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Research Journal of Applied Sciences, Engineering and Technology 7(17): 3478-3490, 2014
DOI:10.19026/rjaset.7.700
ISSN: 2040-7459; e-ISSN: 2040-7467
© 2014 Maxwell Scientific Publication Corp.
Submitted: October 19, 2013 Accepted: October 25, 2013 Published: May 05, 2014
Corresponding Author:
Costas A.
Anagnostopoulos, Department of Civil Engineering, School of Technological Applications,
Technological Educational Institute of Thessaloniki, 57400 Thessaloniki, Greece
This work is licensed under a Creative Commons Attribution 4.0 International License (URL: http://creativecommons.org/licenses/by/4.0/).
3478
Research Article
Effect of Epoxy Resin Mixtures on the Physical and Mechanical Properties of Sand
Costas A. Anagnostopoulos, Panagiotis Kandiliotis, Malvina Lola and Sarafianos Karavatos
Department of Civil Engineering, School of Technological Applications, Technological Educational
Institute of Thessaloniki, 57400 Thessaloniki, Greece
Abstract: The use of new materials for soil strengthening is crucial for geotechnical engineering, especially in
foundation construction. The main objective of this study was to investigate the potential use of two-component
water-soluble epoxy resin to improve the physical and mechanical properties of medium sand, because the efficacy
of these resins on soil strengthening has not yet been properly investigated. The experiments were conducted using
resins with different epoxy resin-to-water ratios. The results of this study indicate that the epoxy resins improve the
physical and mechanical properties of the sand significantly and if successfully grouted into a formation, the resins
could provide a suitable solution for the stabilization of the foundation material. In separate experiments, electro
osmotic treatment of sand/resin mixtures was conducted with the aim of identifying the effectiveness of electro
kinetic method on the early strength development of sand/resin mixtures. From the results it was observed that the
electroosmotically treated specimens appeared to have much greater strength enhancement than the one of the
untreated specimens.
Keywords: Chemical grouting, electro osmosis, epoxy resin
INTRODUCTION
Grouting is a common technical method with
numerous applications (Cambefort, 1977). For example,
it is used for stabilizing and strengthening the
foundation soil, especially in the case of coastal
engineering structures, for reducing the ingress of water
to underground facilities, or leakage through a dam site.
Cement suspensions and chemical solutions are the
two main types of materials that are utilized for
grouting purposes. Cement suspensions have been used
successfully in granular soils with large voids or in
fractured rock with wide crack openings, because they
penetrate easily into soil pores, propagate large
distances under low pressure, completely fill the voids,
maintain the required properties in the hardened state
and are inexpensive (Widmann, 1996). According to
the previous experience, micro fine cement is expected
to flow sufficiently through soils with coefficient of
permeability (k) greater than 10
-5
m/s. As a result, the
use of chemical grouts is restricted to soils with very
small void size or rock mass with narrow joints, where
cement suspensions cannot be inject able or their
penetration is very limited.
Various materials are used for chemical grouting
depending on the purpose of grouting and the properties
of ground. The most common are calcium chloride in
combination with sodium silicate (joosten method),
sodium silicate with form amide as a reactant to form
silica gel, acrylate, lignin, urethane and resin grouts
(Al-Khanbashi and Abdalla, 2006). In particular, epoxy
resins are one of the principal resins used for grouting.
They generally consist of two components. The epoxy
component (A-component) is mixed with an amine
component (B-component) to obtain the epoxy resin.
The final product is characterized by a high strength
under compression and tension, a strong bond, high
durability, high resistance to acids, alkalies and organic
chemicals and low shrinkage when cured. In addition,
some epoxies may be diluted with water up to twice
their volume to provide a low cost product, but their
strength consequently decreases. This reduction of
strength is proportional to the amount of water added to
the epoxy resin. Although, numerous studies have been
conducted concerning the application of epoxy
compounds for structural repair or in fractured concrete
(Issa and Debs, 2007), there is limited published data
(Ajayi-Majebi et al., 1991; Anagnostopoulos et al.,
2011) on the efficacy of epoxy resin grouts, especially
low-cost water-soluble epoxy resin grouts, for soil or
rock strengthening. Additionally, Anagnostopoulos
et al. (2011) from mechanical tests on medium sand,
mixed with different epoxy resin grouts, demonstrated
the retarding action of water on the early strength
development of resin/sand mixtures at all Epoxy Resin-
to-Water (ER/W) ratios. Consequently, it is worth
checking if the application of electro osmosis (Ou et al.,
2009; Abdullah and Al-Abadi, 2010; Liaki et al., 2010)
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3479
Fig. 1: Particle size distribution of the tested sand
can be beneficial in dewatering and improving the
development of strength of resin/sand mixtures, since
no information is available on the implementation of
this method with such purpose.
