Strength and Durability Characteristics of Bio

Strength and Durability Characteristics of Bio-Improved Sand of AlSharqia Desert, Oman
*Mohsin U. Qureshi1), Ilhan Chang2) and Khaloud Al-Sadarani3)
1), 3)
Faculty of Engineering, Sohar University, PO Box. 44, PC. 311, Sohar, Sultanate of
Oman
2)
Department of Civil Engineering, Korean Advanced Institute for Science and
Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea
1)
[email protected]
2)
[email protected]
3)
[email protected]
ABSTRACT
Bio-improvement of geomaterial to develop sustainable geotechnical systems is
an important step towards the reduction of global warming. The cutting edge
technology of bio-improvement is not only environment friendly but also has
widespread application. This paper presents the strength and slake durability
characteristics of bio-improved sand sampled form Al-Sharqia Desert in Oman. The
specimens were prepared by mixing sand at various proportions by weight of xanthan
gum biopolymer. To make a comparison with conventional methods of ground
improvement, cement treated sand specimens were also prepared. A series of strength
tests were conducted on dry specimens as well as at saturated state. To demonstrate
the effects of wetting and drying on bio-improved and cement treated sand, standard
slake durability tests were conducted on the specimens. According to the results of
strength tests, bio-improvement has increased the strength of sand, similar to
strengthening effect of mixing cement in sand. The slake durability test results indicated
that the resistance of bio-improved sand to disintegration upon interaction with water is
stronger than that of cement treated sand. The percentage of xanthan gum to treat
sand is proposed to be 2-3 % for optimal performance in terms of strength and
durability. The present study concludes that the bio-improvement is an eco-friendly
technique to improve the mechanical properties of desert sand. However, the
strengthening effect due to the bio-improvement of sand can be weakened upon
interaction with water in unconfined state. Therefore it is expected that the bio1)
Assistant Professor
Senior Researcher, Ph.D.
3)
Technician
2)
improvement technique may perform well in confined geotechnical systems.
KEYWORDS : Desert sand; bio-improvement; strength; durability
1. Introduction
Anthropogenic global warming is not only responsible for the rise in sea levels and
abnormal climate problems but is also due to geo-environmental hazards from the
unsustainable geotechnical systems supporting the civil infrastructure. Both new
construction sites and rehabilitation works on weak soils require ground improvement.
Over the past century, various ground improvement methods have been developed,
and today many of them are widely employed to build geotechnical systems. It is
appropriate to classify a wide variety of soil treatment methods as mechanical or
chemical. Mechanical methods improve the soil by densification/dewatering, however in
the chemical methods cementation is induced mainly by ordinary Portland cement or
chemical additives. The basic principles of these techniques have not changed since
the early of the twentieth century. The practices, however, have been changing with the
time mainly because of the development of new materials, new machinery, and new
technologies. A largely unrecognized fact is the impact of traditional geotechnical
construction processes that can be on biological processes. Such as, during, soil
compaction the reduction in void ratio introduces a fundamental shift in biological
processes (from aerobic to anaerobic metabolism), which creates conditions harmful to
biodiversity, consequently affecting the vegetative growth (DeJong et al. 2006).
Some of the products used in soil improvement are not considered as environment
friendly due to high emission of greenhouse gases during their production and toxic
nature after application. The addition of these materials, while beneficial from an
engineering performance perspective, might not necessarily be advantageous for the
environment. Ordinary cement production emits carbon dioxide, a significant
greenhouse gas, during chemical calcination and fuel burning. It has been reported that
5% of the global carbon dioxide emissions are induced by the cement industries
(Worrell et al. 2001). Both the disuse and recycling of cement-concrete waste are
potentially hazardous to the environment due to the potential for pollutant leakage into
the soil and groundwater. Meanwhile, several alternatives such as geo-polymers, alkali
activated cement, geo-cement, and inorganic polymer concrete have been developed
in an attempt to reduce or replace cement use.
