International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
Assessing the Freezing and Melting Point of
GGBS Concrete
Adama Lami Kawu1, Mahmud Abba Tahir2, Mohammad Balteh3, Yusuf Mohammed Nuruddeen4,
Raji Mohammed Mudashir5
1
Department of Building Technology, Abubakar Tafawa Balewa University, Bauchi. Nigeria
2,3&4
Department of Building Technology, Federal Polytechnic, Bauchi. Nigeria
5
Department of Quantity Surveying, Federal Polytechnic, Bauchi. Nigeria
Abstract-The pore structure of a concrete material is
made up pores of various sizes. This study is aimed
at assessing the freezing and melting point of
concrete within the cover zone by monitoring the
formation of ice and melting at different
temperatures
using
electrical
measurement
technique. A multi-electrode array system was used
to obtain the temperature of ice formation and
melting at discrete depths within the cover zone of
the concrete. A total number of four concrete
specimen (250mm x 250mm x 150mm) made of
ordinary Portland cement concrete and ordinary
Portland cement replaced by 65% ground
granulated blast furnace slag (GGBS) with
water/binder ratios of 0.35 and 0.65 were produced
and ponded with water to ensure full saturation and
then subjected to freezing and melting process in a
refrigerator within a temperature range of -300C
and 200C over a period of time 24 hours each. The
data was collected and analysed. Results obtained
shows that the freezing and melting behavior of all
specimens differs. It was also observed that at a
much lower depth of 75mm which is close to the
rebar, the pores freezes at a much lower
temperature of about -290C but melts at different
temperatures irrespective of w/b ratio and GGBS
additive.
Keywords—GGBS, Concrete, durability, Freezing,
Melting
I. INTRODUCTION
Concrete durability to freezing and thawing is
closely related to its pore structure. The freezing
point depression of the pore solution and the volume
of ice formed in the pores are greatly influenced by
the volume, radius and pores size distribution.
Commonly, within a particular temperature interval,
more frozen concrete pore solution induces greater
internal hydraulic pressure and therefore, further
serious damages. Once ice is formed within the pore
system, ice cannot propagate instantaneously
through the whole material because of its porous
microstructure features such as the pore size
distribution and geometry. The temperature at which
ice is formed or solidification of water in a particular
pore depends on the size and shape of the throat
which connects the pores within the pore network.
The pore neck usually freezes at a lower temperature
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and once that happens, the pores will freeze at a
higher temperature due to the hydraulic pressure
developed. According to [3], the larger pores freezes
at low temperature and any further drop in
temperature leads to further freezing of the water in
the pores due to the different pore sizes. Studies
conducted by [2] suggest that freezing takes place at
about -100C and that the pore solution freezes more
quickly beyond -100C than below -100C.
Freezing is a function of temperature. The rate at
which pore water in concrete freezes depend on the
temperature, pore connectivity, pore size and the
pore neck. The pore water freezes due to the
percolation of the ice front through the connected
pore network because the pores, whether frozen or
unfrozen, depends on the state of their neighbours.
According to [5], pores are larger than their neck and
pores with radius bigger than the breakthrough
radius may freeze at a particular temperature.
However, the freezing of the pores highly depends
on the pore system connectivity. Because, freezing is
a gradual percolation process of an ice front through
the connected network, some pores with pores
bigger than the breakthrough radius will not freeze at
that particular temperature but rather at a much
lower temperature. Freezing requires the ice front to
be able to reach the pores and for those pores which
are far away from the ice front, there is likely going
to be constraints along the way that may slow the ice
front from reaching them and hence, they will
remain unfrozen until temperatures lower than the
exposed temperature is applied. Therefore, freezing
of pores is solely dependent on the direction of the
ice front as well as the position of the pores [4].
Unlike freezing, thawing is independent of the
surrounding pores. Pores of the same radius and
shape will thaw at a particular temperature. Small
crystals of a liquid in the concrete pores melt at a
temperature below that for the bulk liquid. The
melting point depression is inversely proportional to
the size of the pores. However, ice expands faster
than the surrounding pore space and as a result
expansive forces are generated into the matrix and
subsequent cracking. Equally, the difference in
entropy of the gel and capillary water causes the
diffusion of the gel to the capillary cavities.
During freezing and thawing, the pore system
pressure can be calculated based on the theory of
thermodynamics. In this theory which is solely based
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
on thermodynamic relationship, the pore structure of
a material is considered partly filled with water and
air. During freezing or ice formation, under pressure
takes place in the pore system because of the fast
contraction of ice than in the surrounding cement
matrix.
