Comparison of short term and long term performances for polymer stabilized sand and clay Q4 ww sciencedirect com 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32[.]
Trang 1Original Research Paper
Comparison of short-term and long-term
performances for polymer-stabilized sand and clay
Q4 Sepehr Rezaeimaleka,*, Abdolreza Nasouria, Jie Huanga,
Sazzad Bin-Shafiquea, Simon T Gilazghib
aDepartment of Civil and Environmental Engineering, The University of Texas at San Antonio, San Antonio, TX
78249, USA
bTexas Department of Transportation, Austin, TX 78701, USA
h i g h l i g h t s
An MDI-based liquid polymer was used to stabilize poorly-graded sand and sulfate-rich clay
The short-term and long-term performances of the stabilized specimens were evaluated
The specimens showcased high durability after undergoing different weathering conditions
The polymer-stabilized sulfate-rich clay specimens showcased minimal swelling potential
a r t i c l e i n f o
Article history:
Available online xxx
Keywords:
Soil stabilization
Liquid polymer
Sand
Expansive clay
Unconfined compressive strength
a b s t r a c t
A series of tests were carried out on sulfate rich, high-plasticity clay and poorly-graded natural sand to study the effectiveness of a methylene diphenyl diisocyanate based liquid polymer soil stabilizer in improving the unconfined compressive strength (UCS) of freshly stabilized soils and aged sand specimens The aged specimens were prepared by exposing the specimens to ultraviolet radiation, freeze-thaw, and wet-dry weathering
The polymer soil stabilizer also mitigated the swelling of the expansive clay For clay, the observations indicated that the sequence of adding water and liquid polymer had great influence on the gained UCS of stabilized specimens However, this was shown to be of little importance for sand Furthermore, sand samples showed incremental gains in UCS when they were submerged in water This increase was significant for up to 4 days of soaking in water after 4 days of ambient air curing Conversely, the clay samples lost a large fraction of their UCS when soaked in water; however, their remaining strength was still considerable The stabilized specimens showed acceptable endurance under weathering action, although sample yellowing due to ultraviolet radiation was evident on
* Corresponding author Tel.: þ1 210 458 7905
E-mail addresses:sepehr.rezaeimalek@utsa.edu(S Rezaeimalek),jie.huang@utsa.edu(J Huang)
Peer review under responsibility of Periodical Offices of Chang'an University
Available online at www.sciencedirect.com
ScienceDirect
journal homepage:w ww.elsevier.com/locat e/jtte
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2095-7564/© 2017 Periodical Offices of Chang'an University Publishing services by Elsevier B.V on behalf of Owner This is an open
access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Trang 2the surface of the specimens Except for moisture susceptibility of the clay specimens, the results of this study suggested the liquid stabilizer could be successfully utilized to provide acceptable strength, durability and mitigated swelling
© 2017 Periodical Offices of Chang'an University Publishing services by Elsevier B.V on behalf of Owner This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/)
Although cementitious materials such as cement and lime
have been widely used as soil stabilizers for many decades,
the geotechnical engineering community has never stopped
searching for alternative stabilizers for circumstances where
traditional cementitious stabilizers are not applicable or
favorable
When cement is used to stabilize soils, shrinkage, caused
by hydration of the cement as well as drying, is a commonly
observed phenomenon, which significantly reduces the
strength and increases the permeability (George, 1973;
Nakayama and Handy, 1965; Sebesta and Scullion, 2004) In
addition, the stabilized soils, although having a high strength,
are rather brittle, especially under dynamic loading (Acar and
El-Tahir, 1986; Schnaid et al., 2001) The cracking and
brittle-ness of cement stabilized soils have greatly influenced the
long-term performance of stabilized soils for many
applications
In addition to the cracking and brittleness, when used for
clay, the cementitious stabilizer can cause significant swelling
if excessive sulfate is present (Celik and Nalbantoglu, 2013;
Hunter, 1988; Mitchell, 1986; Mitchell and Dermatas, 1992;
Puppala et al., 1999, 2005; Wang et al., 2004) The clay with
excessive sulfate content is usually called sulfate-rich clay It
has been found that under pH conditions created by the
cementitious materials, sulfate reacts with calcium ions to
form ettringite (Ca6[Al(OH)6]2(SO4)3$26H2O) and thaumasite