However, the carbon dioxide reduction efficiency of these methods is insufficient due
to their dependency on ordinary cement and heavy industry by-products (e.g. blast
furnace slag, fly ash, etc.). Alternative, natural biologically – based treatment methods
could meet the same engineering requirements without environmental concerns.
Therefore, demand for the development of environmentally friendly construction
materials that are relatively harmless and easily reused without environmental impacts
is increasing significantly in the 21st century (Cabalar and Canakci 2011). Thus, the
biopolymers can not only applicable in the development of geotechnical systems also a
renewable source as a component of greenhouse gas reduction strategies (Vink et al.
2003). The great promise of the use of biological treatments has been already
demonstrated in other fields such as in petroleum industry to directing the oil flow in the
required direction, in concrete technology to remediate cracks (Ramachandran et al.
2001), development of shields for zonal remediation and stabilization of contaminated
soils (Khachatoorian et al. 2003). Biopolymers are sustainable, because they are made
from anthropogenic agricultural nonfood crops.
Biopolymers are polymers produced by living organisms, and most biopolymer
applications are in the field of medical engineering, such as drug delivery systems,
wound healing, and surgical implantations (Van de Velde and Kiekens et al. 2002).
More recently, research in biology and earth science has enabled important advances
in understanding the crucial involvement of microorganisms in the evolution of the earth,
their ubiquitous presence in near surface soils and rocks, and their participation in
mediating and facilitating most geochemical reactions (Mitchell and Santamarina 2005).
According to Ivanov and Chu (2008), biocementation can replace the high energy
demanding mechanical compaction or the expensive or environmentally harmful
chemical grouting. To achieve the aim of environment friendly development, in the fields
of soil science, geotechnical engineering, and geo-environmental engineering,
biopolymers have been employed as soil stabilizers to enhance the mechanical
response of ground against the external loading and the environment.
Table 1 Generalized review of soil improvement by using biopolymers
Sr.
The effects of bio
Reference
Soil Type Biopolymer
No.
improvement
Efficiency in undisturbed
1
Sutterer et al. 1996
Soil
Agar
sampling
Khachatoorian et al.
Reduction in hydraulic
2
Silty sand Xanthan gum
2003
conductivity
Xanthan
gum, guar
3
Bouazza et al. 2009 Silty sand gum and
Reduction in permeability
sodium
alginate
Increase in undrained shear
4
Nugent et al. 2009
strength and liquid limit
Cabalar and Canakci
Improvement in shear
5
Sand
Xanthan gum
2011
strength
Chang and Cho 2012
Beta-glucan Improvement in uniaxial
6
Soil
compressive and tensile
strength
Chang et al. 2013
Beta-glucan Reduction in Water erosion
7
Soil
Xanthan gum and increased potential of
vegetation growth
8
Khatami and O’Kelly Sand
Agar and
Increase in unconfined
2013
9
10
Qureshi et al. 2015
Chang et al. 2015
11
Ayeldeen et al. 2016
12
Chang et al. 2016
modified
compressive strength,
starch
cohesion and stiffness
Sand
Xanthan gum Slake durability
Xanthan gum Soil strengthening
Xanthan
gum,
Increase in shear resistance
Sand, silt modified
and reduction in
starch, guar permeability
gum
Increase in shear strength at
various moisture contents
Sand
Gellan gum
and decrease in
permeability
Xanthan gum is a polysaccharide that is made by the Xanthomonas campestris
bacterium, and is generally used as a viscosity thickener due to its hydrocolloid
rheology (Barrére et al. 1986). Xanthan gum has been introduced to geotechnical
engineering to reduce the hydraulic conductivity of silty sand via pore filling
(Khachatoorian et al. 2003; Bouazza et al. 2009) as well as to increase the undrained
shear strength of soil by increasing the liquid limit (Nugent et al. 2009). Another recent
study has studied possibilities for using xanthan gum as a soil strengthener, and
showed that xanthan gum preferentially forms firm xanthan gum-clayey soil matrices
via hydrogen bonding (Chang et al 2015). More recently, Khatami and O’Kelly (2013)
reported the mechanical behavior of sand treated with agar and six modified. Their
results showed the increase in unconfined compressive strength, cohesion and
stiffness of the treated sand. Qureshi et al. (2015) investigated the effects of wetting
and drying on the xanthan gum treated sand and concluded that the xanthan gum
treated sand is durability against slaking. A remarkable increase in shear resistance
and reduction in permeability of sand and silt is reported by Ayeldeen et al. (2016).
