1. Report No. 2. Government Accession No. 3. …Unconfined compressive strength, California Bearing...

1. Report No. FHWA/OH-2004/017

2. Government Accession No.

3. Recipient's Catalog No.

5. Report Date November 2004

4. Title and Subtitle Structural Support of Lime or Cement Stabilized Subgrade Used with Flexible Pavements 6. Performing Organization Code

7. Author(s) Dr. Eddie Chou Laurent Fournier Zairen Luo Jason Wielinski

8. Performing Organization Report No.

10. Work Unit No. (TRAIS)

9. Performing Organization Name and Address The University of Toledo College of Engineering Department of Civil Engineering 2801 West Bancroft Street Toledo, OH 43606

11. Contract or Grant No.

State Job No. 14746(0)

13. Type of Report and Period Covered

Final Report

12. Sponsoring Agency Name and Address Ohio Department of Transportation 1980 W Broad Street Columbus, OH 43223 14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

Lime or cement stabilizations have been used to modify wet and soft roadbed soils so that the roadbed can carry the load of construction vehicles without excessive rutting. Lime stabilization is recommended for fine-grained and high plasticity soils, and cement stabilization is recommended for coarse-grained and low plasticity soils. The durability and structural benefits of the stabilized roadbed soils have been investigated in this study through four tasks. First, the in-situ conditions of stabilized subgrade were investigated using the Dynamic Cone Pentrometer (DCP) test. The results show that the moduli of stabilized soils are generally higher than non-stabilized soils several years after construction. The second task investigated the durability and strength characteristics of stabilized soils through laboratory tests. Unconfined compressive strength, California Bearing Ratio, and resilient modulus of stabilized soils are all higher than non-stabilized soils. After freezing and thawing cycles, the stabilized soils retain more strength and modulus than the non-stabilized soils. The third task evaluated the conditions of 4 test sections on State Route 2 in Erie County, with subgrade stabilized with 6% cement, 5% lime, 3% lime with 3% cement, respectively, and a control section with no stabilization. Pavement deflection measurements were taken during different stages of construction and for each of the 3 years after construction. The back calculated subgrade moduli show that stabilization increases the subgrade modulus, with the cement treated soil being the strongest initially, followed by the 3% lime plus 3% cement section. However, the lime stabilized subgrade continues to gain strength three years after construction. The cement stabilized section has sandy soils, while the other sections have clayey soils. Task 4 developed a design procedure to quantify the increase in strength and modulus as an “effective” subgrade modulus in order to include the structural benefit of stabilized subgrade in the current pavement thickness design procedure.

17. Key Words

Lime stabilization, cement stabilization, durability, pavement, effective subgrade modulus

18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages 132

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

Structural Support of Lime or Cement Stabilized Subgrade Used with Flexible Pavements

Draft Final Report

State Job No. 14746

Principal Investigator: Eddie Y. Chou

Co-Authors: Laurent Fournier, Zairen Luo, and Jason Wielinski

The University of Toledo

Prepared in Cooperation with

The Ohio Department of Transportation

and

The U. S. Department of Transportation

Federal Highway Administration

November 2004

D-ii

DISCLAIMER

The contents of this report reflect the views of the authors who are responsible for the

facts and the accuracy of the data presented herein. The contents do not necessarily

reflect the official views or policies of the Ohio Department of Transportation or the

Federal Highway Administration. This report does not constitute a standard,

specification or regulation.

D-iii

ACKNOWLEDGMENTS

The authors would like to thank the Ohio Department of Transportation and the Federal

Highway Administration for supporting this study.

The assistance provided by the technical liaisons of this project: Mr. Roger Green, Mr.

Aric Morse, and Mr. Randy Morris are greatly appreciated. Mr. Nick Donofrio, project

engineer with District 3, and Mr. Mike Gramza of District 2, also provided necessary

assistance in soil sample collection. Mr. Issam Khoury of the Ohio University also

provided the DCP data used in this study. Without their assistance, this project could not

be completed.

D-iv

TABLE OF CONTENTS

Page

List of Figures ...........................................................................................................v

List of Tables .............................................................................................................vii

Executive Summary ..................................................................................................I

Introduction ...............................................................................................................1

Objective of Research ...............................................................................................6

General Description of Research ..............................................................................7

Findings of the Research Effort ................................................................................21

Conclusion and Recommendations ...........................................................................64

Implementation Plan .................................................................................................68

Appendix A: Subgrade Stabilization and Structural Contributions Accounted for

by Different States ..............................................................................A1

Appendix B: DCP Test Results .................................................................................B1

Appendix C: Tests Results in-Laboratory..................................................................C1

Appendix D: Back-Calculated Moduli ......................................................................D1

Appendix E: Comparisons of Two Clay Soils ...........................................................E1

Appendix F: Test Parameters Chosen for the Resilient Modulus Test .....................F1

Appendix H: List of Reference Literature ................................................................G1

D-v

LIST OF FIGURES

Figure 1. Deflection Data Taken at Multiple Surfaces........................................................15

Figure 2. Schematic Diagram Showing the Development of the Equivalent Resilient

Modulus ...............................................................................................................19

Figure 3. Subgrade Moduli Estimated from DCP from Various Sites................................23

Figure 4. Subgrade Moduli estimated from DCP from ERI-SR2 .......................................24

Figure 5. Estimated Modulus at Different Depths from DCP Test Result of Field

Sections ................................................................................................................25

Figure 6. UCS Tests for Recompacted Soil from ERI-2 (24-hour capillary soaking

before UCS tests) .................................................................................................30

Figure 7. A-ratio from UCS Tests Testing of Soil from ERI –SR2 (24-hour capillary

soaking before UCS tests) ...................................................................................31

Figure 8. Unconfined Compressive Strength of Laboratory Compacted Specimens from

ERI –SR2 ............................................................................................................32

Figure 9. UCS versus Moisture Content for Laboratory Compacted Specimens ...............33

Figure 10. UCS Strength versus Number of Freeze-Thaw Cycles for Clayey Soil from

Lorain County ......................................................................................................34

Figure 11. UCS of Soil Samples with Various Treatments on Clayey Soil from Lorain

County..................................................................................................................35

Figure 12. CBR of Soil Specimens after Various Treatments and Freeze-Thaw Cycles in

Laboratory for Soils from ERI-SR2 (56 Blows)..................................................36

Figure 13. A-ratio from CBR Testing ...................................................................................37

Figure 14. Resilient Modulus of Untreated Soil from Nevada, Wyandot County ................38

Figure 15. Resilient Modulus of Untreated Soil from the Maumee River Crossing.............39

Figure 16. Resilient Modulus of Maumee and Nevada Clay, at 2% above Optimum

Water Content and with Different Stabilizers......................................................40

Figure 17. A Ratio from Resilient Modulus, Maumee and Nevada Clay, at 2% Optimum

Water Content and with Different Stabilizers......................................................41

Figure 18. Resilient Modulus of Natural and Stabilized Nevada Soil, Compacted at

Optimum Proctor plus Two Percent Moisture Content ......................................42

D-vi

Figure 19. Resilient Modulus of Natural and Stabilized Maumee River Crossing Soil,

Compacted at Optimum Proctor plus Two Percent Moisture Content ...............43

Figure 20. Correlation of Unconfined Compressive Strength and Resilient Modulus for

Various Mixtures after Durability Testing...........................................................45

