Engineering Properties of Stabilized Subgrade Soils for Implementation by phv84830

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									                     Oklahoma Department of Transportation
                          Planning & Research Division
                                                   Research News
__________________________________________________________________

Engineering Properties of Stabilized Subgrade Soils for
Implementation of the AASHTO 2002 Pavement Design Guide
ODOT SPR Item No. 2185                                                                            June 2009
By Pranshoo Solanki, E.I. Naji N. Khoury, Ph.D. and Musharraf M. Zaman, Ph.D., P.E.

             avement conditions data for Oklahoma          stabilized layers are recommended. These

  P          show that 46% of major roads in the
             state are in poor condition or mediocre
             condition due to weak subgrade soils as
                                                           properties include resilient (Mr) or elastic (ME)
                                                           modulus, unconfined compressive strength (UCS),
                                                           and durability. The evaluation of these inputs is
one of the main factors. Driving roads in need of          required to pursue a Level-1 (most accurate)
repairs threaten public safety and cost Oklahoma           design under the hierarchical scheme. For a Level-
motorist over $ 1 Billion annually in extra vehicle        2 (intermediate) design, however, design inputs
repairs. In the last few decades, state                    are user selected possibly from an agency
transportation agencies and industry have been             database or from a limited testing program or could
challenged to build, repair and maintain pavement          be estimated through correlations (AASHTO,
systems with enhanced longevity and reduced                2004). Level-3, which is the least accurate,
costs. Specifically, efforts have been made to             requires only the default values and is generally
improve the design methodology and to establish            not recommended.
techniques for modification of pavement materials               To this end, the current study was undertaken
(NCHRP). Cementitious stabilization is considered          to     determine     engineering    properties    of
one of these techniques; it enhances the                   cementitiously stabilized common subgrade soils in
engineering properties of subgrade layers, which           Oklahoma for the design of roadway pavements in
produces structurally sound pavements. However,            accordance with the AASHTO 2002 MEPDG.
the enhancement in engineering properties and the          These properties include resilient modulus (Mr),
field performance of a stabilized subgrade layer in        modulus of elasticity (ME), unconfined compressive
pavement system are influenced by many factors             strength (UCS), moisture susceptibility and three-
such as stabilizing agent type, the type of soil to be     dimensional (3-D) swell. Additionally, mineralogical
stabilized, curing time, the required strength, the        studies such as scanning electron microscopy
required durability, cost, and environmental               (SEM), energy dispersive spectroscopy (EDS) and
conditions.                                                X-ray diffraction (XRD) were used to verify the
     Cementitious stabilization is widely used in          findings from the macro test results.
Oklahoma and elsewhere as a remedial method to
                                                           Materials and Test Procedure
ameliorate subgrade soil properties (e.g., strength,
                                                                In this study, four different types of soils
stiffness, swell potential, workability, and durability)
                                                           encountered in Oklahoma, namely, Port Series (P-
through the addition of cementitious additives. It
                                                           soil), Kingfisher Series (K-soil), Vernon Series (V-
consists of mixing stabilizing agents such as lime,
                                                           soil, sulfate content ≈ 15,400 ppm), and Carnasaw
class C fly ash (CFA) and cement kiln dust (CKD)
                                                           Series (C-soil) were used. A summary of the soil
with soil. In the presence of water, these agents
                                                           properties determined in the laboratory are
react with soil particles to form cementing
                                                           presented in Table 1. These soils were stabilized
compounds that are responsible for the
                                                           with three locally produced and economically
improvement in engineering properties such as
                                                           viable stabilizers used in Oklahoma, namely,
strength and stiffness.
                                                           hydrated lime (or lime), class C fly ash (CFA), and
     With the movement toward implementation of
                                                           cement kiln dust (CKD). The percentage of
the new Mechanistic-Empirical Pavement Design
                                                           stabilizer used (3%, 6% and 9% for lime; 5%, 10%
Guide (MEPDG), new material properties required
                                                           and 15% for CFA and CKD) was selected on the
for critical performance prediction of cementitiously