(Ca6[Si(OH)6]2(SO4) (CO3)2$24H2O), which are highly expansive
The swelling could be as high as 200% (Faure, 1991; Harris
et al., 2004; Little et al., 2010) Such a phenomenon is
commonly referred to as sulfate-induced heave by
geotech-nical engineers
The advent of unconventional, non-cementitious
mate-rials such as foams, emulsions of petroleum, enzymes, acids,
and industrial waste materials have shown promising results
in stabilizing problematic soils While these materials are
different in nature and chemical composition, they can be used to reduce permeability, mitigate soil liquefaction, and increase soil strength by filling the voids and providing bonding between the particles (Ajalloeian et al., 2013; Ajayi
et al., 1991; Al-Khanbashi and Abdalla, 2006; Anagnostopoulos
et al., 2013; Mohammad and Vipulanandan, 2013; Moustafa
et al., 1981; Naeini et al., 2012; Ohama, 1995; Rauch et al., 2002;
Santoni et al., 2002; Zandieh and Yasrobi, 2007) Among these unorthodox stabilizers, liquid polymers have gained attention due to their relative ease of use and promising outcomes
However, there is a lack of systematic studies on the stabili-zation methods of polymers for different soils, such as mixing
or curing methods As a result, the reported studies showed different outcomes even for the same soil For instance, varying the polymer content of the specimens did not result in
a consistent outcome in terms of resultant UCS (Rauch et al.,
2002), and more saliently, in another case, adding polymer
to soil samples decreased the strength of the specimens compared to untreated soil (Santoni et al., 2002) This inconsistency hindered the wide applications of polymers as
a soil stabilizer for many situations Considering the dilemma, this study focuses on investigating the mixing and curing methods as well as the short-term and long-term performances for sand and sulfate-rich clay
The scope of the study includes the following:
1 Determination of suitable mixing and curing methods, and duration for a liquid polymer that was used to stabilize sand and sulfate-rich clay
2 Determining the short-term behavior of the two stabilized soils An unconfined compressive stress (UC) test was carried out for such purpose, and the clay samples were tested for their swelling potential
3 Long-term performance of the stabilized soils was studied
For this purpose, clay specimens were subjected to soaking
in water for prolonged time before their UCS and swelling potential were measured In contrast, sand specimens
Fig 1 e Soils used in the tests (a) Sulfate-rich high plasticity clay (b) Poorly graded sand
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Trang 3polymer-were subjected to three aging conditions, i.e., wet-dry
cy-cles, freeze-thaw cycy-cles, and accelerated UV-B weathering
The aged sand samples were tested for their UCS
2.1 Sand
The selected sand was a light brown natural river sand as
shown inFig 1(a), for which the D60is 0.45 mm, D30is 0.3 mm,
and D10is 0.2 mm The gradation curve of the sand is shown in
Fig 2 According to the Unified Soil Classification System
(USCS), the sand is classified as poorly graded sand (SP) with
Cc¼ 1.1 and Cu¼ 2.5 The soil has maximum and minimum
densities of 18.64 kN/m3 and 15.22 kN/m3, respectively,
determined by the ASTM D4253 and ASTM D425 test methods
2.2 Sulfate-rich clay
A yellowish clay soil was employed throughout this study To
determine the percentage of fines (i.e., silts and clays) of the
soil, wet sieve analysis following ASTM C325-07 was
per-formed and the results indicated a fine content of 94% The
results of the Atterberg limits test on the soil showed a liquid
limit (LL) of 53 and a plasticity index (PI) of 23, which classifies
the soil as high plasticity clay (CH) under USCS protocol The
soil had negligible sulfate content (i.e., less than 100 ppm) To
prepare sulfate-rich clay with a sulfate concentration of
20,000 ppm (2%) by weight, the soil was oven-dried and then
sodium sulfate was added After thorough mixing, the
pre-pared sulfate-rich clay was set in an outdoor environment for
2 weeks to reach chemical equilibrium The utilized clay soil is
illustrated inFig 1(b)
2.3 Liquid polymer
The polymer used as a soil stabilizer in this study, which relies
on chemical reactions to polymerize and bond soil particles
together, has wide ranging engineering applications The
chemical structure and properties of the polymer are
dis-cussed in this section
Polymer M is a single component, moisture activated,
hy-drophobic polyurethane prepolymer commercially known as
AP Soil 600™ manufactured by Alchemy Polymers, LLC This
polymer belongs to the generic family of Methylene Diphenyl
Diisocyanate (usually addressed as MDI) and its chemical
structure is shown inFig 3 The NitrogeneCarboneOxygen