They employed xanthan gum, modified starch and guar gum to improve sand and silt.
The application of agar for temporary stabilization of soil has been described by
Sutterer et al. (1996) to development procedures for undisturbed sampling. Chang et al.
(2016) reported an increase in shear strength parameters and reduction in permeability
of sand treated with gellan gum. Further, they interpreted that the gellan gum treated
sand is sensitive to moisture however, durable enough for the application to support
shallow foundations.
Fig. 1 Location of sampling site at Al-Bidiya, Wahiba sand Dunes, Al-Sharqia,
Oman (Pease et al. 1999)
2. Materials
2.1 Al-Sharqia Desert Sand
Sand is sampled from Al-Bidiya in northern part of Wahiba sand dunes (Fig. 1), in AlSharqia Region which is about 200km to the south of Capital Muscat. The Wahiba
Sand formed in Quaternary period (Glennie 1998) is composed of two physiographic
units that can be roughly divided into northern and southern regions. The Northern
Wahiba is predominantly a large megaridge system, whereas the Southern Wahiba
mostly comprises linear dunes, sand sheets, and sabkha fields (Pease and Tchakerian
2003). Carbonate sands are present throughout the Wahiba sand area with some
quartz-rich sands in the Southern region. The Al-Sharqia sand (AS) used in this study is
sampled from the Northern region. The grain size distribution (BS 1990a) of the sand is
shown in Fig. 2(a). The sand can be classified as poorly-graded fine sand (SP)
according to the Unified Soil Classification System (USCS). The sand has a specific
gravity (BS 1990b) of 2.62 and a fine content of 1.1%. The standard Proctor
compaction test (BS. 1990c) gave a maximum dry density of 1.64g/cc at an optimum
water content of 19.5%. The micrograph of AS indicates sub-rounded particles and
lacking in fines as shown in Fig. 2(b).
Percent Passing by weight (%)
100
80
60
40
Gs=2.62
Fc=1.1%
emax=2.52
emin=0.484
Cc=0.8
Cu=1.8
20
0
0.01
0.1
1
Particle size (mm)
(a) Gradation Analysis
(b) Photomicrograph
Fig. 2 Physical properties of Al-Sharqia Sand (AS)
2.2 Xanthan Gum
Xanthan gum (C35H49O29) which has high viscous rheology was discovered in the
1950s, is a natural anionic polysaccharide composed of D-glucuronic acid, D-mannose,
pyruvylated mannose, 6-O-acetyl D-mannose, and a 1,4-linked glucan (Garcia-Ochoa
et al., 2000; Hassler and Doherty, 1990), which is the most rigid biological repeating
molecule (Yevlampieva et al., 1999). The most well-known characteristic of Xanthan
gum is pseudo plasticity (viscosity degradation with an increase of shear rate) (Milas
and Rinaudo, 1986) and high shear stability (Chen and Sheppard, 1980) even at low
concentrations. Moreover, it has several properties including, pH stability, storage
stability, and ionic salt compatibility (Hassler and Doherty 1990). Because of these
properties, xanthan gum itself has found a wide range of applications in the cosmetic,
oil, paper, paint, pharmaceutical, food and textile industries as a gelling, thickening,
suspending agent, as a flocculent or for viscosity control.
