CORROSION features ………………………………………………………………………… 12Figure 9: The typical AE signal

CORROSION STUDY OF CARBON STEEL EMBEDDED IN CONCRETEVIA ACOUSTIC EMISSION(P2 PROJECT REPORT)Company: SSA Acoustic & Specialised InspectionsReport Compiled By: Sigoba TshianeoStudent No: 209052945DeclarationThis is to certify that Work Integrated Learning Report entitled ‘P2_Corrosion Study of CarbonSteel Embedded in Concrete via Acoustic Emission’ which is submitted by Sigoba Tshianeoin final fulfilment of the requirement for the award of National Diploma in Non-Destructive Testing at Vaal University of Technology, the report comprises of only originalwork and due acknowledgement has been made in the text to all other material used.StudentName of Student : Sigoba TshianeoSignature : ____________________Student Number : 209052945Date : 24/01/2018SupervisorName : Malcolm HowseCompany : SSA Acoustic & Specialised Inspections (Pty) LtdPosition : API 653, 570 Tank & Pipeline InspectorSignature : __________________________Date : __________________________Table of ContentsChapter 1 …………………………………………………………………………………………………………………….. 62.3. Introduction ……………………………………………………………………………………………………. 6Chapter 2 …………………………………………………………………………………………………………………….. 62.1. Practical………………………………………………………………………………………………………. 62.1.1. Purpose ……………………………………………………………………………………………………. 62.1.2. Apparatus used …………………………………………………………………………………………. 62.1.3. Sample Preparation …………………………………………………………………………………… 82.1.4. The setup of AE system …………………………………………………………………………….. 92.1.5. Data acquisition device ……………………………………………………………………………. 112.1.6. The AE signal feature descriptions …………………………………………………………….. 112.1.7. The pencil lead break test setup and procedure……………………………………………. 132.1.8. Samples to be used ………………………………………………………………………………….. 152.1.9. Procedure ……………………………………………………………………………………………….. 152.1.10. Results and Discussions ……………………………………………………………………….. 16Chapter 3 …………………………………………………………………………………………………………………… 253.1. Conclusion ……………………………………………………………………………………………………. 253.2. References ……………………………………………………………………………………………………. 25List of FiguresFigure 1: Concrete Blocks ……………………………………………………………………………………………… 6Figure 2: Mild steel (20cm) ……………………………………………………………………………………………. 7Figure 3: Mild steel coated with spray mate paint …………………………………………………………….. 7Figure 4: Grading of the mild steel …………………………………………………………………………………. 8Figure 5: 30kHz AE Sensor …………………………………………………………………………………………. 10Figure 6: Pre-amplifier ………………………………………………………………………………………………… 10Figure 7: Data acquisition device ………………………………………………………………………………….. 11Figure 8: The typical AE signal features ………………………………………………………………………… 12Figure 9: The typical AE signal features (Grosse and Ohtsu 2008)……………………………………. 13Figure 10: pencil lead break (not research work) …………………………………………………………….. 14Figure 11: Samples ……………………………………………………………………………………………………… 15Figure 12: Test Activity Screen ……………………………………………………………………………………. 16Figure 13: Test peak frequency …………………………………………………………………………………….. 17Figure 14:Cumulative Data per Sample …………………………………………………………………………. 18Figure 15: Hits for Channel 1 ……………………………………………………………………………………….. 19Figure 16: Hits for Channel 2 ……………………………………………………………………………………….. 19Figure 17: Hits for Channel 3 ……………………………………………………………………………………….. 20Figure 18: Hits for Channel 4 ……………………………………………………………………………………….. 20Figure 19: Hits for Channel 4 ……………………………………………………………………………………….. 21Figure 20: Normalised Hits vs Time Graph ……………………………………………………………………. 22Figure 21: Total Energy vs Time Graph ………………………………………………………………………… 23Figure 22: Cumulative Data per Sample ………………………………………………………………………… 24AbbreviationsAE – Acoustic EmissionRebar – Reinforcement BarNDT – Non Destructive TestingChapter 12.3. IntroductionThis is a project about corrosion study and practical experiment of carbon steel metalsembedded in concrete via acoustic emission. I have specifically chosen rebar corrosion as it hasthe most severe deterioration in concrete structures i.e. Bridges due to vibrations caused byheavy vehicles, Acoustic emission method will be used to monitor corrosion in concretestructures.Chapter 22.1. Practical2.1.1. PurposeThe goal of this practical is to inspect for corrosion on concrete immersed in different liquidsusing acoustic Emission testing and to compare the rate of corrosion on metals embedded inconcrete.2.1.2. Apparatus used? Concrete – the below ratios of concrete was used:? Cement -1kg? Aggregate-3kg? Sand-3kg? Water-1100LFigure 1: Concrete Blocks? Mild SteelFigure 2: Mild steel (20cm)Figure 3: Mild steel coated with spray mate paintFigure 4: Grading of the mild steel? 