                                     Subgrade Soil Stabilization                                             1
basis of pH test and literature review. Cylindrical                                                     A complete setup of Mr testing on stabilized
specimens of stabilized soil were compacted and                                                   subgrade soil specimen is shown in Figure 1. ME
cured for 28 days in a moist room having a                                                        and UCS tests were conducted in accordance with
constant temperature (73.4±3oF) and controlled                                                    the ASTM D 1633 test method. Specimens were
relative humidity (>96%). The curing period is                                                    loaded in a MTS frame at a displacement rate of
consistent with the new MEPDG that the required                                                   0.05 in/min. Deformation values were recorded
Mr, ME and UCS for design are the 28-day values.                                                  during the test using two LVDTs fixed to opposite
                                                                                                  sides of and equidistant from piston rod with a
Table 1Testing Designation and Soil Properties                                                    maximum stroke length of 0.5 in. Each specimen
      Method
      ASTM D 2487
                   Parameter/Units
                   USCS Symbol
                                                  P-soil
                                                  CL-ML
                                                               K-soil
                                                               CL
                                                                           V-soil
                                                                           CL
                                                                                       C-soil
                                                                                       CH         was subjected to two unloading-reloading cycles
      AASHTO M 145 AASHTO
                   Designation
                                                  A-4          A-6         A-6         A-7-6
                                                                                                  and loaded up to failure in the third sequence of
      ASTM D 2487  USCS Name                      Silty clay
                                                  with sand
                                                               Lean clay   Lean clay   Fat clay
                                                                                                  reloading to determine the ME and UCS.
      ASTM D 2487          % finer than 0.075
                           mm
                                                  83           97          100         94
                                                                                                        The TST procedure used in this study consists
      ASTM D 4318
      ASTM D 4318
                           Liquid limit
                           Plastic limit
                                                  27
                                                  21
                                                               39
                                                               18
                                                                           37
                                                                           26
                                                                                       58
                                                                                       29
                                                                                                  of placing Mr tested specimens in an oven at 95oF
      ASTM D 4318
      …
                           Plasticity index
                           Activity
                                                  5
                                                  0.24
                                                               21
                                                               0.47
                                                                           11
                                                                           0.28
                                                                                       29
                                                                                       0.69
                                                                                                  until no more significant weight changes are
      ASTM D 854
      ASTM D 698
                           Specific gravity
                           Optimum moisture
                                                  2.65
                                                  13.1
                                                               2.71
                                                               16.5
                                                                           2.61
                                                                           23.0
                                                                                       2.64
                                                                                       20.3
                                                                                                  observed. After drying, specimens were allowed to
                           content (%)                                                            cool down at room temperature. Specimens were
      ASTM D 698           Max. dry unit
                           weight (pcf)
                                                  113.4        110.6       101.9       103.7
                                                                                                  then placed on a porous plate and covered with a
      ASTM D 6276
      OHD L-49
                           pH
                           Sulfate content
                                                  8.91
                                                  <40
                                                               8.82
                                                               <40
                                                                           8.14
                                                                           15,400
                                                                                       4.17
                                                                                       267
                                                                                                  membrane         in   an   ice   chest     containing
                           (ppm)
      USCS: Unified Soil Classification System; OHD: Oklahoma Highway Department
                                                                                                                                         approximately
                                                                                                                                     12.7 mm (0.5
     After curing, specimens were tested for Mr, ME                                                                                  in.) of de-ionized
and UCS. Selected specimens were also tested for                                                                                     (DI) water under
moisture susceptibility (tube suction test) and                                                                                              controlled
three-dimensional swell during 60 days of capillary                                                                                        temperature
soaking. A total of four replicates were prepared for                                                                                         o
                                                                                                                                     (73.4±3 F) and
each additive content, of which two specimens                                                                                        relative humidity
were tested for Mr and then followed by tube                                                                                         (>96%). During
suction test (TST) and three-dimensional (3-D)                                                                                       wetting          of
swell test by subjecting samples to 60 days of                                                                                       specimens in DI
capillary soaking. The other two specimens were                                                    Figure 2 Setup for TST            water,         the
tested for Mr and then followed by ME and UCS                                                                                        dielectric values
tests, without capillary soaking. After UCS test                                                  (DV) increased with time due to capillary soaking
broken specimens were air dried for approximately                                                 of water in the specimens. Four measurements
2 days, and then pulverized and passed through a                                                  were taken along the circumference of the sample
No. 40 sieve. The finer material was reconstituted                                                in separate quadrants and the fifth reading was
with moisture for 1 day, and then tested for liquid                                               taken at the center of specimen and an average of
limit and plastic limit in accordance with ASTM D                                                 all five readings was reported. Measurements were
                           4318.                                                                  taken daily, until the DV became constant. Figure 2
                                The Mr tests were                                                 shows photographic view of setup used for TST.
                           performed in accordance                                                      To investigate the swelling potential of
                           with the AASHTO T 307                                                  specimens, 3-D swell test were conducted on the
                           test method. A 500-lb                                                  same specimens under TST testing. The 3-D swell
                           load cell was used to                                                  values were measured by determining the height to
                           apply the load. Two linear                                             the nearest 0.001 in at 3 places that are 120
                                                                                                                                                       o