[1] Stated that, the shape of the pores upon freezing
and thawing varies. Upon freezing (cooling), the
ice/water interface is assumed or considered to be
hemispherical (f=1) and therefore, the relationship
for the freezing point depression can be expressed
as:
ΔTcool = - 64.67/rp-0.57 ……………… Equation 1
Upon melting (heating), the interface is considered
to be cylindrical (f=2) and the ice fills the cylindrical
pores and hence, the hydraulic radius of the melting
point is different and therefore, the relationship for
the melting point depression can be expressed as:
ΔTheat = -32.33/rp-0.68 ……………… Equation 2
II. MATERIAL, SAMPLE AND CURING
The sample comprised of OPC clinker combined
with ground granulated blast furnace slag as
Supplementary Cementitious Materials (SCM) used
in blending was combined in accordance with BS
EN 197-1:2000. A water binder ratio of 0.35 and
0.65 were used. The sand used was concreting sand
with a maximum particle size of 4mm along with
two grades of crushed granite (10mm and 20mm) of
low
porosity
(~0.7%-0.9%).
Plasticizer
polycarboxylate SikaPlast, conforming to BS EN
934-2 was used. Specimens were 250×250×150mm
(thick) slabs, the upper surface of each slab had a
20mm high ponding area which held water, hence,
allowing water to be ponded on the surface of the
slab
III. EXPERIMENTAL AND TEST PROCEDURE
A. Two-point multi-electrode array set-up
This experiment used a two point embedded multielectrode array system. The set-up of the inverted T
shaped PVC which holds the electrode in place is
illustrated in Figure 1. Each electrode was made up
of stainless steel pins of 1.6mm diameter. A stainless
steel of 10mm diameter was exposed on the end of
each electrode. The electrodes were spaced
horizontally at 10mm interval, and then vertically
spaced at depths of 10mm, 20mm, 30mm, 40mm,
50mm, and 75mm respectively from the surface of
the specimen. In order to ensure better distribution
around the probes when pouring, the electrodes were
overlapped against each other in a vertical plane.
The tip of each probe exposed was placed at a
distance of 45mm from the face of the T shaped
PVC so as to reduce the aggregate-wall-effect. In
order to take temperature readings during the
experiment, thermistors were integrated into the face
of the PVC former at varying depths of 10mm,
30mm, 50mm and 75mm. the data collected were
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then corrected to temperature. The thermistor
resistances were then converted to temperature
readings in (0C) and kelvin (K) using the Stein-Hart
equation:
T = [A + BlnR + C (lnR) 3]-1- 273.15 … Equation 3
T = [A + BlnR + C (lnR) 3]-1 ………….. Equation 4
Where,
R = the measured resistance of the thermistor (ohms)
T = temperature (ºC) and K;
A, B, C = coefficients which depend on the type of
thermistor, were calculated from manufacturer data,
respectively, to be: 1.287600011×10-3 K-1;
2.357183092×10-4 K-1 and 9.509464377×10-8 K-1.
Ln = natural logarithm.
Fig 1: Multi Electrode sensor array
B. Freezing and thawing procedure
The samples were ponded using pure tap water
which has been allowed to cool at room temperature
to ensure that the specimens are fully saturated
before subjecting them to the freezing and thawing
process. The ponding process lasted for 7 days.
Before subjecting the specimens into the freezing
and thawing chamber, the surface of the specimens
were de- ponded by the use of clean dry sponges and
also covered with a thick plastic lid to prevent any
further moisture loss. After attaining full saturation,
each of the four specimens X1(65% GGBS and 0.35
w/b ratio), X3(65% GGBS and 0.65 w/b ratio), C1
(100% OPC and 0.35 w/b ratio) and C3 (100% OPC
and 0.65 w/b ratio) was separately put in a freezing
and thawing chamber for 24 hours for the freezing
cycle. The freezer temperature was dropped to -300C
from the room temperature of 20 0C. After 24 hours,
the freezing and thawing chamber was then switched
off and the specimen was allowed to melt for 24
hours at room temperature for the thawing cycle to
take place. The same procedure was repeated for
specimen C3, X1 and X3. The set up can be seen in
figure 2.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
readings were used to analyse both the resistivity
data and conductivity data. Equally all the data
recorded by the logger was in resistance, and
therefore it was decided to use resistance for the
analysis. The temperatures after correction in the
region of approximately 230C and -290C during the
experimental programme which is quite okay as the
laboratory temperature is supposed to be controlled
at 200C and the refrigerator temperature ranges was
set at -300C for the freezing cycle and then possibly
down to the laboratory temperature of 20 0C.
Figure 2: Freezing and thawing chamber setup
C. Electrical Measurement System
An automated measurement system was used to
gather two-point resistance data from the electrode
embedded array system in the concrete slabs. The
system consists of a concrete resistance logger
linked to a multiplexing unit, which allows up to
seventy two 2-point channels to be monitored via six
37-way D-type connector and cable assemblies.
Measurements are obtained using a 1000 mV peak to
peak ac voltage signal (350 mV rms) at 1000 Hz.
The logger stores measured resistance data in an
operator pre-programmed format to a non-volatile
memory. As-measured data is uploaded in 39
Microsoft Excel csv format for subsequent
processing to a personal computer (PC) via an
RS232 port connector. The logger was set to record
a cycle reading at every 5minutes interval for a
period of 24 hours.
