accepted manuscript a comparison of methods to evaluate mass transport in damaged mortar
TRANSCRIPT
Accepted Manuscript
A comparison of methods to evaluate mass transport in damaged mortar
Farnam Ghasemzadeh, Reza Rashetnia, Danny Smyl, Mohammad Pour-Ghaz
PII: S0958-9465(16)30045-2
DOI: 10.1016/j.cemconcomp.2016.03.007
Reference: CECO 2616
To appear in: Cement and Concrete Composites
Received Date: 3 April 2015
Revised Date: 13 February 2016
Accepted Date: 26 March 2016
Please cite this article as: F. Ghasemzadeh, R. Rashetnia, D. Smyl, M. Pour-Ghaz, A comparison ofmethods to evaluate mass transport in damaged mortar, Cement and Concrete Composites (2016), doi:10.1016/j.cemconcomp.2016.03.007.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service toour customers we are providing this early version of the manuscript. The manuscript will undergocopyediting, typesetting, and review of the resulting proof before it is published in its final form. Pleasenote that during the production process errors may be discovered which could affect the content, and alllegal disclaimers that apply to the journal pertain.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
1
A Comparison of Methods to Evaluate Mass Transport in Damaged Mortar
Farnam Ghasemzadeha, Reza Rashetniaa, Danny Smyla, Mohammad Pour-Ghazb∗
a Graduate Research Assistant, Dept. of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, NC, USA. b Assistant Professor, Dept. of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, NC, USA.
Abstract:
The service life of reinforced concrete (RC) structures is directly influenced by the
transport properties of concrete. These transport properties are adversely affected by the
presence of cracks. Therefore, for accurate service life estimation of RC structures the effect
of cracks on mass transport needs to be understood and quantified. To quantify the effect of
cracks, different measurement methods have been developed. In this paper, we compare
different mass transport measurement methods for quantifying the effect of damage, and
investigate which method is more sensitive and provides the most information on the effect of
damage.
In this work, damage was induced by freeze-thaw in mortar specimens. Mass transport
properties were measured using electrical resistivity, rapid chloride permeability, sorptivity,
drying, air permeability, water permeability, and desorption isotherm. The results indicate
that the measured effect of damage depends on the mechanisms of transport used in the
measurement technique, and therefore, different measurement techniques do not necessarily
provide the same measure of the effect of damage. The water and air permeability are
comparatively more sensitive to the presence of damage.
Keywords: Cracking; Distributed Damage; Durability; Freeze-thaw; Transport Properties.
∗ Corresponding author Address: Dept. of Civil, Construction and Environmental Engineering, North Carolina State Univ., Campus Box 7908. 431C Mann Hall, Raleigh, NC 27695, USA. Email address: [email protected]
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
2
1. Introduction
Distributed micro-cracking, referred to as damage hereafter, is commonly observed in
concrete structures. Damage may result from different deterioration processes, such as freeze-
thaw and alkali silica reaction. The presence of damage can significantly alter the transport
properties of concrete, adversely affecting the service life of structures. Therefore, in order to
account for the effect of damage on the service life of structures, its effects on mass transport
need to be quantified. Different methods have been developed to measure and quantify the
transport properties of cement-based materials. Many of these methods utilize different
transport mechanisms and, as such, provide different measures of the effect of damage on
mass transport properties [1]. We pose the following research questions: (i) how do different
measurement techniques show the effect of damage on mass transport? (ii) Which transport
measurement methods are more sensitive to the presence of damage? In line with these
questions, we experimentally compare different mass transport measurement techniques and
produce laboratory results that enable us to answer these questions.
Broadly, cracking in cement-based materials can be regarded as discrete cracking or
distributed cracking (damage). Researchers have investigated mass transport in cement-
based materials containing discrete cracks in fundamental works, such as the following:
Aldea et al. (1999) [2], who found that discrete cracks (40 -200µm crack widths) have a more
profound effect on water permeability than chloride permeability. Rodriguez (2001) [3]
showed that chloride diffusion increases in material with saw-cut simulated cracks and that
the lateral diffusion of chloride along the crack wall is nearly constant. Rodriguez and
Hooten (2003) [4] found that the depth of chloride penetration increases in cracked samples,
irrespective of the presence of mineral admixtures. Picandet et al. (2009) [5] found that crack
permeability increases with the cube of crack opening displacement in specimens with
discrete cracks in the range of 20-177 µm. They also concluded that the use of fibre
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
3
reinforcement increases the tortuosity of cracks. Pour-Ghaz et al. (2009) [6,7] investigated
the role of saw-cut geometry as an idealized physical model of discrete cracks using X-Ray
radiography and numerical simulations; their results indicated that the geometry of cracks
significantly affects the ratio of the rate of unsaturated flow parallel and perpendicular to the
crack. Akhavan et al. (2012) [8] quantified the effects of tortuosity on the rate of flow in
saturated discrete cracks and found that water permeability increases with the square of crack
width and increasing tortuosity decreases water permeability by a factor of 4-6. Bentz et al.
(2013) [9] simulated the influence of transverse cracking on chloride penetration into
saturated concrete. They concluded that a simple 2-D simulation that considers diffusion may
provide a conservative estimate on the influence of cracking of the projected service life of
the concrete structures.
An early study investigating the effects of distributed damage on mass transport in
concrete was presented by Samaha and Hover (1992) [10]. In this study, distributed cracking
was induced by loading a specimen to 75% of its compressive strength; their results showed
that chloride mitigation, tested by the Rapid Chloride Permeability Test, increased by
approximately 20%. Breysse et al. (1994) [11] found that water permeability increases in
concrete with distributed cracking generated from tensile loading. Some examples of
continued research in this area include the works of Gérard and Marchand (2000) [12], who
developed a simulation model for distributed cracking in concrete, finding that the presence
of fracture networks increases diffusivity of cement-based material by a factor of 2-10. Yang
et al. (2006) [13] subjected concrete to freeze-thaw as well as compressive loading (up to
90% of the compressive strength), finding that distributed cracks resulting from both damage
mechanisms increased the connectivity of the fracture network, resulting in a reduction in
electrical resistivity and increased sorptivity of the materials. Torrijos et al. (2010) [14]
experimentally investigated the effects of ASR and thermally-induced cracking on concrete
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
4
sorptivity. Their findings showed that sorptivity generally increases proportional to thermal
damage but deceases after a threshold value. Chunsheng et al. (2012) [15] used compressive
loading to induce distributed damage in concrete; these authors quantified damage using
ultrasonic pulse velocity and found that damage increases air permeability significantly,
while sorptivity and electrical resistivity were more strongly correlated to the total open
porosity than damage alone. Chunsheng et al. (2012) [16] continued previous work in [15]
finding that many transport properties, such as sorptivity, air permeability, electrical
resistivity, and effective porosity are significantly affected by crack density. M’Jahad et al.