Figure 21. Scatter Plots for Deflections Taken on ERI-SR2 in 2001....................................47

Figure 22. Scatter Plots for Deflections Taken on the Surface of Pavement on ERI-SR2 ...49

Figure 23. Scatter Plot of Back Calculated Modulus from FWD Deflections on ERI-SR2.50

Figure 24. Subgrade Modulus Back Calculated from Deflections Taken on Various

Surfaces ...............................................................................................................51

Figure 25. Backcalculated Subgrade Modulus with Time ....................................................54

Figure 26. Backcalculated Median Modulus from ERI – SR2..............................................55

Figure 27. B Ratio from Backcalculated Median Modulus...................................................55

Figure 28. Scatter Plot of Model Obtained B versus Equation Obtained B ..........................58

Figure 29. B versus D3 for a Typical AASHTO/ODOT Flexible Pavement Design ...........59

Figure 30. AASHTO Equation Design Curve.......................................................................59

Figure A1. Subgrade Stabilization and Structural Contributions Accounted for by

Different States (Adopted from Kentucky DOT Report) ...................................A1

Figure E1. Hydrometer Analysis of the Nevada Clay ..........................................................E2

Figure E2. Hydrometer Analysis of Maumee River Crossing Clay ......................................E3

Figure E3. Resilient Modulus of Soil from Nevada, Wyandot County.................................E4

Figure E4. Resilient Modulus of Soil from the Maumee River Crossing..............................E5

Figure E5. Proctor Curve of Nevada Clay ............................................................................E6

Figure E6. Proctor Curve of Nevada Clay with 5% Lime .....................................................E7

Figure E7. Proctor Curve of Maumee River Crossing Clay ..................................................E8

Figure E8. Proctor Curve of Maumee River Crossing Clay with 5% Lime ..........................E8

D-vii

LIST OF TABLES

Table 1. DCP Test Locations .............................................................................9

Table 2. Summary of the Soil Characterization Tests .......................................10

Table 3. Test Section on ERI - SR2...................................................................10

Table 4. Summary of Laboratory Tests Performed............................................12

Table 5. Input Parameters Used in Modulus Back Calculation .........................17

Table 6. Parameters Used for AASHTO and Mechanistic Design ....................20

Table 7. Changes in Soil Characteristics Due to Laboratory Stabilization........27

Table 8. Chemical Composition of Lime Obtained from X-Ray Diffraction....28

Table 9. CBR Test Result for Soils from ERI - SR2 .........................................37

Table 10. A Estimation from Lab Tests ...............................................................56

Table 11. B Estimation from Back Calculation Results.......................................57

Table 12. Pavement Reduction for Different Values of B, Mr, and A .................61

Table 13. Summary of the Research Efforts .........................................................62

Table B1. DCP Result for Stabilized Sections.......................................................B1

Table B2. DCP Result for Non-Stabilized Sections ..............................................B2

Table B3. DCP Result for ERI - SR2 ....................................................................B3

Table C1. Properties of Soil Samples from ERI-SR2............................................C1

Table C2. Properties of Soil Samples from Lorain County ..................................C3

Table C3. Unconfined Compressive Strength (psi) of Laboratory Compacted

Specimens ............................................................................................C4

Table C4. UCS Test Result for Soil Samples from Lorain County.......................C5

Table C5. Freeze-thaw Test (with 5% dolomitic lime)..........................................C6

Table C6. Freeze-thaw test (ERI-2, station: 23+400, with 6% cement) ................C7

Table D1. Medians of Back-Calcualted Moduli by Using "MODULUS' and "EVERCALC" (ksi).............................................................................D3

Table D2. 80-Percentiles of Back-Calcualted Moduli by Using "MODULUS' And "EVERCALC" (ksi) ......................................................................D4

Table D3. Back-Calculated Subgrade Modulus Using Boussinesq Equation ......D5

Table D4. Back-Calculated Subgrade Modulus Using Two-Layer Model............D7

D-viii

Table D5. Back-calculated Moduli Based upon Deflections Taken at Intermediate Course (Lime ........................................................................................D8

Table D6. Back-calculated Moduli Based upon Deflections Taken at Intermediate Course (Cement) ...................................................................................D9

Table D7. Back-calculated Moduli Based upon Deflections Taken at Intermediate Course (Control) ..................................................................................D10

Table D8. Back-calculated Moduli Based upon Deflections Taken at Intermediate Course (Lime with Cement)..................................................................D11

Table D9. Back-calculated Moduli Based upon Deflections Taken at Surface Course Lime 2001) ...............................................................................D12

Table D10. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Cement 2001) ..........................................................................D13

Table D11. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Control 2001) .........................................................................D14

Table D12. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Lime with Cement 2001).........................................................D15

Table D13. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Lime 2002) ..............................................................................D16


Table D15. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Control 2002) ..........................................................................D18

Table D16. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Lime with Cement 2002)........................................................D19

Table D17. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Lime 2003) ..............................................................................D20


Table D19. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Control 2003) ..........................................................................D22

Table D20. Back-calculated Moduli Based upon Deflections Taken at Surface Course (Lime with Cement 2003).........................................................D23

��

��

Structural Support of Lime or Cement Stabilized Subgrade Used with

Flexible Pavements

Start Date: April 28, 2000 Duration: 55 months Completion Date: November 28, 2004 Report Date: January 2, 2004 State Job Number: 14746(0) Report Number: Funding: $157,330 Principle Investigators:

Eddie Y. Chou, Ph.D.,P.E. University of Toledo 419-530-8123 [email protected]

ODOT Contacts:

Technical: Roger Green Office of Pavement Engineering 614-995-5993 Administrative: Monique R. Evans, P.E. Administrator, R&D 614-728-6048

For copies of this final report go to

http://www.dot.state.oh.us/divplan/research or call 614-644-8173.

Ohio Department of Transportation Office of Research & Development

1980 West Broad Street Columbus, OH 43223

Problem Lime and cement stabilizations have been used to modify soft and wet soils to provide a suitable construction platform. This study was initiated to ascertain the long-term durability of lime (or cement) stabilized roadbed soils, and to quantify the structural benefit, if any, of lime or cement stabilized roadbed soils, so that it can be incorporated into the flexible pavement thickness design.

Objectives 1. To determine the long-term performance

of lime or cement stabilized subgrades subjected to Ohio climatic conditions.

2. To determine the effect of lime and cement stabilized roadbed soils on flexible pavement life and performance

3. To quantify the subgrade support of lime or cement stabilized soils so that the added support may be used to reduce pavement thickness with both empirical and mechanistic design procedures.

