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This research was sponsored by the South Carolina Department

of Transportation and the Federal Highway Administration. Theopinions, findings and conclusions expressed in this report are

those of the authors and not necessarily those of the SCDOT or

FHWA. This report does not comprise a standard, specification

or regulation.Department of Civil and

Environmental Engineering300 Main Street

Columbia, SC 29208

(803)777 3614

[email protected]

INVESTIGATION OF GRADED

AGGREGATE BASE (GAB)

COURSES

R.L. BausT. Li

submitted to

The South Carolina Department of Transportation

and

The Federal Highway Administration

February 2006

(FHWA/SCDOT Report No. FHWA-SC-06-03)

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1. Report No.

FHWA-SC-06-032. Government Accession No. 2. Recipients Catalog No.

5. Report Date

February 20064. Title and Subtitle

Investigation of Graded Aggregate Base (GAB) Courses

6. Performing Organization Code

7. Author(s)

R.L. Baus and T. Li8. Performing Organization Report No

9. Performing Organization Name and Address

Department of Civil and Environmental EngineeringUniversity of South CarolinaColumbia, South Carolina 29208

10. Work Unit No. (TRAIS)

11. Contract or Grant No.12. Sponsoring Agency Name and Address

South Carolina Department of TransportationP.O. Box 191Columbia, South Carolina 29202 14. Sponsoring Agency Code

15. Supplementary Notes

Prepared in cooperation with the Federal Highway Administration

16. Abstract

This report summarizes a study undertaken to investigate the feasibility of relaxing current South CarolinaDepartment of Transportation (SCDOT) graded aggregate base (GAB) gradation specifications and layerthickness restrictions. The study included a review of historical and current SCDOT specifications and practices, aliterature review and survey of state highway agency practice, and laboratory and field data collection andanalysis. Seven granular base materials used by the SCDOT were included in laboratory plate load and SoilStiffness Gauge (SSG) tests. In addition, two field test sections were constructed and tested using a FallingWeight Deflectometer (FWD) and SSG. Routine laboratory tests were also performed on the granular materials todetermine basic physical properties and compliance with SCDOT specifications.

Based on tests results, it is proposed that the maximum percent passing the No. 4 sieve for Macadam be relaxedfrom the current specification limit of 50 % to 60% (the current SCDOT limit for passing the No. 4 sieve for MarineLimestone). It is also proposed that the SCDOT allow GAB layer thickness greater than 8 in. on a trial basis.

Differences in backcalculated layer coefficients for base layers constructed in the laboratory and at field siteswere observed in this study. Laboratory test results are in good agreement with results reported by otherresearchers. It is recommended that the SCDOT consider the feasibility of re-evaluating layer coefficients usedfor GAB materials.

Also included in the study was a preliminary investigation of SSG applicability for assessing compacted GABmaterials. Study results suggest that the SSG offers an alternative tool for pavement material quality assuranceand construction control. It is suggested that the SCDOT study the SSG further and consider SSGimplementation for material characterization in future mechanistic-empirical pavement design approaches.

17. Key Words

Flexible Pavement Structure, Base Layer, GranularMaterial, Gradation, Base Thickness, ResilientModulus, Plate Loading Test, FWD Test, SoilStiffness Gauge

18. Distribution Statement

No restrictions. This document is available to the publicthrough the National Technical Information Service,Springfield, VA 22161.

19. Security Classif. (of this report)

Unclassified20. Security Classif. (of this page)

Unclassified21. No. of Pages 22. Price

Form DOT F 1700.7 (872) Reproduction of completed page authorized

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ACKNOWLEDGEMENTS

This project was funded by the South Carolina Department of Transportation and the

Federal Highway Administration. Their support is greatly appreciated.

The authors would like to acknowledge the assistance provided by personnel at theResearch and Materials Laboratory of the South Carolina Department of Transportation.

