PAPER

1. This content has been downloaded from IOPscience. Please scroll down to see the full text.
Download details:
IP Address: 130.133.8.114
This content was downloaded on 18/05/2017 at 15:33
Please note that terms and conditions apply.
Characterization of cement-based materials using a reusable piezoelectric impedance-based
sensor
View the table of contents for this issue, or go to the journal homepage for more
2011 Smart Mater. Struct. 20 085023
(http://iopscience.iop.org/0964-1726/20/8/085023)
Home Search Collections Journals About Contact us My IOPscience
You may also be interested in:
Piezoelectric sensor based nondestructive active monitoring of strength gain inconcrete
Sung Woo Shin, Adeel Riaz Qureshi, Jae-Yong Lee et al.
Non-destructive concrete strength evaluation using smart piezoelectric transducer—a comparative
study
Yee Yan Lim, Kok Zee Kwong, Willey Yun Hsien Liew et al.
A technique for improving the damage detection ability of the electro-mechanical impedance method
on concrete structures
S Na and H K Lee
Smart piezoelectric transducers for in situ health monitoring of concrete
Kevin K Tseng and Liangsheng Wang
Calibration of piezo-impedance transducers for strength prediction and damage assessmentof concrete
Chee Kiong Soh and Suresh Bhalla
Fatigue life estimation of a 1D aluminum beam under mode-I loading using theelectromechanical
impedance technique
Yee Yan Lim and Chee Kiong Soh
Practical issues related to the application of the electromechanical impedance technique inthe
structural health monitoring of civil structures: I. Experiment
Yaowen Yang, Yee Yan Lim and Chee Kiong Soh
Influence of loading on the electromechanical admittance of piezoceramic transducers
Venu Gopal Madhav Annamdas, Yaowen Yang and Chee Kiong Soh

2. IOP PUBLISHING SMART MATERIALS AND STRUCTURES
Smart Mater. Struct. 20 (2011) 085023 (9pp) doi:10.1088/0964-1726/20/8/085023
Characterization of cement-based
materials using a reusable piezoelectric
impedance-based sensor
R Tawie1
and H K Lee2,3
1
Faculty of Civil Engineering, UiTM Sarawak, 94300 Kota Samarahan, Malaysia
2
Department of Civil and Environmental Engineering, KAIST, Daejeon 305-701, Korea
E-mail: rudy@sarawak.uitm.edu.my and leeh@kaist.ac.kr
Received 12 November 2010, in final form 26 May 2011
Published 22 July 2011
Online at stacks.iop.org/SMS/20/085023
Abstract
This paper proposes a reusable sensor, which employs a piezoceramic (PZT) plate as an active
sensing transducer, for non-destructive monitoring of cement-based materials based on the
electromechanical impedance (EMI) sensing technique. The advantage of the sensor design is
that the PZT can be easily removed from the set-up and re-used for repetitive tests. The
applicability of the sensor was demonstrated for monitoring of the setting of cement mortar.
EMI measurements were performed using an impedance analyzer and the transformation of the
specimen from the plastic to solid state was monitored by automatically measuring the changes
in the PZT conductance spectra with respect to curing time using the root mean square deviation
(RMSD) algorithm. In another experiment, drying-induced moisture loss of a hardened mortar
specimen at saturated surface dry (SSD) condition was measured, and monitored using the
reusable sensor to establish a correlation between the RMSD values and moisture loss rate. The
reusable sensor was also demonstrated for detecting progressive damages imparted on a mortar
specimen attached with the sensor under several loading levels before allowing it to load to
failure. Overall, the reusable sensor is an effective and efficient monitoring device that could
possibly be used for field application in characterization of cement-based materials.
(Some figures in this article are in colour only in the electronic version)
1. Introduction
Cement-based materials have been used extensively in
the construction industry. Despite considerable progress in
research, efficiency in using the materials is still not easily
predicted due to the fact that there are many factors that need
to be considered, such as the type and amount of cement
used, admixtures, water–cement ratio and curing temperature.