Figure 4: Natural logarithm of conductance vs
1000/T for specimen C1
Figure 5: Natural logarithm of conductance vs
1000/T for specimen C3
Figure 3: Measurement system
IV. RESULT AND DISCUSSION
The freezing and melting points and pore sizes of
each specimen at different depths were obtainedfrom
the plots of natural logarithm of conductance (s/m)
versus 1000/T(k) and Equation 1 and Equation 2
respectively, presented and discussed.
A. Temperature Correction
The logger record or measures thermistor resistance
and therefore they were converted to temperature
readings (0C) and kelvin (K) using equation 3 and
equation 4 respectively. These corrected temperature
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Figure 6: Natural logarithm of conductance vs
1000/T for specimen X1
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
takes place at different temperature. At depths 10mm
and 30mm, temperature at which the pores freezes is
approximately 00C, but at depths 50mm and 30mm,
the freezing point temperature is observed to be
approximately -10C. This could be that there is no
much change in the pore structure as the pores are of
same sizes However, it is quite interesting to see that
the pores at all depths melts at the same temperature
at approximately 20C. Also, there is not any change
in the pore structure at all the depths because the
pores are of same sizes.
Figure 7: Natural logarithm of conductance vs
1000/T for specimen X3
Figure 8: Natural logarithm of conductance vs
1000/T for specimen C110mm 3 cycles subjected to
3 cycles of freezing and thawing
TABLE I: Freezing and melting point for Specimen
C1, C3, X1 and X3
In analysing specimen C1, it can be observed that at
depth 10mm, the concrete pores freezes at
approximately -30C, but was different at lower
depths. At depths 30mm, 50mm and 75mm, the
temperature at which ice is formed in the pores is
much lower than that at depth 10mm at
approximately -290C. This could also be attributed to
the change in the pore structure at lower depths with
pores at the surface 10mm depth larger in size than
at lower depths. However, the temperature at which
the pores melt does not coincide with that of ice
formation. At depth 10mm, the pores melting point
temperature is observed to be approximately -10C,
but is much higher at lower depths of 30mm, 50mm
and 75mm with a temperature of approximately
140C. This again could be due to change in the pore
structure at lower depths.
In analysing specimen C3, it can be seen that the
freezing and melting of the pores at various depths
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In analysing specimen X1, it can be observed that at
depth 10mm, the concrete pores freezes at
approximately -190C, but was different at lower
depths. At depths 30mm, 50mm and 75mm, the
temperature at which ice is formed in the pores is
much lower than that at depth 10mm at
approximately -290C. This could be attributed to the
change in the pore structure at lower depths with
pores at the surface 10mm depth larger in size than
at other depths. However, the temperature at which
the pore melts does not coincide with that of ice
formation. At depth 10mm, the pores melting point
temperature is observed to be approximately 2 0C,
but is much higher at lower depths of 30mm, 50mm
and 75mm with a temperature of approximately
130C. This again could be due to changing pore
structure at various depths.
In analysing specimen X3, it can be seen from Table
5.4 that at depth 10mm, the concrete pores freezes at
approximately 00C, but was different at lower
depths. At depths 30mm, 50mm and 75mm, the
temperature at which the pores freezes is observed to
be much lower than that at depth 10mm at
approximately -290C. This could also be attributed to
the change in the pore structure at lower depths with
pores at the surface 10mm depth larger in size than
at other depths. However, it can be observed that the
pore does not melt at the same temperature with ice
formation. At depth 10mm, the pores melt above at
approximately 40C, but melts at a much lower
temperature below freezing point at approximately 30C at depths 30mm, 50mm, and 75mm respectively.
This again could be due to changing pore structure at
various depths.
TABLE II:Freezing and melting point for Specimen
C1 Subjected to 3 freezing and thawing cycles
Specimen C1 was subjected to 3 repeated cycles of
freezing and thawing. It can be observed from that
the analysis was done at only depth 10mm and
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 6- March 2016
75mm because they are the depths at the surface and
close to the rebars. At depth 10mm for all the 3
cycles, the pores freezes at the same temperature of
approximately -30C and melts at the same
temperature of approximately -10C for all cycles but
at a different temperature with the temperature of ice
formation. At depth 75mm, the pores freezes at a
much lower temperature than that at depth 10mm
with a temperature of approximately -290C. Also,
the pores melt at the same temperature of
approximately 140C for all the cycles. This could
also be due to change in the pore structure at lower
depths with pores at the surface 10mm larger than
that at lower depths
V. CONCLUSION
In conclusion, it can be observed that the freezing
and melting behavior of all specimens differs.
Specimen C3 was observed to perform poorly by
freezing at between 00C to -10C at all depths and
melts at about 20C. However, because the depth
75mm is the depth close to the rebar, it can be seen
that irrespective of w/b ratio and additive, the pores
freezes at a much lower temperature of about -290C
but melts at different temperatures. This could be
that the pore structure changed at much lower depths
possibly with much larger pores.
For specimen C1 was subjected to 3 repeated cycles
of freezing and thawing, the number of cycles did
not change its behaviour as the freezing and melting
points remain the same in all the 3 cycles.
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