Several individuals at the SCDOT provided their time and insights to the project. They

include Dr. Andy Johnson, Melissa Campbell, and Mike Lockman. The authors wouldalso like to thank Vulcan Materials Company and Martin Marietta Aggregates for their

donations of GAB materials.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ............................................................................................ ii

TABLE OF CONTENTS ............................................................................................... iii

CHAPTER 1 - INTRODUCTION....................................................................................1

Background Information......................................................................................................1Project Objectives ................................................................................................................2

Scope of Study .....................................................................................................................2

Research Approach ..............................................................................................................2Justification .....................................................................................................................2

Project Tasks ...................................................................................................................4

CHAPTER 2 LITERATURE REVIEW ......................................................................5

SCDOT Practice...................................................................................................................5Gradation and Compaction Requirements (Historical and Current) ..............................5

GAB Layer Coefficient ..................................................................................................7

State Agency Survey............................................................................................................8Summary of Survey Responses ......................................................................................9

Related Technical Information ........................................................................................13

Characterization of Unbound Granular Materials ........................................................13Resilient Modulus ...................................................................................................13

Triaxial Test .............................................................................................................14

CBR Test .................................................................................................................14

Falling Weight Deflectometer (FWD) .....................................................................15Other Testing Techniques ........................................................................................16

Factors that Influence Resilient Modulus of Unbound Granular Materials .............16

Permanent Deformation Resistance..........................................................................18

CHAPTER 3 LABORATORY PLATE LOAD TESTING PROGRAM ................22

Introduction........................................................................................................................22

Laboratory Testing Program..............................................................................................22

Test Pit and Plate Load Apparatus ................................................................................22

Materials for Laboratory Testing ..................................................................................24Subgrade ...................................................................................................................24

Base Materials ..........................................................................................................25Placement and Test Procedures.....................................................................................28

Experimental Results .........................................................................................................30

Static Plate Loading and CBR Tests on Subgrade ........................................................30GAB Cyclic Plate Load Tests .......................................................................................32GAB Static Load Tests .................................................................................................37

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CHAPTER 4 LABORATORY PLATE LOAD TEST RESULTS ...........................42

Cyclic Plate Load Test Results and Analysis ....................................................................42

Summary .......................................................................................................................48

Static Plate Load Test Results and Analysis......................................................................48

Introduction ...................................................................................................................48Finite Element Analysis ................................................................................................49

Linear Programming to Determine Deflection at Optimum Water Content .................52

Backcalculation of Resilient Modulus .........................................................................57Summary .......................................................................................................................61

CHAPTER 5 LABORATORY SOIL STIFFNESS GAUGE TESTING

PROGRAM AND RESULTS .........................................................................................62

Introduction........................................................................................................................62Experimental Program .......................................................................................................62

SSG Laboratory Testing Results........................................................................................64Comparison between SSG and Plate Modulus .................................................................68

Summary............................................................................................................................69

CHAPTER 6 - FIELD SOIL STIFFNESS GAUGE AND FWD TESTING

PROGRAM AND RESULTS .........................................................................................72

Introduction........................................................................................................................72

US 601 Field Test Sectionwithout HMA ..........................................................................73SC 72 Field Test Sectionwithout HMA ............................................................................76

US 601 and SC 72 Field Test Section with HMA in Place ...............................................80Summary............................................................................................................................85

CHAPTER 7 SUMMARY AND CONCLUSIONS....................................................86

Summary............................................................................................................................86

Conclusions........................................................................................................................86

Influence of Gradation...................................................................................................86Influence of Base Layer Thickness ...............................................................................87

Recommendations and Future Studies...............................................................................90

REFERENCES.................................................................................................................91

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CHAPTER 1

INTRODUCTION

Background Information

For flexible highway pavement construction, the South Carolina Department ofTransportation (SCDOT) uses three types of unbound graded aggregate base (GAB)

materials (Macadam, Marine Limestone, and Recycled Portland Cement Concrete). Each

type of GAB is described in the SCDOTs Standard Specifications for HighwayConstruction as follows:

Macadam base course materials are composed of crushed stone (excluding marinelimestone) or slag filled and bound with screenings. The fine aggregate component of

Macadam GAB is produced by the crushing operations. Marine Limestone base course

materials are produced from crushed limestone from a single source or deposit. The fineaggregate component of Marine Limestone GAB is limestone particles produced by the

crushing or mining operations. Recycled Portland Cement Concrete base coursematerials consist of crushed, graded, recycled portland cement concrete mixed together

with sand, sand-gravel, soil or other materials. The coarse aggregate component ofRecycled Portland Cement Concrete GAB consists of sound, durable particles of recycled

portland cement concrete excluding crushed concrete block or pipe. The fine aggregate

component is produced by the concrete crushing operations, or may be sand, soil, or otheracceptable fine-grained material. Materials retained and passing the No. 4 sieve are the

coarse and fine aggregate components of GAB, respectively. Cost and availability govern

the contractors selection of the GAB type to be used on a construction project. Relativeusage of the three types of GAB materials for flexible highway construction is as follows:

Macadam GAB is commonly used, Marine Limestone GAB is used for some CoastalPlain projects, and Crushed Recycled Portland Cement Concrete GAB is used

infrequently.