(2014) [17] found that gas breakthrough pressure was a reliable indicator of damage presence
in concrete. Concrete with freeze-thaw damage was shown to increase the amount of
absorbed water and chloride penetration depth in Wang and Ueda (2014) [18]. Most recently,
Ghasemzadeh and Pour-Ghaz (2014) [1] investigated the effects of freeze-thaw damage in
concrete on transport mechanisms by providing experimental measurements and analytical
models describing the effects of damage. They concluded that measurement techniques that
are not based on the same transport mechanism will show the effects of damage on mass
transport differently. Ghasemzadeh and Pour-Ghaz (2014) [1] provided this argument mainly
based on their analytical models and suggested that further experimental work is necessary to
better understand how the observed effect of damage depends on the method of observation.
A brief summary of previous research on the effects of discrete and distributed fractures is
shown in Table 1. Note that, for brevity, only experimental works investigating the effect of
damage on specific mass transport mechanisms are included in Table 1.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
5
Table 1: Summary of previous studies on mass transport in cracked cement-based materials 1
Study Mechanism of cracking
Type of cracking
Type of materials
Measurement methods Highlights
Aldea et al. (1999) [2]
Split tensile load-induced cracking
Discrete Concrete Water and chloride permeability Water permeability is a more sensitive parameter, than chloride permeability, to crack width.
Rodriguez (2001) [3], Rodriguez and Hooten [4] (2001)
Split tensile load-induced cracking and saw-cut cracking
Discrete Concrete Water and chloride permeability Lateral chloride diffusion is roughly the same along the crack length, chloride diffusion increases in the presence of cracks, and water permeability is more significantly affected by crack presence than chloride diffusivity.
Picandet et al. (2009) [5]
Split tensile load-induced cracking
Discrete Concrete Gas and water permeability Cracks provide direct paths to convey a large portion of flow, with no influence from the degree of saturation. Permeability could be considered as an intrinsic parameter to evaluate the global effect of load-induced damage on concrete durability.
Pour-Ghaz et al. (2009a,b) [6.7]
Saw-cut crack Discrete Concrete Attenuation of X-Ray radiation the geometry of cracks significantly affects the ratio of the rate of unsaturated flow parallel and perpendicular to the crack
Akhavan et al. (2012) [8]
Split tensile load-induced cracking
Discrete Mortar Water permeability and image analysis on cracks
Permeability is a function of the square of crack width. Crack tortuosity and roughness reduce the permeability.
Samaha and Hover (1992)[10]
Compressive load-induced cracking
Distributed Concrete &
Mortar RCPT and Water absorption
The water absorption and chloride ion penetration differently reflect the effect of damage on transport properties of concrete as load levels increases.
Breysse et al. (1994) [11]
Tension-induced cracking (P.I.E.D.)
Distributed Concrete Water permeability Water permeability, measured perpendicular to tensile loading, is shown to increase as damage (load) increases.
Yang et al. (2006) [13]
Freeze-thaw loading Distributed Concrete Water absorption and electrical resistivity
Sorptivity increases linearly with damage; electrical conductivity increases in a bilinear fashion.
Torrijos et al. (2010) [14]
Low RH with high temperature and ASR
Distributed Concrete Water absorption and water permeability
Depending on the main transport mechanism, crack width, type of cracks and crack density differently affect the transport properties.
Chunsheng et al. (2012)[15]
Compressive load-induced cracking
Distributed Concrete Air permeability, sorptivity and electrical resistivity
While gas permeability correlated with damage, sorptivity and electrical resistivity correlated with open porosity – the connected pores available for fluid flow.
Chunsheng et al. (2012)[16]
Compressive load-induced cracking
Distributed Concrete Water absorption, gas permeability, electrical resistivity and crack geometry analysis
Crack geometry (i.e., length, orientation, and connectivity) and crack density have strong impact on transport properties.
M’Jahad et al. (2014) [17]
Freeze-thaw loading Distributed Concrete Mercury intrusion porosimetry, desorption isotherm, and gas breakthrough pressure
Gas breakthrough pressure seems to be a more sensitive indicator of damage than other studied methods.
Wang and Ueda (2014) [18]
Freeze-thaw loading Distributed Concrete Water absorption and chloride ion penetration
Water absorption and chloride penetration occurs at a higher rate in damaged specimens compared with undamaged concrete. The total amount of absorbed water in damaged specimens is more than undamaged specimens.
Ghasemzadeh and Pour-Ghaz (2014) [1]
Freeze-thaw loading Distributed Concrete Water absorption, electrical resistivity, desorption isotherm and saturated hydraulic conductivity
The rate of moisture transport increases with damage. The extent to which damage affects the rate of transport is dependent on the mechanism of transport. Saturated hydraulic conductivity is a much more sensitive parameter to damage due to the higher dependence of saturated hydraulic conductivity to crack width.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
6
Four conclusions can be drawn from the above literature review and the summary
provided in Table 1. (1) The effect of discrete cracking is better understood as compared to
the effect of damage. (2) It is unclear as to which transport mechanism, and subsequently
which measurement technique, is more sensitive to the presence of damage. (3) The majority
of these studies have used only a few mass transport measurement methods and, to the
knowledge of the authors, the effect of damage has not been interpreted in the light of
transport mechanisms used in these measurement methods. For example, it has been shown
that while cracking can increase water permeability several orders of magnitude [19],
diffusivity is less affected by cracking [2,3,4,18], but the relationship of the data to the
mechanisms of mass transport was not discussed. (4) The sensitivity of different methods to
the presence of damage is not discussed in the previous works.
The present work aims to develop a better understanding of the effects of damage on mass
transport in damaged cement-based materials by investigating the mechanisms of mass
transport involved. In this work, damage was induced by freeze-thaw loading in mortar
specimens. Active acoustic emission (AE) was used to quantify the degree of damage.
Passive AE was also used to monitor damage formation during the freeze-thaw cycles.
Electrical Impedance Spectroscopy (EIS) and four-electrode Wenner methods were used to
measure the bulk and surface electrical resistivity, respectively. Rapid Chloride Permeability
Test (RCPT), sorptivity, drying, air permeability, water permeability, and desorption
isotherm measurements were also carried out. In the following sections, the materials and
methods used are described. Then, the results are presented and discussed. Finally, the
conclusions of this study are presented.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
7
2. Materials and Specimen Preparation
2.1. Mixture proportioning and specimen preparation
The mortar mixture was made with Ordinary Type I Portland Cement (OPC) and had a
water-to-cement ratio (w/c) of 0.42. The fine aggregate consisted of natural river sand with a
fineness modulus of 2.65 and a maximum aggregate size of 2 mm. The fine aggregate mainly
consisted of silica and had 0.90% saturated surface dry (SSD) moisture content. The cement,
aggregate, and water reducer content in the mixture were 609 kg/m3, 1466 kg/m3, and 0.50
kg/m3, respectively. The mortar mixture was prepared following ASTM C192 [30].