820g Tin – 5 Tins were used for this project? 800ml Plastic Containers – 5 Plastic Containers were used for this project? Pool Acid (hydrochloric acid) – 500ml of pool acid was used for one sample? Salt? copper wire2.1.3. Sample Preparation? Concrete Mixture? Mix 1kg of cement, 3kg aggregate, 3kg sand and 110L of water in a bowl.? Fill up the tins with the concrete mixture? Place the 20cm mild steel in the middle of the concrete in each tin (vertically)? The tins were exposed to the sun for three days, to allow the concrete to partiallydry before removing the concrete.? Drill the holes around the tins, penetrating the concrete into the metals, so that themetals must be exposed to the liquid which is going to be used for the experiment.? Cut the tins out to remove concrete inside the tin, and allow the concrete to dry fullyfor a week.? Place the concrete inside the plastic containers and number the containers todifferentiate them.? Salt water mixture? Mix 35g(2tablespoon) salt in 1000ml (1L) of water? Concentration 500ml? Water? Pour 500ml of tap water into a container? Hydrochloric acid? Pour 500ml of hydrochloric acid into a plastic container? Put the plastic container in a well ventilated area to avoid the smell of the acidwhich is dangerous to our body.? Galvanic cell? Pour 500ml of tap water into the container? Pour salt into the water until it does not dissolve anymore? Insert a copper wire vertically in the container to form a galvanic cell.2.1.4. The setup of AE systemThe typical setup for an AE system consists of one to several AE sensors, a preamplifier, amain amplifier, and computer-based data acquisition devices. Additional, other accessories arenecessary such as couplant and connecting cables.? The AE sensorThe role of the AE sensor is acting as a receiver to convert detected dynamic displacements orsound waves into electric signals. Today, AE sensors are already commercially available.There are two categories of sensors usually applied in the AE testing: resonant and broadbandsensors. The sensitivity of a sensor can be interpreted in voltage output per vertical second.Resonance type sensors, which are usually applied in the material with high attenuation likeconcrete, gain higher sensitivity but lower frequency range than the broadband sensors.The typical AE resonance sensors primarily utilized today are based on piezoelectric effect oflead zirconate titanate (PZT). This piezoelectric based sensor is known to be the most idealsensor balancing the low financial cost, high performance, and friendly operating. Generallyspeaking, every sensor needs to be calibrated before the testing. “The face-to-face method”,which is conducted by attaching the wear plates of the two same type sensors together to renderone is transmitter and the other one is receiver; “The defined sharp pulse method”, which isconducted by breaking material like glass capillary on a homogenous material likesteel(Pollock 1989).Figure 5: 30kHz AE Sensor? AmplifierAE signals are generally magnified by pre-amplifier and main-amplifier, and then processed bydata acquisition system to exclude noise. Typically, AE signals are filtered by band-pass filter.The gain of amplifier (dB) is expressed,dB = 20. log10 (V0 / Vi )where V0 is input voltage, Vi is output voltage. As a reference, the signals from concrete areusually magnified 60dB to 100dB. The filter ranging from 1 kHz to 2 MHz is recommended.Figure 6: Pre-amplifier? CouplantThe choice of couplant is crucial to the test sensitivity. The properties of ideal couplant shouldfeature low impedance comparing to the materials under tested and high fidelity when signalstransmit. Wax and grease are of this kind to be selected. In the testing, high vacuum grease isemployed as recommended in some papers. When placing a sensor, the contacting surfacebetween sensor and material should be smooth. Surface grinding is needed if necessary. Thecouplant layer should be even and it is essential to