The specific objectives of this comprehensive
laboratory project are as follows:
• To supplement the available data from the
literature on the effect of two-component water-
soluble epoxy resin grouts, with different resin to
water ratios, on the physical and mechanical
properties of medium sand
• To investigate the influence of electro osmotic
processing on the acceleration of strength
development of sand/resin mixtures
MATERIALS USED
Commercially available CEN, a standard medium
siliceous natural sand that conforms to standard CEN
EN 196-1 (2005) was used. It was clean with a round
shape and generally isometric particles. The grains
ranged from 0.074 to 0.85 mm in size. The particle size
distribution of the used sand is shown in Fig. 1. It has a
coefficient of uniformity C
u
of 4.64 and it is classified
as poorly graded sand based on the USCS
classification. The physical properties of the sand with
a relative density (D
r
) of 50% are the following: dry
unit weight (γ
d
) of 15.8 KN/m
3
, porosity (n) of 41.6%
and permeability coefficient (k) of 4·10
-4
m/s. The
friction angle φ is 32.3° and was determined from direct
shear tests conforming to ASTM D 3080 (2005).
The epoxy resin used is a commercial product with
the trading name EPOXY PRIMER-W and it is
distributed by ISOMAT SA, Greece. It is water soluble
and composed of two components, A and B. The
mixture ratio by weight of the two components A
(epoxy resin) and B (hardener) is A: B = 2.5:1.
According to the manufacturer, the epoxy resin, without
any addition of water, attains its final strength after 7
days. The compressive strength reaches the maximum
value of 70 MPa and the flexural and adhesive strengths
are in excess of 35 and 3 MPa, respectively.
The viscosity of epoxy resin emulsions, especially
when mixed with large amounts of water, is slightly
higher than that of water. This low viscosity of epoxy
resin emulsions in combination with the small size (25 -
100 nm) of the dispersed resin particles in the water
enable their use for grouting purposes, even in
especially fine sands.
Laboratory procedure: Mixtures were prepared with
Epoxy Resin/Water (ER/W) ratios (by weight) of 2, 1.5,
1 and 0.5, respectively. All mixtures were prepared
with a high-speed rotating stirrer. An adequate quantity
of epoxy resin in the mix ensured that the intergranular
voids were completely filled. Mixing was performed by
using a three-blade paddle mixer as suggested by the
ASTM C 938-80 (1993) specifications. Concerning the
preparation of the specimens, the filling and the
compaction process were performed carefully to ensure
the uniformity and reproducibility of the specimens.
The weight of sand/resin mixture required to fill the
mould and obtain the required relative density was
calculated. This amount of material was poured in
cylindrical moulds 5.43 cm in diameter and 11.00 cm
high and compacted, so that specimens would be
created consistently with a relative density of about
50%. The required density was achieved with a metal
rammer weighing 4.5 kg and slightly tapping on the
sides of the mould. These cylindrical specimens, with a
height to diameter ratio of about 2, were used for
compressive and triaxial strength tests after 3, 7, 28, 90
and 180 days, respectively in order to study the
development of the strength parameters with time. Free
water in the sand/resin mix samples was removed by
drying at room temperature. According to manufacturer
specifications, the effect of this drying procedure on the
polymerization of resin macromolecular chains and,
consequently, on strength development or permeability
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3480
of sand/resin mixes is negligible. The end surfaces of
the sand/resin mix samples prepared were cut with a
saw to be parallel and smooth to prepare them for the
uniaxial or triaxial compression tests. Unconfined
compression and triaxial tests were performed under a
constant axial strain rate of 1%/min. The compression
tests were performed according to ASTM D 4219-02
(2005). The elastic modulus E was determined from the
linear part of the compressive stress-strain curve.
Splitting tensile tests were conducted following the
instructions of ASTM D 3967-95a (2005) on specimens
with a thickness to Diameter ratio (t/D) of 2.00/5.43
cm = 0.37.
