution of the magnitude of both amplitude and absolute energy of AE
Table 3 AE parameter setting. Sensor
Sampling rate (MSPS)
HLTs (m)
HDTs (m)
PDTs (m)
S1 S2 S3 S4
5 5 5 5
2 2 2 2
800 800 100 100
400 400 50 50
Fig. 10. Accumulated AE hits caused by electrolyte absorption of concrete during the test before corrosion.
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
7
Fig. 11. Distribution of AE amplitude and ABS energy during the test before corrosion.
and the amplitude of hits as well as whose numbers can be seen as the load in pipe increased to a level more than experienced before.
10000 9000
Cumulative AE hits
8000 7000
4.3. Phase III
6000 5000 4000 3000 2000 1000 0
0
1
2
3
4
5
6
7
8
Internal water pressure (Bar) Fig. 12. Cumulative AE hits generated during 4-step cyclic water pressure loading.
In the third phases, the current was charged for another 4 days, and then the electrolyte pool got completely empty and the saturated concrete was dried over a period of 4 days. After drying the concrete, the loading was performed based on the second phases. Consequently, it was found that the absolute energy of dry concrete increased significantly in comparison to saturated concrete. The absolute energy recorded in dry conditions versus time is presented in Fig. 14 as well as the corrosion of the spiral bars at the end of the test is illustrated in Fig. 15. The measurement indicates 25% of weight loss in the bars due to corrosion.
Fig. 13. Distribution of AE amplitude and ABS energy during corrosion along with internal pressure fluctuation.
8
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
Fig. 14. Distribution of AE energy during corrosion with internal pressure fluctuation.
Fig. 15. Corroded states of post-tensioned circular bars.
5. Conclusion The current paper presented a new method by using the Acoustic Emission ‘‘AE” technique for identification of damage in PreStressed Concrete Cylinder Pipelines ‘‘PCCP”. The results of this study are summarized as follows: Working pressure for 2000-mm-diameter PCCP in Iran is equal to 15 bars in which the elongation in spiral rebars have been measured 35 l-strain due to the internal pressure variation of 1 bar. In this experimental study, the bonded strain gauges on the bars showed about 25 l-strain elongation for internal pressure variation of 2 bar. It means that the elongation of the rebars in experimental sample is equal to the elongation of real pipe as its internal pressure variation is about 5% of the working pressure. Therefore, in prestressed concrete pipelines in corrosion conditions, signals with high energy and strength are generated by the pressure increment to about 5% of their working pressure. By using this method, it will be simplified to detect and identify damages caused by corrosion in PCCP.
The current measurement between the anode and the cathode during the corrosion process by the multimeter indicated that using 4% solution of NaCl, which was used as the electrolyte, is an optimal percentage. Higher values of more than 4% solution of NaCl do not make any significant effect on the corrosion process acceleration. It was also observed that due to the presence of pores in concrete, water absorption of the concrete pipe, can generate acoustic signals. The signals caused by water absorption of concrete have yet to be investigated in studies related to rebars corrosion in reinforced concrete structures. Since hydrogen bubbles blast are a part of the corrosion process, the separation of corrosion and the water absorption signals is a complicated problem because of their similarity in AE source nature, which is of great importance to be considered in the interpretation of the results. Applying the Kaiser effect phenomenon, it was observed that increasing load to the previously loaded stage generates no signals; on the contrary, load increment to a higher level can generate AE waves that indicate presence of damage in the pipe. Hence, both active and passive damages could be simply identified. The strength and energy of the signals produced in the saturation and dry specimens were different as if the strength and amplitude of signals were more in the dry specimen. Due to long length of spiral bars in pipes the generated signals attenuate in their path and, consequently a large number of sensors are required for capturing AE waves. For this reason, in the present work, two sensors were mounted on the cathodic protection plate and the attenuation phenomenon was investigated. The results indicated that, the amplitude drop due to the discontinuity between the cathodic protection plate and spiral bar at their conjunction was about 10 dB. Therefore, it can result that by mounting only a piezoelectric sensor, the signals of damage can be received at any point on a whole pipe with optimal quality.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2020.118053.