get rid of bubbles and make couplant layeras thin as possible to guarantee good acoustic transmission.2.1.5. Data acquisition deviceA data acquisition system is capable of analysing AE parameters including count, hit, event,rise time, duration, amplitude, energy, RMS voltage, frequency spectrum, arrive-time and soforth. This device employed in this research is purchased from MISTRAS Group.The Express-8 is a high-speed, 8-channel AE system on a board, based on the PCI-Express busarchitecture. The added feature of the Express-8 boards is the capability for real –timewaveform streaming which is useful in some applications such as rockfall monitoring.Figure 7: Data acquisition device2.1.6. The AE signal feature descriptionsIn the AE testing, count, amplitude, duration, rise time, and energy are the five most frequentlyused parameters. Other parameters (Pollock 1989) like threshold, RA value, frequency, to namea few are also widely employed in crack classification. They are defined as,Count: As shown in Figure 15, the number of times that an AE signal exceeds a thresholdwithin duration. The terms “count” is also named ring-down count or threshold crossing count.Amplitude: The maximum value of AE signal, which is in the unit of voltage when processedin the data acquisition device. It can be converted into decibel as followsDB = 20.log10(Vmax/1?V) – preamplifier gainDuration: It designates the time span from the starting point of the AE signal to the time oftermination. The unit is usually in microsecond.Rise time: It is referred to the time interval starting from the time of AE signal generation andthe time of signal reaching its amplitude.Energy: Area under the rectified signal envelope. It describes the magnitude of the sourceevent over the duration of the AE hit.Threshold: the triggering value of AE system to record waves as AE signals. The set ofthreshold has influence on the measuring of other AE parameters such as count, amplitude,duration and so on.Hit: when magnitude of a signal is beyond the threshold, it will cause the data acquisitiondevice to accumulate data.RA value: The ratio of rise time and amplitude, which is used to identify the classification offractures (Berkovits and Fang 1995; Grosse, Reinhardt et al. 1997). The decreasing RA valuesuggests the tendency of tensile fracture (Soulioti, Barkoula et al. 2009).Figure 8: The typical AE signal featuresAverage Frequency (AF): Average frequency is defined as the ratio of AE counts to duration.This parameter is mainly used when AE signals are difficult to obtain (Labuz,Daietal.1996;Soulioti, Barkoula et al. 2009)Average Frequency = AE Count/DurationCount to peak: the number of counts between triggering point and peak amplitude.Initial frequency: the feature derived from “count to peak” divided by “rise time.”RMS: Root-mean-square. It is recommended to use in continuous AE signals detection.Peak frequency: the peak value in the power spectrum, which has the unit kHz.Figure 9: The typical AE signal features (Grosse and Ohtsu 2008)2.1.7. The pencil lead break test setup and procedureThis test consists of breaking 0.5mm, 2Hb mechanical pencil lead on the surface of thematerial with the lead extending 2mm – 3mm from the pencil tip. The breaks are usuallycarried out 30mm away from the sensor at 30 degrees break angle. This generates an intenseacoustic signal, quite similar to a natural AE source that the sensors detect as a strong burst.The purpose of this test is twofold. First, it ensures that the transducers are in good acousticcontact with the part being monitored. Generally, the lead breaks should register amplitudesof at least 90dB for a reference voltage of 1mV and a total system gain of 90dB. Second itchecks the accuracy of the source location setup. This last purpose involves indirectlydetermining the actual value of the acoustic wave speed for the object being monitored.14The pencil lead break test is usually conducted to test the performance of the AE system byanalysing the AE signal waves. The purpose of this test was to determine the attenuation ofAE signals when transmitting through concrete materials. Also, as a preliminary test, pencillead test was a good attempt on how to set up the parameters for the following test and checkthe workability of the AE