Therefore, testing and quality control at different stages is very
important to ensure structures built using such materials is of
acceptable quality and safe for use. For example, knowing
the setting and hardening states of the materials allows us
to determine the right time for formwork removal, time for
prestressing and time for loading of structural elements.
Due to the advent of smart materials such as optical fibers,
piezoelectric materials and self-diagnosing fiber-reinforced
3 Author to whom any correspondence should be addressed.
composites, we have seen the emergence of new non-
destructive evaluation and monitoring techniques. Each of
these materials has a unique property that enables them to
be used for sensing applications. In particular, piezoelectric
materials can be used for both actuating and sensing.
Compared to other types of sensors, piezoelectric sensors
offer economy and simplicity when integrated to a host
structure and they have excellent mechanical strength, low
acoustic impedance, a flat response over a wide frequency
range and a broad dynamic response [1]. About 15 years
ago, a non-destructive method known as the impedance-based
monitoring or electromechanical impedance (EMI) technique
has emerged, which utilizes piezoelectric ceramic (PZT)
transducers as collocated sensors and actuators [2]. The
method has shown great potential in the fields of structural
health monitoring (SHM) and non-destructive evaluation
(NDE) [3–10]. The application of surface bonded techniques
0964-1726/11/085023+09$33.00 © 2011 IOP Publishing Ltd Printed in the UK & the USA
1

3. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
based on the impedance-based method for characterization
of cement-based materials has been studied by a number
of researchers [6–9]. Soh and Bhalla [6] showed that a
strong correlation exists between cube compressive strength
of concrete and the first resonant frequency of the PZT
conductance spectra, and an empirical relationship was
established by Tawie and Lee [8] to predict the relative strength
gain of concrete by monitoring the resonant frequency shift.
In Tawie et al [9], a quality index was introduced to assess
the quality of concrete in terms of strength and porosity based
on calibration of specimens from dry to saturated conditions.
The disadvantage of the surface bonded techniques is that it is
not possible to monitor the hydration process of specimens in
their fresh state. Attaching the PZT is also not possible if the
concrete surface is not dry and up to 24 h is required for the
surface-bonded PZT to be properly cured.
Embedding PZT in a host structure is an ideal technique
to ensure good coupling with the surrounding matrix. It
is suggested that embedded PZT is more efficient when it
is less stiff than the host structure [11]. The confined
behavior of a PZT embedded inside an epoxy layer of
a sandwiched aluminum beam has been investigated by
Annamdas and Soh [12] using the thickness vibration of the
PZT in electromechanical admittance formulations and was
verified experimentally. In another study [13], the authors
introduced a method of embedding PZT for monitoring of
concrete curing and damage analysis. Their study showed that
the capability of the embedded PZT is similar to that of surface-
bonded PZT in the monitoring of concrete strength gain and
detection of damage.
The application of reusable PZT is still new and the idea is
to reduce the cost of monitoring because the same PZT could
be re-used as many times as possible and therefore ensure
better repeatability and reliability in measurements. So far
limited studies [14, 15] have been reported on the development
of the reusable PZT technique for monitoring hydration and
structural health of concrete based on the EMI method. They
attached a PZT on a metal enclosure with holes and two bolts
tightened inside which are embedded in fresh concrete. It
is designed such that the two bolts can be unscrewed after
concrete has hardened and the enclosure with the bonded
PZT can be removed for future applications. However, their
reusable set-up is not suitable for long-term health monitoring
of concrete structures because the solid connection to the
concrete will be lost if the bolts are unscrewed. In this study,
a new reusable sensor as shown in figure 1, which employs a
PZT plate as an active sensing transducer, is proposed for non-
destructive monitoring of cement-based materials based on the
EMI sensing technique. The prime objective of this research
is to develop a more effective and efficient monitoring device
that could be used for field application. The advantage of the
proposed reusable sensor design is that the bolt attached with
the PZT can be removed from the rod so that it can be re-used
for repetitive tests.