Macadam and Recycled Portland Cement Concrete share the same SCDOT gradation

specifications. Marine Limestone gradation specifications are similar, but allow

somewhat fine gradations (specifically, higher percentages passing the -inch, No. 4, No.

30, and No. 200 sieves are permitted). It is not known how current SCDOT gradationspecifications were established. Current SCDOT flexible pavement design policy limits

GAB thickness to a maximum of 8 inches. It is believed that this policy resulted from an

investigation of the relative strength of flexible pavement components conducted for theSCDOT at Clemson University (Busching et al., 1971).

Current SCDOT Standard Specifications for Highway Construction state that fieldcompaction shall be done with equipment capable of obtaining the required density to the

full depth. Compaction shall be done at near optimum moisture until the entire base

course is compacted to not less than 100% of maximum laboratory density as determined

by AASHTO T 180 (Method D). If the total compacted thickness of the graded aggregate

base course is more than 8 inches (a condition not allowed by current SCDOT design

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practice), the Standard Specifications state that the base course should be compacted in

two or more layers of approximately equal thickness.

Project Objectives

This report summarizes a study conducted for the SCDOT to 1) investigate the feasibilityof relaxing current GAB gradation specifications and 2) investigate the feasibility of

allowing GAB layer thicknesses greater than 8 inches in flexible highway pavement

structures. The study included only a limited number of the GAB materials used by theSCDOT and a limited number of laboratory and field tests.

Scope of Study

Time and resource limitations as well as the timeliness of new highway construction

projects suitable for the inclusion of GAB test sections necessitated a study of limitedscope. Therefore, the general objectives to investigate the technical and construction

issues associated with relaxation of GAB gradation specifications and layer thicknessrestrictions were limited as described below.

The investigation related to relaxing current SCDOT gradation specifications was limited

to relaxing the passing No. 4 sieve specification for Macadam. More specifically,

relaxing the maximum percent passing the No. 4 sieve from the current limit of 50% to60% (the current SCDOT limit for passing the No. 4 sieve for Marine Limestone) was

investigated. This investigation included full-scale laboratory tests on three commonly

used Macadam GABs (tested with the percent passing the No. 4 sieve meeting currentSCDOT specifications and with the percent passing the No. 4 sieve increased to near

60%). No Recycled Portland Cement Concrete GAB material testing was conducted toinvestigate the feasibility of relaxing the passing the No. 4 sieve specification from the

current value of 50% to the Marine Limestone value of 60%.

The investigation related to relaxing the current SCDOT GAB thickness maximum of 8

inches was limited to the following. Four commonly used GAB materials (two granite

GABs, one marble-schist GAB, and one Marine Limestone GAB) were subjected to full-

scale laboratory tests with compacted layer thicknesses of 6, 9, and 12 inches. The twogranite GABs and one marble-schist GAB are Macadam and were tested in both the

meeting and exceeding the maximum percent passing the No. 4 sieve specification

condition (as mentioned above). All laboratory GAB layers were compacted in 3 inchlifts on a supporting subgrade material of compacted sand. Two Macadam GAB materials

were tested at field test sections with compacted layer thicknesses between 6 and 12

inches. All field test section GAB layers were compacted as a single lift.

Research Approach

Justification

The performance of unbound GAB pavement layers depends on the properties of the

aggregates used. NCHRP Report 453 (Saeed et al., 2001) states the poor performance of

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unbound GAB layers in flexible pavements may be manifested by fatigue cracking,

rutting, and other pavement distresses. Two important aggregate properties cited ascontributors to pavement performance are shear strength and stiffness. Other important

properties cited are durability (as might be determined by the Magnesium Sulfate

Soundness test), and toughness (as might be determined by the Los Angeles abrasion or

Micro-Deval test). Frost susceptibility is also cited for cold weather applications.

The SCDOT uses AASHTO flexible pavement design methods and Structural Number(SN) to quantify pavement structure. The GAB layers contribution to SN is the product

of GAB layer thickness D2 (in inches) and layer coefficient a2 (in 1/inches). The value of

layer coefficient quantifies the material quality (influenced by the materials mineralogy,gradation, and other factors that affect mechanical properties) and is a measure of the

ability of a unit thickness of the material to function as a structural component of the

pavement. Layer coefficient may also be influenced by layer thickness, layer location inthe pavement structure, traffic level, and failure criterion (Appendix GG, AASHTO

1986).