system.The threshold of the AE system was set to 40 dB on channels (1, 2, 3 and 5), its operatingfrequency range was from 20 kHz to 200 kHz. In this test, an ordinary mechanical pencil wasused and an example of concrete beam served as the medium where AE waves traveling(shown in Figure 19).Figure 10: pencil lead break (not research work)152.1.8. Samples to be used2.1.8.1. Insulated steel embedded in concrete and submerged in salt water2.1.8.2. Non insulated steel embedded in concrete and submerged in water2.1.8.3. Non insulated steel embedded in concrete and submerged in salt water2.1.8.4. Non insulated steel embedded in concrete and submerged in acid(hydrochloric acid)2.1.8.5. Non insulated steel embedded in concrete and submerged in salt waterAnd copper wire (galvanic cell)Figure 11: Samples2.1.9. Procedure? Set up the system? Connect the acquisition system (MGL micro express system-8) with the in-line 20dBpre-amplifiers.? Connect the pre-amplifiers to the sensors? Apply grease on sensors and attach to each sample.? Use pencil lead break to verify the sensors sensitivity by breaking the lead on thesurface of the metal? Record the reading while breaking the lead, the amplitude reading must be 90dB orwithin 2dB proximity to 90dB? Switch on the pre amplifier16? Run the test for an hour? Record the results2.1.10. Results and DiscussionsFigure 12: Test Activity ScreenThe above figure shows the reaction rate of the samples, channel 4 is very active or it iscorroding fast because of the acid used, then follows channel 2, channel3, channel5 and lastlyis channel 1 because the metal is coated with paint.17Figure 13: Test peak frequency? Peak frequency occurred in all channels at 35,5kHz due to noise.? Noise is due to:? People? Frictional noise? mechanical noise due to loose fitting parts? Rain? Nearby machinery, equipment or vehicular noise? Leaks? Electrical noise18Figure 14:Cumulative Data per Sample? Energy is the integral of the rectified voltage signal over the duration of AE hit.? In channel 4 there is more energy because it is very active and the threshold is seton 45dB which is higher than other channels, so the area in the graph will alsoincrease, and channel1 has the least energy even though the threshold is set on40dB like other channels because it is less active.9206195 2002253665839258 98141638 85232834397420701314114322711921110100100010000100000100000010000000100000000Cumulative Data per SampleTotal Energy Total HitsData Filename Days Hours Minutes SecondsDuration(sec)Channel 1TotalHitsNormalisedHitsTotalEnergyNormalisedEnergy Sum of ASLNormalisedASL2017 08 25 – Test – 02.dta 0 0 38 42 2322 1036 1606 1.31E+06 2033377 02017 09 14 – Test – 02 no wfFFFFF.dta 0 0 43 52 2632 573 784 3.29E+05 449522 02017 09 15 – Test – 04 no wfF.dta 0 5 2 45 18165 566 112 1.94E+05 38488 02017 09 18 – Test – 01.dta 0 1 31 4 5464 145 96 1.20E+05 79100 02017 10 03 – Test – 00.dta 0 6 35 33 17688 6179 1258 2.93E+07 5958946 0F_2017 10 5 – Test – 00.dta 2 16 40 33 232833 2744 42 6.86E+05 10611 02017 10 09 – Test – 00.dta 0 1 45 33 6333 103 59 6.18E+05 351094 02017 10 10 – Test – 01.dta 0 2 38 23 9503 46 17 7.52E+05 285057 238835 45Figure 15: Hits for Channel 1Data Filename Days Hours Minutes SecondsDuration(sec)Channel 2TotalHitsNormalisedHitsTotalEnergyNormalisedEnergy Sum of ASLNormalisedASL2017 08 25 – Test – 02.dta 0 0 38 42 2322 1622 2515 1.92E+06 2973442 02017 09 14 – Test – 02 no wfFFFFF.dta 0 0 43 52 2632 9089 12432 1.10E+06 1509816 02017 09 15 – Test – 04 no wfF.dta 0 5 2 45 18165 12105 2399 4.70E+05 93181 02017 09 18 – Test – 01.dta 0 1 31 4 5464 1087 716 2.50E+05 165008 02017 10 03 – Test – 00.dta 0 6 35 33 17688 9458 1925 7.15E+07 14543406 0F_2017 10 5 – Test – 00.dta 2 16 40 33 232833 37070 573 5.63E+06 86986 02017 10 09 – Test – 00.dta 0 1 45 33 6333 143 81 3.79E+05 215339 02017 10 10 – Test – 01.dta 0 2 38 23 9503 157 59 1.15E+06 435360 241068 46Figure 16: Hits for Channel 220Data Filename Days Hours Minutes SecondsDuration(sec)Channel 3TotalHitsNormalisedHitsTotalEnergyNormalisedEnergySum ofASLNormalisedASL2017 08 25 – Test – 02.dta 0 0 38 42 2322 413 640 1.59E+06 2468113 02017 09 14 – Test – 02 no wfFFFFF.dta 0 0 43 52 2632 336 460 2.48E+07 33912287 02017 09 15 – Test – 04 no wfF.dta 0 5 2 45 18165 1111 220 4.20E+07 8322294 