References [1] L. Bertolini, B. Elsener, P. Pedeferri, E. Redaelli, R.B. Polder, Corrosion of Steel in Concrete: Prevention, Diagnosis, Repair, John Wiley & Sons, 2013. [2] K.Y. Ann, J.H. Ahn, J.S. Ryou, The importance of chloride content at the concrete surface in assessing the time to corrosion of steel in concrete structures, Constr. Build. Mater. 23 (2009) 239–245. [3] D.L. Atherton, K. Morton, B.J. Mergelas, Detecting breaks in prestressing pipe wire, Am. Water Work. Assoc. J. 92 (2000) 50. [4] H.A. Elfergani, R. Pullin, K.M. Holford, Damage assessment of corrosion in prestressed concrete by acoustic emission, Constr. Build. Mater. 40 (2013) 925–933, https://doi.org/10.1016/J.CONBUILDMAT.2012.11.071. [5] J. Huang, Z. Zhou, D. Zhang, Q. Wei, A fiber Bragg grating pressure sensor and its application to pipeline leakage detection, Adv. Mech. Eng. 5 (2013) 590451. [6] A. Alavinasab, Do Broken Prestressing Wire Wraps at the Joint Impact the Safe Operation of a Pipe?, (2014). [7] A. Alavinasab, E. Padewski, M. Higgins, Effects of the location of broken prestressing wires wraps in structural integrity of a damaged PCCP, ASCE Pipelines (2013). [8] A. Zaki, H.K. Chai, D.G. Aggelis, N. Alver, Non-destructive evaluation for corrosion monitoring in concrete: a review and capability of acoustic emission technique, Sensors 15 (2015) 19069–19101. [9] P.O. Moore, R.K. Miller, R.K. Hill, Nondestructive Testing Handbook, vol 6, American Society for Nondestructive Testing, Acoustic Emission Testing, 2005. [10] S.E. Dunn, J.D. Young, W.H. Hartt, R.P. Brown, Acoustic emission characterization of corrosion induced damage in reinforced concrete, Corrosion 40 (1984) 339–343. [11] C. Hellier, Handbook of nondestructive evaluation, (2001). [12] F. Li, Y. Yuan, C.-Q. Li, Corrosion propagation of prestressing steel strands in concrete subject to chloride attack, Constr. Build. Mater. 25 (2011) 3878–3885. [13] G.E. Monfore, G.J. Verbeck, Corrosion of prestressed wire in concrete, J. Proc. (1960) 491–516. [14] R.M. Schroeder, I.L. Müller, Stress corrosion cracking and hydrogen embrittlement susceptibility of an eutectoid steel employed in prestressed concrete, Corros. Sci. 45 (2003) 1969–1983. [15] L. Djeddi, R. Khelif, S. Benmedakhene, J. Favergeon, Reliability of acoustic emission as a technique to detect corrosion and stress corrosion cracking on prestressing steel strands, Int. J. Electrochem. Sci. 8 (2013) 8356–8370. [16] H. Mazille, R. Rothea, C. Tronel, An acoustic emission technique for monitoring pitting corrosion of austenitic stainless steels, Corros. Sci. 37 (1995) 1365– 1375. [17] Y.P. Kim, M. Fregonese, H. Mazille, D. Féron, G. Santarini, Ability of acoustic emission technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel, Ndt E Int. 36 (2003) 553–562. [18] L. Jaubert, M. Fregonese, D. Caron, F. Ferrer, C. Franck, E. Gravy, P. Labeeuw, H. Mazille, L. Renaud, On the opportunity to use non-intrusive acoustic emission recordings for monitoring uniform corrosion of carbon steel and austenitic
[19]
[20]
[21]
[22]
[23]
[24]
[25] [26]
[27]
[28]
[29]
[30]
[31]
[32] [33]
9
stainless steel in acid and neutral solutions, Insight-Non-Destructive Test. Cond. Monit. 47 (2005) 465–471. W. Hwang, S. Bae, J. Kim, S. Kang, N. Kwag, B. Lee, Acoustic emission characteristics of stress corrosion cracks in a type 304 stainless steel tube, Nucl. Eng. Technol. 47 (2015) 454–460. P. Tscheliesnig, A. Jagenbrein, G. Lackner, Detecting corrosion during inspection and maintenance of industrial structures using acoustic emission, (n.d.). X. Qiu, J. Xu, S. Xiao, Q. Yang, Acoustic emission parameters and waveforms characteristics of fracture failure process of asphalt mixtures, Constr. Build. Mater. 215 (2019) 135–147, https://doi.org/10.1016/J. CONBUILDMAT.2019.04.150. T. Nguyen-Tat, N. Ranaivomanana, J.-P. Balayssac, Characterization of damage in concrete beams under bending with Acoustic Emission Technique (AET), Constr. Build. Mater. 187 (2018) 487–500, https://doi.org/10.1016/J. CONBUILDMAT.2018.07.217. W. Li, C. Xu, S. Ho, B. Wang, G. Song, W. Li, C. Xu, S.C.M. Ho, B. Wang, G. Song, Monitoring concrete deterioration due to reinforcement corrosion by integrating acoustic emission and FBG strain measurements, Sensors 17 (2017) 657, https://doi.org/10.3390/s17030657. A. Thirumalaiselvi, S. Sasmal, Acoustic emission monitoring and classification of signals in cement composites during early-age hydration, Constr. Build. Mater. 196 (2019) 411–427, https://doi.org/10.1016/J. CONBUILDMAT.2018.11.067. A.A. Abouhussien, A.A.A. Hassan, STR-844: cover crack growth monitoring in RC structures subjected to corrosion with acoustic emission sensors, (2016). Y. Wu, S. Li, D. Wang, G. Zhao, Damage monitoring of masonry structure under in-situ uniaxial compression test using acoustic emission parameters, Constr. Build. Mater. 215 (2019) 812–822, https://doi.org/10.1016/J. CONBUILDMAT.2019.04.192. M. Aminfar, A.T.-M.M. Engineering, undefined 2017, Experimental study on corrosion detection of prestressed pipe using Acoustic Emission method, Jast. Modares.Ac.Ir. (n.d.). http://jast.modares.ac.ir/article-15-7967-en.html (accessed December 21, 2019). R. Goldaran, M.A. Lofollahi-Yaghin, M.H. Aminfar, A. Turer, undefined 2017, Investigation of attenuation and acoustic wave propagation path caused by corrosion for reliability assessment of pre-stressed pipe monitoring using Acoustic Emission technique, Modares Mechanical Engineering (n.d.). http:// msa.modares.ac.ir/article-15-7523-en.pdf (accessed December 21, 2019). A. Ebrahimkhanlou, S. Salamone, A. Ebrahimkhanlou, S. Salamone, Singlesensor acoustic emission source localization in plate-like structures using deep learning, Aerospace 5 (2018) 50, https://doi.org/10.3390/aerospace5020050. A. Ebrahimkhanlou, B. Dubuc, S. Salamone, A deep learning-based framework for two-step localization and characterization of acoustic emission sources in metallic panels using only one sensor, in: P. Fromme, Z. Su (Eds.), Heal. Monit. Struct. Biol. Syst. XIII, SPIE, 2019: p. 6. doi:10.1117/12.2514228. J. Kaiser, Erkenntnisse und Folgerungen aus der Messung von Geräuschen bei Zugbeanspruchung von metallischen Werkstoffen, Steel Res. Int. 24 (1953) 43–45. C.U. Grosse, M. Ohtsu, Acoustic Emission Testing, Springer Science & Business Media, 2008. M. Ohtsu, Acoustic emission characteristics in concrete and diagnostic applications. J. Acoustic Emission 6 (2) (Apr./Jun. 1987) 99–108. ScienceDirect, (n.d.). https://www.sciencedirect.com/science/article/pii/ 096386959190495O (accessed December 19, 2019).