3. Experimental Program
3.1 Equipments
A standard Proctor compaction test was performed in accordance with BS 1377-4.3
(BS 1990c). The test was essential for determining the maximum dry density for each
soil type and its corresponding optimal moisture content. The consistency limits of the
xanthan gum treated specimens were obtained in accordance with the BS 1377-2.4.5
(BS 1990d) and BS 1377-2.5.3 (BS 1990e). Unconfined compressive strength tests
were obtained—according to BS 1377-7.7 (BS 1990f) by using a strain rate of
approximately 1%/min for xanthan gum treated sand (ASG). To study the mechanical
behavior of dry and saturated ASG specimens in confined state, unconsolidated
undrained triaxial tests were performed in accordance with BS 1377-7.8 (BS 1990g). A
state-of-the-art triaxial test equipment manufacture by Utest, Turkey, was employed as
shown in Fig. 3(a). The salient features of the equipment were, 50kN loadcell, LVDT of
50mm stroke length, maximum confining pressure 2MPa, axial strain controlled loading
and eight channel data logging system. The effects of wetting and drying on the
durability of ASG is elucidated by performing standard slake durability test (Franklin
and Chandara 1972). The slake durability test device used in this study is shown in Fig.
3(b).
(a) A-state of-the-art triaxial test equipment
(b) Slake durability test device
Fig. 3 Equipment
3.2 Specimen Preparation
The Al-Sharqia sand (AS) was oven dried at 105 °C for 24 h. The xanthan gum used
in this study was delivered as powder and mixed with water to produce gels to
supplement as colloids for thickening water-based systems, which can act as binder.
Distilled-deaired water was used to dissolve the biopolymer powder with different
concentrations to avoid the effect of any additional factors such as the chemical
components that may exist in portable water (Chen et al. 2013). The solution
concentration was calculated as the ratio between the weight of the used powder and
the overall weight of the sand. The powder was gently added into the water to avoid
clumping, and then the solution was mixed until a homogeneous solution was obtained.
Xanthan gum concentrations of 1, 2, 3 and 5% by weight were used in this study.
Finally, the sand was mixed with the solution until homogeneity had been achieved in
the mixture. It was difficult to obtain certain densities for all specimens with several
concentrations. Therefore, all the specimens (Fig. 4) were prepared at the maximum
dry density according to their compaction characterizations. All specimens were cured
at 45°C within an oven until tested after 1 week. The summary of prepared specimens
is presented in Table 2. To compare the level of improvement achieved by the treatment
of sand with xanthan gum, cement treated sand specimens were also prepared by
adding 10% cement to the sand at water-cement ratio of 0.5 and cured at the same
conditions. All the specimens prepared for strength tests were 5cm in diameter and
10cm in height.
Fig. 4 Typical specimens for Unconfined compression and triaxial compression
tests
Table 2 Summary of the specimens for compression tests
Xanthan gum
Sr. No.
Specimen ID
Cement (%)
(%)
1
AS
0
2
ASG1
1
3
ASG2
2
4
ASG3
3
5
ASG5
5
6
ASC10
10
Dry density
(g/cc)
1.64
1.67
1.64
1.635
1.63
1.58
4. Results and Analysis
4.1 Compaction
The density and void ratio are very important parameters which control the stre
ngth of geomaterial. Standard proctor tests were performed on Al-Sharqia sand (A
S) and xanthan gum treated Al-Sharqia sand (ASG) specimens. The plot of dry d
1.7
1.68
d(max)
Max. Dry Density,d(max), (g/cc)
Dry Density,  (g/cc)
ZAV of AS
1.6
24
OMC
1.66
21
1.64
1.5
AS
ASG1
ASG2
ASG3
ASG5
1.4
1.62
Standard Proctor
1.3
0
5
18
15
1.60
10
15
20
Moisture Content, w (%)
25
30
12
0
1
2
3
4
5
6
Optimum Moisture Content, OMC, (%)
ensity and moisture content is shown in Fig. 5(a). The maximum dry density beg
an to increase with the increase in gum content up to 1%. A further increase in t
he concentration of gum decreased maximum dry density. It can be seen in Fig.
5(b) that the maximum dry density of specimen ASG1 is 1.67g/cc in comparison t
o the untreated sand which has 1.64g/cc. The increase in maximum dry density
of sand to a gum percent of 1% can be attributed to the reduction in friction bet
ween sand particles. Too high percentage of gum, i.e. more than 1 percent may
have separated the sand particles. Simultaneously, the OMC was the lowest for t
he sand-gum mix ASG1. Ayeldeen et al. (2016) observed the similar behavior an
d concluded that the increase in maximum dry density is due to the increase in
viscosity of water-gum solution. However, after a certain limit, increase in the visc
osity results in the separation of sand particles with no further enhancement in m
aximum dry density.