(N]C]O) group of the polymer precursor reacts chemically
with the OxygeneHydrogen (eOeH) groups of added water
to form a mixture of diisocyanates and amines resulting in
an inert, insoluble polyuria and emission of carbon dioxide
as shown by Eqs.(1) and (2) The resultant polyuria coating the soil particle surface has two effects, (1) acting as“glue”
to bond soil particles together and (2) acting as a barrier to mitigate moisture infiltration The reported properties of the polymer are presented inTable 1 The applications for such
a product include a wide range of areas in ground improvement, such as soil stabilization, permeation grouting and sinkhole remediation The measured unit weight of the polymer in the laboratory environment (temperature
20C± 2C) was 11.39 kN/m3
(2)
2.4 Mixture preparation and specimen casting
As suggested by previous studies (Harris et al., 2004; RauchQ1
et al., 2002; Santoni et al., 2002), the mixing method has a great influence on the outcome when a polymer is used as a soil stabilizer The following section describes the specimen preparation procedure for sand and clay specimens using Polymer M The specimens were initially prepared using 10%
water and 10% polymer by weight for all the soils
Considering that the polymerization of Polymer M is triggered by moisture as indicated by Eqs (1) and (2), the Polymer M stabilized sand and clay specimens were prepared by two methods For Method-1, the dry soil was first mixed with polymer and then water was added In contrast, for Method-2, dry soil was first mixed with water and then polymer was added
Once mixed thoroughly, the sand-polymer mixture was compacted into a cylindrical mold of 50 mm by 175 mm (D H) It was only filled up to 125 mm high (aspect ratio:
2.5:1), which left 50 mm of extended space This mixture was then poured into the molds in 5 sequential layers of equal thickness, and each layer was individually blown to ensure an acceptable level of compaction The relative density of the samples throughout the study was 77% A thin layer of pe-troleum jelly was applied to the interior walls of the molds To facilitate the extraction of the samples from the molds, eliminate skin friction, and the boundary effect between the samples and the molds, each mold half was sealed with plastic wrap After compaction, the mold was capped to pre-vent moisture loss The caps and the molds were removed
24 h after specimen preparation These samples were then subjected to curing in two different media: laboratory room environment (20C± 2C) and submerged in water
(1)
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Trang 4Similar to sand, Polymer M stabilized sulfate-rich clay
specimens were also prepared following Method-1 and
Method-2 The clay specimens were compacted to their
maximum dry unit weight at the optimum moisture content
based on the standard proctor test for 10% polymer (by weight)
All the prepared specimens were subjected to curing before
they were tested or set in an aging environment
3.1 Testing outline
The primary objective of this study is to evaluate the
effec-tiveness of a liquid polymer soil stabilizer on improving the
short-term and long-term performances of sulfate-rich clay
and poorly-graded sand, by studying the strength
improve-ment for both sand and clay as well as the swelling mitigation
for clays that are stabilized by the polymer To fulfill this
objective, a study was carried out in three major steps In the
first step, the appropriate mixing method and curing time
were determined for the studied soils and polymer In Step 2,
the strength improvement of the freshly stabilized sand and
clay specimens was assessed and the swelling mitigation for
the freshly stabilized clay was studied In Step 3, the long-term
performance of the polymer stabilized soils was evaluated In
this step, the clay soil was soaked for a prolonged period;
thereafter, the strength and swelling potential were measured
as indications of long-term performance In contrast, the sand was subjected to three scenarios of aging, that is, UV radia-tion, wet-dry cycles, and freeze-thaw cycles The aged sand samples were tested for their UCS, which was then compared with that of the un-aged samples.Fig 4summarizes the study outline
3.2 Specimen curing
The prepared specimens were cured in three different envi-ronments, i.e., in ambient air, in 100% humidity, and in water
to find the appropriate curing environment Upon the selec-tion of the appropriate curing environment, the specimens were cured for different durations to determine the suitable curing duration
3.3 Specimen aging