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Identification of corrosion in a prestressed concrete pipe utilizing acoustic emission technique Reza Goldaran a,⇑, Ahmet Turer b, Mehdi Kouhdaragh c, Kezban Ozlutas a a
Civil Engineering Department, Faculty of Engineering, Girne American University, Girne, N. Cyprus Via Mersin 10, Turkey Civil Engineering Department, Faculty of Engineering, Middle East Technical University, Ankara, Turkey c Civil Engineering Department, Malekan Branch, Islamic Azad University, Malekan, Iran b
h i g h l i g h t s It is simplified to identify both active and passive damages caused by corrosion. Misleading information caused be concrete water absorption could be recognized. Cathodic protection plate as a wave collector is a best place for bonding sensors. The strength and amplitude of AE signals are more in the dried reinforced concrete.
a r t i c l e
i n f o
Article history: Received 17 July 2019 Received in revised form 21 December 2019 Accepted 2 January 2020
Keywords: Acoustic emission Corrosion identification Prestressed concrete Accelerated corrosion Health monitoring
a b s t r a c t One of the significant imperfections of prestressed cylinder concrete pipe (PCCP) which leads to fatal failure is corrosion in spiral rebars. The use of PCCP is very widespread, but most often, their instantaneous failures are experienced. In this paper, acoustic emission (AE) technique was employed to detect corrosion in PCCP. To achieve this object three experimental specimens were made in the laboratory of Middle East Technical University. Each specimen was built for the specific aim in which the third one was the almost full-scale sample of PCCP. The pipe was loaded internally by water pressure and accelerated corrosion test was conducted on the specimens. For detecting the corrosion, especially for identifying the passive damages, water pressure was fluctuated during the experiment in both dry and wet conditions along with using the Kaiser Effect phenomenon in both conditions. It was observed that significant changes in some captured AE parameters occur as the pipe pressure exceeds the previous level by which the condition assessment is made feasible. Results indicated that the proposed technique is an efficient procedure for evaluating both active and passive damage types in PCCP. Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction Prestressed concrete has been extensively used in many structures such as bridges, concrete pipes, pressure vessels, dams, protective shells of nuclear reactors, rail traverses, and piles. The main purpose of using prestressed concrete is to improve the tensile strength of concrete which leads to tensile cracks minimization under service loads. High-strength steel used in prestressed concrete has a specific strength of nearly five times that of mild steel tendons. Many studies indicate that corrosion phenomenon is the reason for prestressed concrete pipes failure that takes place in a relatively short period of time after construction. Presence of cover concrete can increase the service life of concrete structures for ⇑ Corresponding author. E-mail address: [email protected] (R. Goldaran). https://doi.org/10.1016/j.conbuildmat.2020.118053 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.
more than 50 years [1]. Nevertheless, the corrosion of reinforcing steel bars, which occurs due to chloride attack and carbonation phenomena, can reduce the structural lifetime significantly [2]. The total length of 50-year-old prestressed concrete pipes in North America, which have been used for drinking water conveyance and sewage transmission, exceeds 35,000 km [3]. Also, about 4000 m of prestressed concrete pipes (PCCP) with 4 m of internal diameter have been used in the Great Man-Made River (GMMR) project in Libya in order to transmit water from the Sahara Desert to coastal areas [4]. In addition, these kinds of pipes have been widely used to transmit water from the north of China to the south recently [5]. Although many factors cause failure in prestressed pipes, main failure reasons for prestressed concrete pipes can be classified into corrosion, hydrogen embrittlement and high internal and external pressure [6,7]. Similarly, Prestressed reinforced concrete pipelines with 2000 mm diameter and 110-kilometer-length were used in
2
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
one of the drinking waters pipelines in Iran. However, corrosion led to major cracks and catastrophic damage in these pipes in a short period time of service. Therefore, because of these structures’ importance, the adverse consequences of failures and also economic considerations, health monitoring of these structures is inevitable especially in cases where the pipes are buried underground. The aim of this paper is to find a way of detecting corrosion at early stage as well as identifying the passive corrosion and cracks. In this study, an experimental specimen of a prestressed pipe was made as close as to real scale in accordance with the technical specification for PCCP manufacturing used in Iran by the Regional Water Company of East-Azerbaijan. Damage detection was performed on the specimen under accelerated corrosion conditions during internal loading–unloading processes. All generated signals were recorded by the acoustic emission (AE) technique over the time and various AE parameters were analyzed. Kaiser effect has been assessed at both dry and wet condition of pipe for detecting any type of damages. This technique is being spread in various industries to identify damage in different types of structures, especially in composites. Since the AE signals are generated by materials due to their damage and defeat, the most important advantage of the system can be defined as real-time detection and monitoring which is possible to be done online.