The mortar mixture was cast in 102 mm x 204 mm cylindrical molds. Mortar cylinders
were kept sealed for the first 24 hours and were then demolded and cut into appropriate
geometries (for different experiments as discussed below in Table 2) using a diamond-tipped
wet saw. Top and bottom ends of the cylindrical specimens (roughly 25 mm) were cut and
discarded to minimize the possible end-effects. While cutting the specimens may result in
microcracking close to the cut surfaces, this damage is significantly smaller than the damage
due to freeze-thaw which was monitored as described later. All of the specimens were cured
in lime-saturated water at 25±1ºC for 18 months after cutting to achieve high degree of
hydration, a uniform saturation, and a uniform initial condition.
2.2. Number of Specimens Used in Each Test
A large number of tests were performed in this work. A detailed description of each test is
provided in the Methods Section. Table 2 reports the total number of specimens and the
number of replicates used in each test. All tests included a set of reference specimens (with
no damage) with the same number of replicates indicated in Table 2. The dimensions of the
specimens used in each test are also reported. The size of the specimens for each test method
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
8
was chosen based on the standard test method or previously published literature when
applicable. It should be noted that the dedicated specimens were made for each test and
specimens were not used in multiple tests. Furthermore, dedicated specimens were made for
each degree of damage in each test, except for acoustic emission and surface resistivity where
measurements were performed on the same set of specimens at all degrees of damage due to
the non-invasive nature of these tests. All the specimens had the same age at the time of
testing.
Table 2: The number of specimens, number of replicates, and specimen dimensions used in each test
Test Method Specimen Information
Total Number of specimens
Number of Replicates*
Diameter [mm]
Thickness [mm]
Acoustic Emission (AE) 6** 3** 102 25 and 50 Rapid Chloride Permeability Test (RCPT)
24§ 4 102 50
Electrochemical Impedance Spectroscopy (EIS)
24§ 4 102 50
Surface Resistivity (SR) 3** * 3** * 102 204 Sorptivity 12§§ 2 102 25 Drying 12§§ 2 102 50 Air permeability 18§§§ 3 102 25 Water Permeability 24§ 4 102 25
Desorption isotherm 8£ 2 Specimens with 0.50-1.5 mm thickness and 50-100 mg weight€
*Indicates the number of samples for each degree of damage. ** Due to the non-invasive nature of the test the same set of specimens were monitored during the freeze-thaw loading. Two different sample thicknesses were used with three replicates for each thickness. *** Due to the non-invasive nature of the test the same set of specimens were monitored during the freeze-thaw loading. §Five degrees of damage and a set of reference with four replicates (6x4 = 24). §§Five degrees of damage and a set of reference with two replicates (6x2 = 12). §§§Five degrees of damage and a set of reference with three replicates (6x3 = 18). §§§Three degrees of damage and a set of reference with two replicates (4x2= 8). €Specimens were cut from the center of 25 mm x 102 mm disk using a precision Scanning Electron Microscope wet-saw.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
9
3. Methods
3.1. Freeze-thaw loading
Freeze-thaw loading was performed in an air-cooled chamber. Each cycle was 4 hours in
duration including a cooling period from 21˚C to -35˚C, and a heating period back to 21˚C.
The cooling and heating periods included two ramps as well as two constant temperature
periods (temperature profile shown Figure 1). These constant temperature periods were
designed to allow the specimen to equilibrate with the surrounding air, decreasing the
temperature gradient across the samples. This freeze-thaw loading profile was chosen
following references [1, 31]. The core temperature of a set of specimens was monitored using
embedded thermocouples. Type K thermocouples with an accuracy of 0.1oC were used. To
keep the specimens saturated, during the freeze-thaw testing, they were wrapped in a water
saturated cloth and then were sealed with a thin layer of plastic sheet [31]. A total of 25
freeze-thaw cycles were used and a set of specimens were removed from the chamber for
testing after 2, 5, 10, 15, and 25 cycles.
3.2. Acoustic Emission
Cracking and permanent deformation of materials results in the release of strain energy.
The released strain energy, in turn, leads to the generation and propagation of elastic stress
waves. These stress waves cover a wide range of audible and inaudible frequencies and are
known as acoustic waves. Passive AE describes a technique that captures and digitizes the
acoustic waves in the form of electric signals at the surface of a material or structure. To
convert the captured acoustic waves into electrical signals, piezoelectric sensors are used. In
this work, passive AE was used to continuously monitor damage formation and cracking
during the freeze-thaw cycles. Circular AE sensors with a peak frequency of 375 kHz were
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
10
used. The diameter of the piezoelectric surface of the AE sensors was 2.00 cm. A Vallen
AMSY-6 acoustic emission equipment set with VS375 sensors manufactured by Vallen
Systeme were used.
In this work, active AE was used to monitor the damage in mortar specimens at the end of
a predefined number of freeze-thaw cycles (Fig. 2). Active AE describes a method in which a
series of pulse (a total of four discrete pulses in this work) is sent by an AE sensor and is
captured by another sensor (pitch-catch). Then, the order of sending and receiving the pulses
is switched between the two sensors. The transmission time is measured for each pulse and
the average value is reported (average of eight transmission times). While similar to
Ultrasonic Pulse Velocity measurements, the active AE measurements are generally more
sensitive due to the high frequency of the AE sensors. In this work, active AE measurements
were performed using the same sensors and equipment set used in passive AE measurements.
To mount the AE sensors on disk specimens, flat surfaces were created on the perimeter of
the circular disk specimens by trimming the specimen perimeter (tangent to the perimeter).
Due to the small size of the sensors, only a maximum trimming depth of 5 mm was necessary
which only negligibly affected the circular shape of the disk. AE sensors were coupled to the
specimen using vacuum grease at 180o with respect to each other, performing measurements
along the diameter of the specimen. Specimens were placed on a layer of acoustic mat resting
on a rigid stainless steel frame which was isolated from the chamber to minimize vibration
and noise. A stainless steel rod was also used as a reference specimen to monitor the
environmental noise during the test and to ensure that the coupling agent did not degrade
during the freeze-thaw cycles [31]. Further detailed information regarding the application of
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
11
AE system on damage monitoring in cement-based materials can be found elsewhere [1, and
31-34].