The long-term performance of the stabilized sand and sulfate-rich clay was evaluated by testing the aged specimens The sand specimens were aged in three different conditions, separately, (1) 2000 h of Ultraviolet (UV) radiation to simulate the effect of long-term sunlight exposure; (2) 24 wet-dry cycles
to simulate the effect of rain; and (3) 24 freeze-thaw cycles to simulate the effect of seasonal changes on the performance of the stabilized specimens The stabilized clay specimens were soaked in water for a prolonged time
3.3.1 Prolonged UV exposure
Extensive exposure to UV radiation in polymers with aromatic isocyanate will result in a phenomenon known as“yellowing”
in which a drastic color change and gradual polymer degra-dation occurs due to an oxidegra-dation reaction at the backbone of the polymer (Rosu et al., 2009) UV radiation from sunlight is divided into wavelength ranges categorized as UV-A, ranging from 315 to 400 nm, UV-B ranging from 280 to 315 nm, and UV-C ranging from 100 to 280 nm (NTP, 1992) Although only 5% of solar radiation accounts for UV-B wavelengths, it is reportedly the contributing element for polymer photo-degradation and the consequent negative impact on polymer life span (Andrady et al., 1998) Given the increasing application of polymers for geotechnical/transportation purposes, it is crucial to have an understanding of the durability of the soil-polymer composites, particularly where the composite is on the surface and exposed to sunlight
Examples of such applications are the use of polymers on slope surfaces to prevent failure and to mitigate erosion The polymer-stabilized sand specimens were tested for their endurance after prolonged exposure to UV radiation UV-B wavelengths were selected for the strength assessment of the soil-polymer composite To evaluate the performance of polymers in different industries, tests have been defined to monitor the possible degradation of the polymers in the course of time To do so, two batches of sand specimens were exposed to accelerated weathering tests following ASTM D4329-13 Cycle A Guidelines The samples were exposed to UV-B radiation for 2000 h The selected exposure duration is beyond what happens in normal exposure to observe the performance of the specimens under worst-case
Fig 2 e Gradation curve for sand
Fig 3 e Chemical composition of methylene diphenyl
diisocyanate
Table 1 e Properties of the polymer
Physical properties Reference/standard Value
Centipoise
Compressive strength
with fine sand
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Trang 5polymer-scenarios The exposed samples were then tested for their
UCS and the results were compared with un-weathered
samples Fig 5 presents the test setup for the accelerated
weathering test Considering the stabilized clay has minimal
chance of being exposed to UV radiation, the clay was not
subjected to UV radiation
3.3.2 Wet-dry cycles
There is no direct test method to perform wet-dry tests for
polymer stabilized soils Consequently, ASTM D559-15, used
for wet-dry cycling of soil-cement mixtures, was adopted to
perform the test The stabilized sand specimens were
sub-jected to 24 wet-dry cycles In each cycle, the specimens were
submerged in water for 24 h and then were dried for 48 h to
permit the dissipation of the excess moisture The specimens
were then tested for their UCS and compared with
non-weathered samples to determine if the cycles had any impact
on their strength
3.3.3 Freeze-thaw cycles
For a similar reason, ASTM D560-15, used for the freeze-thaw
cycling of soil-cement mixtures, was adopted for freeze-thaw
cycles of the stabilized sand specimens The samples were set
in a18C environment for 24 h and then were put in a
lab-oratory environment (i.e., 20C± 2C) to thaw Consequently,
the samples were tested for their UCS and compared with
un-weathered specimens
3.3.4 Prolonged soaking for clay specimens
Although the wet-dry and freeze-thaw cycles had been plan-ned for the clay specimens, they showed susceptibility in water when different curing methods were compared As a result, the clay specimens were only conditioned in water for
a prolonged time to assess their strength and volume stability
in that environment
3.4 Testing procedure
The UCS of the stabilized soils prepared with various curing and mixing methods was assessed for short-term and long-term performances For the evaluation of the short-long-term performance of both soils, the UCS of specimens made with the two different mixing methods and cured in a laboratory environment was acquired In addition, the clay specimens were tested for their swelling potential For the long-term performance, the sand and clay specimens were first aged in the afore-mentioned environments After the conditioning, the sand specimens were subjected to UCS tests, whereas the
Fig 5 e Accelerated UV-B weathering test setup Fig 6 e UCS test setup