An accepted way to quantify the quality of GAB as a component in a flexible pavement

structure is to compute layer coefficient a2 as a function of modulus. GAB materials are

nonlinear and therefore the value of modulus within a GAB layer will depend on thestress magnitude within the layer (which is influenced by the magnitude of the load,

depth and thickness of the GAB layer, and other factors). At the AASHO Road Test, the

average value for layer coefficient for untreated granular base course materials was 0.14.A well-known relationship between a2-value for untreated granular base course materials

and resilient modulus (MR) was developed by Rada and Witczak (1981). The relationship

is:

a2 = 0.249 x log10MR 0.977

Using this equation, a GAB resilient modulus value of 30,000 psi gives the averageAASHO Road Test a2-value of 0.14. Higher modulus values give higher values of a2.

Clearly, factors that affect GAB stiffness (including in situ stress level, gradation, layer

depth and thickness, etc) affect a2 (and, as stated above, the layers ability to function as astructural component of the pavement). The SCDOT currently uses an a2-value of 0.18

for all graded aggregate base course materials (corresponding to MR= 44,300 psi by the

Rada and Witczak equation above).

The two classic failure mechanisms for flexible pavements are fatigue cracking and

rutting. Fatigue cracking is influenced by tensile strains in the hot mix asphalt layer.

Strain magnitude is influenced by load magnitude, layer thicknesses, and the stiffness ofthe underlying layers. Rutting is indicated by permanent deformations that appear in the

wheelpaths. One important AASHO Road Test finding was that rutting was due primarilyto decrease in thickness of the pavement layers. Results summarized in Huang (2004)

indicate that about 60% of rutting was due to permanent deformation of base and subbase

layers (with the remaining 40% due to surface layer deformation (about 30%) and

subgrade deformation (about 10%)). This suggests that a GAB materials ability to resist

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permanent deformations under repeated wheel load repetitions may be important when

assessing GAB performance.

In this study, the research approach used was to measure GAB stiffness and resistance to

permanent deformation to assess the affects of relaxing current SCDOT gradationspecifications for Macadam GAB and allowing layer thicknesses greater than 8 inches for

Macadam and Marine Limestone GAB. In situ GAB stiffness was measured in full-scale

laboratory pit tests (static plate tests and GeoGauge tests) and in field test sections(Falling weight deflectometer and GeoGauge tests). Resistance to permanent deformation

was measured by full-scale laboratory pit tests (100,000 cycle plate tests).

Project Tasks

The basic research approach for this project included the following tasks:

Task 1. Literature review including a state agency survey.

Task 2. Full-scale laboratory plate tests on GAB materials.

Task 3. Installation and testing of GAB test sections at SCDOT highway construction

projects.

Task 4. Analysis of test results.

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CHAPTER 2

LITERATURE REVIEW

SCDOT Practice

Gradation and Compaction Requirements (Historical and Current)

A review of SCDOT gradation and compaction requirements for untreated granular

base materials revealed the following. The earliest gradation specifications that could

be found dated back to 1939. Specifications at that time stated that base courses were

to be placed in two 3-inch layers and were to consist of hard, durable stone with stone

dust and screens spread evenly on the surface. No compacted density requirement was

specified. Acceptable density was determined by the opinion of the Engineer.

Gradation specifications are listed in Table 2.1 below.

Table 2.1 Macadam Base Course Gradation Specifications (1939)

Crushed Stone Screen and Dust

Min. Max.

Passing 1 Screen 100% ..

Passing No. 4 Sieve 0% 4.0%

Passing No. 4 Sieve 100%

SCDOT Macadam base specifications dated 1955 specified that the base course be

placed in one uniform layer. The grading requirements for composite mixture of

coarse and fine aggregate are listed in Table 2.2. Maximum base course layer

thickness and density were not specified.


Percentage by Weight PassingSieve Designation

Min. Max.

2 100 ..

2 95 100

1 85 98

1 70 88

40 65

No. 4 25 50

No. 10 18 40

No. 40 10 25

No. 200 0 12

Maximum single lift for base courses were specified in the SCDOT specifications

dated 1964. For a required base layer thickness of 8 inches or less, the base may be

constructed in one layer. Where the required thickness is more than 8 inches, the base

was to be constructed in two or more layers of approximate equal thickness and the

maximum compacted thickness of any one layer should not exceed 6 inches. A few

small changes were made to the grading requirements of Macadam base course

material as listed in Table 2.3.