3.3. Rapid Chloride Permeability Test (RCPT)
Rapid chloride permeability test (RCPT) is often used as an indirect measure of material
permeability. In this test, a constant potential difference (typically 60 volts) is applied across
a concrete disk specimen, through solutions of sodium hydroxide and sodium chloride on two
different sides of the specimen, and the amount of electric charge passing through the
specimen is measured by monitoring the current required to maintain the constant potential
difference. The total amount of electric charge passed through the specimen is then estimated
based on the measured current during the first six hours of the test. The total charge (in
coulombs) is then used as an indirect measure of permeability. In the present work, RCPT
was performed according to ASTM C1202 [35] using an in-house developed equipment set
meeting all of the specifications of ASTM C1202.
3.4. Surface Resistivity
In this work, surface resistivity was measured using a four-electrode Wenner probe on 102
mm x 204 mm cylinders. The equipment utilized a 40 Hz alternating current (AC). Note that
the ends of the specimens used for surface resistivity were not cut. This however does not
affect the measurements since the distance between the outer two electrodes of Wenner probe
equipment was smaller than the total length of the cylinder, and therefore, the Wenner probe
measured the average properties between the outer two electrodes (i.e., the results are not
influenced by the end of the specimens) [36]. Before measurements, specimens were taken
out of the chamber and were kept in a large water container until they reached thermal
equilibrium with the ambient temperature (approximately 24 hrs). Note that, the specimens
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
12
were not taken out of the plastic wrap before placing them in the water tank. Therefore, the
plastic wrap prevented entry of extra water into the specimen. After each measurement,
specimens were placed back in chamber to undergo the same number of freeze-thaw cycles as
other specimens.
3.5. Electrical Resistivity
The bulk electrical resistivity measurements were performed on 50 mm thick disk
specimens. Three different arrangements were used in measuring bulk electrical resistivity.
First, the specimens were sandwiched between two stainless steel plate electrodes and, to
improve electrode contact, a copper sulphate based conductive gel was used. Stainless steel
plate electrodes were connected to the EIS equipment [36, 37]. Second, specimens were
installed in a RCPT cell and EIS was used to measure the bulk resistivity [38]. Finally, the
initial currents from the RCPT measurements were utilized to measure the bulk electrical
resistivity [39]. Note that in all three measurement arrangements, the direction of the
measurement was perpendicular to the circular cross-section of the specimen. To provide a
better comparison, the same specimens were used in all three measurement arrangements for
each degree of damage. EIS measurements were performed with amplitudes of 500 mV over
the frequency range of 1.0 Hz to 1.0 MHz. Before measurements, specimens were kept in a
large water container while wrapped in plastic sheets until they reached to thermal
equilibrium with the ambient temperature (6-8 hours).
3.6. Sorptivity
The sorptivity test, in general, describes the upward water absorption by capillary suction
in concrete. To measure the amount of the absorbed water by the specimen, the specimen is
placed in contact with water and the mass of the specimen is monitored over time. In this
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
13
work, water absorption was carried out following ASTM C1585 [40] on 25 mm thick disks.
The perimeter of the specimens were sealed using epoxy coating. To avoid contamination of
circular cross-sectional surfaces with epoxy, they were covered with pieces of paper during
the application of epoxy. The top circular cross-sectional surface that was not in contact with
water was covered with a loose layer of plastic that was secured to the specimen with a
rubber band as specified by ASTM C1585 and similar to the works by Castro [41, 42]. The
measurements were carried out up to 150 days.
3.7. Drying test
The drying rate of mortar specimens with different degrees of damage were measured by
monitoring mass loss in a chamber with a relative humidity of 50 ±5 % at 23±1°C. Prior to
weight loss measurements, specimens were saturated under high vacuum (0.015 mm
Mercury). Weight loss was continuously recorded with one minute intervals for the first 10
hrs using an automated digital scale and then the measurements were continued daily, up to 7
days, and weekly up to 60 days. Only one surface of the sample was subjected to drying and
all other surfaces were sealed using epoxy coating.
3.8. Air Permeability
The air permeability of mortar specimens were measured using the method outlined in [43,
44]. In this method, a circular disk specimen is placed against a cylindrical chamber of
known volume. The air in the chamber is evacuated to a known pressure using a vacuum
pump. Then, the pressure drop in the chamber is monitored as a function of time while air
permeates through the specimen. In this work, a vacuum pressure of 736 mm Hg was induced
and the time to reach to 635 mm Hg was measured. Depending on the permeability of the
specimens, measurements were completed in 1 to 30 minutes. To ensure air tightness of the
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
14
equipment seals, initial tests were performed on a 25 mm thick aluminium disk and no
pressure decay was observed for 24 hours.
The circumference surface of the specimens was coated with a rapid-setting epoxy to
induce one-dimensional air flow through the circular cross-section of the disk. All the
specimens were dried in an oven at 50+2°C for 48 hrs before the measurements. This
essentially resulted in complete drying of the specimen eliminating the effect of initial
moisture content of the samples while minimizing additional cracking since this drying does
not produce large temperature gradients across the specimen [45]. A thin strip of soft clay
was also used to seal the chamber to the face of specimen.
The Boyle-Marriotte law was used to calculate the air permeability assuming that the
specimen is a homogeneous porous material. Air permeability index is calculated per Eq. 1
[44].
������ =� − ����
�∆�� �� −������ �
�� ��. 1
where ������ is the air permeability index (m2/s), � and are the initial and final vacuum
pressure in the chamber (Pa) respectively, �� is the volume of vacuum chamber (m3), ∆� is the
duration of measurement (s), � is the atmospheric pressure (Pa), � is the thickness of
specimen (m), and � is the cross sectional area of the specimen (m2).
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
15
3.9. Water Permeability
Water permeability describes flow of water through water-saturated porous material under
a pressure gradient. In this work, measurements were performed using in-house developed
equipment. The details of the water permeability equipment are discussed in the previous
study by the authors [1]. Briefly, this equipment works by measuring the pressure of a
column of water on top of the specimen using an ultra-sensitive pressure sensor. As the water
permeates in the porous material, the pressure drops and permeability of material can be
calculated using this pressure drop. All measurements were performed at 23±1°C.
3.10. Desorption Isotherm
The desorption isotherm of mortar specimens with different degrees of damage were
measured using an automated vapour sorption analyser (Q5000SA manufactured by TA
Instruments). The measurements were performed at 23˚C. In each measurement, the
specimen was equilibrated at 97.5% RH (relative humidity) and the RH was sequentially
dropped from 97.5% to 0% RH, in 5% RH increments to 2.5% and then to zero RH. The
sample was held at each RH step until it reached to equilibrium. The equilibrium was defined
as a mass change less than 0.001mg within 15 min [46]. This equilibrium criterion is tested
and validated based on the extensive works in [31, 37, 42, 46, and 47]. The specimens were
0.50-1.5mm thick and 50-100mg in weight. A full description of desorption isotherm
experiment using automated sorption analyser has been discussed in [31, 37, 42, 46, and 47].