For the purpose of studying the shear strength
parameters of the sand/resin mix (friction angle φ and
cohesion c) under triaxial loading, a triaxial testing
apparatus (Hoek and Franklin, 1968) was used in a
BETA 5 (FORM+TEST PRÜFSYSTEME) 3000 KN
compression testing machine to apply the axial load,
which incorporates an instrument for measuring the
digital load-strain. Triaxial tests were performed under
constant confining pressures σ
3
of 1, 2 and 3 MPa,
respectively. The same testing machine was used also
for all the compression and splitting tensile tests.
Specimens of the same size as the one for the
mechanical tests, aged 28 days, were used for the
evaluation of water permeability according to ASTM D
5084-03 (2005) and dry unit weight according to
ASTM C 29/C 29M-91a (1993). Porosity n was
calculated according to the method found in Perret et al.
(2000). An age of 28 days was chosen for the
estimation of the physical parameters. It is considered
that beyond this age, the values of physical parameters
do not change because the solidification process of the
epoxy resin does not influence the density or the
volume of the sand/resin mix and the free water has
almost completely evaporated.
The method proposed by ASTM D 4320-04 (2005)
is a classical laboratory method for the estimation of the
physical or the mechanical properties of chemically
grouted soils and it has been adopted by many
researchers (Anagnostopoulos, 2005, 2006; Dano et al.,
2004; Vipulanandan and Ata, 2000; Bolisetti et al.,
2009; Akbulut and Saglamer, 2003). This method is
important in estimating the strength of a grouted soil
with cement grouts, which appears to decrease with
increasing distance from the injection point due to the
clogging mechanism observed during the injection
process. Epoxy resin, in contrast, can penetrate easily
and uniformly (the viscosity of the used resin emulsions
in this study ranged from 14 to 32 mPa·s), without
clogging, into soil voids. This results in the
development of isotropic strength along the injection
distance (Anagnostopoulos and Hadjispyrou, 2004).
Consequently, the authors deemed the method of
ASTMD 4320-04 (2005) unnecessary and chose a
Fig. 2: Experimental set up for electroosmotic treatment of
fine sand/resin mixes
simpler method for making epoxy resin/sand
specimens.
The effect of electro osmosis in the dewatering of
epoxy resin/sand mixes and consequently in the
acceleration of early strength development was studied
in the laboratory. All the electro osmotic experiments
were carried out in a laboratory environment with the
temperature ranging from 20 to 25°C. The details of the
experimental set-up are shown in Fig. 2. The
experiments were conducted on a cylindrical PVC tube
with diameter of 15 cm and height of 30 cm. The plastic
tube was chosen because of its high electrical resistance
and water impermeability. The different epoxy
resin/sand mixes were prepared and placed, in the tube,
in three layers. Each layer was subjected to a slight
vibration in order to achieve a relative density of 50%.
Afterwards, two tubular electrodes to pass the Direct
Current (DC) were encapsulated along the sample, apart
and diametrical near the tube walls. Both electrodes
(anode and cathode) were connected to a DC power
supply device. The electrodes were made of graphite
with copper coating, having 5 mm diameter. The
sample was then subjected to a DC current with a
constant voltage gradient of 3 V/cm, as suggested by
Abdullah and Al-Abadi (2010), which maintained for a
period of 7 days for mixtures with ER/W ratio of 0.5
and 1, a period of 6 days for mixtures with ER/W ratio
of 1.5 and a period of 4 days for mixtures with ER/W
ratio of 2. All the digital monitoring data (voltage and
amperage) were recorded through a data logger system
incorporated in the DC device. Samples with thick
epoxy mixes were electroosmotically treated for a
smaller period than the one of thinner epoxy resin
mixes because DC current stopped passes through their
mass. This is attributed to the quick formation of a
dense polymer matrix which reacts as an electrical
insulator. Figure 3 shows the variation of current versus
time during electro osmotic treatment of sand at all
ER/W ratios. In all cases, the current never remained
steady but was decreasing continuously with time from
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3481
Fig. 3: Variation of current with time during electroosmotic treatment of sand/resin mixes
beginning to end of test. At the end of the processing
period, cylindrical specimens with diameter of 5.43 cm
and height of 11 cm were extracted from the
electroosmotically treated mixtures by using a drilling
machine and were tested in compression and splitting
tensile strength tests.
