Research Article Corrosion Monitoring and Evaluation of ...downloads.hindawi.com/journals/ijdsn/2014/827130.pdf · Corrosion Monitoring and Evaluation of Reinforced Concrete Structures

Research ArticleCorrosion Monitoring and Evaluation of Reinforced ConcreteStructures Utilizing the Ultrasonic Guided Wave Technique

Dongsheng Li,1 Shuaifang Zhang,1 Wei Yang,2 and Wenyao Zhang2

1 School of Civil Engineering, Dalian University of Technology, Dalian 116024, China2 Fujian Academy of Building Research, Fuzhou 350025, China

Correspondence should be addressed to Dongsheng Li; [email protected]

Received 10 July 2013; Revised 6 December 2013; Accepted 2 January 2014; Published 20 February 2014

Academic Editor: Gangbing Song

Copyright © 2014 Dongsheng Li et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Corrosion of reinforced concrete structures has become a major problem worldwide, leading to very high repair costs. A dearth ofstudies has focused on the corrosion damage evolution of reinforced concrete. In this paper, the ultrasonic guided wave (UGW)technique is adopted tomonitor the reinforced concrete corrosion damage evolution process.The properties of different guide wavemodes were studied by steel rebar dispersion curves of UGWs through numerical calculation. The availability and validity of theUGW testing-reinforced concrete corrosion damage is proved by corrosion experiment. The experiment shows that the first wavepeak value could describe the whole process of steel rebar corrosion. As the corrosion damage level increases, the relative variationfor the first UGW peak value increases first and then decreases.

1. Introduction

Reinforced concrete has been employed as an economicalconstruction material in civil engineering structures, suchas buildings, bridges, and dams. However, environmentalfactors such as acid rain, chloride, loading fatigue, andcarbonization have simultaneous harmful effects on concrete.The results lead to steel corrosion. At present, steel corrosionhas become a major problem worldwide, especially forstructures exposed to aggressive environments.This problemhas reached alarming proportions in the past three decades,leading to very high repair costs, sometimes even abovethe initial construction cost, or to the final collapse of thestructures in extreme situations [1].

The current methods of detecting concrete structuraldamage of steels include electrochemistry detection, ultra-sonic wave testing, acoustic emission technique, and FiberBragg Grating sensors [2, 3]. However, these methods haveshortcomings. Electrochemical methods are sensitive to thesurface state of engineering structures and have been widelyutilized for corrosion monitoring [4]. As the double layer

does not result from pure capacitive conditions and thedata cannot be actually analyzed according to partial dataof electrochemical impedance spectroscopy, the corrosionmonitoring methods based on electrochemical impedancetechniques still need to be improved [5]. Ultrasonic wavespropagate in short distances and are only sensitive to signif-icant defects [6]. Acoustic emission is not sensitive to slightcorrosion damage degree because of the low corrosion energyrelease. Thus, a more precise and efficient method is urgentlyneeded.

A type of ultrasonic wave propagation involves a wavethat is guided between two parallel surfaces of the testobject. Ultrasonic guidedwaves (UGWs), as a developed tool,have many advantages compared with traditional detectionmethods. It can propagate in long distances because of itsslight attenuation in steel [7]. This characteristic is especiallysuitable to detect long range bridges. Guided waves werechosen because of the possibility of analyzing guided wavebehavior in certain frequency ranges to distinguish betweenthe loss of bar cross-sectional area and change of interfaceconditions [8]. High sensitivity is another merit of this

Hindawi Publishing CorporationInternational Journal of Distributed Sensor NetworksVolume 2014, Article ID 827130, 9 pageshttp://dx.doi.org/10.1155/2014/827130

2 International Journal of Distributed Sensor Networks

method. UGWs have many different modes at a singlefrequency, and these modes are sensitive to different defects[9].