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Min. Max.

2 100 ..

2 95 100

1 85 98

1 70 88

40 67

No. 4 25 50

No. 10 19 42

No. 40 11 27

No. 200 0 12

A compacted density requirement was specified in the SCDOT specifications dated

1986. The in-place density was required to be not less than 100 percent of maximum

laboratory density as determined by AASHTO T 180 (Method D). Maximum single

lift was increased from 6 inches to 8 inches. Gradations specifications were altered

with the most notable change being substantial increases in the maximum percentpassing the 1 and sieves (from 88 to 100%, and 67 to 75%, respectively). The

revised gradation specifications are given in Table 2.4 below.



Min. Max.

2 100 ..

1 95 100

1 70 100

48 75

No. 4 30 50No. 30 11 30

No. 200 0 12

Liquid Limit: 25 Maximum

Plasticity Index: 6 Maximum

It should also be mentioned that on page 45 of Busching et al. (1971) there is a

reference to an additional SCDOT base course gradation specification that was

apparently in effect in 1971. This specification (referenced as South Carolina

Department of Highways Specification 45B3) is different from the 1964 and 1986

gradation specifications cited above. SCDOT Research and Materials Laboratory

personnel were unable to provide any historical record of this specification.

Current Macadam base course gradation specifications (2000) remain the same as in

SCDOT specifications dated 1986. As mentioned in Chapter 1, the same gradation

specifications also apply for Recycled Portland Cement Concrete GAB. A gradation

specification for Marine Limestone GAB was added and is shown in Table 2.5.

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Table 2.5 Marine Limestone Base Course Gradation Specifications (2000)

Sieve Designation Percentage by Weight Passing

2" 100

1 1/2" 95 100

1" 70 100

1/2" 50 85

No. 4 30 60No. 30 17 38

No. 200 0 20

Liquid Limit 25 Max.

Plasticity Index 6 Max.

Current (2000) compaction specifications (summarized in Chapter 1 of this report)

require GAB compaction at near optimum moisture until the entire base course is

compacted to not less than 100% of maximum laboratory density as determined by

AASHTO T 180 (Method D). If the total compacted thickness of the graded aggregate

base course is more than 8 inches (a condition not allowed by current SCDOT design

practice), the base course should be compacted in two or more layers ofapproximately equal thickness.

GAB Layer Coefficient

The SCDOT uses a layer coefficient (a2-value) of 0.18 to represent the quality of all

unbound GAB materials. This value was established as a result of the investigation

conducted by Busching et al. (1971). This investigation is also believed to have led to

the SCDOTs current design policy of limiting untreated granular base layer thickness

to 8 inches.

The Busching study involved the construction and testing of flexible pavement test

sections. The test sections were constructed within the confines of two concrete testpits. Each test section was approximately 8 ft x 12 ft in plan area. The GAB materials

used were South Carolina GAB materials (unbound crushed Granite-gneiss and

Fossiliferous Limestone) and a Dolomitic Limestone from the AASHO Road Test.

GAB layer thicknesses of 5 and 10 inches were tested (supported by different subbase

materials placed either 5 or 15 inches thick). Two subgrade conditions were

investigated (modulus of subgrade reaction, k = 50 pci and 275 pci). All test sections

had a 3-inch asphaltic concrete surface layer. Surface displacements were produced

by a dual tire hydraulic loading system. The loads required to produce 0.01-inch and

0.02-inch surface deflections were used for data analysis. Stiffness modulus values

were computed using the increments of load per inch of base per inch of deflection

(using loads corresponding to deflection increments from 0 to 0.01 inch and 0.01 to

0.02 inch). Base layer coefficients were then computed for assumed base layerthicknesses of 4, 6, 8 and 10 inches.

A comparison of selected recommended layer coefficients for base thicknesses of 4, 6,

8, and 10 inches constructed with AASHO Dolomitic Limestone and South Carolina

Type 2 Macadam (crushed Granite-gneiss) is given in Table 2.6.