2. Principle of EMI measurement and data
processing
EMI transducers such as PZT are known to provide a means of
coupling electrical and mechanical impedance. The basis of an
Figure 1. A reusable PZT sensor with different length of rods.
impedance-based monitoring approach is basically to monitor
variation in mechanical impedance of a structural element via
electrical impedance of a PZT bonded to or embedded in the
host structure. The PZT behavior is governed by the following
piezoelectric relations [16]:
D3 = ε̄T
33 E3 + d31T1 (1)
S1 =
T1
Ȳ E
+ d31 E3 (2)
where D3 and E3 are the electrical displacement and field,
respectively, acting along axis ‘3’, T1 and S1 are the axial
stress and strain, respectively, in the direction of axis ‘1’, ε̄T
33
is the complex electric permittivity at constant stress, d31 is the
piezoelectric strain coefficient and Ȳ E
is the complex Young’s
modulus of elasticity of the piezoelectric material at constant
electric field. PZT transducers, when driven by an alternating
electric field, will induce vibration (converse effect). When
bonded onto a host structure, the resultant vibration responses,
which are characteristics of the structure, modulate the current
flowing through the piezoelectric transducers (direct effect).
This modulation is a function of the degree of mechanical
interaction between the transducers and the structure. Liang
et al [17] introduced a one-dimensional EMI equation to model
the interaction of the coupled relationship between electrical
and mechanical impedance of the PZT and the structure,
respectively, as follows [17]:
Y(ω) = iωa
εT
33(1 − iδ) −
Zs(ω)
Zs(ω) + Za(ω)
d2
3xȲ E
xx
(3)
where Y(ω) is the electrical admittance (inverse of impedance)
of a PZT, ω is the excitation frequency, a is the geometric
constant of the PZT, εT
33 is the dielectric constant at zero
stress, δ is the dielectric loss tangent of the PZT, Zs(ω) is
the structure’s mechanical impedance, Za(ω) is the mechanical
impedance of the PZT, d3x is the PZT coupling constant in
the arbitrary x direction at zero stress and Ȳ E
xx is the complex
Young’s modulus of the PZT at zero electric field. It can be
seen in equation (3) that the coupled electrical admittance of
PZT is a function of the stiffness, mass and damping of the
2

4. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
Figure 2. Experimental equipment.
host structure, and also the geometrical properties of the PZT.
High frequencies in the range of 30–400 kHz [2] are generally
used to vibrate PZT transducers and measure its electrical
response at the same time using a commercial impedance
analyzer, such as the Agilent 4294A impedance analyzer as
shown in figure 2. In figure 2, a multifunction switch can be
used for multiple measurements from a number of PZTs. A
laptop with data acquisition software such as Matlab can be
used to control the measurements automatically via the LAN.
The electrical admittance, Y(ω), measured using an impedance
analyzer consists of real and imaginary parts as follows:
Y(ω) = G(ω) + jB(ω) (4)
where G is the conductance (real part) and B is the susceptance
(imaginary part). Measured conductance or susceptance
spectra vary over a range of frequencies (ω). Generally, only
the conductance spectra of the PZT is used in monitoring
applications [2], while the susceptance spectra is used to
evaluate the integrity of the PZT [18].
The changes in a PZT conductance spectrum may indicate
that properties change in the host structure. These changes
may constitute lateral and vertical shifts or the appearance of
new peaks in the PZT spectrum. The changes between two
G spectra were analyzed using root mean square deviation
(RMSD) as follows [19]:
RMSD =
N
i=1[G1
i − G0
i ]2
N
i=1[G0
i ]2
(5)
where G0
i is the baseline value of the ith frequency point for the
prior monitoring time and G1
i is the value of the ith frequency
point for the subsequent monitoring time. N is the upper limit
of the frequency range. In general, the RMSD value increases
as the changes between the G spectra become larger.