The progressions of rebar corrosion in concrete in chlo-ride and oxide environments were monitored by UGWs.Theeffect of corrosion rates, surface and core-seeking guidedwave modes, and effective combination of guided wavemodes were introduced [9]. Corrosion has been simulatedin various ways, such as by introducing debonding betweensteel and concrete in the form of polyvinyl chloride pipesor by wrapping a tape on the bar [10, 11]. The sweepfrequency technique was adopted to optimize the guidedwave exciting frequency. The waveform energy attenuationat different frequencies was presented and discussed interms of corrosion damage. The testing results were verifiedbecause the fundamental longitudinal mode of propagationcan correctly express steel corrosion damage. Ervin et al.[12] employed high-frequency UGWs monitoring corrosionof rebar embedded in mortar. Through different guidedmode comparisons, the 𝐿(0, 9)mode was adopted tomonitoruniform and localized corrosion in reinforced mortar under-going accelerated corrosion.Thus, ample evidence shows thatcorrosion could be detected by UGW techniques. However,the whole steel corrosion process and damage evolution hasnot been reported utilizing UGW testing. This study reportsthat the steel corrosion damage monitoring adopted UGW.The testing results were verified through another corrosionevaluation method.

2. UGW Propagation Theories in Steel Rebar

The geometry profile of a rebar is presented in Figure 1.Threedifferent modes propagate in cylindrical waveguide, longi-tudinal modes 𝐿(0,𝑚), torsion modes 𝐹(𝑛,𝑚), and flexuralmodes 𝐹(𝑛,𝑚). In this expression,𝑚 and 𝑛 stand for circum-ferential order and modulus, respectively. The displacementis symmetrical corresponding to 𝑛 = 0, where 𝑛 = 1, 2, 3 . . .that refers to asymmetrical displacements.Therefore, 𝐿(0,𝑚),𝑇(0,𝑚) are symmetricalmodes and𝐹(𝑛,𝑚) are asymmetricalmodes.

The longitudinal modes that propagate in steel rebaronly have two types of displacement: radical and axialdisplacements. The boundary condition is 𝑢𝜃 = 0, and 𝑢𝑧 𝑢𝑟are independent of 𝜃. Considering the boundary condition𝜎𝑟𝑟 = 𝜎𝑟𝑧 = 0 (𝑟 = 𝑎), the Pochhammer frequency equationcan be achieved by solving the wave equation [13]:

2𝛼

𝑎(𝛽2+ 𝑘2) 𝐽1 (𝛼𝑎) 𝐽1 (𝛽𝑎) − (𝛽

2− 𝑘2) 𝐽0 (𝛼𝑎) 𝐽1 (𝛽𝑎)

− 4𝑘2𝛼𝛽𝐽0 (𝛽𝑎) = 0,

(1)

where 𝜆 is the length of guided waves, 𝜔 is the angularvelocity, 𝑘 is the wave number, 𝐽 is the Bessel function,coefficients 𝛼2 = 𝜔2/𝑐2

𝐿, 𝛽2 = 𝜔2/𝑐2

𝑇− 𝑘2, 𝑐𝐿 is the velocity

of longitudinal guided wave, 𝑐𝑇 is the velocity of transverseguided waves, and 𝑐𝑃 is the phase velocity. This expressionis a transcendental equation with independent variables 𝜔

𝜃rz

Figure 1: Geometry profile of steel rebar.

and 𝑘; thus, the same frequency 𝜔 corresponds to multiplewave numbers; namely, more than one solution existing at asingle frequency 𝜔. This phenomenon corresponds well withthe fact that many modes exist at a single frequency. Thiscondition is the multiple modes property of UGW.

3. Dispersion Curves of UGW Propagation inSteel Rebar

The curves that depict the relationships between frequencyand eigenvalue, as well as phase velocity and group velocity,are called dispersion curves. The parameters utilized tocharacterize the properties of wave guided propagation arephase velocity and group velocity, which have been describedabove. All waveguides, both symmetrical and asymmetrical,and other irregular shapes have special dispersion curves.Besides, only with the dispersion curves of UGW in steelrebar could an ideal UGW mode be excited by selecting theappropriate excitation frequency.

Take a 20mm diameter rebar as an example. HRB335ribbed bars were employed in this study, whose properties areshown in Table 1.

The effect of ribs on a ribbed bar can be ignored whenthe ratio of the diameter and the length is less than 0.4 [8].The ratio between the diameter and the length is 0.029; thus,the steel rebar can be seen as a smooth cylinder. Based onSection 2, the transcendental equation can be solved withguided wave propagation theory. The dispersion curve ofguided waves propagating in the steel rebar can be obtainedby numerical calculation. The relationship between wavevelocity and frequency (wave number and frequency) isrepresented by dispersion equation (1) and dispersion curve.However, as a transcendental equation, wave velocity andfrequency (wave number and frequency) analytic solutionsare too complicated to be obtained from dispersion equation(1), which could only be solved by the numerical analysismethod.The program is divided into several steps as follows:

(a) The cutoff frequency that corresponds with the corre-spondingmode is determined.The solution of the dis-persion equation is based on the cutoff frequency, andthe roots that meet the equation are determined byscanning the frequency range. These roots are cutofffrequencies that correspond with the correspondingmode, and these roots are set as initial points of eachmodal dispersion curve.