RESULTS AND DISCUSSION
Figure 4 depicts the compressive stress-strain
relation of sand/resin specimens with different epoxy
resin/water ratios after 7, 28 and 90 days of curing,
respectively. The corresponding curves for 180 days of
curing are not presented since they are almost identical
with the ones for 90 days of curing. Figure 5 shows the
development of compressive strength, splitting tensile
strength and elastic modulus with increasing curing
time. All specimens with different ER/W ratios did not
approach any strength value within a time period of 3
days. Mixes with ER/W ratio of 0.5 did not gain any
strength even after a curing period of 7 days. Also, it
can be observed that beyond 90 days of curing the
increase of strength was insignificant at all ER/W
ratios. The results reveal the adverse influence of water
on the strength development of sand. The strength
values, for all ages tested, decrease with increasing
water content. The water content had the most
pronounced effect on the retardation and reduction of
the final strength of the sand/resin mix in the case of
grouts with ER/W ratio of 1 and 0.5. The retarding
phenomenon may be attributed to the amount of water
that is retained by the hydrophilic parts of the epoxy
resin, which inhibits to some extent its chemical
reaction with the hardener and thus, the development of
strength. We attribute the reduction of the final
strength, even after the evaporation of water, to the
formation of a weaker epoxy resin polymer membrane-
sand matrix, because of the high dispersion of chemical
substances that occurs in highly diluted epoxy mixes. In
the case of epoxy resin mixtures with ER/W ratios of 1
and 0.5, a low strength development was observed at
the age of 28 days. However, for ER/W ratios of 1.5
and 2, the strength parameters were multiple times
higher. For example, the samples with the thinner
ER/W ratio of 0.5 appeared to have mean values for
compressive strength, splitting tensile strength and
elastic modulus of 0.6, 0.1 and 68.4 MPa, respectively.
The same parameters, for the samples with the thicker
ER/W ratio of 2, appeared to be 5.23, 0.9 and 420 MPa,
respectively.
The strength exhibited an increasing tendency over
time, resulting in significantly higher strength values.
This tendency was strongly dependent on the ER/W
ratio. Nevertheless, samples with thick epoxy mixes
(ER/W = 2, 1.5) appeared to have much greater strength
enhancement than the samples with thinner epoxy
mixes for all curing ages. The lowest final strength
values after 180 days of curing were observed for mixes
with ER/W ratio of 0.5 and were equal to 1.1 MPa for
the compressive strength, 155 MPa for the elastic
modulus, 0.21 MPa for the splitting tensile strength. In
contrast, mixes with ER/W ratio of 2 resulted in a
compressive strength of 8 MPa, elastic modulus of 585
MPa, splitting tensile strength of 1.15 MPa.
Figure 4, which represent the relation between
compressive stress and strain, reveals an almost linear
initial elastic segment that extends over a large range of
strains with a subsequent extended plastic zone that
occurs before and after fracture for all ER/W samples
and at all ages. All the specimens with the different
ER/W ratios did not fail at the end of test but were
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3482
(a)
(b)
(c)
Fig. 4: Typical stress-strain curves of sand/resin mixes with different ER/W ratios (a) 7 days, (b) 28 days, (c) 90 days
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3483
(a)
(b)
(c)
Fig. 5: (a) Compressive strength, (b) splitting tensile strength, (c) elastic modulus development of sand/resin mixes
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3484
Table 1: Values of major principal stress taken from triaxial tests on treated sand specimens with different ER/W ratios
Major principal
stress σ
1
(MPa)
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
ER/W = 1/2 curing time (days)
---------------------------------------
ER/W = 1/1 curing time (days)
-------------------------------------------
ER/W = 1.5/1 curing time (days)
--------------------------------------------
ER/W = 2/1 curing time (days)
-----------------------------------------
σ
3
(MPa)
7
28
90
180
7
28
90
180
7
28
90
180
7
28
90
180
1
-
4.2
5.1
5
.0
2.4
5.4
6.2
6.3
3.0
7.6
9.5
9.7
3.4
8.9
12.5
12.7
2
-
6.3
6.9
6.8
4.5
6.9
8.3
8.4
5.3
10.7
12.3
12.1
5.5
11.3
14.6
14.9
3
-
7.6
8.7
8.7
6.1
9.4
10.3
10.4
6.9
12.3
14.4
14.6
7.3
13.7
16.7
17.0
Table 2: Values of elastic modulus taken from triaxial tests on treated sand specimens with different ER/W ratios
Elastic modulus (MPa)
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
ER/W = 1/2
curing
time (days)
---------------------------------------
ER/W = 1/1
curing
time (days)
-----------------------------------------
ER/W = 1.5/1
curing
time (days)
-------------------------------------------
ER/W = 2/1
curing
time
(days)
--------------------------------------------
σ
3
(MPa)
7
28
90
180
7
28
90
180
7
28
90
180
7
28
90
180
1
-
333
360
375
87.5
429
590
602
105
535
716
725
132
655
1,080
1,092
2
-
375
422
430
101
487
742
749
123
625
772
788
170
822
1,350
1,365
3
-
425
460
466
125
569
966
978
141
912
1,330
1,342
226
1,200
1,511
1,528
Fig. 6: Typical deviatoric stress-strain curves of sand/resin mixes with ER/W ratio of 1.5 cured for 180 days
continuously deformed, up to a strain of at least 2.5 to
4%, at which point the test was stopped. This is an
indication of the strong adhesion between the formed
polymer film and sand grains. It also demonstrates the
domination of the elastoplastic behavior of the epoxy
resin on the mechanical response of the whole mixture.