well as fracture failure process of asphalt mixtures [21,22]. Damage of reinforced concrete due to bars corrosion was evaluated using this method in 2017 [23] and it used for monitoring and classification of signals in cement composites during early-age hydration [24]. The AE method is also used to monitor crack growth caused by corrosion in reinforced concrete structures [25] and for damage monitoring of masonry structures [26]. The reliability of this technique for monitoring of PCCPs has been proved [27,28]. Attempts were made to localize and characterize acoustic emission sources just using a single sensor in plate-like structures [29,30]. Along with the AE method, Kaiser effect phenomenon was also used in this study. The Kaiser effect was proposed by Joseph Kaiser in 1953 in a metal tensile test [31]. As shown in Fig. 1, when a substance is placed under mild cyclic loading, the AE signals are not significant unless the stress exceeds previously applied maximum stress (point B). From point A to B, the AE signals are released continuously, but after unloading up to point C and reloading until point B, no signal can be observed unless it exceeds point B. This phenomenon is called irreversibility and is known as the Kaiser effect. As long as the loading continues, the AE signals are emitted. When the loading cycles reach higher stress in point D, the material enters an unstable phase in which the previous microcircuits expand significantly and serious damage occurs. AE signals can be seen even before reaching point D, which means that the Kaiser effect at the higher stress level tends to decrease [32].
2. Non-destructive testing (NDT) in identification of corrosion Recently, several methods have been used in corrosion evaluation of reinforced concrete structures, which can be classified into six distinct categories: visual inspection (VI), electrochemical methods, electromagnetic methods (EM), optical sensing methods, infrared thermography (IRT) and elastic waves methods. In the elastic waves methods category, there are three major techniques; Ultrasonic Pulse Velocity (UPV), Impact Echo (IE) and Acoustic Emission (AE) which are used for corrosion monitoring in RC structures [8]. In this study, AE technique is employed. The AE method refers to the released elastic energy from materials under deformation or generated transient elastic wave by the rapid release of energy from certain sources in a material [9]. 2.1. Kaiser effect and the AE data analysis method For the analysis of AE data there are two different forms of analysis, (i) the classical and qualitative or the AE parameter-based analysis, and (ii) a quantitative or the signal-based analysis [8]. The parameter-based analysis is useful for better source characteristic of AE [8]. In this study, a parameter-based analysis has been used. The first application of the AE method in corrosion monitoring was proposed by Devon in 1984, it was indicated that AE is corrosion sensitive and a suitable monitoring method for concrete structures [10]. Indeed, the main AE application for concrete began in late 70s in which AE was used in metals and then it was developed for heterogeneous materials by applying some changes [11]. The most important factors causing damage in prestressed pipes reinforcement are pitting corrosion [12], stress corrosion cracking [13], and hydrogen embrittlement [14]. The sensitivity and capability of the acoustic emission method in various kinds of corrosion, such as stress corrosion cracking [15], cavitation corrosion [16], crevice corrosion [17], and uniform acidic corrosion [18] have been proved. This method has been used to identify the cracks caused by stress corrosion in hollow and stainless-steel sections [19] and industrial structures during operation and maintenance [20]. Acoustic emission technique was employed for characterization of damage in concrete beams under bending as
3. Experimental study Three specimens were made for implementing specific tests, which are described separately in the following sections. The first and second tests conducted as a preliminary experiment in which the first one implemented for evaluating the attenuation caused by the connection between rebars and plate as well as the effect of distance between sources and sensor on attenuation, and assessment of the feasibility of installing the sensor on the plate. The second one carried out for identifying the signals due to the water absorption of concrete along with finding a way for filtering corresponding signals. The last one was the core experiment of the present study. The prestressed concrete pipes that are produced in Iran, as shown in Fig. 2, are made up of a concrete core with 28day cylinder compressive strength of 50 MPa, high-tensile spiral bars with 7 mm diameter and ultimate strength of 1670 MPa,
Fig. 1. Kaiser effect [32].
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
3
Fig. 2. Manufactured prestressed pipe.
and mortar coating sections. High length of spiral bars, about 3000 m, can cause a current attenuation in cathodic protection which can be overcome by installing a metal plate below the bars as shown in Fig. 2. In this study, a Physical Acoustic Corporation (PAC) system including a USB-AE Node, type 1283, with 4 channels, AEwin software package and piezoelectric sensors, PK-15I, with a resonant frequency of 150 kHz was employed to capture and record the AE signals. The AE sensor is of paramount importance for improving the performance of AE testing. Its effect on reliability and accuracy of test result is considerable, so calibration of sensitivity of AE sensors in frequency domain is essential to prevent misleading evaluations. To this end, before commencing experiments all sensors have been calibrated by MISTRAS Group as well as providing a printout results of the calibration response curve.
Fig. 3. A scheme of the experimental specimen for attenuation evaluation.