3. Sensor response and repeatability
One of the characteristics of PZT is that it is frequency-
dependent. If a voltage of varying frequency is applied to a
PZT, a very strong vibration is produced at a certain frequency
Figure 3. Conductance spectra obtained from three developed
sensors.
depending on the PZT’s elastic resonance. Figure 3 shows
the responses from three developed sensors. One was made
using PZT type A and the other two with PZT type B. The
difference between these two types of PZT was in their prices.
PZT type A was the more expensive one because it was
specifically ordered from PI Ceramic GmbH [20] with the
required size of 10 mm × 10 mm × 0.3 mm. It was made with
wrapped-around electrodes on the upper surface. PZT type
B, from Piezo System [21], was sold with a standard size of
72.4 mm×72.4 mm ×0.508 mm and made with electrodes on
both surfaces. In this study, several pieces were obtained from
a single PZT type B plate by cutting it into the required size of
10 mm × 10 mm. As can be seen in figure 3, the locations of
the resonant frequencies of the three sensors are quite similar
although some peaks are split. The peaks for sensor 1 (PZT
type A) are much clearer than the peaks for sensors 2 and
3 which were attached with the low cost PZT type B. It is
noted that stability of the sensor’s response can be improved
by minimizing the variation in the bonding condition and the
PZT’s geometry imperfection [22]. In figure 3, the observed
split peaks could be due to imperfect cutting of the PZT edges.
At the beginning of this research, the repeatability of the
reusable set-up has been checked using sensor 1 by unscrewing
and screwing again the bolt and taking measurements several
times. As can be seen in figure 4, the repeatability of the
sensor at the first resonant frequency is quite good. The
slight variation observed for the screwed case is because of
the tightened condition of the bolt. For section 4, the use of
the sensor made with PZT type B was recommended because
of its low cost. Sensor 2 was eventually used repetitively in all
the experiments to assess its reliability.
4. Experimental studies
4.1. Monitoring setting of cement mortar
The control of the setting time of cement is significant due to
the availability of various kinds of admixtures in the market.
ASTM C 807 [23] specifies the test method for determining the
setting time of cement mortar by penetration resistance using a
3

5. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
Figure 4. Repeatability of conductance spectra at first resonant
frequency (sensor 1).
Vicat needle. As cement mortar stiffens or sets, the resistance
required for the Vicat needle to penetrate into the mortar will
increase. The depth of the needle into the mortar sample
must be measured and recorded at regular time intervals. In
this experiment, three kinds of mortar mixes were evaluated:
without admixture (mix 1), with 3% accelerator (mix 2) and
with 0.5% retarder (mix 3). Both the accelerator and retarder
from CNG Korea Co. are a polycarboxylate-type admixture
that improves workability of mortar mixes. The mortar sample
without admixture was prepared by mixing cement, river sand
(passing through a 1.18 mm sieve) and water by a weight ratio
of 1:2:0.5. For samples with admixtures, the admixtures were
mixed with water first before adding them into the mixing
bowl. For all the samples, the total mixing time was 3.5 min
including pre-mixing of cement and sand for about 1 min.
Figure 5 shows the Vicat needle test results for all the mortar
samples. The setting time of the mortar can be determined as
follows [23]:
H − E
C − D
x(C − 10)
+ E (6)
where E is the time in minutes of the last penetration greater
than 10 mm, H is the time in minutes of the first penetration
less than 10 mm, C is the penetration reading at time E and D
is the penetration reading at time H.
This paper proposes an automated monitoring of setting
of cement-based materials, comparing the EMI measurement
results with the Vicat needle test results using the same
mortar samples explained earlier. When mixed with water,
cement mortar gradually transforms from the plastic to solid
state. Since measuring the penetration resistance of the mortar
samples by the Vicat needle has to be determined manually
and regularly, the proposed reusable sensing device presents
much less effort to monitor the physical changes of cement
mortar during hydration. The experiment was conducted using
a 50 mm × 50 mm × 50 mm mold with the sensor set-up as
shown in figure 6. Fresh cement mortar was poured in the mold
and the rod of the reusable sensor was embedded in the mortar
by suspending it using an acrylic plate.