Table 1 and 2 present the values of major principal
stress at failure and the values of elastic modulus taken
from triaxial tests on sand/resin mix specimens. Also,
typical trends in the deviatoric stress (σ
1
-σ
3
) -strain
obtained from triaxial tests on specimens with ER/W
ratio of 1.5 cured for 180 days are shown in Fig. 6.
These results reveal the beneficial effect that epoxy
resins have on the strength and stiffness of the sand. As
expected, the peak strength and initial stiffness strongly
increased with an increase in the ER content and
confining pressure. For example, the application of a 3
MPa confining pressure on specimens with an ER/W
ratio of 2 that were cured for 180 days caused a
deviator peak value increment of about 146% compared
to the unconfined test. Generally, the degree of post-
peak strength loss tends to decrease with increasing
confining pressure and ER/W ratio resulting in
relatively constant peak strength. The strain at which
the peak stress was achieved generally increased with
increasing confining pressure and ER/W ratio, although
some scatter was observed. The effect of the confining
pressure and ER content on the enhancement of (σ
1
-
σ
3
)
max
stress is seen in Table 1.
A significant extension of the plastic zone for all
grouted samples with the different ER/W ratios is
observed. Undoubtedly, one of the main advantages of
the epoxy resin mix is the strain hardening behavior
induced even at large deformations. This behavior
suggests potential application of the epoxy resin
grouting in shallow foundations, embankments
overlying soft soil deposits and other earthworks that
may suffer excessive deformations. Generally, no strain
localization with inclined shear bands occurred and the
failure was associated with a fairly uniform, strong
expansion of the specimen for high ER/W ratios.
However, strain localization with inclined shear bands
did occur for low ER/W ratios.
The shear strength parameters (friction angle φ and
cohesion c) of sand/resin mixes with different ER/W
ratios were determined by plotting the modified failure
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3485
envelope in p-q diagrams. The failure envelopes for all
cases appeared to be linear with correlation coefficients
R
2
ranging from 0.98 to 0.99. Table 3 illustrates the
values of φ and c over time for the different ER/W
ratios. It is observed that φ reduced for all ER/W ratios,
at all ages and varied between 15.5° to 29.9° with
significant scatter. The reduction of φ can be attributed
to the polymer coverage of particle surfaces which
reduced the friction. Strong evidence supporting the
above hypothesis is the considerable higher values of φ
for the mixes with ER/W ratio of 1, 1.5 and 2 at 7 days
of curing; a time at which the cross linked formation of
polymer film coatings is still very limited, as it is
revealed from the low strength of the specimens.
However, the values obtained for c confirmed the
considerable influence of the ER/W ratio and curing
time. By increasing the ER/W ratio and curing time, the
value of c substantially increased, to a maximum value
of 3.6 MPa, which was observed for an ER/W ratio of 2
with a curing time of 180 days.
The failure envelopes of mixes with the different
ER/W ratios that were cured for 180 days are plotted in
comparison with the failure envelope of untreated sand
and presented in Fig. 7. The intersection of the two
lines (dotted one corresponds to the failure envelope of
untreated sand) shows the value of critical vertical
stress after which epoxy resin is no longer effective in
improving the sand strength. Table 4 summarizes the
values of critical normal stress (direct shear conditions)
and the values of critical confining pressure (triaxial
conditions) of sand/resin mixes with different ER/W
ratios that were cured for 180 days.