02017 09 18 – Test – 01.dta 0 1 31 4 5464 222 146 3.07E+05 202296 02017 10 03 – Test – 00.dta 0 6 35 33 17688 7425 1511 9.86E+07 20060976 0F_2017 10 5 – Test – 00.dta 2 16 40 33 232833 1905 29 6.98E+06 107995 02017 10 09 – Test – 00.dta 0 1 45 33 6333 162 92 6.79E+05 385784 02017 10 10 – Test – 01.dta 0 2 38 23 9503 112 42 1.00E+06 379512 249255 47Figure 17: Hits for Channel 3Data Filename Days Hours Minutes SecondsDuration(sec)Channel 4Total HitsNormalisedHitsTotalEnergyNormalisedEnergySum ofASLNormalisedASL2017 08 25 – Test – 02.dta 0 0 38 42 2322 621 963 1.48E+06 2292802 02017 09 14 – Test – 02 no wfFFFFF.dta 0 0 43 52 2632 15227 20827 2.52E+06 3447581 02017 09 15 – Test – 04 no wfF.dta 0 5 2 45 18165 141051 27954 3.36E+07 6664616 02017 09 18 – Test – 01.dta 0 1 31 4 5464 10874 7164 2.76E+06 1819440 02017 10 03 – Test – 00.dta 0 6 35 33 17688 110921 22576 1.56E+08 31723860 0F_2017 10 5 – Test – 00.dta 2 16 40 33 232833 1641818 25385 1.23E+09 18983304 02017 10 09 – Test – 00.dta 0 1 45 33 6333 40615 23088 3.41E+07 19396752 02017 10 10 – Test – 01.dta 0 2 38 23 9503 40310 15271 3.65E+07 13813283 1310305 79525Figure 18: Hits for Channel 421Data Filename Days Hours Minutes SecondsDuration(sec)Channel 5/6TotalHitsNormalisedHitsTotalEnergyNormalisedEnergy Sum of ASLNormalisedASL2017 08 25 – Test – 02.dta 0 0 38 42 2322 6315 9791 5.50E+06 8531665 02017 09 14 – Test – 02 no wfFFFFF.dta 0 0 43 52 2632 285 390 1.02E+06 1399655 02017 09 15 – Test – 04 no wfF.dta 0 5 2 45 18165 665 132 2.91E+05 57658 02017 09 18 – Test – 01.dta 0 1 31 4 5464 552 364 3.17E+05 208819 02017 10 03 – Test – 00.dta 0 6 35 33 17688 5305 1080 3.60E+08 73364939 0F_2017 10 5 – Test – 00.dta 2 16 40 33 232833 2126 33 1.04E+06 16101 02017 10 09 – Test – 00.dta 0 1 45 33 6333 169 96 8.22E+05 467091 02017 10 10 – Test – 01.dta 0 2 38 23 9503 97 37 3.13E+06 1186907 240280 46Figure 19: Hits for Channel 422Figure 20: Normalised Hits vs Time Graph101001000100001000001 2 3 4 5 6 7HitsCh1 HitsCh 2 HitsCh 3 HitsCh 4 HitsCh 5/6 Hits23Figure 21: Total Energy vs Time Graph1001000100001000001000000100000001000000001 2 3 4 5 6 7EnergyCh 1 EnergyCh 2 EnergyCh 3 EnergyCh 4 EnergyCh 5/6 Energy24Figure 22: Cumulative Data per Sample92061952002253665839258 98141638 85232834397420701314114322711921110100100010000100000100000010000000100000000Cumulative Data per SampleTotal Energy Total HitsChapter 33.1. ConclusionThe AE system was setup to detect the rate of corrosion on metals in concrete for spallingcorrosion in this study, five samples where tested using AE system.Channel 4- was very active because the metal was exposed to hydrochloric acid, which isvery corrosive to metals.Channel 2-flat bar submerged in water is active more than channel 3 (flat bar submerged insaltwater) , the water used in the experiment corrodes faster, however after a short time itcreates a thin film around the rust block preventing it from rusting any further. The saltywater however corrodes at a slower rate, but because it uses electrochemical corrosion(because the salt in it creates a more conductive environment) it does not create the thin filmthat fresh water does. It is because of this that the salty water can rust until there is no moremetal left.Chanel 5- flat bar in galvanic cell, is also active because two dissimilar metals where incontact under water and corrosion occurred.Channel1- insulated flat bar submerged in saltwater is less active because the metal is coatedwith paint.The experiment was successful.3.2. References3.2.1. P. A. Schweitzer, Corrosion and Corrosion Protection Handbook (Marcel Dekker,Inc., NewYork, 1988).3.2.2. Pollock, A. A. (1989). “Acoustic Emission Inspection.” Metals Handbook 17: 278-294.3.2.3. Berkovits, A. and D. Fang (1995). “Study of fatigue crack characteristics by acousticemission.” Engineering Fracture Mechanics 51(3): 401-409.3.2.4. Grosse, C., H. Reinhardt, et al. (1997). “Localization and classification of fracturetypes in concrete with quantitative acoustic emission measurement techniques.” NDT & E International 30(4): 223-230.3.2.5. Soulioti, D., N. M. Barkoula, et al. (2009). “Acoustic emission behavior of steel fibrereinforced concrete under bending.” Construction and Building Materials 23(12):3532-3536

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