Figure 5. Vicat needle test results.
Figure 6. Test set-up for monitoring setting of cement mortar.
The EMI measurements were performed for the frequency
range between 100 and 150 kHz, and the setting of cement
mortar was monitored by automatically measuring the changes
in the conductance spectra with respect to time at 10 min
intervals up to 24 h of curing at room temperature. Samples of
conductance spectra obtained using sensor 2 for the three mixes
are shown in figures 7(a)–(c). As can be seen, as curing time
passes by, the conductance spectra also change. As explained
before, the RMSD algorithm can be used for comparative
processing of two conductance spectra to quantify any changes
between the two. In this experiment, the RMSD values were
calculated between two successive data and presented with
4

6. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
Figure 7. Evolution of conductance spectra over time (sample 1).
respect to the curing time and compared with the Vicat needle
test results as shown in figures 8(a)–(c). The average RMSD
values for the three samples of each mix are shown to assess
the repeatability of the results. Mix 1 shows quite a variation
among the three samples but the variations in the RMSD
values reduced after about 200 min of curing. Compared to
mix 1, mixes 2 and 3 show better repeatability. The better
results observed for the two mixes compared to mix 1 could
be due to the use of the admixtures which helps to improve
the workability of the mixes. It is also noted that, for all the
mixes, the RMSD values decrease as the curing time passes
Figure 8. Data processing using RMSD.
and when the cement mortar is transformed from the plastic to
solid state. It can be seen that the RMSD values remain low
after the cement mortar has set.
4.2. Monitoring drying of hardened mortar
Monitoring moisture changes in concrete structures is
particularly useful because large moisture loss may cause
cracking in the concrete surface that impairs the aesthetics
5

7. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
Figure 9. Test set-up for monitoring drying of hardened mortar.
of the structures [24]. Moisture loss is also an indicator of
a durability problem in hardened concrete since moisture can
evaporate or diffuse from concrete through the pores within to
the surface. High porosity in concrete as a result of various
factors such as high water–cement ratio and poor compaction
is not favorable as the higher the porosity the lower the strength
of the concrete would be [25].
Recently, there have been studies carried out for
monitoring moisture changes in concrete by smart sensing
techniques. Yeo et al [26] embedded a sensor fabricated using
a fiber Bragg grating (FBG) coated with a moisture-sensitive
polymer for the detection of moisture in concrete. Stojanović
et al [27] successfully installed a wireless electronic sensor
in a clay brick and a concrete block to track the sensor’s
resonant frequency using an antenna, which is sensitive to
the presence of water in the materials. The proposed smart
monitoring device in this paper has also the potential to be used
for monitoring moisture changes in materials. The concept is
similar to the two described techniques where only a relative
moisture state can be detected and not the absolute value of
moisture content in a material. A calibration function needs to
be established in order to predict the moisture changes in the
material.
In this experiment, a 80 mm × 80 mm × 80 mm cubic
specimen was prepared using fresh cement mortar without
admixture as already described in section 4.1. The specimen
was demolded after 24 h and put in water for up to 28 days
of curing. At the end of the curing day, the specimen was
taken out from the water and surface-dried with cloth to ensure
a saturated surface dry (SSD) condition before measuring its
weight with a balance and obtaining the initial conductance
spectrum of the reusable sensor that was attached to the
hardened specimen as shown in figure 9. The weight loss and
the change in the conductance spectrum were monitored after
each day of exposure to ambient room temperature for five
days.
Figure 10 shows the total weight loss of the specimen
versus time, and the comparison between the RMSD values
and moisture loss rate is shown in figure 11. The RMSD values
are calculated between two compared exposure times while
the moisture loss rate is obtained by computing the percentage
Figure 10. Total weight loss of specimen due to drying over time.