Fig 4 e Outline of study
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Trang 6clay specimens were subjected to UC and swelling potential
tests
3.4.1 Unconfined compression strength test
The UC test was carried out following ASTM
D2166/D2166M-13 A digital Pneumatic Universal Testing Machine (UTM) was
employed to provide the compressionestrain curve for the
specimens.Fig 6illustrates a UCS test specimen
3.4.2 Free swelling test
A free swelling test was used to evaluate the swelling potential
of the polymer stabilized sulfate-rich clay and it was
per-formed following ASTM D4546-14 guidelines The entire
assembly and a typical soil specimen for the free swell test are illustrated inFig 7 Specimens were carefully prepared at their maximum dry unit weights The overburden stress due to the weight of porous stones on top of the soil was 1 kPa The vertical swell was measured at certain time intervals
4.1 Mixing methods evaluation
The two mixing methods (Method-1 and Method-2) employed
in this study showed insignificant differences in terms of
Fig 8 e Visual differences between different specimens (a) Method-1 for sand (b) Method-2 for sand (c) Method-1 for clay
(d) Method-2 for clay
Fig 7 e Free swelling test setup (Gilazghi et al., 2016)
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Trang 7polymer-appearance and UCS in the sand specimens (Fig 8(a) and (b)).
Conversely, for clay, the resultant samples from the mixing
methods were significantly different from each other both in
appearance and their gained UCS The specimens prepared
following Method-2 (Figs 8(d) and 9(b)) appeared clear with a
shiny, smooth, yellowish surface suggesting the proper
coating of the surface with polymer However, the
specimens made using Method-1 (Figs 8(c) and 9(a)) had a
dark brown surface with numerous voids, whereas the
polymer coating was generally missing from the surface
In terms of UCS, the sand specimens made with Method-1
and Method-2 were similar as shown inFig 10(a), whereas in
the case of clay, the UCS of the specimens made with
Method-2 were significantly higher than that of mixing Method-1 as
shown in Fig 10(b) Basically, the observed performance of
the specimens stabilized by employing mixing Method-1 did
not differ significantly with that of the unstabilized control
specimen, suggesting the ineffectiveness of the method The
maximum UCS gained for Method-1 as well as the
unstabilized control specimens of clay was approximately
400 kPa, while the specimens made with Method-2
sustained up to 1400 kPa (Fig 10(b)) Therefore, the results
suggest following mixing Method-2 for clay soil Because the
use of Method-1 and Method-2 made no difference for sand,
Method-2 was adopted for convenience While sand and clay
specimens behaved similarly under the maximum
compressive pressure, the strain at failure for the clay
samples (8%) was higher than that of the sand (6.5%)
4.2 Curing method and duration evaluation
To study the curing procedure and their overall gained strength, sand and clay specimens were soaked in water for various du-rations and different scenarios The reason for evaluating water soaking was the triggering role of water in the polymerization process as previously discussed in Eqs.(1) and (2)
When clay samples were soaked in water they only kept a fraction of their strength after 48 h Alternatively, when the specimens were cured in a humid environment for a total of 4 days, similar to what was suggested byGilazghi et al (2016) instead of being soaked, significant improvements were observed in their performance under the UC test Conversely, the humid environment did not result in any salient improvements on sand specimens A comparison of all of the above-mentioned cases is illustrated in Fig 11 The term
“Soaked” refers to 4 days of curing in air followed by 4 days
of curing in water, while “Unsoaked” means the specimens were only cured in air and no water curing was performed
For sand, Rezaeimalek et al (2016) found that a combination of air and soaking curing yielded the maximum strength, suggesting that a total curing of 8 days including 4 days of air curing followed by 4 days of soaking in water as the minimum curing duration.Fig 12 shows that 4 days of water soaking the specimens after 4 days of air curing resulted in the maximum UCS and extending the curing beyond 8 days did not result in salient improvement of UCS for sand specimens
Fig 9 e Mixture of sulfate-rich clay with water and polymer (a) Dry soil mixing (Method-1) (b) Wet soil mixing (Method-2)
for sulfate-rich clay
Fig 10 e UCS results for different mixing methods (a) Sand (b) Clay stabilized with the polymer
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Trang 84.3 Short-term and long-term performances of stabilized sand