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
16
4. Results and Discussion
4.1. Acoustic Emission
Figure 1 illustrates the results of passive AE testing during the freeze-thaw cycles. Figure
1a and 1b show the AE peak amplitude distribution during the first and the last 5 freeze-thaw
cycles for mortar disks with 25 mm thickness. Figure 1c shows the total number of AE hits in
each freeze-thaw cycles for 25-mm thick samples. The same plots presenting the results for
50-mm thick samples are shown in Figs. 1d, 1e, and 1f respectively. Clearly, in Figs. 1c and
1f a higher numbers of hits are captured during the first few cycles as compared to the
subsequent cycles, signifying that a large number of cracks develops in the first few freeze-
thaw cycles and the rate of formation of cracks decreases in subsequent cycles [1, 31].
Figure 2 shows the degree of damage measured with active AE after a given number of
freeze-thaw cycles. The degree of damage (D) is calculated based on the wave travel time in
damaged and undamaged specimens using � = 1 −�� �⁄ �� where � and � are wave
transmission time in undamaged and damage material respectively. In Fig. 2 results for
specimens with 50 mm and 25 mm thickness are labelled by AE-50 and AE-25 respectively.
Note that the error bars in Fig. 2 show the range of the measurements. A linear increase of
damage with the number of freeze-thaw cycles is observed. Slightly higher damage is
observed in 25-mm thick samples. This may in part be a result of a lower core temperature in
25-mm thick disks as compared to 50-mm thick samples.
Note that while in Fig. 2 damage increases approximately linearly with the number of
cycles, the number of AE hits significantly decreases in later cycles as seen in Figs. 1c and 1f,
the latter indicating the reduction in the rate of development of new cracks. This observation
is consistent with previous study by the authors which indicates that in the later freeze-thaw
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
17
cycles (or higher degrees of damage) the average crack width increases with a higher rate as
opposed to the formation of new cracks. In fact, the increase of degree of damage at higher
damage levels can be mainly attributed to the increase in the crack width. An analytical
model to describe this was previously presented in [1]. In addition to increased crack width,
crack density increases, resulting in crack network percolation. Crack network percolation
results in a high degree of damage.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
18
Figure 1: Damage formation during the freeze-thaw loading monitored by passive acoustic emission: (a) peak amplitude distribution during the first 5 cycles in 25-mm thick samples, (b) peak amplitude distribution during the last 5 cycles in 25-mm thick samples, (c) the total number of AE hits in each freeze-thaw cycle in 25-mm thick samples, (d) peak amplitude distribution during the first 5 cycles in 50-mm thick samples, (e) peak amplitude distribution during the last 5 cycles in 50-mm thick samples, (f) the total number of AE hits in each freeze-thaw cycle in 50-mm thick samples.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
19
Figure 2: Damage measured using active acoustic emission.
4.2. Rapid Chloride Permeability Test (RCPT)
Figure 3 illustrates the results of RCPT for specimens with different degrees of damage.
Figures 3a and 3b show the current flow over time and the total charge passed (coulombs),
respectively. In both Figs. 3a and 3b the error bars indicate the full range of measurements
(maximum and minimum). In Fig. 3a while the current continuously increases over time at
low damage levels, at higher damage levels current initially increases and then decreases.
This reduction of current at later times affects the total charge passed in specimens with
higher damage levels: in Fig. 3b the total charge passed increases with damage and then it
reaches to a plateau at high degrees of damage. Consequently, the difference between the
total charged passed from D=25.21% to D=44.09% is rather insignificant, making the
reliability of RCPT questionable at high damage levels.
There are three possible explanations for the observed plateau in Fig. 3b. First, in high
damage levels, the chloride concentration reduces in the NaCl solution cell due to the rapid
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
20
transfer of high amount chloride ions to NaOH solution cell. This in turn reduces the amount
of current transfer by chloride ions through the specimen. Second, the chloride concentration
may be reduced in the system due to the chloride binding of hydration products [48]. In the
presence of high degree of damage, a higher amount of chloride ions can move into the
specimen, thus increasing the chance of chloride binding, and therefore, decreasing the
amount of current transfer by chloride ions [49]. Third, during the chloride binding a portion
of chloride ions can be replaced by the OH ¯ ions. Once OH ¯ ions are released, simultaneous
diffusion and migration occurs, and therefore, OH ¯ ions could either move to the catholyte
solution (NaCl solution) side through diffusion mechanism or to the anolyte solution (NaOH
solution) side through the migration mechanism [50]. The OH ̄ ions movement mechanism
depends on the concentration of OH ¯ ions in the pore solution. According to the results in
Fig. 3, it seems that the OH ¯ ions movement mechanism changes into diffusion mechanism
in specimens with high damage levels, thus reducing the current passed through the
specimen. It should be also noted that specimens were kept 18 months in lime-saturated
water and it could be safely assumed that cement particles were well hydrated. Therefore,
healing of the cracks could not be a potential contributor to the current reduction in damaged
specimens.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
21
Figure 3: The results of Rapid chloride penetration test (RCPT): (a) current flow during the
test, (b) total change passed.
4.3. Electrical Resistivity
Figure 4a illustrates the normalized bulk resistivity of mortar specimens measured using
the three bulk resistivity measurements discussed in Section 3.5 (i.e., stainless steel plates
with EIS, RCPT cell with EIS, and using initial RCPT current). The results are normalized to
the initial resistivity of the undamaged specimen. In all three sets of measurement, the
normalized bulk resistivity decreases with damage. The error bars in Fig. 4a and 4b show the
range of measurements. Resistivity decreases with a high rate initially when a large number
of cracks form in the specimens. With further increase of damage, the electrical resistivity
decreases with a lower rate, consistent with AE results. The results obtained using stainless
steel plates show a lower resistivity at all damage levels as compared to other methods. This
is mainly due to reduced contact impedance when conductive gel is used in measurements
[51].
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
22
Figure 4: (a) Normalized bulk electrical resistivity, to the resistivity of undamaged mortar
measured using stainless steel plates with EIS, using RCPT cell with EIS, and using initial
RCPT current, (b) normalized surface resistivity as a function of damage.