Xanthan Gum content (%)
(a) Plot of dry density and moisture co (b) Max. dry density and moisture con
ntent
tent plotted against xanthan gum cont
ent
Fig. 5 Compaction characteristics of xanthan gum treated Al-Sharqia sand
4.2 Consistency
The addition of xanthan gum forms a gel around the sand particles which may
introduce the plasticity in cohesion-less sand. To investigate this fact, Atterberg limits
(liquid limit and plastic limit) were elucidated by performing standard tests (BS 1990d)
on sand treated with xanthan gum at different concentrations. The consistency limits of
untreated sand could not be obtained due to its non-cohesive nature. The plot of
moisture content and xanthan gum content in sand is shown in Fig. 5. Liquid limit of 1,
2, 3 and 5% xanthan gum-treated sand was determined to be 18.9, 23.6, 28 and
35.3 %, respectively. The liquid limit was observed to be increasing with the increase in
xanthan gum content indicating the effect of hydrophilic property of xanthan gum on the
plasticity behavior of Al-Sharqia. As the concentration of xanthan gum biopolymer in
the soil mass would increase, the water retention capacity of soil would also become
larger. Thus the non-plastic nature of cohesionless Al-Sharqia sand is changed to
cohesive by treatment with xanthan gum. Simultaneously, an increase in plastic limit is
observed with the increased percentage of xanthan gum. The difference in liquid and
plastic limit, i.e. plasticity index also increases with the increased percentage of
xanthan gum to treat sand (Fig. 5).
40
Liquid limit
Plastic limit
Plasticity Index
Moisture content (%)
35
30
25
20
15
10
5
0
1
2
3
4
5
Xanthan gum content (%)
Fig. 5 Change in consistency limits of xanthan gum treated Al-Sharqia sand at
different gum contents
4.3 Unconfined Compression
The unconfined compression tests were performed on the dry specimens of xanthan
gum treated Al-Sharqia sand. The plot of axial stress and axial strain is shown in Fig.
6(a). The unconfined compression response of untreated cement treated specimen is
also plotted in Fig. 6(a). The unconfined compression strengths (UCS) for all the tested
specimens are plotted against xanthan gum content in Fig. 6(b). The unconfined
compressive strength of untreated sand is 15kPa, and when treated with 1, 2, 3, and
5% of xanthan gum, the elucidated UCS was 1076, 1700, 753 and 1024 respectively.
So there is a remarkable improvement in UCS for all the mix percentages of xanthan
gum in comparison to untreated sand. Cement treated sand on the other hand also
showed higher UCS of 1767kPa. Further it can be observed in Fig. 6(a), that the
residual response of xanthan gum treated specimens is higher than the cement treated
specimens. Further the specimen having mix proportion of 2 percent of xanthan gum
was strongest in unconfined compression and is comparable to the strength developed
by 10% of cement treatment. In the case of residual response, the specimens treated
with small percentage xanthan gum took precedence over specimens treated with
higher percent of cement. The results reported by Chang et al. (2016) about the
unconfined compression tests on dry specimens of gellan gum treated sand observed a
similar behavior. Thus, the inter-particle strengthening resulted from the formation of
thick and high-tensile dehydrated gel of xanthan gum among the sand particles which
keep supporting the sand after failure.