                           variable          differential                                         apart. The diameter was measured to the nearest
                           transformers        (LVDTs)                                            0.001 in near the top, in the middle, and near the
                           were used to measure                                                   base of each sample. The three height and
                           the     resilient     vertical                                         diameter measurements were averaged and the 3-
                           deformation.           These                                           D volume change was calculated.
  Figure 1 Setup for Mr    LVDTs were attached to                                                       To facilitate macro-behavior comparison and
  Test                     two aluminum clamps                                                    explanation, the Scanning Electron Microscopy
that were mounted on the specimen at a distance                                                   (SEM) technique was employed to qualitatively
of approximately 2.0 in from both ends of the                                                     identify the micro-structural developments in the
specimen. The LVDTs had a maximum stroke                                                          matrix of the stabilized soil specimens. A JEOL
length of 0.2 in.                                                                                 JSM 880 scanning electron microscope operating



                                                                        Subgrade Soil Stabilization                                                   2
at 15 kV was used to visually observe the
specimens. The JEOL JSM 880 was fitted with an
energy-dispersive X-ray spectrometer (EDS). The
EDS was used to analyze chemical compositions
of the specimens. To confirm ettringite formation in
some of the specimens, XRD tests were also
performed on raw soil and capillary soaked
specimens.
Results and Discussion
     Results for the tested stabilized soil specimens
showed that all three stabilizers improved the
strength/stiffness properties, namely, Mr, UCS and
ME values, of P-, K-, V- and C-soil specimens. The
mean Mr at a deviatoric stress of 6.0 psi and a
confining pressure of 4.0 psi has been compared
for this purpose (Figure 3). As evident from Figure                                                                                                                                                                                                 Figure 4 SEM Micrographs of the Indicated 28-Day
3, at lower application rates (3% to 6%), the lime-                                                                                                                                                                                                 Stabilized Soil Specimens
stabilized soil specimens showed the highest                                                                                                                                                                                                             All the three additives used in this study,
improvement in the Mr values. At higher application                                                                                                                                                                                                 namely, lime, CFA and CKD, are effective in
rates (10% to 15%), however, CKD treatment                                                                                                                                                                                                          reducing the plasticity of soils. However, lime-
provided maximum enhancements. Overall, K-soil                                                                                                                                                                                                      stabilization is more effective as compared to CFA
and C-soil specimens showed the highest and the                                                                                                                                                                                                     and CKD-stabilzation in reducing the PI of soils. In
lowest improvements in the Mr values. Similar                                                                                                                                                                                                       addition, the percentage of reduction in PI was
trend of behavior were observed for ME and UCS                                                                                                                                                                                                      observed maximum with K-soil among all the three
values of different stabilized soil specimens. One                                                                                                                                                                                                  soils (K-, V- and C-soil). This could also be one of
of the explanations could be differences in the pH                                                                                                                                                                                                  the reasons for the highest improvement in Mr
values of K- and C-soil. For example, raw K- and                                                                                                                                                                                                    values of stabilized K-soil specimens.
C-soil had the highest and the lowest pH value of                                                                                                                                                                                                        The tube suction test (TST) results revealed
9.07 and 4.17, respectively, among the four soils                                                                                                                                                                                                   that lime- and CFA-treatment is helpful because it
used in this study. It is believed that the difference                                                                                                                                                                                              reduces the moisture susceptibility. On the other
in Mr values are attributed to the differences in                                                                                                                                                                                                   hand,      CKD-stabilization     makes     stabilized
physical and chemical properties of the soils and                                                                                                                                                                                                   specimens more susceptible to moisture, as
stabilizing agents which leads to various                                                                                                                                                                                                           compared to raw soil specimens. For sulfate
pozzolanic reactions.                                                                                                                                                                                                                               bearing soil (V-soil), however, only CFA-treatment
                                                                                                                                                                                                                                                    showed promising results.
                               500,000
                                              P-Soil
                                                                                                                                                                                                                                354,022
 Resilient Modulus, Mr (psi)