The critical normal stress σ
n
and the critical
confining pressure σ
3
were calculated as follows:
σ
n
=
mixsand
mix
tanφtanφ
c
−
(1)
σ
3
= σ
n
·sin (2·θ) - τ
n
·(1 + cos (2·θ)) (2)
where,
c
mix
= The cohesion of sand/resin mix
φ
sand
= The friction angle of sand
φ
mix
= The friction angle of sand/resin mix
θ = 45 + φ
mix
/2
τ
n
= σ
n
·tan φ
sand
As a result, the epoxy resin mixes could be applied
in ground improvement applications because the values
of σ
n
and σ
3
, beyond which the use of epoxy resin
grouting is detrimental to the soil strength, are
especially high.
The physical parameters of the sand/resin mixes
are included in Table 5. Similar to the mechanical
properties, the improvement of the physical properties
is dependent directly on the ER/W ratio. In the case of
thick mixes, the permeability test results confirm the
formation of a dense polymer film-sand matrix in which
Table 3: Shear strength parameters of treated sand specimens
Friction angle φ (degrees) curing time (days)
-----------------------------------------------------------------------------------
Cohesion c (MPa) curing time (days)
-------------------------------------------------------------------
ER/W 7 28 90 180 7 28 90 180
1/2 - 15.50 17.10 17.20 - 0.98 1.18 1.15
1/1 27.30 20.03 20.16 20.20 0.20 1.10 1.45 1.48
1.5/1 29.72 23.99 24.90 24.70 0.32 1.78 2.28 2.32
2/1 29.90 24.20 21.20 21.40 0.40 2.10 3.54 3.60
(a)
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3486
(b)
(c)
(d)
Fig. 7: Failure envelopes of untreated and treated sand with ER/W ratio of (a) 0.5, (b) 1, (c) 1.5, (d) 2
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3487
Table 4: Critical confining and normal stress values of sand
specimens treated with different ER/W ratios, cured at 180
days
ER/W ratio
Confining pressure (MPa)
Normal stress (MPa)
1/2
1.81
3.56
1/1
2.94
5.60
1.5/1
7.24
13.40
2/1
7.90
14.93
Table 5: Physical properties of treated sand specimens with different
ER/W ratios
Properties
ER/W ratio
--------
---------------------------------------------------
1/2
1/1
1.5/1
2/1
Dry unit weight
(KN/m
3
)
1.63
1.67
1.71
1.74
Porosity (%)
27.80
23.20
20.10
16.10
Coefficient of
permeability (m/s)
3.15×10
-
5
7.84×10
-
6
1.63×10
-
6
8.2×10
-
7
a large number of pores are filled or sealed resulting in
a significant reduction of the water permeability. The
permeability coefficient k decreased almost three orders
of magnitude for an ER/W ratio of 2 and about two
orders of magnitude for an ER/W ratio of 1.5. Despite
the weakening of the polymer membrane-sand matrix in
the case of thin mixes, a noticeable decrease of the
water permeability was obtained.
The porosity and dry unit weight values confirm
the aforementioned observations about the influence of
ER/W ratio. There is an adverse impact of water when
it exists in high concentrations within the mix
composition.
The observed improvement of the physical and
mechanical properties of the sand/epoxy mix can be
further assessed through scanning electron micrographs.
Figure 8 shows micrographs of an untreated sand
specimen in which the sand particles appear almost
unconnected with large voids around their periphery. In
contrast, Fig. 9 shows a micrograph of the view
perpendicular to the failure surface of a sand/resin mix
specimen with ER/W ratio of 2. The micrographs reveal
that a large number of voids are filled with polymer
particles that act as adhesive ties to the sand grains to
form a dense impermeable high strength structure and
impart a significant cohesion factor. Furthermore, the
inter-particle contacts seem to be reduced due to the
disturbance of the particle assembly and the coating of
their surface with the epoxy resin polymeric membrane
which can explain the appreciable reduction of the
friction angle.
Figure 10 shows the values of compressive
strength, splitting tensile strength and elastic modulus
of mixed fine sand specimens with different ER/W
ratios at 7 and 28 days of curing in comparison with the
strength values of electroosmotically treated specimens.