Figure 11. Calculated RMSD values and moisture loss rate of
specimen.
change in weight loss of the hardened mortar after each day of
exposure to ambient room temperature. It is shown in figure 11
that greater change in the conductance spectrum occurs during
the first day of exposure and the RMSD values reduce as
the drying exposure time increases. It is also encouraging to
see that the moisture loss rate of the specimen as shown in
figure 11 has about the same pattern, where the rate followed
a decreasing trend until the fifth day. According to Azenha
et al [24], the drying process is mainly controlled by the
surrounding environment such as air temperature, wind and
humidity rather than moisture profile inside the material. As
drying proceeds, the rate of moisture loss decreases with less
water supplied to the material surface through the capillary.
Based on the decreasing trend of the RMSD values and the
moisture loss rate, it can be said that the specimen was almost
dried after five days of exposure to the ambient environment.
From figure 12, we can see that the RMSD values and the
moisture loss rate have a strong correlation, and by regression
6

8. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
Figure 12. Regression analysis between RMSD values and moisture
loss rate.
analysis, it is shown that the moisture loss rate can be predicted
based on the RMSD values using a logarithmic trend.
4.3. Monitoring damage in hardened mortar
There is an increasing interest in SHM and NDE of civil
infrastructures to monitor their serviceabilities under applied
loadings. Detection of minor incipient damages in critical
structural members is important because there have been many
cases of civil infrastructures such as bridges and buildings
that collapsed due to initiation of local cracks which were
not detected earlier. A range of well-developed techniques
such as acceleration-based modal testing, ultrasonic and x-
ray inspection are available for the detection of damage
in civil concrete structures, but these techniques require
complex algorithms or expensive and bulky equipment,
which are not attractive for real applications [28]. The
development of wireless impedance sensor nodes [29–31] has
made the EMI method more suited for field monitoring of
infrastructures. Traditionally, the EMI method is performed
using an impedance analyzer which is bulky. The key point
Figure 14. Load versus elapsed time.
in using sensor nodes for SHM is that they can be deployed
on large structures for continuous SHM, and the built-in
wireless communication can solve the problem of cabling of
the traditional monitoring system.
The previous study [15] had shown that the reusable set-
up is capable of detecting both surface and internal cracks
inside the concrete. In this experiment, the effectiveness of
the new reusable sensor proposed in this paper for monitoring
damage in hardened mortar is investigated. Figure 13 shows
the photographs of the experiment to monitor damage in a
hardened mortar specimen subjected to compression force.
The test was conducted using an Instron testing machine under
the displacement control at a constant head-loading rate of
0.015 mm s−1
. Damages were imparted on the specimen under
several loading levels (1050 kg (load 1); 5250 kg (load 2);
10 125 kg (load 3); 21 750 kg (load 4)) by performing repetition
of loading, unloading and reloading before allowing it to load
to failure as shown in figure 14. The EMI measurements were
taken under the unloading condition after each loading level.
Figure 15 shows the conductance spectra obtained using
sensor 2. The frequency range of 120–127 kHz was zoomed
in to examine the changes in the resonant frequency of the
measured conductance spectra more clearly. In the figure,
a large shift in the resonant peak can be observed after the
Figure 13. Monitoring damage in hardened mortar.
7

9. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
Figure 15. Changes in the conductance spectra as damage
propagated in the specimen.
specimen was loaded to failure. In figure 16, it is shown that the
calculated RMSD value with respect to the intact case (load 0)
of the specimen and the 1050 kg load level (load 1) is less than
5% (load 0 1). For the compared load1 2 and load2 3 cases,
the increase in the RMSD values was double that with load0 1.
During the experiment, hairline surface cracks were noticed
on the specimen after the load2 3 case but the calculated
RMSD value was only slightly higher than the load1 2 case.