(b) Each modal begins with the initial point. The nextpoint that meets the dispersion equation with acertain step length is searched (e.g., 5Hz). The initial

International Journal of Distributed Sensor Networks 3

Table 1: Properties of HRB335 ribbed bars.

Diameter Length Cross-sectional area Density Young’s module Poisson ratio20mm 700mm 254.5mm2 7858.5 kg/m3 206GPa 0.28

Table 2: C30 mix proportion of concrete (kg/m3).

PC32.5R cement Water Medium grained sand Rock fragment434 182.5 524.9 1226.5

0 100 200 300 400 500 600 700 800 900 10000

1000

2000

3000

4000

5000

6000

Frequency (kHz)

Gro

up sp

eed

(m/s

)

L(0, 1)

L(0, 2) L(0, 3) L(0, 4)L(0, 5)

T(0, 1)

T(0, 2) T(0, 3) T(0, 4) T(0, 5)

F(1, 1)F(1, 3)

F(2, 1) F(3, 1)

Figure 2: Dispersion curves of group velocity.

point is then renewed until all the points in thefrequency range are obtained.

(c) Let the cutoff frequency in (a) be the initial point.A dispersion curve is obtained by connecting all thepoints searched in the frequency range. This stepbegins with the next initial point, and the aboveprocess is repeated. Finally, all dispersion curves areobtained.

The 20mm diameter rebar dispersion curve is displayedin Figure 2. Only three modes can be produced, namely,𝐿(0, 1) longitudinal mode, 𝑇(0, 1) torsion mode, and 𝐹(1, 1)flexural mode.These modes could be acquired in the vicinityof the 40 kHz frequency, where the slopes degree of UGWin these three modes is most mild. 40 kHz is selected asthe excitation frequency to excite the longitudinal UGWmode.Theguidedwave of𝐿(0, 1)mode,which dispersesmostindistinctly and propagates fastest at this frequency, is chosento detect the corrosion damage of reinforced concrete.

4. Steel Rebar Corrosion UGW DetectionExperiment and Results Analysis

4.1. Reinforced Concrete Corrosion Specimen Preparation. Inthis experiment, the size of the specimen was 500mm ×120mm × 150mm, in which the thickness of steel rebar’sprotective layer was 20mm and the concrete grade was C30.

500mm 100mm100mm

150

mm

C30 concrete

∅20 steel rebar

Figure 3: Reinforced concrete beam.

Power supply

Block

Electrode Water trough

Water level

− +

Steel rebar

Figure 4: Reinforced concrete corrosion experimental devices.

The hot rolled ribbed steel rebar had a diameter of 20mm.The steel rebar was outstretched by 100mm outside theconcrete to satisfy the need of UGW detection when thespecimen was corroded. The weight of the steel rebar wasweighed before the concrete specimen was casted. OrdinaryPortland cement 32.5R from the China Dalian Jinzhou thirdcement factory was utilized to prepare concrete. Mediumgrained sand was selected for the experiment. The rockfragment particle size was 5mm to 15mm.The water cementratio was 0.42, whose detailed mix proportion is shown inTable 2.The laboratory temperaturewas 25∘C, and the relativehumidity was 80% when the specimen was casted. The testwas conducted after a 28 d of storage in a standard curingroom.The detailed size is presented in Figure 3.

The corrosion of reinforced concrete in the naturalenvironment is so slow that themethod of electrochemistry isemployed to accelerate corrosion to obtain a higher amountof corrosion within a short time. The device utilized in theexperiments was a stable DC power supply (Figure 4), whichcould ensure the stability of the current. The device modelwas PS-603D with exporting current of 0A to 3A (precisionof 10mA) and exporting voltage of 0V to 60V (precision of0.1 V). In the electrochemistry experiment, the steel rebar wasselected as the anode, whereas stainless steel was the cathode.


Table 3: Parameters of the piezoelectric ceramic.