Description

Most of the subgrade soils in Ohio are fine-grained clayey or silty soils occasionally mixed with sandy soils. Fine-grained soils are highly sensitive to moisture content and their strength decreases drastically as moisture content

D-II

increases. Chemical stabilization has been used to modify wet and soft fine-grained soils so that the roadbed can carry the load of construction vehicles without excessive rutting. The durability and structural benefits of the stabilized roadbed soils have been investigated in this study through four tasks. In the first task, the long-term, in-situ conditions of several stabilized subgrade were investigated through the Dynamic Cone Penetrometer (DCP) testing. The DCP results show that the in-situ strengths of stabilized soils are generally higher than non-stabilized soils, several years after construction. The second task investigated the durability and strength characteristics of stabilized soils through a series of laboratory tests. The results show that unconfined compressive strength, California Bearing Ratio, and resilient modulus of stabilized soils are all higher than non-stabilized soils. After repeated freeze-thaw cycles, the strength and modulus of soils generally decrease, yet the stabilized soils retain more strength and modulus than the non-stabilized soils. Several different soils ranging from clayey to sandy were tested. Cement stabilization is more effective for sandy soils and lime or lime plus cement are more effective for clayey soils. The third task evaluated the four test sections constructed as part of the State Route 2 reconstruction project in Erie County. Three of the test sections have subgrades stabilized with 12 inches of 6% cement, 5% lime, 3% lime with 3% cement, respectively, and the fourth section is the control section with no stabilization. Pavement deflections were measured during different stages of the construction and for each of the three years after construction. The subgrade modulus values were back calculated from the measured deflections. The results show that all three stabilized sections have higher subgrade modulus than the control

section. Although stabilization with cement had the fastest stiffness increase initially, the lime stabilized subgrade was the strongest after 2-3 years of field service. The average increase in subgrade modulus is between 10 to 35 percent. Task 4 developed a design procedure to quantify the increase in strength and modulus as an “effective” subgrade modulus in order to include the structural benefit of stabilized subgrade in the flexible pavement thickness design procedure. The ‘effective’ subgrade modulus is a function of the depth of stabilization, characteristics of the original subgrade, the type of chemical stabilizer used, and the design traffic loadings.

Conclusions & Recommendations Lime and cement stabilizations are effective ways to modify soft and wet roadbed soils that allow construction of pavements on these soils. Although most fine-grained soils in Ohio are considered non-reactive, meaning the initial strength increase due to lime stabilization is likely to be less than 50 psi (345 kPa), the strength continues to increase with time. This study shows that lime or cement stabilized soils maintain the strength increase with time. Considering the structural benefit of soil stabilization can result in the reduction of pavement thickness. Therefore, it is recommended that lime or cement stabilized subgrade be used more systematically and be considered as part of the pavement structure when designing and constructing flexible pavements.

Implementation Potential The recommendation to use more soil stabilization and the developed design

D-III

procedure may be implemented immediately.

D-1

INTRODUCTION

Chemical stabilization with lime or cement is an effective way to improve fine-grained

roadbed soils. The addition of lime or cement to soils reduces the plasticity and the water

content of the soils thereby increasing the workability. Stabilized soils facilitate

construction by providing a stronger roadbed to carry construction traffic. Lime and

cement also chemically react with soil that results in the increase of strength and stiffness.

Other benefits include increased permeability and decreased volume changes. However,

the effects of stabilization vary depending on soil type, amount of stabilizer used,

temperature and duration of curing. At this time, the structural benefits of soil chemical

stabilization are not accounted for in ODOT flexible pavement thickness design.

Whereas lime stabilization significantly improves roadbed soils initially, the potential long-

term strength improvement may not be fully developed due to non-reactive soil, freeze-

thaw damage, or high sulfate content in the soil. Cement stabilized soil may also suffer

from freeze- thaw deterioration and sulfate deterioration. The initial strength of both

materials may decrease over time. These effects have not been quantified and vary among

different soil types. This study was initiated to ascertain if there are long-term benefits of

chemical (lime/ cement) stabilization in Ohio, and to enable engineers to include potential

structural benefits of chemical stabilization into pavement thickness designs.

Background

Roadbed soil is one of the most critical components in the design and construction of

highway pavements. Its properties can very significantly depending on numerous

parameters such as soil composition, gradation, moisture content, state of stress and degree

of compaction.

Lime and cement have been used to improve pavement roadbed soils and base materials for

many years in the United States. Recently, the shortage of high quality aggregates in many

D-2

areas has led to an increasing interest in stabilized subgrade in order to reduce the demand

for those aggregates. The use of lime/cement stabilization also reduces the amount of

energy required to produce paving materials.

ODOT currently uses lime or cement stabilized subgrades as an alternative to soil

undercutting (i.e. replacement), when soft or unstable roadbed soils are encountered.

According to the ODOT Construction Inspection Design Manual (2002), lime stabilized

subgrade (Item 206) is recommended for A-7-6 or A-6-b with a PI greater than 20. Either

quicklime or hydrated lime can be used. The amount of lime used is between 4% to 8% by

weight, with a planned amount of 5%. Cement stabilized subgrade (Item 804) is

recommended for A-3-a, A-4-a, A-4-b, A-6-a, and some A-6-b soils with a Plasticity Index

of less than 20. The amount used is between 4% to 10% by weight, with a planned amount

of 6%.

Lime reacts with medium, moderately fine, and fine-grained soils that result in decreased

plasticity and swelling, and increased workability and strength. The National Lime

Association states that lime stabilization may be effective whenever clay contents (particle

size

D-3

attract each other. Flocculated soil has higher strength, lower compressibility, and higher

permeability than the same soil in a dispersed state. The higher strength and lower

compressibility result from the particle-to-particle attraction and the greater difficulty of

displacing particles when they are in a disorderly array instead of parallel to each other as

in the case of dispersed soils. The higher permeability in the flocculated soil are due to the

larger (although fewer) channels available for flow, resulting in less flow resistance

through a flocculated soil than through a dispersed soil.

Another reaction, called pozzolanic reaction, occurs when calcium ions react with water

and various forms of soil silica and alumina that exist in the clays, to form cementing

materials. The addition of lime to soil increases the pH of the soil water to a high level

(pH of saturated lime water is 12.4). At elevated pH levels, the silica and alumina in soil

become soluble and start to react with calcium ions to form hydrated calcium silicates

and hydrated calcium aluminates. Pozzolanic reactions are time and temperature

dependent. Therefore, the strength gain is gradual but may continue for several years.

Temperatures less than 50 to 55 degrees Fahrenheit (10 to 13 degrees Celsius) may

impede the reaction and higher temperatures accelerate the reaction.

The most important factors controlling the development of pozzolanic cementing materials

in a lime-stabilized soil are the characteristics of the soil. The major characteristics which

affect the ability of the soil to react with lime to produce cementitious materials are soil

pH, organic carbon content, natural drainage, presence of excessive quantities of

exchangeable sodium, clay mineralogy and particle size distribution, degree of weathering,

presence of carbonates, extractable iron, and silica-aluminum ratio. If a soil is “non-

reactive”, extensive pozzolanic strength gain will not be obtained regardless of the amount

of lime or the curing conditions. However, such soils can be stabilized with lime when fly

ash or other sources alumina/ silica are added to the soil/lime mixture. Lime-fly ash

stabilization is beyond the scope of this project.

Strength development in cement stabilized soil is much more rapid than lime stabilized

soil, because the finely ground cement already contains an ample amount of silica and

D-4

alumina which allows the cementation to occur immediately. Cement stabilization is also

suitable for less “reactive” soil or coarser-grained soils. Cement stabilization may not be

suitable for very fine grained, high clay content soils due to difficulties in mixing the

cement with soils of high plasticity.

The use of stabilizers (lime, cement) can greatly improve the mechanical properties of the

fine grain roadbed soils, transforming them into a suitable structural material. The state of

Ohio constructs a significant portion of its pavement on fine grain soils. These clays and

silts usually have a moderate to low montmorillonite content, suggesting low lime

reactivity. ODOT currently does not assign any structural value to stabilized roadbed soils.

The 1993 AASHTO Design Guide does not have a specific design procedure for stabilized

roadbed soils.