This can be explained by the results obtained by Yang et al
[15] that shows a reusable PZT set-up is less sensitive to fine
localized cracks compared to surface-bonded PZT. In figure 16,
the RMSD value calculated cumulatively between the loading
levels increases as the damage state of the specimen becomes
more severe, where a dramatic increase in the RMSD value
can be observed after the specimen had failed. Overall, the
reusable sensor can be used for detecting progressive damages
in concrete structures due to applied loadings. The results show
that the proposed technique with the embedded rod is sensitive
to internal damage inside the structures at a certain depth.
Based on the sensitivity of the reusable sensor, the proposed
technique might be applicable for evaluating the prestress loss
of tension cables in prestressed concrete structures.
5. Conclusions
The new reusable impedance-based sensor introduced in this
paper has been shown to be effective when re-used for
repetitive tests. Experimental studies were conducted to
demonstrate the applicability of the reusable sensor for non-
destructive monitoring of cement-based materials. Using the
RMSD algorithm, the repeatability of the reusable sensor for
automatic monitoring of the setting of cement mortar of various
mixes was assessed. Setting time of the mortar samples was
verified using the conventional Vicat needle test, and it is found
that the RMSD values decreased as the curing time passed
and remained low after the cement mortar has set. In another
experiment, the reusable sensor was used to monitor moisture
changes in a mortar specimen and to verify the time taken
Figure 16. Calculated RMSD values due to progressive damages.
for complete dryness. As drying proceeded, the decreasing
trend of the RMSD values has a strong correlation with the
moisture loss rate, which can be predicted using a logarithmic
function. The experimental results of the damage monitoring
using the reusable sensor show that the proposed reusable set-
up is sensitive to internal damages due to the embedment of the
rod inside the mortar. The experimental demonstrations show
that the reusable sensor has good repeatability and reliability
even when used repetitively, and therefore is cost-effective.
Acknowledgments
The financial support by the Smart Infra-Structure System
Technology Center (SISTeC), KAIST and the Korean Science
and Engineering Foundation (KOSEF) through grants funded
by the South Korean government (MEST20090080587) is
greatly appreciated. The authors are also pleased to
acknowledge the Smart Systems and Structures Lab at KAIST
for the use of the Agilent 4294A impedance analyzer and
Ms Jiyoung Min for the help with Matlab programming.
References
[1] Song G, Gu H and Li H 2004 Application of the piezoelectric
materials for health monitoring in civil engineering: an
overview Earth Space 680–7 (doi:10.1061/40722(153)94)
[2] Park G, Sohn H, Farrar C R and Inman D J 2003 Overview of
piezoelectric impedance-based health monitoring and path
forward Shock Vib. Dig. 35 451–63
[3] Soh C K, Tseng K, Bhalla S and Gupta A 2000 Performance of
smart piezoceramic patches in health monitoring of a RC
Bridge Smart Mater. Struct. 9 533–42
[4] Naidu A and Bhalla S 2002 Damage detection in concrete
structures with smart piezoceramic transducers Int. Conf. on
Smart Materials Structures and Systems (Bangalore, July,
2002) ISSS2002/SA-538
[5] Park S, Ahmad S, Yun C-B and Roh Y 2006 Multiple crack
detection of concrete structures using impedance-based
structural health monitoring techniques Exp. Mech.
46 609–18
[6] Soh C K and Bhalla S 2005 Calibration of piezo-impedance
transducers for strength prediction and damage assessment
of concrete Smart Mater. Struct. 14 671–84
8

10. Smart Mater. Struct. 20 (2011) 085023 R Tawie and H K Lee
[7] Shin S W, Qureshi A R, Lee J Y and Yun C B 2008
Piezoelectric sensor based nondestructive active monitoring
of strength gain in concrete Smart Mater. Struct. 17 055002
[8] Tawie R and Lee H K 2010 Monitoring the strength
development in concrete by EMI sensing technique Constr.