3.1. Feasibility of sensor installation on the cathodic protection plate The attenuation in the metal is much less than concrete [33]. On the other hand, due to the higher length of the spiral bars in the real pipes, a large number of piezoelectric transducers is required to be installed which is not economical. Therefore, a cathodic protection plate was used as an ultrasonic waves’ collector. However, due to the discontinuity between the bars and metal plate connection, a part of waves passes through and a part of them would return which cause wave amplitudes to drop and attenuate. To evaluate the attenuation value, a specimen was used as illustrated in Fig. 3. The experimental and prototype specimens are shown in Figs. 3 and 4, respectively. The experimental specimen was made up of a bar and a metal plate, which were tightened with metal fasteners using rubber strip between fastener and other members. The cathodic protection metal plate and prestressed spiral bar in the main pipe shown in Fig. 2. Represented by the metal plate and bar respectively, in this specimen. In this study, the attenuation was evaluated by using the Hsu-Nielsen source considering two S1 and S2 sensors which were mounted on the metal plate. Pencil Lead Break (PLB) test was performed at 8 distinct points of which 4 of them were on the bar (m1, m2, m3, and m4) and the rest (n1, n2, n3 and n4) were on the plate. The first set of AE sources were assumed on the bar for obtaining the attenuation caused by discontinuity between bars and cathodic protection plate, as waves travel from sources on the bar towards the platebonded sensors. Further set of AE sources on metal plate are for comprising of the AE hits amplitude of both sets of AE sources and determination of the attenuation due to the discontinuity. If the magnitude of amplitude drops (attenuation) is remarkable, plate-bonded sensors would not be able to detect and record the
Fig. 4. Experimental specimen for attenuation evaluation.
AE hits due to any damage on the bars. A scheme of the experiment is shown in Fig. 3. The recorded amplitudes are listed in Table 1. 3.2. Identification of the signals for water absorption of concrete Concrete is a porous material which can absorb water. A new specimen was built for identifying signals caused by water absorption shown in Fig. 5. In the new specimen, one end of the existing bar was covered by cube shaped concrete. The cathodic protection metal plates, prestressed spiral bars and cover concrete in the main pipes represented by the metal plate, bar and concrete, respectively, in this specimen. The dry concrete specimen was placed inside a water container for saturation. Two sensors, S1 and S2 were bonded on the metal plate and concrete, respectively, as shown in Fig. 5. Sensors settings were chosen differently depending on the installed materials so that the AE parameters settings are listed in Table 2. For both sensors, the threshold level, gain,
4
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
Table 1 Recorded amplitude in PLB test. Points number
n1
n2
n3
n4
m1
m2
m3
m4
Recorded amplitude by S2 sensor (dB)
76
75
75
77
66
64
65
65
Fig. 5. (a) A scheme of experimental specimen and (b) Experimental specimen; for signals detection due to water absorption of concrete.
Table 2 AE parameter setting.
1 2 3 4
Sensor
Sampling Rate (MSPS1)
HLTs2 (m)
HDTs3 (m)
PDTs4 (m)
S1 S2
5 5
2 2
800 100
400 50
Mega Sample Per Second. Hit Lockout Time. Hit Definition Time. Peak Definition Time.
hit length, and the band-pass filter was set to 23 dB, 40 dB, 1 k, and 20 kHz to 1 MHz, respectively. Both cumulative distribution of generated hits and the amplitude of them during water absorption are illustrated in Fig. 6 for sensor S1. It is observed that water absorption of concrete generates acoustic signals that are similar to the signals caused by blasting of hydrogen bubbles during corrosion.
Since this process can lead to significant errors in results, these signals must be identified and eliminated. The test result for sensor S2 indicates that by setting threshold magnitude, no signal was recorded. As a result, it is simply possible to filter unnecessary signals generated by the concrete water absorption just by setting the threshold line value.
Fig. 6. Amplitude distribution and Accumulated AE hits during water absorption of concrete.
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
3.3. Identification of corrosion in prestressed concrete pipe A specimen as detailed in Fig. 7 was built in the laboratory based on the instructions of the piping manufacturer of the East Azerbaijan Regional Water Company. Instead of an inner reinforced concrete core, a precast non-reinforced concrete pipe was employed. The inner and outer diameter of the concrete core was 300 mm and 420 mm, respectively. High tensile bars with 5 mm diameter and ultimate strength of 1670 MPa were posttensioned around the pipe with a tensile stress of 500 MPa. Finally, a mortar coating with 28-day cylinder compressive strength of 45 MPa and dimensions of 360 440 30 mm was concreted on the pipe as a cover concrete. According to Fig. 7, a container was conducted on the cover concrete to place the electrolyte and apply corrosion. Two sides of the pipe were closed with two metal plates, one of which had an air valve and the other end including a pump for applying the internal water pressure. Two AE sensors (S3 and S4) were mounted on the concrete and two sensors (S1 and S2) were bonded on the metal plate that acts as a cathodic protection plate in the main pipes. In the present study, among different means of coupling and various methods of fixing sensors to the structure, the glue has been used as coupling. Using glue allows the sensor to be in stationary state in addition to operating as a coupling. Thus, 4 AE sensors were glued to the surface of the specimen. FAL-5-11 strain gauges were installed on the bars to control both stress and strain as shown in Fig. 8. In this experiment, the accelerated corrosion technique was conducted. The conducted pool on cover concrete is filled with the 4% NaCl solution, as the electrolyte. A 340 300 3 mm metal plate was located on the concrete surface to act as a cathode. The 12-volt power supply was used and its negative and positive poles were connected to the metal plate (cathode) and circular bars, respectively. A current with a density of 2000 lA/cm2 was charged between the anode and the cathode. Fig. 9 shows the experimental specimens.