However, some states have assigned structural coefficient to stabilized materials. See

Figure A1 of Appendix A. For example, South Carolina uses 0.15, Mississippi uses 0.05 –

0.10, Arkansas uses 0.07 for lime and 0.20 for cement, and Kansas uses 0.11 for lime

stabilization.

The Kentucky DOT and the University of Kentucky studied the performance of stabilized

subbase highways constructed during the last 20 years. They used 85th percentile in situ

CBR values to estimate the structural layer coefficient of treated soils. The resulting

structural coefficient for soils treated with hydrated lime is 0.106, for soils treated with

Portland cement, 0.127, for soils treated with lime/cement, 0.11, and for soils treated with

lime and kiln dust, 0.10. They also used actual pavement performance (PSI) to back

estimate the structural coefficient of stabilized materials. They found that some stabilized

sections do provide structural benefit while others do not. The back estimated structural

coefficients of the stabilized materials range from -0.03 to +0.19.

In Ohio, soil stabilization is currently used primarily as an alternative to soil undercutting

(i.e., replacement of soft soils with stronger materials such as granular soils) to provide a

construction platform to carry the load of heavy construction vehicles without excessive

D-5

rutting. Subgrade stresses induced by construction traffic are likely to be higher than the

stresses that the subgrade will experience after the completion of pavement construction.

Therefore, it is logical and desirable to include the improvement of soil strength due to soil

stabilization in pavement design.

Given that the current AASHTO flexible pavement design procedure, which is adopted by

ODOT, uses subgrade resilient modulus to characterize roadbed soil support, a procedure

to reflect any structural benefit of soil stabilization into the design subgrade resilient

modulus is desirable. Such a procedure is described in the finding section of this report.

D-6

OBJECTIVE OF THE RESEARCH

Objective of the Study:

The objectives of the proposed study are:

1. To determine the long-term performance of lime and cement stabilized subgrades

subjected to Ohio climatic conditions.

2. To determine the effect of lime and cement stabilized subgrades on flexible pavement

life and performance

3. To quantify the subgrade support of lime and cement stabilized soils so that the added

support may be used to reduce pavement thickness with both empirical and mechanistic

design procedures.

D-7

GENERAL DESCRIPTION OF RESEARCH

This study was intended to investigate if lime or cement stabilization of roadbed soils

provides long-term structural benefits, and if so, how to incorporate the structural benefits

of soil stabilization into pavement thickness design.

The properties of lime or cement stabilized roadbed soils were measured from soil samples

obtained in the field. Comparisons between initial strength gains versus long-term

developed strength were made. Laboratory studies were conducted to study the effects of

various parameters on the strength and durability of stabilized soils. Nondestructive

pavement deflection testing was used to determine the increased roadbed soil modulus

resulting from lime or cement stabilization. The structural benefits were quantified in

pavement design procedures in terms of increases in effective roadbed soil resilient

modulus.

This research project consists of five separate tasks.

• Task 1 was to collect data related to existing pavements constructed with lime

or cement stabilized roadbed soils.

• Task 2 was to perform laboratory investigation of stabilized and non-stabilized

soils in order to compare their characteristics including durability under

freezing-and-thawing.

• Task 3 was to compare the test pavement sections on SR 2 in Erie County (ERI-

SR2) constructed with stabilized and non-stabilized roadbed soils.

• Task 4 was to analyze the findings of Tasks 1 through 3 and establish a

procedure to quantify the structural benefit of soils stabilized with lime or

cement in pavement thickness design.

• Task 5 was to draw conclusions and make recommendations based on the

findings of this study.

D-8

Task 1: Investigate Ohio Experience on Lime Stabilized Roadbed Soils

The first task was to investigate the experience of using lime (or cement) stabilized

subgrade in Ohio. Although lime/cement stabilization has been recognized to be beneficial

during construction, its impact on pavement performance has not been well documented.

A number of flexible pavement sections with lime stabilized roadbeds were identified.

Originally, in-situ stabilized roadbed soil samples were to be obtained from these

pavements. However, after several attempts, it was determined that it was not possible to

extract soil specimens undisturbed, due to the granular nature of the soils. Instead,

Dynamic Cone Penetrometer (DCP) data were obtained. Table 1 lists the pavement

sections where DCP test data were obtained. As indicated in the table, some sections that

were planned to be stabilized were found to have been non-performed. Therefore, only a

limited number of in-service pavement sections with stabilized roadbed soils were

available for analysis.

D-9

Table 1. DCP Test Locations

County Route District Project No. Logs Year Depth and Treatment Performed

?

Adams SR-32 9 431-82 0-2.62 1982 6” Lime No

Fayette US-35 6 298-96 17.54-23.75 1996 6” Lime No

Logan US-33 7 375-96 27.76-29.71 1996 6” Lime No

Erie SR-2 3 23-00 12.58 Blog 2000 12” Lime or

Cement Yes

Delaware US-23 6 335-97 19.24 Blog 1997 12” Lime Yes

Franklin Livingston 9 637-92 - 1992 12” Lime Yes

Hamilton SR-126 8 645-94 6.61-10.79 1994 6” Lime Yes

(1 inch = 2.54 centimeters)

From the DCP data, the Penetration Index (PI), in mm/blow, is determined. The California

Bearing Ratio (CBR) is correlated with Penetration Index. In turn, the resilient modulus of

the roadbed soils, MR (in psi) is correlated with CBR by equation (2).

075.0)][log(7.02.2)log(: 5.1 +−=− PICBRLimitUpper (1.a)

075.0)][log(7.02.2)log(: 5.1 −−=− PICBRLimitLower (1.b)

MR = 1200 CBR (2)

Using the in-situ DCP data, the structural characteristics of lime stabilized subgrade are

compared with those of non-stabilized subgrade.

D-10

Task 2: Perform Laboratory Durability Study under Simulated Ohio Climate

Laboratory compacted soil specimens were used to determine the immediate and long term

effects of soil stabilization. Soil samples were taken from four different locations. Table 2

shows the origins and classifications of these soils. On SR 2 in Erie County, untreated,

natural soil samples were obtained from each of the four test sections prior to the

stabilization work, as shown in Table 3.

Table 2. Summary of the Soil Characterization Tests

State Route 2 Erie County

Soil Origin

Property

(1)

Sandy Soils (Section b)

(2)

Clayey Soils

(Sections a, c, d) (3)

Lorain County

(4)

Maumee

River Lucas

County

(5)

Nevada, Wyandot County

(6)

Plastic Limit N/A* 13-21 21 20.9 26.5 Liquid Limit N/A* 25-34 35 32 35.2 Plasticity Index N/A* 8-13 14 11.1 8.7 Color Brown

Yellow Brown Dark

Brown Dark Grey Yellow

% Passing #200 13-22 39-54 88% 40% 43% Classification A-3a A-4a. A-4b,

A-6a A-6a A-6a A-4a

* Not applicable for coarse grain soils

Table 3. Test Sections on ERI- SR2

5% Lime Treated (a)

6% Cement Treated

(b)

Control Section (c)

3% Lime & 3% Cement Treated

(d)

Beginning Station 24+180 23+240 22+400 21+400

End Station 24+500 24+180 22+800 22+400

Length (meters) 320 940 400 1000

D-11

Soil samples were obtained with the cooperation of ODOT personnel from Districts 2 and

3. Special effort was made to insure that representative samples were obtained in each site.

Soil samples were first air-dried, pulverized and sieved pass a #4 sieve, as required by

ASTM D 698 for determination of moisture-density relationship and ASTM D 2166 for

unconfined compressive strength using a 4-inch diameter mold.