PZT constant 𝑑33 Density kg/m3 Dielectric loss Relative permittivity𝜀𝑟3

Curie temperature ∘CElectromechanicalcoupling coefficient

𝑘33

10−12 C/N 7500 0.02 1700 320 0.75

4.2. Design of Reinforced Concrete Corrosion. The amountof electrochemical corrosion of the steel reinforcement wascalculated in accordance with Faraday’s law:

𝑚 = 𝑘𝐼𝑡, (2)

where 𝑚 is the loss of corroded metal (g), k is the coefficientof different metals with different properties, I is the currentsize (A), and 𝑡 is the conduction time (s).

Based on Faraday’s law, the amount of electrochemicalcorrosion of steel reinforcement could also be calculated with

𝑚 =𝑡 × 𝐼 × 55.487

2 × 96487. (3)

The amount of electrochemical corrosion of the steelreinforcement is in proportion to the conduction time andcurrent size. In this equation, 55.487 is themolar mass of ironatoms, 2 is the number of electrons lost when an iron atomturns into a ferrous ion, and 96487 is the charge needed aselectrolysis consumes one mole of substance.

The corrosion current should be neither too large nor toosmall. If the current was too large, the reinforcement wouldcorrode faster and the damage of the steel rebar would beconcentrated at both ends of the steel rebar; thus, the steelrebar does not corrode uniformly. If the current was toosmall, the reinforcement would corrode slower and the timeof corrosion would last much longer, resulting in the loss ofhuman and financial resources. Approximately 1mA/mm2 isthe standard value, wherein the corrosion current equal tothe parcel area of the steel rebar in reinforced concrete ismultiplied by 1mA/mm2 and calculated as follows:

𝐼 = 1 × 3.14 × 20 × 500 = 314mA = 0.314A. (4)

Thus, 0.3 A is selected as the corrosion current of elec-trochemical corrosion of steel rebar. Five specimens werecorroded for 0, 5, 10, 15, and 20 d. During the corrosion, aUGWdevice was employed to detect the specimens every dayto record the voltage and current sizes.

4.3. Experimental Results and Analysis. A UGW device wasutilized to detect guided waves of the steel rebar in rein-forced concrete.The specified detection principle is shown inFigure 5.

The oscilloscope was utilized to acquire data. Two signalchannels were chosen: one received the output waveform ofpower amplifier, whereas the other received the waveformobtained by the sensor receiver. In this paper, lead zirconatetitanate piezoelectric ceramics (PZT-5) was adopted as theultrasonic sensor. The performance parameters are shown inTable 3.

Power amplifier

Function generator

Specimen

Oscillograph

PC

Figure 5: Sketch of ultrasonic guided wave detection.

Figure 6: The UGW sensors placement for reinforced concretestructures corrosion.

Two piezoelectric ceramics were arranged at both sides,one of which was the exciting sensor while the other was thereceiving sensor. The sensor placement is shown in Figure 6.

Five-cycle sinusoidal waves with central frequencyof 40 kHz are modulated utilizing the Hanning windowemployed as UGW excitation signals (Figure 7).

4.3.1. Appearance of the Specimen. The appearance of thereinforced concrete beam after corrosion is shown inFigure 8.

No. 5 specimen was kept from corrosion, which greatlycontrasted with the other specimens. By comparing Figures8 and 5, the steel rebar would expand during the corrosionof the reinforcing steel, and then longitudinal through-going cracks would appear along the length of the surfacedirection of the concrete protective layer that caused damage.As the corrosion time increased, cracks on each specimen’sappearance becamewider and even the protective layerwould


0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045

0.0

0.5

1.0

Am

plitu

de (V

)

Time (ms)

−1.0

−0.5

Figure 7: Five-cycle sinusoidal waves modulated by Hanningwindow.

No. 1

No. 2

No. 3

No. 4

No. 5

Figure 8: The case of the specimen after corrosion.

fall off, as No. 4 specimen shows. The four specimens werecorroded for 5, 10, 15, and 20 d.

4.3.2. UGW Monitoring for Steel Rebar Corrosion. Duringthe corrosion, a UGW device was utilized to detect thespecimens’ corrosion every day. The UGW testing signals ofthe reinforced concrete before and after corrosion were onlylisted to save space.