Figure 4b illustrates the normalized change of surface resistivity with damage. It should be
noted that the degrees of damage were not measured for these cylinders and we have assumed
the same degree of damage for the cylinder specimens and 50-mm thick disks at equal
number of freeze-thaw cycles. While this may not be a completely correct assumption, it
provides a first order approximation. In Figure 4b the normalized surface resistivity decreases
with increase of damage with a similar trend observed in bulk resistivity in Fig. 4a. While
there is a slight difference between the bulk and surface measurements, the simplicity of
surface resistivity measurements potentially put forward the idea that this technique might be
used to evaluate freeze-thaw damage on cement-based materials provided the boundary
conditions and temperature effects are well controlled. More investigation, however, required
to correlate surface resistivity to damage.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
23
4.4. Sorptivity
Figure 5 illustrates the results of water absorption during the first 150 days. Figures 5a
shows the volume of the absorbed water (mm3) normalized to the surface area of the
specimen (mm2) as a function of square root of time. Figure 5b shows the same results
presented in terms of degree of saturation. Figure 5a shows that the total water absorption
increases with damage, indicating the physical change in pore structure [1]. Also, at early
stages of water absorption, the rate of water absorption increases with damage. Furthermore,
in Fig. 5a, specimens with high levels of damage plateau more rapidly. This observation
indicates that unsaturated cracks and capillary pores are rapidly filled with water, and then,
water diffuses into the larger air voids. Figure 5b also shows that specimens with high level
of damage reach to higher degree of saturation earlier as compared to specimens with a lower
level of damage.
Figure 5c illustrates the normalized initial and secondary sorptivity of the damage
specimens (normalized to the initial and secondary sorptivity of the undamaged samples,
respectively). Both normalized initial and secondary sorptivity are indicated by S/So on the
vertical axis. The initial sorptivity is the slope of the first linear region of the sorption test in
Figure 5a, and the secondary sorptivity is the slope of the second (late stage) linear region in
Figure 5a. Figure 5c shows that initial sorptivity increases almost linearly with increase of
damage. The secondary sorptivity, however, initially decreases with an increase of damage at
low damage levels, and then, remains constant at higher damage levels. It seems that the
secondary sorptivity is independent of degree of damage at high levels of damage. Authors
have previously discussed that cracks change water absorption mechanism in damaged
specimens [1]. Briefly, in the initial phase of water absorption, cracks act as capillary tubes
that absorb water rapidly, provide access to capillary pores away from the exposed surface,
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
24
and provide access to large air-filled voids. At later stage, air diffusion and dissolution
mechanisms play a more significant role in water absorption [1, 52].
Figure 5: (a) Water sorption of mortar specimens with different degrees of damage during the
first 150 days; (b) water sorption results expressed in terms of degree of saturation for mortar
specimens with different degrees of damage; (c) normalized initial and secondary water
sorptivity of mortar specimens as a function of damage.
4.5. Water and Air Permeability
Figures 6a and 6b illustrate the results of air permeability and water permeability
measurements, respectively. Both results are normalized to the respective permeability of the
undamaged mortar. Note that in Fig. 6a, K(air) is air permeability index as opposed to the
actual permeability. The results in Figs. 6a and 6b show that air and water permeability
exponentially increase with damage. The rapid increase of air and water permeability with
damage can be attributed to the high volume of crack density, increase in crack width, and
crack percolation.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
25
Figure 6: Normalized permeability of damaged specimens to the permeability of
undamaged specimen: (a) air permeability, and (b) water permeability.
4.6. Drying
Figure 7 illustrates the results of the drying test presented in terms of total remaining water
in the specimens as a function of square root of time (to better illustrate the water loss at early
ages). In Fig. 7, it is observed that the rate of drying increases with damage since cracks
provide paths for water to migrate to the surface. This mechanism is commonly referred to as
the wicking [53]. Once water dries from the surface, cracks start to drain the interior water in
cracks and capillary pores. From Fig. 7, it seems that once all the water in cracks is wicked to
the surface, the mechanism of drying changes to the diffusion of water vapour. However,
there is certainly some overlap between these two mechanisms in a transition period.
It is also important to note that in Fig. 7, the total amount of water present in the samples
increases significantly with damage. In Table 3, the saturation water content, the residual
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
26
water content (the remaining water at the end of drying experiment after 60 days), and the
amount of evaporated water (difference between initial and residual water) are provided for
specimens with different degrees of damage. The saturation and residual water were
determined by drying specimens in an oven at 50˚C for two days (different samples were
used). As shown in Table 3, specimens retain significantly more water in the cracks as
damage increases, resulting in supplying more water to the surface of specimen during drying
test, and consequently, increasing the rate of drying.
Figure 7: Weight loss due to evaporation of water from mortar specimens with different
degrees of damage during the first 60 days.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
27
Table 3: Change in water content in specimens with different degrees of damage.
Damage
Amount of water in different conditions (g)
Water content at Saturation
Residual Water Evaporated
Water 0.00% 30.92 17.74 13.18
3.17% 35.26 18.86 16.4
7.57% 49.00 18.1 30.90
14.00% 59.37 21.25 38.12
25.21% 63.95 22.72 41.23
44.09% 69.72 25.42 44.30
4.7. Desorption Isotherm
The desorption isotherm of specimens with different degrees of damage are shown in the
Figure 8. Clearly, the water content gradually increases with damage at intermediate relative
humidity values, followed by a rather large increase at high relative humidity values. The
higher water content in mortar specimens with higher levels of damage can be explained by
the contribution of cracks acting as capillary porosity and retaining more water within the
material. The desorption isotherms can be used to provide a quantitative measure of size
distribution of the cracks. Note that, however, the desorption isotherms are obtained up to
97.5% RH, while cracks within the samples cover equivalent crack widths (Kelvin radius)
much larger than that corresponding to relative humidity of 97.5%. Therefore, the entire
information about the crack distribution is not necessarily included in the isotherms in Fig. 8.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
28
Figure 8: Desorption isotherm of mortar specimens with different degrees of damage.
5. Evaluating Transport Measurement Methods
Results of the laboratory tests on moisture transport in mortar specimens with different
degrees of damage shows that transport measurement methods reflect the effects of damage
differently. Table 4 summarizes how each measurement technique shows the effect of
damage. Depending on the mechanism of mass transport used in the measurement, the effect
of damage changes significantly. It can be seen that RCPT and electrical resistivity are not
sensitive methods at high damage levels (above 20% damage) while total amount of charge
measured with RDPT and electrical resistivity linearly vary with damage at low damage
levels (below 20% damage). Initial sorptivity increases linearly with damage in the entire
range of damage measured in this work, but secondary sorptivity initially decreases with
damage (up to 10% damage) and then remains approximately constant at all damage levels.