Fig. 8. Strain gauge used during the test.
4. Discussion of results The results of the first test, as listed in Table 1, indicate that the attenuation of the AE waves caused by the discontinuity at the connection between the spiral bars and the cathodic protection plate is about 10 dB, which is not a significant attenuation for receiving the corrosion signal. Therefore, the cathodic protection plate can be considered as the location of bonding piezoelectric sensors which are of great importance due to the capability of the plate in receiving the damage signals at any point of the entire length and cross
Fig. 9. Prestressed pipe made in the laboratory.
Fig. 7. Schematic overview of experimental set up.
5
6
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
hits during the test. For evaluating the effect of pressure increment before the commencement of applying accelerated corrosion, cyclic pressure loading–unloading process up to 9 bars was carried out between 500 and 700 s. As shown in Fig. 10, graph slope is approximately constant over the entire time interval between 0 and 900 s, which indicates that no additional signal occurs by pressure increment between 500 and 700 s. On the other hand, in Fig. 11, the distribution of points over time is almost uniform which represents that the magnitude of amplitude and absolute energy are not fluctuated due to applying pressure load and unloading.
section of the pipe. According to Fig. 6, the results of the second experiment show that water absorption of concrete generates ultrasonic signals. On the other hand, due to the blasting of hydrogen bubbles which occurs during corrosion process, separation of their AE waves from each other is an issue of great complexity. In this study, pipe internal water pressure decrement and increment method were used for passive corrosion detection. The third experiment was performed to identify corrosion and damage in the main pipe. The changes in the pipe internal pressure were made in essential steps: the first stage (before the corrosion), the second stage (during the corrosion with the saturated cover concrete (filled pool), and the third stage (dried concrete). The AE parameters settings for the pipe installed sensors are listed in Table 3. Also, for sensors S1 and S2, the threshold level was set to 23 dB, while it was 33 dB for sensors S3 and S4. The gain and the hit length were chosen as 40 dB and 1 k respectively and the band-pass filter (20 kHz to 1 MHz) was used. At the beginning of the experiment, the Kaiser effect was employed to eliminate the construction related signals and the signals that were not caused by the pipe damage. For this purpose, the inside pressure of the pipe increased gradually up to 9 bar and then reduced to zero. As the pipe experienced a 9 bars pressure in leakage test for a while and all additional signals not related to damage and corrosion had been omitted, AE hits were not observed at this stage.
4.2. Phase II For the second phase, accelerated corrosion was applied for a week, then the inside pressure of the pipe was increased in 4 steps. For this purpose, the water pressure was increased to 2, 4, 6, and 8 bars respectively as shown in Fig. 12. The distribution of magnitude of amplitude and absolute energy, corresponding to above mentioned 4 steps of loading–unloading during corrosion are illustrated in Fig. 13. When the pressure was increased from zero to 2 bars, zone 1 in Fig. 13 formed a peak which indicates that the pressure increment produces both amplitude and absolute energy increments. In the next step, the pressure was reduced to zero and increased from zero to 4 bars. It was observed that no additional signal was generated up to 2 bars. According to Fig. 13, after exceeding 2 bars a peak in the amplitude and absolute energy were formed in zone 2. The same process was repeated by reducing the pressure to zero and increasing to 6 bars. The process was also repeated for 8 bars pressure. The same peaks in the amplitude and absolute energy were observed in zones 3 and 4 as the load exceeded 4 and 6 bars. During the water pressure loading–unloading in the mentioned four phases, Kaiser effect was observed in all cycles of loading as shown in Fig. 12. Significant changes in the magnitude of energy
4.1. Phase I For this phase, after 3 days of experiment that starts with filling up the container with electrolyte and not connecting the power supply, the inside pressure of the pipe was increased up to 9 bars and reduced to zero. The signals generated due to the electrolyte absorption of concrete were captured for 3 days that 900 s of which is plotted in Fig. 10. The mentioned figure represents the number of AE hits and the cumulative of them, and Fig. 11 shows distribution of the magnitude of both amplitude and absolute energy of AE
Table 3 AE parameter setting. Sensor
Sampling rate (MSPS)
HLTs (m)
HDTs (m)
PDTs (m)
S1 S2 S3 S4
5 5 5 5
2 2 2 2
800 800 100 100
400 400 50 50
Fig. 10. Accumulated AE hits caused by electrolyte absorption of concrete during the test before corrosion.
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
7
Fig. 11. Distribution of AE amplitude and ABS energy during the test before corrosion.
and the amplitude of hits as well as whose numbers can be seen as the load in pipe increased to a level more than experienced before.
10000 9000
Cumulative AE hits
8000 7000
4.3. Phase III
6000 5000 4000 3000 2000 1000 0
0
1
2
3
4
5
6
7
8
Internal water pressure (Bar) Fig. 12. Cumulative AE hits generated during 4-step cyclic water pressure loading.
In the third phases, the current was charged for another 4 days, and then the electrolyte pool got completely empty and the saturated concrete was dried over a period of 4 days. After drying the concrete, the loading was performed based on the second phases. Consequently, it was found that the absolute energy of dry concrete increased significantly in comparison to saturated concrete. The absolute energy recorded in dry conditions versus time is presented in Fig. 14 as well as the corrosion of the spiral bars at the end of the test is illustrated in Fig. 15. The measurement indicates 25% of weight loss in the bars due to corrosion.