Figures 9, 10, 11, and 12 show that, although the signalsof the UGW propagation in reinforced concrete were verycomplex, the signals of the first wave were very significantandhad the typical characteristics of a first-order longitudinalguided wave. With the arrangement of the sensor in thistest, only the longitudinal wave guide mode was excited interms of theory. According to the waveform observed in thistest, a series of waveforms after the first wave had otherforms of modals apart from the longitudinal modal. Thisscenario was mainly caused by the manufacturing errorsat the end of the steel rebar induced bending mode. The

reflection and refraction of the guided wave at the end ofthe steel rebar and in the contact interface of the steel rebarand concrete make the modes convert. Both reflection andrefraction could occur again when the guided wave arrives atthe receiving end, and the superposition of the incident wavemakes the guided wave more complex. The steel rebar in thereinforced concrete also defected after corrosion because thedefects disorganizing the reflection, refraction, and the modeconversion of the guided wave could occur repeatedly. Themodes of the testing signal aremuch richer after the corrosiontest. Thus, the amplitude of the first wave was only needed inthis study. As seen in Figures 9–12, the amplitude of the headwave of UGW decreased gradually as time progressed aftercorrosion, except for the No. 1 specimen. The UGW devicewas employed to detect the specimens every day to recordthe amplitude of the first wave. The relationship of this set ofspecimens fromNos. 1 to 4 between the amplitude of the firstwave and the time of corrosion is presented as in Figure 13.

Figure 13 shows that the UGW first wave peak valuefirst increased and then decreased slowly. The peak valueof the first wave of reinforced concrete specimens with thesame degree of corrosion also decreased over time. Thiscondition is because the corrosion products increased duringthe steel rebar corrosion process, resulting in an increase inthe delamination degree between the steel rebar and concrete.The decrease in theUGWenergy in the steel rebar leaked intothe concrete; thus, the peak value of the first wave of UGWincreases. However, as the reinforced concrete corrosion levelincreases, the pit on the steel becomes larger. This conditionwould lead to great reflection in the first wave energy, and thedirect transmission wave energy would become low.The firstwave peak value then decreased slowly.

A steel rebar was removed from reinforced concreteafter the test to examine the accuracy of the UGW test.The steel rebar with different degrees of corrosion is shownin Figure 14. The weight was measured after washing thecorrosion on the steel rebar with pure water and hydrochloricacid. By evaluating the degree of corrosion with the massloss rate method, the calculation formula is presented as informula (5). The degrees of corrosion of reinforced concretespecimens are shown in Table 4:

𝑐 =𝑚𝑏 − 𝑚𝑎

𝑚𝑏

× 100%, (5)

where 𝑐 is the mass loss rate, 𝑚𝑏 is the mass of the steelrebar before corrosion, and𝑚𝑎 is the mass of steel rebar aftercorrosion.

We made a graph shown in Figure 15 to quantitativelydescribe the changing rule of the UGW signal of reinforcedconcrete. The 𝑥-coordinate is the mass loss rate of reinforcedconcrete and the 𝑦-coordinate is the change in the peak value(first wave peak value before corrosion subtracted from thefirst wave peak value after corrosion) of the UGW first wave.No. 1 specimen is not considered in this figure as its peak valueincreased. From Figure 15, the relative variation peak valueof the UGW first wave increased along with the increase inthe degree of corrosion, which shows that utilizing the peakvalue change of the UGW first wave could roughly judge thedamage degree of reinforced concrete.


0.0000 0.0005 0.0010 0.0015 0.0020

0.0

0.2

0.4

Am

plitu

de (V

)

Time (s)

−0.1

−0.2

−0.3

L(0, 1)

(a) UGW waveform before corrosion

0.0000 0.0005 0.0010 0.0015 0.0020

0.0

0.2

0.4

0.6

0.8

Am

plitu

de (V

)

Time (s)

L(0, 1)

−0.4

−0.6

−0.8

−0.0010 −0.0005

−0.2

(b) UGW waveform after corrosion

Figure 9: UGW waveform for No. 1 corrosion specimen.