AS
ASG1
ASG2
ASG3
ASG5
ASC10
1500
1000
500
0
0
1
2
3
4
Axial Strain,  (%)
5
Unconfined Compression Strength
qu (kPa)
Axial Stress, a (kPa)
Axial strain rate: 1%/min
2000
2000
ASC10 Peak
1500
1000
500
0
ASC10 Residual
0
1
2
3
4
5
Xanthan Gum content (%)
(a) Stress strain plot
(b) UCS plotted against xanthan gum c
ontent
Fig. 6 Unconfined compression test results of xanthan gum treated Al-Sharqia sand
4.4 Triaxial tests
Unconsolidated undrained response of the untreated and xanthan gum treated
Al-Sharqia sand was delineated by performing a series of triaxial tests on dried s
and (AS) and sand (ASG) that had been treated with 1, 2, 3 and 5% of xanthan
gum by weight. The tests were performed at three different radial stresses
r) i.
e. 50, 100 and 150kPa. All the tested specimens were having moisture content l
ess than 1%, here noteworthy are that the xanthan gum gel was already dehydra
ted before testing. A typical deviatoric stress–strain response for the triaxial tests
on untreated Al-Sharqia sand (r=1.64g/cc) is shown in Fig. 7(a). Thereafter, peak
shear strength parameters, i.e. angle of internal friction and cohesion were determ
ined by the Mohr Coulomb failure criterion.
The delineated cohesion for the mix percentage of 0, 1, 2, 3 and 5% xanthan
gum specimens was 0, 36, 334, 343 and 223kPa is shown in Fig. 7(b). A remar
kable increase in cohesion can be seen in Fig. 7(b) with the increase in xanthan
gum content of treated sand; however this increase appears to diminish when th
e percentage of xanthan gum exceeds 3%. The angle of internal friction of untre
ated sand was 38o and that of xanthan gum treated sand ranges between 58o a
nd 67o as shown in Fig. 7(b). The highest value of peak internal friction angle is
observed in sand treated with a xanthan gum content of 1%. Generally it can b
e observed that both cohesion and angle of internal friction increases with the inc
rease in xanthan gum content. However, at around 2-5% of the xanthan gum, th
e rate of increase shear strength parameters decreases. Therefore, the optimal co
ncentration for the treatment of sand is around 2% if the improvement in shear st
rength of sand is in question.
70
400
60
300
50
200
r=150kPa
300
Axial strain rate: 1%/min
0
0
1
2
3
4
5
6
7
8
100
40
Cohesion, c (kPa)
o
r=100kPa
600
Peak Friction angle,p
Deviator Stress, (kPa)
r=50kPa
Cohesion
Peak Angle of
Internal Friction
0
30
0
Axial strain,  (%)
1
2
3
4
5
6
Xanthan Gum content (%)
(a) A typical plot of deviator stress an (b) Shear strength parameters plotted
d axial
strain of Al-Sharqia Sand
against xanthan gum content
Fig. 7 Triaxial test results of xanthan gum treated sand specimen in dry state
0 cycle ASG1
0 cycle ASG2
0 cycle ASG3
0 cycle ASG5
0 cycle ASC10
1 cycle ASG1
1 cycle ASG2
1 cycle ASG3
1 cycle ASG5
1 cycle ASC10
2 cycles ASG1 2 cycles ASG2 2 cycles ASG3 2 cycles ASG5 2 cycles ASC10
3 cycles ASG1 3 cycles ASG2 3 cycles ASG3 3 cycles ASG5 3 cycles ASC10
4 cycles ASG1 4 cycles ASG2 4 cycles ASG3 4 cycles ASG5 4 cycles ASC10
Fig. 8 Changes in xanthan gum treated (ASG) and cement treated (ASC) specimens du
e to slaking cycles
4.5 Slake Durability
The slake durability tests was initially designed to investigate the slaking behav
ior of clay bearing rocks (Franklin and Chandara 1972). One of main concern in t
he bio treatment of soil is the water effects on the strengthening behavior. So, th
e authors performed slake durability tests on xanthan gum treated and cement tr
eated sand specimens. Ten pieces of each treated specimens weighing 40-50gm
were oven died at 105oC. Those specimens were then shifter in to the wire mes
h drum of slake durability device (Fig. 3(b)). The drum for rotated at 20rpm for 1
0 minutes half submerged in water. Thereafter, specimens were dried for 24 hour
s at 105oC in oven to complete one standard slaking cycle. Slake durability index
after each slaking cycle is reported as the percentage of initial dried weight to t
he dried weight at the end of each slaking cycle. The qualitative changes in the
specimen at the end of each slaking cycles is presented in Fig. 8. It can be see
n that the specimen ASG1 is the least durable as compared to the sand treated
with 2, 3 and 5 % xanthan gum. The cement treated specimen (ASC10) also sho
wed a weak response against slaking as compared to sand treated with 3 and 5
% xanthan gum (ASG3 and ASG5).