Finally, both air and water permeability increase exponentially with damage.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
29
Table 4: Comparison of different transport measurement methods
Method Effect of Damage Mechanism of measurement
Rapid Chloride Penetration Test (RCPT)
Linearly increases at low damage levels; remains approximately constant at high damage levels
Electrophoresis
Electrical resistivity (EIS and surface resistivity)
Decreases at a high rate at low damage levels and decreases with a low rate at high damage levels
Electrical conduction (AC current)
Sorptivity Initial sorptivity increases linearly with damage; secondary sorptivity initially decreases with damage and then remain constant at higher damage levels
Capillary suction
Drying The initial rate of drying increases with damage increase
Moisture diffusion
Air permeability Air permeability exponentially increases with damage
Flow under pressure gradient
Water Permeability Water permeability exponentially increases with damage
Flow under pressure gradient
Desorption isotherm
The water content gradually increases with damage at intermediate RH values, followed by a larger increase at high RH values; generally does not account for all crack widths
----
6. Conclusion
In this paper, we posed the following questions: (i) How do different measurement
techniques show the effect of damage on mass transport? (ii) Which transport measurement
method is more sensitive to the presence of damage? To this end, we experimentally
measured the effect of damage, induced by freeze-thaw loading in mortar samples, using
different mass transport measurement techniques. It was observed that mass transport
increases with damage irrespective of the measurement method. However, different
measurement methods differently reflect the effect of damage on mass transport depending
on the mechanism of transport utilized in the measurement method. Different methods also
show different sensitivity to the presence of damage. Rapid chloride permeability test and
electrical resistivity are only sensitive at low damage levels (below 20%). Initial sorptivity
increases linearly with damage at all levels. Water and air permeability increase
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
30
exponentially with damage and seem to be the most sensitive parameter to the presence of
damage.
Acknowledgments
This work was conducted in the Materials and Sensor Development Laboratory (MSDL)
and Constructed Facilities Laboratory (CFL) at North Carolina State University. The authors
would like to acknowledge the support which has made these laboratories and this research
possible.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
31
References
[1] Ghasemzadeh F, Pour-Ghaz M. The Effect of Damage on Moisture Transport in Concrete. Journal of Material in Civil Engineering 2014; DOI: 10.1061/(ASCE)MT.1943-5533.0001211.
[2] Aldea CM, Shah SP, and Karr A. Effect of cracking on water and chloride
permeability of concrete. Journal of Materials in Civil Engineering 1999; 11(3): 181-187. [3] Rodriquez, OG. Influence of Cracks on Chioride Ingress into Concrete. MS Thesis,
University of Toronto, Toronto, Ontario, Canada. 2001. [4] Rodriguez OG, & Hooton RD. Influence of cracks on chloride ingress into concrete,
ACI Materials Journal, 2003; 100(2): 120-126. [5] Picandet V, Khelidj A, and Bellegou H. Crack effects on gas and water permeability of
concretes. Cement and Concrete Research 2009; 39(6): 537-547. [6] Pour-Ghaz M, Rajabipour F, Couch J, & Weiss J. Modelling fluid transport in
cementitious systems with crack-like (notch) geometries, Proceeding of International RILEM Workshop on Concrete Durability and Service Life Planning, Bagneux, France, 2009.
[7] Pour-Ghaz M, Rajabipour F, Couch J, & Weiss J. Numerical and experimental
assessment of unsaturated fluid transport in saw-cut (notched) concrete elements, American Concrete Institute (ACI) Special Publication 266, Farmington Hills, MI, 2009: 73-86.
[8] Akhavan A, Shafaatian S, and Rajabipour F. Quantifying the effects of crack width,
tortuosity, and roughness on water permeability of cracked mortars. Cement and Concrete Research, 2012; 42(2): 313-320.
[9] Bentz DP, Garboczi EJ, Lu Y, Martys N, Sakulich AR, and Weiss WJ. Modeling of the
influence of transverse cracking on chloride penetration into concrete. Cement and Concrete Composites 2013; 38: 65-74.
[10] Samaha HR, Hover K. Influence of microcracking on the mass transport properties of concrete. ACI Materials Journal 1992; 89(4): 416-424.
[11] Breysse D, Gerard B, & Lasne M. An Experimental Device to Study Cracking and Deterioration of Concrete, Durability of Concrete, Third International Conference, Nice, France; CANMET/ACI SP-170, Detroit, Michigan, 1994: 1013-1032.
[12] Gérard B, and Marchand J. Influence of cracking on the diffusion properties of cement-based materials: Part I: Influence of continuous cracks on the steady-state regime. Cement and Concrete Research 2000; 30(1): 37-43.
[13] Yang Z, Weiss WJ, and Olek J. Water transport in concrete damaged by tensile
loading and freeze–thaw cycling. Journal of Materials in Civil Engineering 2006; 18(3): 424-434.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
32
[14] Torrijos MC, Giaccio G, and Zerbino R. Internal cracking and transport properties in damaged concretes. Materials and Structures 2010; 43(1): 109-121.
[15] Chungsheng Z, Kefei L, and Jianguo H. Characterizing the effect of compressive damage on transport properties of cracked concretes. Materials and Structures 2012; 45(3): 381-392.
[16] Chungsheng Z, Kefei L, and Xiaoyun P. Geometry of crack network and its impact on transport properties of concrete. Cement and Concrete Research 2012; 42(9): 1261-1272.
[17] M'Jahad S, Davy CA, Bourbon X, and Skoczylas F. Water Retention and Gas
Migration of Two High Performance Concretes after Damage. Journal of Materials in Civil Engineering 2014; DOI: 10.1061/(ASCE)MT.1943-5533.0001028.
[18] Wang L, and Ueda T. Mesoscale modelling of the chloride diffusion in unsaturated
concrete damaged by freeze-thaw cycling. Journal of Material in Civil Engineering 2014; 26(5): 955-965.
[19] Daïan, J. and Salbia, J. Transient Moisture Transport in a Cracked Porous Medium. Transport in Porous Media 1993; 13; 239-260.
[20] Fagerlund G. On the service life of concrete exposed to frost action. Freeze-thaw
durability of concrete, J. Marchand, M. Pigeon, and M. J. Setzer, eds., E & FN Spon, London, 1997: 23–42.
[21] Lockington D, Parlange JY, & Dux P. Sorptivity and the estimation of water
penetration into unsaturated concrete. Materials and Structures 1999; 32(5): 342-347. [22] Thomas MDA, & Bentz EC. Life-365 computer program for predicting the service
life and life-cycle costs of reinforced concrete exposed to chlorides, American Concrete Institute 2000, Farmington Hills, MI.
[23] Bentz EC, & Thomas MDA. Life-365 service life prediction model, Computer
program for predicting the service life and life-cycle costs of reinforced concrete exposed to chlorides, 2001 University of Toronto, Toronto.
[24] Henchi K, Samson E, Chapdelaine F, & Marchand J. Advanced finite-element
predictive model for the service life prediction of concrete infrastructures in support of asset management and decision-making. Journal of Computing in Civil Engineering 2007: 870-880.
[25] Barde V, Radlinska A, Cohen M. & Weiss WJ. Relating material properties to
exposure conditions for predicting service life in concrete bridge decks in Indiana. Joint Transportation Research Program Technical Rep., Purdue University, West Lafayette, IN, 2009.