                                              K-Soil                                                                                                                                                                                                                 30.0
                               400,000                                                                                                                                                                                                                                              K-Soil                  V-Soil
                                                                                                                                                                                                     303,952




                                              V-Soil                                                                                                                                                                                                                 25.0           C-Soil
                                                                                                                                                                                                                        273,829
                                                                                                                                                                                                                        271,519




                                              C-Soil
                                                                                                                                                                                              229,194




                               300,000                                                                                                                                                                                                                               20.0
                                                                                                                                                                                                                                                     3-D Swell (%)




                                                                                                                                                                                                                                                                                                                                                                                                                                                                         15.1
                                                                                                                                                        185,884




                                                                                                                                                                                                                                                                                                                                                                                                                                                     13.3
                                                                                                                                                      168,413




                                                                                                                                                                                        159,231




                                                                                                                                                                                                                                                                                                                          12.4
                                                          154,453




                                                                                                                                                                                                                                                                                                                                                                                                                                                            12.1
                                                                                                                                                                                                                                                                                                                                               12.0




                                                                                                                                                                                                                                                                     15.0
                                                                                    145,740




                                                                                                                                                                                                                                                                                                                                                                                                                                 11.2
                                                                                                                                                                                                                                                                                                     11.1




                                                                                                                                                                                                                                                                                                                                                                                                                                        11.1
                                                                                                                                 139,883



                                                                                                                                                    136,940
                                                        131,003




                                                                                                                                125,424




                                                                                                                                                                                                                                          122,094




                               200,000
                                                                                                                                                                                                                                                                                                                                                                                                                     9.6
                                                                                                   106,086
                                                                                                   105,018
                                                                                 104,694
                                                                                103,795




                                                                                                  97,340




                                                                                                                                                                                                                                                                     10.0
                                                    91,754




                                                                                                                                                                                                                                                                                         7.1
                                                                                                                   80,282


                                                                                                                            78,852




                                                                                                                                                                                                                                                                             6.1




                                                                                                                                                                                                                                                                                                                                                                                                                                                                   5.7
                                                                                                                                                                               68,870
                                                                             65,381




                                                                                                                                                                                                                                                                                                                                                                         5.4




                                                                                                                                                                                                                                                                                                                                                                                            5.1
                                                                                                                                                                                                                                                                                                                                                             5.0
                                                                                                                 57,756




                                                                                                                                                                                                                                                                                                                                                                                                               4.8
                                                                                                                                                                                                               53,818
                                                                                                                                                                             50,708
                                                                                              48,571




                                                                                                                                                                            44,029
                                                                                                                                                                  42,545




                                                                                                                                                                                                                                                                                                                                                                                3.2
                                                                    34,391




                                                                                                                                           33,655




                                                                                                                                                                                                                                                                                                                                                                                                  2.8




                               100,000
                                                                                                              27,478




                                                                                                                                                                                                                                                                      5.0
                                                                                                              26,802




                                                                                                                                                                           26,488
                                          17,156

                                         15,435
                                         12,924




                                                                                                                                                                                                                                                                                                                                                                                                                                               1.1
                                                                                                                                                                                                                                                                                   0.8




                                                                                                                                                                                                                                                                                                                                                                                                                           0.6
                                                                                                                                                                                                                                                                                                                                                                   0.5
                                                                                                                                                                                                                                                                                               0.3




                                                                                                                                                                                                                                                                                                                                                                                      0.2
                                         8,839




                                                                                                                                                                                                                                                                      0.0
                                                                                                                                                                                                                                                                                                            -0.1

                                                                                                                                                                                                                                                                                                                   -0.1




                                                                                                                                                                                                                                                                                                                                                                                                        -0.4
                                                                                                                                                                                                                                                                                                                                        -0.4
                                                                                                                                                                                                                                                                                                                                 -0.5




                                    0
                                                                                                                                                                                                                                                                                                                                                      -2.8




                                         Raw Soil   3% Lime                  6% Lime          9% Lime         5% CFA        10% CFA 15% CFA 5% CKD 10% CKD 15% CKD                                                                                                    -5.0
                                                                                                                                                                                                                                                                             Raw Soil          3% Lime             6% Lime              9% Lime              5% CFA            10% CFA 15% CFA                       5% CKD 10% CKD 15% CKD
                                                                                                             Additive type                                                                                                                                           -10.0

Figure 3 Variation of Mr Values with Soil and Additive                                                                                                                                                                                                                                                                                                       Additive type