When the curing procedure and the duration were deter-mined, a number of polymer, water combination ratios were assessed, and then the strongest specimens were selected for further evaluation For sand, the specimens with a polymer to water ratio of 2:1 provided the strongest case The strongest stabilized sand specimens showed 4931 kPa of UCS and strain
at the failure was 6.45%, approximately 2 days after comple-tion of curing that allowed the samples to dry at laboratory temperature.Fig 13illustrates the results.Consoli et al (2012) showed that for the uniform sand which was approximately similar to the one used for the present study and stabilized using cement, a linear relationship between the cement content and the UCS could be observed Their work indicated a UCS in the order of 500e1000 kPa when 7%
cement was used for stabilization If the linear relationship between the cement content and UCS is extrapolated to 15%e20% polymer content which is the amount used for the present study, a UCS in the order of 2142e2857 kPa should
be anticipated, which is approximately half of the UCS achieved with Polymer M, suggesting the advantageous outcome of the stabilization process when compared to traditional approaches
Fig 14 shows the results of accelerated UV-B radiation
Fig 14(a) illustrates the specimens prior to radiation and Fig 14(b) illustrates the specimens after 667 h of radiation
Evidently, the stabilized specimens significantly transformed
in color from light to dark brown after exposure, although
no evidence of cracks or damage was observed This color change confirms the yellowing phenomena Compared to photos taken at 667 h of radiation, the color of the stabilized specimens darkened further However, the color change was applicable only to the surface of the specimens and the interior sections of the samples stayed similar to those prior
to radiation as shown in Fig 14(c) When tested for their UCS, the specimens did not show salient strength loss due
to UV radiation as a result of polymer degradation The specimens, however, were more brittle than the non-weathered specimens, as shown in Fig 15 The UV-B radiated specimens sustained 4.08% of strain at the peak stress, whereas the non-weathered samples showed 6.45%
strain at the peak stress, indicating an increase in brittleness after exposure to radiation
Fig 16 summarizes the results of the UC test on sand specimens after freeze-thaw cycles The UCS remained
Fig 12 e Effect of curing time on UCS of Polymer M
stabilized sulfate-rich clay and sand
Fig 14 e Polymer M specimens (a) Prior to radiation (b) After 667 h of radiation (c) Tested for UCS after 2000 h of radiation
Fig 11 e Comparison of performance for polymer
stabilized specimens
Fig 13 e UC test results for optimal stabilization of sand
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Trang 9polymer-unchanged However, the specimens became more brittle as
the aged specimens failed at a much lower strain compared
with unaged specimens
Fig 17summarizes the UC test results after wet-dry cycles
The stabilized specimens did not show a significant loss of
strength after wet-dry cycles The peak stress sustained by
these specimens was 3933 kPa, which was approximately
85% of the peak compressive stress sustained by
unweathered specimens and the final UC test curve was
close to what was observed for non-weathered specimens
4.4 Short-term and long-term performances of
stabilized sulfate-rich clay
As for clay, the results suggested a different pattern than
sand For freshly cured specimens (short-term results), the
strongest in terms of UCS were observed when the water content of the soils was optimum, and the amount of polymer was equal to the volume of voids minus the volume of opti-mum water content (Exhibit A,Fig 18) The maximum UCS reached was 3422 kPa, with approximately 8.51% of strain at failure for non-sulfated and sulfated cases, respectively A close yet more ductile alternative to this batch was when the volume of the added liquid (polymer and water) was equal to the volume of the voids (Exhibit B) with a polymer to water ratio of 2:1 for the stabilized samples For this latter alternative, the clay samples yielded 2464 kPa
Fig 18 e UC test results for optimal stabilization of clay
Fig 19 e Free swelling test results for unstabilized and polymerized sulfate-rich clay
Fig 20 e Short-term and long-term swelling of unstabilized and polymerized sulfate-rich clay
Fig 16 e UC test results after 24 freeze-thaw cycles
Fig 17 e UC test results after 24 wet-dry cycles
Fig 15 e UC test results after 2000 h of UV radiation
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Trang 10of compressive strength with 7.54% of strain at failure.