Build. Mater. 24 1746–53
[9] Tawie R, Lee H K and Park S H 2010 Non-destructive
evaluation of concrete quality using PZT transducers Smart
Struct. Syst. 6 851–66
[10] Tawie R and Lee H K 2010 Piezoelectric-based non-destructive
monitoring of hydration of reinforced concrete as an
indicator of bond development at the steel-concrete interface
Cem. Concr. Res. 40 1697–703
[11] Benjeddou A, Trindade M A and Ohayon R 2000 Piezoelectric
actuation mechanisms for intelligent sandwich structures
Smart Mater. Struct. 9 328–35
[12] Annamdas V G M and Soh C K 2006 Embedded piezoelectric
ceramic transducers in sandwiched beams Smart Mater.
Struct. 15 538–549
[13] Annamdas V G M, Radhika M A and Soh C K 2009 Health
monitoring of concrete structures using embedded PZT
transducers based electromechanical impedance model Proc.
SPIE 7292 729225
[14] Divsholi B S and Yang Y 2009 Application of reusable PZT
sensors for monitoring initial hydration of concrete Proc.
SPIE 7292 729222
[15] Yang Y, Divsholi B S and Soh C K 2010 A reusable PZT
transducer for monitoring initial hydration and structural
health of concrete Sensors 10 5193–208
[16] Ikeda T 1990 Fundamentals of Piezoelectricity (Oxford:
Oxford University Press)
[17] Liang C, Sun F P and Roger C A 1994 Coupled
electromechanical analysis of adaptive materials—
determination of actuator power consumption and system
energy transfer J. Intell. Mater. Syst. Struct. 5 12–20
[18] Park G, Farrar C R, Lanza di Scalea F and Coccia S 2006
Performance assessment and validation of piezoelectric
active sensors in structural health monitoring Smart Mater.
Struct. 16 1673–83
[19] Giurgiutiu V 2008 Structural Health Monitoring with
Piezoelectric Wafer Active Sensors (London: Elsevier)
[20] PI Ceramic 2010 Datasheet http://www.piceramic.de/
[21] Piezo System 2010 Product Catalog http://www.piezo.com/
[22] Tseng K K-H and Naidu A S K 2002 Non-parametric damage
detection and characterization using smart piezoceramic
material Smart Mater. Struct. 11 317–29
[23] ASTM C 807 2008 Standard Test Method for Time of Setting of
Hydraulic Cement Mortar by Modified Vicat Needle
(West Conshohocken, PA: ASTM International)
[24] Azenha M, Maekawa K, Ishida T and Faria R 2007 Drying
induced moisture loss from mortar to the environment. Part
I: experimental research Mater. Struct. 40 801–11
[25] Mehta P K and Monteiro P J M 2006 Concrete: Microstructure,
Properties, and Materials 3rd edn (New York:
McGraw-Hill)
[26] Yeo T L, Eckstein D, McKinley B, Boswell L F, Sun T and
Grattan K T V 2006 Demonstration of a fiber-optic sensing
technique for the measurement of moisture absorption in
concrete Smart Mater. Struct. 15 N40–5
[27] Stojanović G, Radovanović M, Malešev M and
Radonjanin V 2010 Monitoring of water content in building
materials using a wireless passive sensor Sensors
10 4270–80
[28] Park S, Park S-K, Kim J-W and Chang H-J 2010 Debonding
condition monitoring of a CFRP laminated concrete using
piezoelectric impedance sensor nodes Proc. FraMCoS-7
(May, 2010) pp 1249–54
[29] Mascarenas D L, Todd M D, Park G and Farrar C R 2007
Development of an impedance-based wireless sensor node
for structural health monitoring Smart Mater. Struct.
16 2137–45
[30] Overly T G S, Park G, Farinholt K M and Farrar C R 2008
Development of an extremely compact impedance-based
wireless sensing device Smart Mater. Struct. 17 065011
[31] Min J, Park S, Yun C B and Song B 2010 Development of
multi-functional wireless impedance sensor nodes for
structural health monitoring Proc. SPIE 7647 764728
9