Type
                                                                                                                                                                                                                                                    Figure 5 Variation of Final 60-Day 3-D Swell Values with
     The mechanical (or macro) behavior could also                                                                                                                                                                                                  Soil and Additive Type
be explained using the SEM micrographs shown in
Figure 4. Visually, it is quite obvious that                                                                                                                                                                                                             The three-dimensional swelling tests on non-
stabilization of soil resulted in hydration coating                                                                                                                                                                                                 sulfate bearing soil (P-, K- and C-soil) showed that
and crystals formation in soil matrix. It is reasoned                                                                                                                                                                                               lime is more effective in reducing the swell of raw
that the crystals within the matrix provide better                                                                                                                                                                                                  specimens, as compared to CFA and CKD (Figure
interlocking between the particles and possible                                                                                                                                                                                                     5). In contrast to lime and CFA, an increase in the
higher resistance to shear deformation and also                                                                                                                                                                                                     percentage of CKD makes specimens more
reduce void within the matrix resulting in overall                                                                                                                                                                                                  susceptible to moisture and three-dimensional
strength gain. The results of the analysis conforms                                                                                                                                                                                                 swell. It is believed that such an increase in volume
to the results of the Mr, ME and UCS tests.                                                                                                                                                                                                         is due to the presence of high sulfate content



                                                                                                                                                     Subgrade Soil Stabilization                                                                                                                                                                                                                                                                                                3
(28,133 ppm) in CKD causing sulfate-induced             About the authors
heaving (ettringite formation).
     The three-dimensional swelling test on sulfate                            Pranshoo Solanki earned his
bearing soil (V-soil) showed an increase in volume                             bachelor of science in civil
for lime- and CKD-stabilized specimens while a                                 engineering from the Malviya
reduction in volume for CFA-stabilized specimens                               National Institute of Technology
                                                                               (India), and master’s degree in
was observed, as compared to raw soil specimens.                               rock mechanics (civil engineering)
This increase in volume is attributed to sulfate-                              from the Indian Institute of
induced heaving which results in the formation of                              Technology, India. Currently, he
expansive mineral ettringite. Further, presence of                             is pursuing his doctoral degree in
ettringite was verified using SEM/EDS tests in                                 civil   engineering    from    the
conjunction with XRD analyses. Figure 6 shows           University of Oklahoma. Soil stabilization using
SEM/EDS       test    results   for  lime-stabilized    cementitious additives covers an important segment of
specimens (V-soil), after 60-days of capillary          Solanki’s doctoral research.
soaking.
                                                                               Naji N. Khoury earned his
                                                                               bachelor of science from the
                                                                               Lebanese American University,
                                                                               Byblos, Lebanon and received his
                                                                               master’s and doctoral degree
                                                                               from the University of Oklahoma.
                                                                               He is currently an assistant
                                                                               professor       of     civil    and
                                                                               environmental engineering at
                                                                               Temple University. Dr. Khoury
                                                        has extensive experience, skills and credentials as a
                                                        researcher particularly in the area of the potential use of
                                                        byproducts and waste materials in pavement and
Figure 6 SEM/EDS of Ettringite Deposited in the Lime-   geotechnical engineering applications.
Stabilized V-soil Specimens (After 60-Day Swell)
                                                                              Musharraf M. Zaman received his
                                                                              bachelor     of   science     from
     As indicated in this study, assessment of
                                                                              Bangladesh            Engineering
stabilized soil specimens on the basis of                                     University, Dhaka. He completed
strength/stiffness (Mr, ME, UCS) alone can be                                 his master’s from Carleton
misleading. In addition, this study generated useful                          University, Canada, and doctorate
information that would enrich the database                                    degree from University of Arizona
pertaining to Mr, ME, UCS, 3-D swell and moisture                             in 1982. Dr. Zaman is currently an
susceptibility of selected soils in Oklahoma. An                              associate dean for research and
enriched database would benefit highway                                       graduate education at University
agencies, specifically pavement engineers, when         of Oklahoma, and also serves as liaison of Oklahoma
                                                        Transportation Center. Zaman is a highly accomplished
dealing with construction of new pavements or
                                                        researcher, who has brought in over $14 million in
rehabilitation of existing pavements. It will also      external funding to support his research and published
facilitate the implementation of the new AASHTO         200 peer-reviewed papers in journals and conference
2002 pavement design guide.                             proceeding.




                                    Subgrade Soil Stabilization                                                  4

								
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