Therefore, selecting the optimal case between these two
alternatives will depend on the project specifications and
other considerations such as economic concerns, since the
higher polymer ratio will result in added overall cost
In addition, benchmarking the findings of the present
study with the one conducted by Horpibulsuk et al (2005)
where the performance of cement-clay admixtures was
investigated showed that when 8%e33% of cement was used
to stabilize soft clay, the axial stress varied between
approximately 400 kPae2100 kPa with the strain ranging
approximately from 1% to 2.5% Polymer-stabilized clay
specimens provided much higher short-term UCS
(approximately 62% for Exhibit A and approximately 17% for
Exhibit B, respectively) and strain at failure (approximately
240% for Exhibit A and 200% for Exhibit B, respectively)
To evaluate the long-term performance of the clay
speci-mens, batches made following Exhibit A and Exhibit B
methods were soaked in water for a specific period of time
Although the specimens significantly lost their strength due to
water susceptibility, the remaining strength was still
consid-erable as shown inFig 18 Specimens from Exhibit A and B
sustained maximum compressive pressures of 1082 and
527 kPa, respectively and their strain at failure were 8.89%
and 6.67%, respectively
Fig 19summarizes the results of the swell test for clay
samples As shown in Fig 12, the curing of the stabilized
clay samples is complete within 4 days Thus, the swelling
occurring within 4 days is taken as the short-term swelling
The swelling occurring after curing is considered as the
long-term swelling Overall, the unstabilized sulfate-rich
clay experienced more than 20% of its swelling within the
first 4 days of the test With the addition of 10% polymer, the
swelling was reduced to a negligible 2%, as shown inFig 20
This study was conducted using a liquid polymer soil
stabi-lizer from the generic family of methylene diphenyl
diiso-cyanate Therefore, the results may be generalized to products
from the same generic family
In the case of sulfate-rich high plasticity clay, for salient
improvements the mixing method should be followed by
thoroughly mixing water with the soil prior to adding the
polymer (mixing Method-2) However, this is not the case
for sand specimens The difference was insignificant in the
resultant UCS of sand specimens made following Method-1
and Method-2
When subjected to UV radiation the tested specimens
became more brittle and yellowing was evident on their
surface with no salient measured strength loss More
var-iations should be expected for longer periods of exposure
However, it should be noted that this length of exposure
may not be observed in real field conditions
The stabilized sand specimens showcased acceptable
long-term performance after repetitive cycles of freeze-thaw
and wet-dry Overall, the aged specimens performed
similarly to unweathered samples
The liquid polymer soil stabilizer is potentially highly effective in mitigating soil swelling By adding 10% poly-mer, the swelling was insignificant For the stabilized sample, the majority of the swelling occurred during its long-term service and only a small fraction occurred dur-ing construction, i.e., curdur-ing
Acknowledgments
The authors would like to greatly acknowledge Alchemy Polymers Company, LLC for their financial support Q2
r e f e r e n c e s
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