A decrease in slake durability index is observed after each slaking cycles for a
ll the specimens as shown in Fig. 9(a). The slake durability indices obtained after
1, 2, 3 and 4 slaking cycles (SD1, SD2, SD3 and SD4) are plotted against the x
anthan gum content in Fig. 9(b). The slake durability indices of ASC10 are also
plotted in the same Fig. 9(b). It can be seen that that durability of treated sand
against slaking increases with the increase in xanthan gum content up to 3%. A
higher content of xanthan gum gel keeps the sand particles amalgamated during
the wetting cycle, however the cement treated specimens loses unrecoverable ce
mentation. During the drying cycle the xanthan gum gel dehydrated but remains
available for the next wetting cycle.
100
Slake Durability Indices (%)
Slake durability index (%)
100
80
60
40
ASG1
ASG2
ASG3
ASG5
ASC10
20
0
0
1
2
Slaking cycles
3
4
80
ASC10
60
SD1
SD2
SD3
SD4
40
20
0
0
1
2
3
4
5
Xanthan Gum Content (%)
(a) Plot of slake durability and slaking (b) Slake durability indices plotted agains
cycles
t xanthan gum content
Fig. 9 Slake durability test results of xanthan gum (ASG) and cement treated (ASC) AlSharqia sand
5. Conclusions
The objective of the current research was to investigate the possibility of improving
the engineering properties of dune sands by treatment with xanthan gum. Sand was
sampled from Al-Sharqia desert of Oman. Al -Sharqia sand characterized as poorly
graded fine sand was treated with xanthan gum at 1, 2, 3 and 5% as well as with
cement at 10% by weight. A series of compaction, consistency limits, unconfined
compression, triaxial and slake durability tests were performed on the treated and
untreated sand specimens. Based on the results presented in this paper, the following
conclusions can be drawn.
The xanthan gum has substantially increases the unconfined compressive strength
of the treated sand. The unconfined compressive strength increases with xanthan gum
content up to 2 % and then after that it decreases with the increase in xanthan gum
content. The unconfined compressive strength of sand treated with a cement content of
10% was of the same order as of 1% treatment with xanthan gum.
The results of unconsolidated undrained triaxial tests showed that the sand treated
with xanthan gum possess both angle of internal friction and cohesion. The dehydrated
xanthan gum gel acted as a cementing agent between the sand particles. The angle of
internal friction of bio-treated sand increases with the xanthan gum content up to 1 %
and then decreases, however remain higher than that of untreated sand. The cohesion
of bio-treated sand also increases with xanthan gum content up to 2% and then
decreases, however remains higher than that of untreated sand. Thus, the treatment
with xanthan gum has effectively improved the strength characteristics of Al-Sharqia
sand. To achieve optimal results in terms of bio-strengthening of sand a mix percentage
of 2-3% is optimal choice.
The standard proctor tests delineated that the maximum dry density of 1% xanthan
gum treatment to sand was the highest. So in the field where compaction is to be
practiced along with bio-improvement 1% xanthan gum content is the optimal choice.
The response of bio-treated sand to the slaking also increases with the content of
xanthan gum. The slake durability index of bio-treated sand increases up to 3% gum
content and remains same thereafter. In comparison, the cement treatment showed a
low durability against slaking. The results suggest that the bio-improvement of sand is a
sustainable and eco-friendly practice in the desert environment which will not after the
biodiversity and it will be very attractive to develop geotechnical systems.
Acknowledgments
The research described in this paper was jointly supported by a Faculty Mentored
Undergraduate Research Award Program (FURAP) funded by the Research council
Oman and the Final Year project support funded by Sohar University, Oman. The
authors are also indebted to their colleagues at sohar University for a continuous
support during the experimentation.
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