Fig. 13. Distribution of AE amplitude and ABS energy during corrosion along with internal pressure fluctuation.
8
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
Fig. 14. Distribution of AE energy during corrosion with internal pressure fluctuation.
Fig. 15. Corroded states of post-tensioned circular bars.
5. Conclusion The current paper presented a new method by using the Acoustic Emission ‘‘AE” technique for identification of damage in PreStressed Concrete Cylinder Pipelines ‘‘PCCP”. The results of this study are summarized as follows: Working pressure for 2000-mm-diameter PCCP in Iran is equal to 15 bars in which the elongation in spiral rebars have been measured 35 l-strain due to the internal pressure variation of 1 bar. In this experimental study, the bonded strain gauges on the bars showed about 25 l-strain elongation for internal pressure variation of 2 bar. It means that the elongation of the rebars in experimental sample is equal to the elongation of real pipe as its internal pressure variation is about 5% of the working pressure. Therefore, in prestressed concrete pipelines in corrosion conditions, signals with high energy and strength are generated by the pressure increment to about 5% of their working pressure. By using this method, it will be simplified to detect and identify damages caused by corrosion in PCCP.
The current measurement between the anode and the cathode during the corrosion process by the multimeter indicated that using 4% solution of NaCl, which was used as the electrolyte, is an optimal percentage. Higher values of more than 4% solution of NaCl do not make any significant effect on the corrosion process acceleration. It was also observed that due to the presence of pores in concrete, water absorption of the concrete pipe, can generate acoustic signals. The signals caused by water absorption of concrete have yet to be investigated in studies related to rebars corrosion in reinforced concrete structures. Since hydrogen bubbles blast are a part of the corrosion process, the separation of corrosion and the water absorption signals is a complicated problem because of their similarity in AE source nature, which is of great importance to be considered in the interpretation of the results. Applying the Kaiser effect phenomenon, it was observed that increasing load to the previously loaded stage generates no signals; on the contrary, load increment to a higher level can generate AE waves that indicate presence of damage in the pipe. Hence, both active and passive damages could be simply identified. The strength and energy of the signals produced in the saturation and dry specimens were different as if the strength and amplitude of signals were more in the dry specimen. Due to long length of spiral bars in pipes the generated signals attenuate in their path and, consequently a large number of sensors are required for capturing AE waves. For this reason, in the present work, two sensors were mounted on the cathodic protection plate and the attenuation phenomenon was investigated. The results indicated that, the amplitude drop due to the discontinuity between the cathodic protection plate and spiral bar at their conjunction was about 10 dB. Therefore, it can result that by mounting only a piezoelectric sensor, the signals of damage can be received at any point on a whole pipe with optimal quality.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
R. Goldaran et al. / Construction and Building Materials 242 (2020) 118053
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2020.118053.
References [1] L. Bertolini, B. Elsener, P. Pedeferri, E. Redaelli, R.B. Polder, Corrosion of Steel in Concrete: Prevention, Diagnosis, Repair, John Wiley & Sons, 2013. [2] K.Y. Ann, J.H. Ahn, J.S. Ryou, The importance of chloride content at the concrete surface in assessing the time to corrosion of steel in concrete structures, Constr. Build. Mater. 23 (2009) 239–245. [3] D.L. Atherton, K. Morton, B.J. Mergelas, Detecting breaks in prestressing pipe wire, Am. Water Work. Assoc. J. 92 (2000) 50. [4] H.A. Elfergani, R. Pullin, K.M. Holford, Damage assessment of corrosion in prestressed concrete by acoustic emission, Constr. Build. Mater. 40 (2013) 925–933, https://doi.org/10.1016/J.CONBUILDMAT.2012.11.071. [5] J. Huang, Z. Zhou, D. Zhang, Q. Wei, A fiber Bragg grating pressure sensor and its application to pipeline leakage detection, Adv. Mech. Eng. 5 (2013) 590451. [6] A. Alavinasab, Do Broken Prestressing Wire Wraps at the Joint Impact the Safe Operation of a Pipe?, (2014). [7] A. Alavinasab, E. Padewski, M. Higgins, Effects of the location of broken prestressing wires wraps in structural integrity of a damaged PCCP, ASCE Pipelines (2013). [8] A. Zaki, H.K. Chai, D.G. Aggelis, N. Alver, Non-destructive evaluation for corrosion monitoring in concrete: a review and capability of acoustic emission technique, Sensors 15 (2015) 19069–19101. [9] P.O. Moore, R.K. Miller, R.K. Hill, Nondestructive Testing Handbook, vol 6, American Society for Nondestructive Testing, Acoustic Emission Testing, 2005. [10] S.E. Dunn, J.D. Young, W.H. Hartt, R.P. Brown, Acoustic emission characterization of corrosion induced damage in reinforced concrete, Corrosion 40 (1984) 339–343. [11] C. Hellier, Handbook of nondestructive evaluation, (2001). [12] F. Li, Y. Yuan, C.