Soil pH value, optimum moisture content, percentage passing No. 200 sieve, Atterberg

limits, maximum dry density, unconfined compressive strength, and resilient modulus of

each soil sample were determined, both before and after being treated with various

stabilizers. Table 4 summarizes the tests performed.

The soil specimens were also subject to freezing-and thawing cycles in controlled

temperature and moisture environments to determine their long-term durability. Freeze-

thaw cycles cause a volume increase and strength reduction. Previous studies have shown

that initial unconfined compressive strength of the cured mixture is a good indicator of

freeze-thaw resistance. The results of these tests are presented in the findings section of

this report. Table 4 is a description of the tests performed on each type of soil.

D-12

Table 4. Summary of Laboratory Tests Performed

Origin Soil Classification

Tests Performed Number of Specimens

ERI-SR2, Section a

A-4a. A-4b, A-6a

pH test (D4972) Atterberg limits (ASTM D4318) 5% lime stabilized Atterberg limits (ASTM D4318) Sieve analysis (D422) 5% lime stabilized sieve Analysis (D422) Proctor test Proctor test, 5% lime stabilized CBR (ASTM D1883) Stabilized CBR, after curing Stabilized CBR, after 12 cycles of freezing- thawing Freeze-Thaw Test (ASTM D560) UCS tests (D2166) Stabilized UCS, after curing (D2166) Stabilized UCS, after Freeze- Thaw

15 15 15 5 5 2 2 2 2 2 2 15 15 15

ERI-SR2, Section b

A-3a 5% Lime stabilized Atterberg Limits (ASTM D4318) Sieve analysis (D422) 5% Lime stabilized sieve Analysis (D422) Proctor test Proctor test, 5% lime stabilized CBR (ASTM D1883) Stabilized CBR, after curing Stabilized CBR, after Freeze- Thaw Freeze--Thaw Test (ASTM D560) UCS tests (D2166) Stabilized UCS, after curing (D2166) Stabilized UCS, after Freeze- Thaw

15 5 5 2 2 2 2 2 2 15 15 15

ERI-SR2, Section c

A-4a, A-6a Ph test (D4972) Atterberg limits (ASTM D4318) Sieve analysis (D422) Proctor test UCS tests (D2166)

15 15 5 2 15

ERI-SR2, Section d

A-6a, A-6b

Ph test (D4972) Atterberg limits (ASTM D4318) 3% Lime + 3% Cement stab. Atterberg Limits (ASTM D4318) Sieve analysis (D422) 3% Lime + 3% Cement stabilized sieve Analysis (D422) Proctor test Proctor test, 3% Lime + 3% Cement stabilized CBR (ASTM D1883) 3% Lime + 3% Cement Stabilized CBR, after curing 3% Lime + 3% Cement Stabilized CBR, after Freeze- Thaw Freeze-Thaw Test (ASTM D560) UCS tests (D2166) Stabilized UCS, after curing (D2166)

15 15 15 5 5 2 2 2 2 2 2 15 15

Lorain County

A-6a pH test (D4972) Atterberg limits (ASTM D4318) 3% Lime + 3% Cement stab. Atterberg Limits (ASTM D4318) 5% hydrated lime Atterberg Limits (ASTM D4318) 5% dolomitic lime Atterberg Limits (ASTM D4318) 10% hydrated lime Atterberg Limits (ASTM D4318) 10% dolomitic lime Atterberg Limits (ASTM D4318)

1 3 3 3 3 3 3

D-13

15% hydrated lime Atterberg Limits (ASTM D4318) 15% dolomitic lime Atterberg Limits (ASTM D4318) 6% Cement stab. Atterberg Limits (ASTM D4318) 9% Cement stab. Atterberg Limits (ASTM D4318) 12% Cement stab. Atterberg Limits (ASTM D4318) Sieve analysis (D422), stabilized and non-stabilized UCS tests (D2166) , non-stabilized UCS tests (D2166), stabilized (10 stabilized mixtures) UCS tests (D2166), after Freeze- Thaw cycles

3 3 3 3 3 5 3 30 30

Maumee River Crossing, Lucas County

A-6a pH test (D4972) Atterberg Limits (ASTM D4318) Hydrometer Analysis (D422) Proctor test 5% Lime stabilized proctor test 5% Cement stabilized proctor test 2% Cement 3% Lime stabilized proctor test Resilient Modulus(T-274-82) Resilient Modulus after Freeze- thaw cycles (T-274-82) UCS tests (D2166)

1 3 1 1 1 1 1 36 36 12

Nevada, Wyandot County

A-4b pH test (D4972) Atterberg Limits (ASTM D4318) Hydrometer Analysis (D422) Proctor test 5% Lime stabilized proctor test 5% Cement stabilized proctor test 2% Cement 3% Lime stabilized proctor test Resilient Modulus(T-274-82) Resilient Modulus after Freeze- thaw cycles (T-274-82) UCS tests (D2166)

1 3 1 1 1 1 1 36 36 12

Task 3: Field Comparison of Non-Stabilized and Stabilized Subgrades

A test pavement was constructed as part of a planned flexible pavement reconstruction

project on State Route 2 in Erie County in District 3. The project was planned with lime-

stabilized subgrade. Four adjacent sections, which consisted of a control section with

nonstabilized subgrade and three stabilized sections, each with the top 12 inches (30.5 cm)

of the subgrade stabilized with: 5% lime, 6% cement, 3% lime with 3% cement,

respectively, were constructed.

During construction, part of the originally planned control section was undercut after proof

rolling showed that the roadbed soil was too soft for construction. The final control section

was reduced to 1312.4 feet (400 meters) long.

D-14

Falling Weight Deflectometer (FWD) deflection data were measured to back-calculate the

subgrade modulus. Dynamic cone penetration testing was also performed to compare the

in-situ strength of the subgrade soils.

Back-Calculation of Modulus

One way to evaluate the effect of soil stabilization is to back-calculate the modulus of the

stabilized subgrade based upon measured pavement deflections. Deflection data were

measured after the completion of the subgrade, intermediate course, and surface course in

2001. Deflection data on the surface course were also measured in 2002 and 2003. Figure

1 shows the pavement structure and the locations where deflection data were measured.

D-15

��

��

��

��

��

�� !��

�"#$��%��&��'��

�"$��'��

(1 inch = 2.54 cm)

Figure 1. Deflection Data Taken at Multiple Surfaces

D-16

For deflection data taken at the surface of the subgrade, the Boussinesq equation was used

to calculate the modulus of subgrade as a uniform half-space with infinite depth. Only the

measured deflection directly below the center of the loading was used. The subgrade

modulus, Mr, was estimated by:

0

2 )1(2w

qaMr

υ−= (3)

where: � is the Poisson ratio, assumed as 0.4

q is the applied pressure, measured in psi

a is the load radius, equal to 6 inches

w0 is the measured deflection at the center of load, in inches

Other deflection data

For deflection data taken on base, intermediate, and surface courses, the entire deflection

basin (measured by seven sensors) is used to back calculate pavement layer moduli for

multiple layers. Two back calculation programs, MODULUS and EverCalc, were

employed. The stabilized layer was combined with the underlying non-stabilized subgrade

as a single layer.

Back calculation results depend on the selected parameters. The following parameters

were used and are shown in Table 5.