It can be seen that the development of strength
parameters of mixes treated by electroosmosis was
much higher than the one obtained for untreated mixes
at the age of 7 days. Especially, in the case of mixtures
with ER/W ratio of 0.5, strengths of the
electroosmotically treated specimens appeared to be a
little higher even than the ones of untreated specimens
for a curing time of 28 days. Generally, as the ER/W
ratio increases the duration of electro osmotic process
and its effectiveness in the enhancement of mechanical
parameters of mixtures decrease. For example, electro
osmotic treatment on specimens with an ER/W ratio of
0.5 caused a compressive strength, splitting tensile
strength and elastic modulus value increment of 15, 10
and 40%, respectively, compared to the strength values
of untreated material for curing time of 28 days. In
contrast, treated mixes with ER/W ratio of 2 exhibited
compressive strength, splitting tensile strength and
elastic modulus values of 53, 63 and 62%, respectively,
the corresponding ones of untreated mixes for a curing
time of 28 days.
It was observed for all sand/resin mixes that after
the end of electro osmotic process the whole mass of
the specimen had dried out except of a small one in the
vicinity of the anode which was still wet and weaken as
a result of the large water quantity still remained. This
result is interesting because it is in opposition to the
results obtained by Ou et al. (2009), Liaki et al. (2010),
Alshawabkeh and Sheahan (2003), Huweg et al. (2010)
and Kaniraj and Yee (2011) which support the
(a) (b)
Fig. 8: A scanning electron micrograph of untreated sand with magnification of (a) 50 times and (b) 200 times
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3488
(a) (b)
Fig. 9: A scanning electron micrograph of treated sand with magnification of (a) 70 times and (b) 110 times
(a)
(b)
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3489
(c)
Fig. 10: Variation of (a) compressive strength, (b) splitting tensile strength, (c) elastic modulus of electroosmotically treated
sand/resin mixes in comparison with the ones of untreated cured for 7 and 28 days
conclusion that the application of DC in a clay soil or
even in a coarser sandy soil generates a relatively
steady flow towards the cathode but the improvement
decreases with the increase of the distance from the
anode. This phenomenon is attributed to the migration
of positive ions towards the cathode (electro migration).
Positive ions do exist in a thin electric layer, close to
the soil particle surface, that allows charge
neutralization of the negatively charged clay particles.
When the electric field is applied to the soil, the cations
move from the particle surface towards the cathode.
This movement determines a force on the fluid and
therefore a flow in the same direction. Electro
migration shortens significantly the treatment time. In
contrast, the electro osmotic experiments of this study
showed that no electro migration occurred (flow from
anode to cathode) due to the low concentration of
cations in the surface of sand particles and their
possible entrapment by the macromolecular chains of
epoxy resin coated to the surface of grains. Obviously,
the reverse flow (from cathode to anode) is stemming
totally from electrolysis reactions in the immediate
vicinity of electrodes causing a subsequent
transportation of hydroxides from anode to cathode, a
fact that explains the wet condition of sand near the
anode after the end of electro osmotic process.
Based on the aforementioned observations of the
electro osmotic experiments, it is concluded that the
duration of treatment of sand/resin mixes and the
subsequent acceleration of strength development is
directly related with the electrolysis of water content.
CONCLUSION
The experimental results showed that the use of
water soluble epoxy resin can considerably improve the
physical and mechanical properties of sand. In
particular, the following conclusions can be drawn:
• The compressive strength, splitting tensile strength
and elastic modulus development of the fine
sand/resin mix depend directly on the water content
of the epoxy resin solution. Mixes with ER/W ratio
of 2 and 1.5 resulted in high strength and low
permeability. Despite the weakening of the
polymer membrane-sand matrix in highly diluted
mixes, the 90 and 180 day mechanical properties
and permeability appeared to be satisfactorily
improved.
• Under triaxial stress conditions, the peak strength
and stiffness of all mix specimens with different
ER/W ratio increased considerably. The amount of
increase depended on the confining pressure and
ER/W ratio. A significant extension of the plastic
zone was obtained and the difference between the
peak strength and ultimate strength was negligible.
• Epoxy resin has a beneficial influence on the shear
strength of sand. The cohesion after 180 days of
curing varied between 1.15 and 3.6 MPa and
increased in proportion to the ER/W ratio, whereas
the friction angle reduced significantly. However,
the overall shear strength of the sand/resin mix
remained much higher than the shear strength of
the untreated sand over a large range of stresses.
Res. J. App. Sci. Eng. Technol., 7(17): 3478-3490, 2014
3490
• Electro-osmotic process can be effectively used to
accelerate the development of mechanical
properties of mixes at early ages. The quality of
electro osmotic improvement is directly related to
the ER/W ratio of the mixture.
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