[26] Kropp J, & Alexander MG. Transport mechanisms and reference tests, chapter two,
RILEM TC 189-NEC: state-of-the-art report, Non-destructive evaluation of the penetrability and thickness of the cover 2007: 13-34.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
33
[27] Abyaneh SD. Wong HS. & Buenfeld NR. Modeling the effect of microcracks on the transport properties of concrete in three dimensions. 10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures 2015: 377-386.
[28] Sanchez C, Saaltink MC, & Willem M. Modelling of multiphase flow in concrete
cells of the radioactive waste storage facility at El Cabril (Spain). A: International Symposium on Cement-based Materials for Nuclear Wastes. "NUWCEM 2014 : 2nd International Symposium on Cement-based Materials for Nuclear Waste : June 3-5, Palais des Papes, Avignon, June 6 CEA Marcoule". Avignon: 2014, p. 1-8.
[29] Chaparro M, Saaltink MW, & Villar MV. Characterization of concrete by
calibrating thermos-hydraulic multiphase flow models. Transport in Porous Media 2015; 109(1): 147-167.
[30] ASTM Standard C192, 2012, "Standard Practice for Making and Curing Concrete
Test Specimens in the Laboratory," ASTM International, West Conshohocken, PA, 2012, DOI: 10.1520/C0192_C0192M-15, www.astm.org.
[31] Li W, Pour-Ghaz M, Castro J, and Weiss J. Water absorption and critical degree of
saturation relating to freeze-thaw damage in concrete pavement joints. Journal of Materials in Civil Engineering 2011; 24(3): 299-307.
[32] Rashetnia R, Ghasemzadeh F, and Pour-Ghaz M. Axisymmetric flexural vibration for estimating the dynamic elastic modulus of damaged concrete and the consequences of material nonlinearity on measurements. Advances in Civil Engineering Materials – ASTM International 2015; Under Review.
[33] Kim B, and Weiss WJ. Using acoustic emission to quantify damage in restrained
fiber-reinforced cement mortars. Cement and Concrete Research 2003; 33(2): 207-214. [34] Farnam Y, Bentz D, Sakulich A, Flynn D, Weiss J. Measuring Freeze and Thaw
Damage in Mortars Containing Deicing Salt Using a Low-Temperature Longitudinal Guarded Comparative Calorimeter and Acoustic Emission. Advances in Civil Engineering Materials 2014; 3(1): DOI: http://dx.doi.org/10.1520/ACEM20130095.
[35]ASTM Standard C1202, 2012, "Standard Test Method for Electrical Indication of
Concrete's Ability to Resist Chloride Ion Penetration," ASTM International, West Conshohocken, PA, 2012, DOI: 10.1520/C1202-12, www.astm.org.
[36] Spragg RP, Castro J, Nantung TE, Paredes M, and Weiss WJ. Variability analysis of
the bulk resistivity measured using concrete cylinders. Joint Transportation Research Program Technical Rep., Purdue Univ., West Lafayette, IN, 2011.
[37] Pour-Ghaz M. Detecting damage in concrete using electrical methods and assessing
moisture movement in cracked concrete. Ph.D. thesis, Purdue Univ., West Lafayette, IN, 2011.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
34
[38] Akhavan A, and Rajabipour F. Evaluating ion diffusivity of cracked cement paste using electrical impedance spectroscopy. Materials and Structures 2013; 46(5): 697-708.
[39] Snyder KA, Ferraris C, Martys NS, & Garboczi EJ. Using impedance spectroscopy to assess the viability of the rapid chloride test for determining concrete conductivity. Journal of Research-National Institute of Standard and Technology 2000; 105 (4): 497-510.
[40]ASTM Standard C1585, 2004, "Standard Test Method for Measurement of Rate of
Absorption of Water by Hydraulic-Cement Concretes," ASTM International, West Conshohocken, PA, 2004, DOI: 10.1520/C1585-11, www.astm.org.
[41] Castro J, Bentz D, & Weiss J. Effect of sample conditioning on the water
absorption of concrete. Cement and Concrete Composites 2011; 33(8): 805-813. [42] Castro J. Moisture transport in cement based materials: Application to transport
tests and internal curing. Ph.D., Purdue University, 2011. [43] Schonlin K, and Hilsdorf HK. Permeability as a measure of potential durability of
concrete development of a suitable test apparatus. Permeability of concrete, ACI SP-108, 1988, D. Whiting and A. Walitt.
[44] Dilek U, & Leming ML. Elastic dynamic Young’s modulus and permeability of
concrete in fire damaged structural members. Journal of Materials in Civil Engineering 2008; 20(2): 102-110.
[45] Villani C, Loser R, West MJ, Bella CD, Lura P, Weiss J. An inter lab comparison of
gas transport testing procedures: Oxygen permeability and oxygen diffusivity. Cement and Concrete Composites 2014; 53(October): 357–366.
[46] Pour-Ghaz M, Spragg R, & Weiss J. Moisture profiles and diffusion coefficients in
mortars containing shrinkage reducing admixtures. In O. M. Jensen, M. T. Hasholt, & S. Laustsen (Eds.), International RILEM conference on use of superabsorbent polymers and other new additives in concrete. Technical University of Denmark, Lyngby, Denmark, 2010.
[47] Villani C, Spragg R, Pour‐Ghaz M, and Weiss WJ. The Influence of Pore Solutions
Properties on Drying in Cementitious Materials. Journal of the American Ceramic Society 2014; 97(2): 386-393.
[48] Spiesz P, & Brouwers HJH. Influence of the applied voltage on the Rapid Chloride
Migration (RCM) test. Cement and Concrete Research 2012; 42(8): 1072-1082. [49] Yuan Q, Shi C, De Schutter G, Audenaert K, & Deng D. Chloride binding of cement-
based materials subjected to external chloride environment–a review. Construction and Building Materials 2009; 23(1): 1-13.
[50] Andrade C. Calculation of chloride diffusion coefficients in concrete from ionic
migration measurements. Cement and Concrete Research 1993; 23(3): 724-742.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT
35
[51] Hallaji M, Seppänen A, & Pour-Ghaz M. Electrical resistance tomography to monitor unsaturated moisture flow in cementitious materials. Cement and Concrete Research 2015; 69(March): 10-18.
[52] Smyl D, Ghasemzadeh F, & Pour-Ghaz M. Numerical simulation of unsaturated moisture transport in damaged mortar and concrete. Journal of Materials in Civil Engineering, ASCE, 2015; Under review.
[53] Brosnan DA, & Robinson GC. An introduction to drying of ceramics. The American
Ceramic Society, Westerville, Ohio, 2003.
MANUSCRIP
T
ACCEPTED
ACCEPTED MANUSCRIPT