D-17

Table 5. Input Parameters Used in MODULUS Back Calculation

Plate Radius: 6.005 inches

Number of Sensors: 7

Distance of Sensors from Plate (inches): 0, 8, 12, 18, 24, 36 and 60.

Weight Factor: 1.0 for each sensor

Moduli Range (ksi) Thickness (inches)

Poisson

Ratio Minimum Maximum

19.25 (deflections on surface course) Bound Layer

17.75 (deflection on intermediate course)

0.30 400 2,000

Base Course 6.00 0.35 50* 52*

Subgrade 324.00 0.40 Starting modulus: 10,000 psi

*These values were chosen after multiple trials (1 inch = 2.54 cm)(145 psi = 1 MPa)

Task 4: Analysis of Results and Establish a Procedure to Facilitate Design

This task was intended to quantify and incorporate the structural benefits of soil

stabilization into existing design procedure. A procedure to determine the design subgrade

resilient modulus value for stabilized soils has been developed.

Based on the findings of tasks 1, 2 and 3, the effective design subgrade resilient modulus of

stabilized soil is estimated as a function of the original soil resilient modulus, the type and

amount of stabilizer added, and the thickness of the stabilized layer.

Procedure Development

Many states that use the AASHTO Pavement Design Guide procedure either assign a layer

coefficient to the stabilized layer or assume a subgrade modulus in order to account for the

structural benefit of a stabilized layer. In this study, an “improved” or “equivalent”

subgrade modulus as a result of stabilization is derived, since it can be adopted by both the

D-18

current procedure and the upcoming Mechanistic-Empirical procedure. Figure 2 illustrates

the computing sequence that derives the “equivalent” subgrade modulus.

A layered elastic mechanistic pavement model, based on Kenlayer software, was used to

evaluate the improvement of the subgrade resilient modulus provided by 6 to 24 inches (15

to 61 cm) of stabilized subgrade. The objective is to find an equivalent subgrade modulus

that combines the overall support of the stabilized layer and the non-stabilized subgrade

below it. The equivalent subgrade modulus is found by making the expected structural life

of the two pavements equal that is, matching tensile strain at the bottom of the asphalt layer

or compressive strain at the surface of the subgrade, whichever matches first.

The improvement of the soil resilient modulus (which can be estimated by the CBR or

UCS values), can be expressed by:

Naturalstabilized MrAMr ×= (4)

The value of A is estimated based on the results of tasks 2 and 3. The type of stabilizer

(cement or lime) used, amount (percent by weight) of stabilizer used, and type of soil being

stabilized all influence the value of A.

The equivalent subgrade modulus can be expressed by:

Naturalequivalent MrBMrMr ×== * (5)

The values of B are computed using the layered elastic models. B is influenced by the A

coefficient, thickness of the stabilized layers, and the thickness of the pavement.

D-19

��

�c2

Mr

��

�t1

•A typical AASHTO equation design is analyzed through a mechanistic model.

•The tensile strain at the bottom of the asphalt layer �t0 and the compressive strain at the top of roadbed soil, �c0, are computed, for further comparison

• A stabilized layer (with modulus Mrstab) is added to the design, providing a 4 layer system•The strain at the bottom of the asphalt layer and at the top of the roadbed soil are computed.

• The equivalent Resilient Modulus Mr* is obtained by keeping constant all the other parameters while increasing the resilient modulus, until the strains in the two systems ��and �� , are the same

•The reduction of the thickness is computed by using the equivalent resilient modulus and decreasing the thickness of the HMA layer until the strain at the bottom of the asphalt layer equals �t0

•The potential saving in the asphaltt layer thickness, d=D1-D1*

�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�c3Mr stab

Mr*

��

�c2

Mr

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�c3Mr stab

Mr*

�c2

Mr

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�c3Mr stab

Mr*Mr

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�c3Mr stab

Mr

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�c3

Mr

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1Mr

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

��

�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�t1�t1







�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1













�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�t0

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

�

dD1

D2

�

��

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

D1

D2

�

D1

D2

�

D1

D2

�

��

D1*D2

�

�t0

��

D1*D2

�

�t0

��

D1*D2

�

�t0 D1*D2

�

D1*D2

�

�t0

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

��

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

D1

D2

E1

E2

Mr

D1

D2

E1

E2

Mr

D1

D2

D3

�t1

�c1

D1

D2

D3

�t1

�c1

D1

D2

D3

�t1D1

D2

D3

�t1

�c1

�c3Mr stab

Mr*

��

Figure 2. Schematic Diagram Showing the Development of the Equivalent Resilient Modulus

20

Parameters

The computation was based on a typical design of a rural highway in Ohio. The typical

pavement structure consists of a hot mix asphalt layer over a granular layer for drainage

purpose. The thickness of the granular layer is assumed to be constant at six inches.

The thickness of the hot mix asphalt layer is adjusted to the subgrade conditions and

other design parameters, such as traffic and design reliability. The design parameters

assumed for this study are shown in Table 6.

Table 6. Parameters Used for AASHTO and Mechanistic Designs

(1.45 ksi = 10 MPa)

(1)

AASHTO Parameters

(2)

Mech. Parameters

(3)

Asphalt Layer Structural Number : 0.35 Modulus : 450 ksi

Granular Layer Structural number : 0.14

Thickness : 6 inches

Modulus : 35 ksi

Design Reliability

90% for W18 50%

Standard Deviation S0 = 0.49

Transfer Function Coefficient Asphalt Inst. Coef.

21

FINDINGS OF THE RESEARCH EFFORT

The findings of this study are reported in this section. They are:

1. The results of comparing the in-situ conditions of lime stabilized versus non-

stabilized subgrades underneath existing pavements using the DCP test.

2. The results of the laboratory investigation of the durability of lime or cement

stabilized soils.

3. The results of monitoring and evaluating the four test pavement sections

constructed on State Route 2 in Erie County.

4. The developed procedure to incorporate the structural benefit of lime or cement

stabilized subgrade through calculating an “equivalent” subgrade modulus for

pavement thickness design.

1. FIELD EVALUATION USING DCP TEST

The DCP tests were performed on several pavement sections, some with stabilized

subgrades, and some without. The effect of stabilization was evaluated through the

following:

1. comparing the subgrade resilient modulus of the stabilized and non-stabilized

sections

2. comparing the resilient modulus of the stabilized layer (0-12 inches, (0-30.5

cm) below the surface of the subgrade) with the non-stabilized layer underneath

The resilient modulus values were estimated from the penetration index (inches per

blow) through indirect correlation with CBR as described earlier.

Figure 3 shows that the median modulus values at various depths below the surface of

the subgrade for the stabilized sections (Hamilton SR 126, Franklin-Livingston Ave.,

22

and Delaware US 23) and the non-stabilized sections (Adams SR 32, Fayette US 35,

and Logan US 33).

The modulus of the first layer (0-6 inches, 0-15.25 cm) is usually significantly higher

than the other layers, in both stabilized and non-stabilized projects. This may be due to

two reasons: (1) the presence of some gravels from the drainage layer above can disturb

the penetration of the Dynamic Cone Penetrometer and (2) the effect of compaction of

the subgrade surface. Therefore, comparing average modulus values between 6 to 12

inches, (15.25-30.5 cm) below the surface of subgrade may be more meaningful.