0.000 0.001 0.002 0.003 0.004

0.0

0.2

0.4

0.6

0.8

Am

plitu

de (V

)

Time (s)

−0.4

−0.6

−0.8

−0.2

L(0, 1)

−0.001


0.0000 0.0002 0.0004 0.0006 0.0008 0.0010

0.0

0.2

0.4

0.6A

mpl

itude

(V)

Time (s)

−0.6

−0.4

−0.0004 −0.0002

L(0, 1)

−0.2



Am

plitu

de (V

)

Time (s)0.0000 0.0005 0.0010 0.0015 0.0020 0.0025

0.0

0.1

0.2

0.3

0.4

−0.1

−0.2

−0.3

−0.4

−0.0005

L(0, 1)


Am

plitu

de (V

)

Time (s)0.0 0.5 1.0 1.5 2.0

0.00

0.02

0.04

0.06

0.08

0.10

−0.02

−0.04

−0.06

−0.08

−0.10

−1.0 −0.5

L(0, 1)




0.0000 0.0005 0.0010 0.0015 0.0020

0.0

0.2

0.4

0.6

0.8

Am

plitu

de (V

)

Time (ms)

−0.2

−0.6

−0.8

−0.0005

L(0, 1)

−0.4


0.0000 0.0002 0.0004 0.0006 0.0008 0.0010

0.0

0.1

0.2

0.3

Am

plitu

de (V

)

Time(ms)

−0.1

−0.2

−0.3

L(0, 1)



−1 0 1 2 3 4 5 60.3

0.4

0.5

0.6

0.7

Time (d)

Firs

t wav

e pea

k va

lue (

V)

(a) UGW peak variation for No. 1 specimen

−1 0 1 2 3 4 5 6 7 8 9 10 11

0.4

0.5

0.6

0.7

Time (d)

Firs

t wav

e pea

k va

lue (

V)

(b) UGW peak variation for No. 2 specimen

−1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Time (d)

Firs

t wav

e pea

k va

lue (

V)

(c) UGW peak variation for No. 3 specimen

0 2 4 6 8 10 12 14 16 18 20 22

0.2

0.4

0.6

0.8

1.0

Firs

t wav

e pea

k va

lue (

V)

Time(d)

(d) UGW peak variation for No. 4 specimen

Figure 13: UGW peak variation during the whole corrosion process.


Table 4: Degree of corrosion.

Specimen number Corrosion time (d) Mass before corrosion (g) Mass after corrosion (g) Mass loss (g) Mass loss rate (%)1 5 d 1583 1543 40 2.592 10 d 1575 1506 69 4.383 15 d 1590 1474 116 7.294 20 d 1584 1426 158 9.975 0 d 1581 0

No. 1

No. 2

No. 3

No. 4

Figure 14: Corrosion steel rebar surface.

4 6 8 100.0

0.1

0.2

0.3

0.4

0.5

Firs

t wav

e pea

k va

riatio

n va

lue (

V)

Mass loss rate (%)

Figure 15: Relationship between the ultrasonic guided first wavechanges and the corrosion damage level of steel rebar.

5. Conclusion

The selection of UGW excitation signals, analysis of UGWdispersion curves, and test of reinforced concrete corrosiondamage are researched in this paper. The principal conclu-sions are as follows.

(1) The properties of different guide wave modes arestudied by steel rebar dispersion curves of UGWthrough numerical calculation. Based on the disper-sion curves, the use of guided waves of 𝐿(0, 1) modewith 40 kHz is proposed in the test for reinforcedconcrete corrosion damage.

(2) The availability and validity of the UGW and the testfor reinforced concrete corrosion damage is provedby the reinforced concrete corrosion experiment.Theexperiment shows that the head wave value coulddescribe the whole process of steel rebar corrosion.

(3) The steel rebar corrosion level could be estimatedroughly with the relationship of the ultrasonic guidedfirst wave changes in amplitude and the corrosiondamage level of the steel rebar. As the corrosion dam-age level increases, the relative variation forUGWfirstwave peak value increases first and then decreases.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgments

The authors are grateful for the financial support fromNational Natural Science Foundation of China (NSFC) underGrant no. 51278083, the Fundamental Research Funds forthe Central Universities (Grant no. DUT12LK12), Scienceand Technology Project of Fujian Province (Grant no.2012Y01010047), and Science and Technology Support Pro-gram of China no. 2011BAK02B04.

References

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[8] B. L. Ervin, J. T. Bernhard, D. A. Kuchma et al., “Estimation ofcorrosion damage to steel reinforced mortar using frequencysweeps of guided mechanical waves,” in Smart Materials andStructures, vol. 6174 of Proceedings of SPIE, p. 12, 2006.

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Modelling & Simulation in EngineeringHindawi Publishing Corporation http://www.hindawi.com Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks


Documents

Research Article Corrosion Monitoring and Evaluation of ...downloads.hindawi.com/journals/ijdsn/2014/827130.pdf · Corrosion Monitoring and Evaluation of Reinforced Concrete Structures