-Q. Li, Corrosion propagation of prestressing steel strands in concrete subject to chloride attack, Constr. Build. Mater. 25 (2011) 3878–3885. [13] G.E. Monfore, G.J. Verbeck, Corrosion of prestressed wire in concrete, J. Proc. (1960) 491–516. [14] R.M. Schroeder, I.L. Müller, Stress corrosion cracking and hydrogen embrittlement susceptibility of an eutectoid steel employed in prestressed concrete, Corros. Sci. 45 (2003) 1969–1983. [15] L. Djeddi, R. Khelif, S. Benmedakhene, J. Favergeon, Reliability of acoustic emission as a technique to detect corrosion and stress corrosion cracking on prestressing steel strands, Int. J. Electrochem. Sci. 8 (2013) 8356–8370. [16] H. Mazille, R. Rothea, C. Tronel, An acoustic emission technique for monitoring pitting corrosion of austenitic stainless steels, Corros. Sci. 37 (1995) 1365– 1375. [17] Y.P. Kim, M. Fregonese, H. Mazille, D. Féron, G. Santarini, Ability of acoustic emission technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel, Ndt E Int. 36 (2003) 553–562. [18] L. Jaubert, M. Fregonese, D. Caron, F. Ferrer, C. Franck, E. Gravy, P. Labeeuw, H. Mazille, L. Renaud, On the opportunity to use non-intrusive acoustic emission recordings for monitoring uniform corrosion of carbon steel and austenitic
[19]
[20]
[21]
[22]
[23]
[24]
[25] [26]
[27]
[28]
[29]
[30]
[31]
[32] [33]
9
stainless steel in acid and neutral solutions, Insight-Non-Destructive Test. Cond. Monit. 47 (2005) 465–471. W. Hwang, S. Bae, J. Kim, S. Kang, N. Kwag, B. Lee, Acoustic emission characteristics of stress corrosion cracks in a type 304 stainless steel tube, Nucl. Eng. Technol. 47 (2015) 454–460. P. Tscheliesnig, A. Jagenbrein, G. Lackner, Detecting corrosion during inspection and maintenance of industrial structures using acoustic emission, (n.d.). X. Qiu, J. Xu, S. Xiao, Q. Yang, Acoustic emission parameters and waveforms characteristics of fracture failure process of asphalt mixtures, Constr. Build. Mater. 215 (2019) 135–147, https://doi.org/10.1016/J. CONBUILDMAT.2019.04.150. T. Nguyen-Tat, N. Ranaivomanana, J.-P. Balayssac, Characterization of damage in concrete beams under bending with Acoustic Emission Technique (AET), Constr. Build. Mater. 187 (2018) 487–500, https://doi.org/10.1016/J. CONBUILDMAT.2018.07.217. W. Li, C. Xu, S. Ho, B. Wang, G. Song, W. Li, C. Xu, S.C.M. Ho, B. Wang, G. Song, Monitoring concrete deterioration due to reinforcement corrosion by integrating acoustic emission and FBG strain measurements, Sensors 17 (2017) 657, https://doi.org/10.3390/s17030657. A. Thirumalaiselvi, S. Sasmal, Acoustic emission monitoring and classification of signals in cement composites during early-age hydration, Constr. Build. Mater. 196 (2019) 411–427, https://doi.org/10.1016/J. CONBUILDMAT.2018.11.067. A.A. Abouhussien, A.A.A. Hassan, STR-844: cover crack growth monitoring in RC structures subjected to corrosion with acoustic emission sensors, (2016). Y. Wu, S. Li, D. Wang, G. Zhao, Damage monitoring of masonry structure under in-situ uniaxial compression test using acoustic emission parameters, Constr. Build. Mater. 215 (2019) 812–822, https://doi.org/10.1016/J. CONBUILDMAT.2019.04.192. M. Aminfar, A.T.-M.M. Engineering, undefined 2017, Experimental study on corrosion detection of prestressed pipe using Acoustic Emission method, Jast. Modares.Ac.Ir. (n.d.). http://jast.modares.ac.ir/article-15-7967-en.html (accessed December 21, 2019). R. Goldaran, M.A. Lofollahi-Yaghin, M.H. Aminfar, A. Turer, undefined 2017, Investigation of attenuation and acoustic wave propagation path caused by corrosion for reliability assessment of pre-stressed pipe monitoring using Acoustic Emission technique, Modares Mechanical Engineering (n.d.). http:// msa.modares.ac.ir/article-15-7523-en.pdf (accessed December 21, 2019). A. Ebrahimkhanlou, S. Salamone, A. Ebrahimkhanlou, S. Salamone, Singlesensor acoustic emission source localization in plate-like structures using deep learning, Aerospace 5 (2018) 50, https://doi.org/10.3390/aerospace5020050. A. Ebrahimkhanlou, B. Dubuc, S. Salamone, A deep learning-based framework for two-step localization and characterization of acoustic emission sources in metallic panels using only one sensor, in: P. Fromme, Z. Su (Eds.), Heal. Monit. Struct. Biol. Syst. XIII, SPIE, 2019: p. 6. doi:10.1117/12.2514228. J. Kaiser, Erkenntnisse und Folgerungen aus der Messung von Geräuschen bei Zugbeanspruchung von metallischen Werkstoffen, Steel Res. Int. 24 (1953) 43–45. C.U. Grosse, M. Ohtsu, Acoustic Emission Testing, Springer Science & Business Media, 2008. M. Ohtsu, Acoustic emission characteristics in concrete and diagnostic applications. J. Acoustic Emission 6 (2) (Apr./Jun. 1987) 99–108. ScienceDirect, (n.d.). https://www.sciencedirect.com/science/article/pii/ 096386959190495O (accessed December 19, 2019).