From Figures 3 and 4, the aforementioned comparisons can be evaluated:

1. the upper layers of the stabilized sections have a much higher average modulus

(50 – 100 ksi or 345-690 MPa) than the non-stabilized moduli (15 -70 ksi or

103 – 483 MPa)

2. the average modulus of the non-stabilized layers decreases rapidly then reaches

a low stable value below 6 inches (15.24 cm) of depth (Adams-32 and Logan-

33). The modulus of the stabilized layer remains high for the first two layers (0-

6 and 6-12 inches) and then decreases rapidly to a low stable value below 12

inches of depth.

The ratio of stabilized modulus to non-stabilized modulus may be estimated to be about

2.

23

0

6

12

18

24

0 50 100 150

Median Subgrade Modulus estimated from DCP, Mr (ksi)

Dep

th (i

n) b

elow

su

bgra

de

1 Hamilton - SR 126

2 Franklin - Livingston Avenue

3 Delaware- US23

6 Adams SR32

7 Fay- US35

8 Log- US33

Stabilized sections

Non stabilized sections

(1 inch = 2.54 cm)

Figure 3. Subgrade Moduli Estimated from DCP from Various Sites

Figure 4 shows the results for the test sections on ERI- SR2. Similarly, the stabilized

soils are stronger than non-stabilized soils. Again, the ratio of stabilized modulus to

non-stabilized modulus seems to be at least 1.5 to 2. The cement stabilized section was

divided into two subsections because one section showed much higher average

modulus than the other, indicating that cement stabilization was not quite successful in

that part of the section. This may be due to some soil characteristics, especially clay

content, varying within the section. Cement stabilization is more effective for soils

with lower clay content. Part of the originally planned control section was undercut

during construction. The DCP result shows the average strength (or modulus) of that

section is the strongest among all sections.

24

0

6

12

18

24

0 50 100 150 200

Median Subgrade Modulus estimated from DCP, Mr (ksi)

Dep

th (i

n) b

elow

su

bgra

de

ERI-2 6% cement-IERI-2 6% cement-II ERI-2 3% cement+ 3% limeERI-2 5% limeERI-2 Control sectionERI-2 Undercut section

(1 inch = 2.54 cm)

Figure 4. Subgrade Moduli Estimated from DCP from ERI-SR2

Figure 5 shows the box plot that includes the minimum, maximum, the lower and upper

quartile, and the median values at each pavement section. It seems that values for the

stabilized soils are higher, but the variations in stabilized sections are also somewhat

higher than the non-stabilized sections. The larger scatter may be attributed to the very

high strength at a few stabilized subgrade locations since only five or six DCP tests

data were obtained at varying interval distances at each pavement section. More

detailed results of DCP analysis are shown in Appendix B.

25

0.0

20.0

40.0

60.0

80.0

100.

0

120.

0

140.

0

160.

0

180.

0

Sta

biliz

edN

on-

Sta

biliz

edS

tabi

lized

Non

-S

tabi

lized

Sta

biliz

edN

on-

Sta

biliz

edS

tabi

lized

Non

-S

tabi

lized

0-6"

6-12

"12

"-18

"18

"-24

"

Dep

th &

Tre

atm

ent

Subgrade Modulus, Mr, ksi

Low

er 2

5%

Min

imum

Med

ian

Max

imum

Upp

er 2

5%

(1.4

5 ks

i = 1

0 M

pa)

Fi

gure

5.

Est

imat

ed M

odul

us a

t Diff

eren

t Dep

th fr

om D

CP

Tes

t Res

ult o

f Fie

ld S

ectio

ns

26

2. LABORATORY INVESTIGATION

Soil Characteristics

Characteristics of the soils before and after being treated with lime or cement in the

laboratory are shown in Table 7. Each characteristic that changed is described below.

More detailed results can be found in Appendix C.

Atterberg Limit

Table 7 shows that the addition of stabilizer, either lime or cement, changed the

Atterberg limits of soil. Plasticity index (PI) decreases by a value of 2 to 5. The

change caused by cement is smaller than that caused by lime. The decrease in PI of

clayey soils indicates an improved workability, which is an immediate benefit of

stabilization.

Grain Size

Table 7 also shows the result of wet sieve analysis. The addition of stabilizer causes

clay particles to agglomerate forming larger particles, therefore, reducing the apparent

percentage of soil particles passing the No.200 sieve.

Optimum Moisture Content Test

Additional changes due to stabilization include an increase of optimum moisture

content by a value of 2 to 4 percent and a slight decrease in maximum dry density for

lime treated soils. For cement treated soil, these changes are less apparent.

27

Table 7. Changes in Soil Characteristics Due to Laboratory Stabilization

Soil Characteristics Soil Sample Location Treatment

Before Treatment

After Treatment

ERIE 2 (21+220~22+440) 3%lime & 3%cement 13 24 ERIE 2 (22+900~23+900) 6% cement NPb NP ERIE 2 (24+180~24+800) 5% D-lime 16 18 Lorain 3%lime & 3%cement 21 27 Lorain 6% cement 21 25 Lorain 5% D-lime 21 27

Averagea

Plastic Limit (%)

Lorain 5% H-lime 21 27

ERIE 2 (21+220~22+440) 3%lime & 3%cement 16 12 ERIE 2 (22+900~23+900) 6% cement NP NP ERIE 2 (24+180~24+800) 5% D-lime 11 8 Lorain 3%lime & 3%cement 14 9 Lorain 6% cement 14 11 Lorain 5% D-lime 14 8

Average Plasticity Index (%)


ERIE 2 (21+220~22+440) 3%lime & 3%cement 65 46 ERIE 2 (22+900~23+900) 6% cement 17 9 ERIE 2 (24+180~24+800) 5% D-lime 46 23 Lorain 3%lime & 3%cement 88 59 Lorain 6% cement 88 54 Lorain 5% D-lime 88 49

Average Percentage Passing No.200 Sieve


ERIE 2 (21+220~22+440) 3%lime & 3%cement 52 91 ERIE 2 (22+900~23+900) 6% cement 11 123 ERIE 2 (24+180~24+800) 5% D-lime 51 73 Lorain 3%lime & 3%cement 3 116 Lorain 6% cement 3 126 Lorain 5% D-lime 3 40

Average UCS (psi)


ERIE 2 (21+220~22+440) 3%lime & 3%cement 7 142 ERIE 2 (22+900~23+900) 6% cement 24 260

Average CBR (%) (56 blows) ERIE 2 (24+180~24+800) 5% D-lime 9c 67 Note: a. average of at least 3 specimens; b. NP = non-plastic sandy soil; c. estimated.

28

Lime characteristics

Several different forms of lime are available for soil stabilization: hydrated lime

(calcium hydroxide), quicklime (calcium oxide), and dolomitic lime (calcium oxide and

magnesium oxide). Quicklime and dolomitic lime both react rapidly with available

water to produce hydrated lime and releasing considerable amount of heat. Therefore,

they are very effective in drying out wet soils. Quicklime contains more calcium per

unit weight than hydrated lime. Dolomitic lime contains the least amount of calcium

per unit weight. The calcium content should obviously be considered in selecting the

stabilizer in design since calcium is the only active ingredient. The selection of the

type of lime to use is dependent upon the cost and availability.

The same type of dolomitic lime used during construction of ERI-SR2 test pavement

was used during laboratory stabilization study. However, the effect of using a high

calcium hydrated lime was also investigated. The chemical composition of samples of

dolomitic lime and hydrated lime were obtained using the X-ray diffraction method.

The results are presented in Table 8.

Table 8. Chemical Composition of Lime Obtained from X-Ray Diffraction

Lime

Sample (1)

CaO* (%) (2)

MgO (%) (3)

SiO2 (%) (4)

Al2O3 (%) (5)

Fe2O3 (%) (6)

TiO (%) (7)

Total

(8)

1 Dolomitic Lime

66.80

28.10

0.84

0.08

0.16

0.01

95.98

2 High Calcium Hydrated Lime

95.80

2.10

0.45

0.16

0.09

0.01

98.60

*Calculated as Ca(OH)2 for sample 2 Sample 1 (Dolomitic Lime) is a mixture of CaO, Ca(OH)2, and MgO Sample 2 (Hydrated Lime) is mainly Ca(OH)2 with low MgO content

29

Unconfined Compressive Strength

Unconfined compressive strength (UCS) of soils increased with the addition of lime or

cement. Figure 6 shows the UCS testing results for soil samples obtained from ERI-

SR2 test sections. UCS of compacted natural soils and UCS of stabilized soils after 7

days of curing at 77 degrees Fahrenheit (25 degrees Celsius) and 100% humidity are

shown. Also shown are the UCS of soil specimens after twelve freeze-thaw cycles in

the laboratory. As shown, sandy soils treated with 6% cement gained the most strength

after curing, followed by 3% lime with 3% cement treatment, and 5% lime treatment.

The average strength gain for 3% lime with 3% cement and 5% lime treated specimens

are both less than 50 psi (345 kPa). Therefore, the soils are considered “non-reactive”

according to previous research (Thompson, Little, 1987). Note that the UCS results for

the lime treated soil were “early age” results and that higher UCS could have resulted if

the specimens were cured for a longer period of time as lime stabilized soils continue to

gain strength due to pozzolanic reaction which may continue on for years if conclusive

condition persists.

The freezing and thawing procedure used is based on the ASTM specification (D560)

for cement stabilized soils. The freeze-thaw cycles in the laboratory are much harsher

than what the soils will actually experience in the field. In the laboratory, soils

specimens are subject to saturated moisture condition and are allowed to expand freely.

Subgrade soils in the field are covered by one to two feet of pavement layer, confined,

and usually in less than saturated moisture conditions. The harsh laboratory freeze-

thaw condition causes all the non-stabilized soil specimens to collapse after just one or

two freeze-thaw cycles.

The natural soils in the subgrade may loose some of its density and strength that were

achieved during compaction due to field freezing and thawing and access to moisture,

but it is very unlikely that the strength will decrease to zero. Therefore, the UCS after

12 laboratory freeze-thaw cycles is likely to be far less than the actual soil strength in

30

the field. That is, the laboratory value should be considered the lower bound. Figure 7

shows the ratio between UCS strength after stabilization and before stabilization.

Sandy soils treated with 6% cement continued to gain strength during freeze-thaw

cycles. By the end of the 12 freeze-thaw cycles (12 days), the strength was nearly

twice of that at the beginning. This may be due to the continuing cement hydration

helped by the high permeability of the sandy soils. The result indicates that cement is

very effective in treating sandy soils. Low UCS strength for natural sandy soil is not an

accurate test due to the absence of confining pressure.

0

50

100

150

200

250

Natural soil After curing After 12 F-Tcycles

UC

S, p

si

6%cement treatedsandy soil

3%lime3%cementtreated clayey soil

5%dolomitic limetreated clayey soil

control section

(145 psi = 1 MPa)

Figure 6. UCS Tests for Recompacted Soil from ERI-SR2 (24-hour capillary soaking before UCS tests)

31

0

1

2

3

4

5

6

7

8

9

10

11

12

Natural soil After curing After 12 F-T cycles

A-r

atio 6%cement treated

sandy soil

3%lime3%cementtreated clayey soil

5%dolomitic limetreated clayey soil

control section

Figure 7. A-ratio from UCS Tests Testing of Soil from ERI –SR2

(24-hour capillary soaking before UCS tests)

Figure 8 shows the UCS of soil samples taken at various stations along the test

pavement. The solid lines show the average of stabilized specimens while the dashed

lines are average of the non-stabilized specimens. The average UCS of 3% lime with

3% cement treated soils increases from 50 psi (345 kPa) to 90 psi (621 kPa), an 80

percent increase. The average UCS of 6% cement treated increased from 10 psi (69

kPa) to 120 psi (828 kPa) , a 1100 percent increase. The average UCS of 5% lime

treated soils increase from 40 psi (276 kPa) to 70 psi (483 kPa), a 75 percent increase.

Again, the soils treated with 6% cement had the largest average improvement in UCS.

However, noted that the cement treated section was sandy, therefore in the natural,

untreated state had very low UCS.

32

0

50

100

150

200

250

300

350

400

21000 21500 22000 22500 23000 23500 24000 24500 25000Station,m

Str

engt

h, p

si

(145 psi = 1 MPa)

Figure 8. Unconfined Compressive Strength of Laboratory Compacted Specimens from ERI –SR2

Figure 9 shows the laboratory UCS values versus moisture content. For fine-grained

clayey soils, UCS values decrease as moisture content increases. After soils are

stabilized and compacted under similar moisture condition, the average moisture

content after curing of the stabilized soils are lower than non- stabilized soils and the

UCS are higher. The stabilized soils absorb less moisture than non-stabilized soils due

to reduced total surface area (larger particles) and reduced water layer thickness (cation

exchange).

3%Cement 3% Lime

Control Section

5%Lime 6%Cement

Natural soil Stabilized Soil Mean Stabilized soil

Natural Soil Mean

33

0

20

40

60

80

100

120

140

160

8 10 12 14 16 18

Moisture Content, %

UC

S, p

si

3%lime3%cement Treated 5% Lime Treated Untreated

(1.45 ksi = 10 MPa) Figure 9. UCS versus Moisture Content for Laboratory Compacted

Specimens

Effect of Freeze-Thaw Cycles on UCS of Clayey Soils

A clayey soil obtained from Lorain County was treated with 5% hydrated lime, 5%

dolomitic lime, 3% dolomitic lime with 3% cement, and 6% cement. The UCS before

freeze-thaw and after 6 and 12 freeze-thaw cycles were measured. Figure 10 shows the

result of the UCS tests. As shown, the strength of stabilized clayey soil generally

decreases with increasing number of freeze-thaw cycles, even for specimens stabilized

with 6% cement. In contrast, the previous section shows that sandy soils treated with

6% cement continued to gain strength during freeze-thaw cycles.

The 3% lime with 3% cement treatment seems to perform the best. The average

strength of 3 specimens decreased by nearly 40% after 12 freeze-thaw cycles. The

strength loss was nearly 70% for 6% cement stabilized clayey soils during the same 12

freeze-thaw cycles. Soils treated with 5% hydrated lime or 5% dolomitic lime seem to

34

perform similarly. The losses of strength due to freeze – thaw cycles were not as

dramatic.

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14

No. of Freeze-Thaw Cycles

UC

S, p

si

6% cement

3%D-lime &3%cement

5% H-lime

5% D-lime

untreated

(145 psi = 1 MPa) Figure 10. UCS Strength versus Number of Freeze-T

1. Report No. 2. Government Accession No. 3. …Unconfined compressive strength, California Bearing...

Documents

Transcript of 1. Report No. 2. Government Accession No. 3. …Unconfined compressive strength, California Bearing...