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Table 2.6 Recommended Layer Coefficients for GAB Materials (Busching et al., 1971)

Base Layer Coefficient for

Base Layer Thickness of:

Pavement Components

4 6 8 10

AASHO Dolomitic Limestone 0.19 0.16 0.13 0.11

0.161

0.131

0.111

0.091

South Carolina Type 2 Macadam

- Crushed Granite-gneiss

(On weak support)1

(On firm support)2

0.112

0.092

0.072

0.062

1,2see Table 28 (page 81) of Busching et al. (1971) for definitions of weak and firm

support

The findings presented in Table 2.6 show a2-values decreased for the 10-inch layer

thickness. Not shown in Table 2.6 are computed a2-values for unbound Fossiliferous

Limestone base (0.21 for all base layer thicknesses). It is presumed that the SCDOTs

current a2-value of 0.18 for all GAB materials (unbound Macadam, Marine Limestone,

and Recycled Portland Cement Concrete) is based on the approximate average of the

Crushed Granite-gneiss, Fossiliferous Limestone, and perhaps the AASHO DolomiticLimestone a2-values presented in the Busching study. The results in Table 2.6 are

based on applied dual tire load vs measured surface deflection data. Modulus values

for base course materials were not determined.

State Agency Survey

To obtain information about relevant recent research activities and state highway

agency (SHA) practice, a survey was conducted. In early 2002, a short survey

questionnaire (Table 2.7) was sent to all US SHAs. The survey included questions on

several topics, including base layer thickness and single-lift thickness requirements,

gradation and compaction specifications, and relevant research activities on unbound

granular base materials. Twenty-five SHAs responded to the survey. Respondingstates are shown in Fig. 2.1. Data from the survey and information obtained from the

literature, SHA websites, etc. are combined and summarized in this chapter.

Table 2.7 Survey Questions______________________________________________

1. For flexible pavement construction, does your agency permit unboundaggregate base course thickness greater than 8 inches?

2. If your agency does permit unbound aggregate base course thickness greaterthan 8 inches,

a) What is the maximum total thickness permitted?b) What is the maximum single-lift thickness permitted?

3. We would greatly appreciate the following (either in paper or electronic form,or a link on your agencys web page to online specifications/information):

a) Your agencys unbound aggregate base compaction and gradationspecifications, and

b) Any research reports or summaries of internal investigations related tounbound aggregate base course thickness for flexible pavement

construction.

____________________________________________________________________

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States Responding (25)

States Not Responding (25)

-

HI

HI

HI

HI

HI

AK

TX

CA

AZ

NV

NM

CO

UT IL

WY

KS

IANE

OK

FL

MO

GAAL

AR

IN

PA

LA

NC

MS

TN

VA

KY

OH

SC

WV

MT

IDOR

SD

MN

ND

WI

WA

MI

NY

ME

MI VTNH

MD

NJ

MA

CT

DE

RI

Fig. 2.1 US SHAs Responding to Survey

Summary of Survey Reponses

Question 1. For flexible pavement construction, does your agency permit unbound

aggregate base course thickness greater than 8 inches?

Of the 25 SHAs responding to the survey, 15 SHAs reported unbound aggregate base

course thickness greater than 8 inches is permitted (see Fig. 2.2). Kansas indicated

unbound aggregate base course is rarely used. Illinois uses unbound GAB for local

roads only. Mississippi uses only bituminous base course.

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Fig. 2.2 SHAs Responses to Question 1

Question 2. a) What is the maximum total thickness permitted?

Twenty SHAs responded explicitly to this question. Colorado and Montana reported

24 unbound GAB (UGAB) layers were implemented in projects. Nebraska uses 4 to

5 layer thickness, and Alaska and Wisconsin limited layer thickness to 6. Kansas

reported no layer thickness limit for dense graded base with 8% to 20% fine content,

and unbound drainable base was limited to 6. Ohio reported using 6 UGAB or 6

UGAB with 4 of permeable base. Fifty percent of the SHAs reported limits greater

than 12, 22% of SHAs had a limit greater than 8 and less than 12, 11% of SHAs

impose a limit of 8, and 17% of SHAs limited UGAB layer thickness to less than 8.

Graphical summaries are provided in Fig. 2.3 and 2.4.

N/A

States Not Responding (25)Greater than 8 in.Less than or Equal to 8 in.

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> 12", 50%

> 8" and

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Question 2. b) What is the maximum single-lift thickness permitted?

Eighteen SHAs gave explicit answers to this question. Illinois reported limiting

single-lift thickness to 4, Louisiana has a limit of 12, and New York has a limit of

15. The remaining 15 SHAs reported a single-lift thickness limit of 6 to 8.

Question 3. a) Your agencys unbound aggregate base compaction and gradationspecifications.

Responding SHAs provided limited information on compaction and gradation and

specifications. Table 2.8 summarizes compaction specification information from

survey results and a review of selected agency web sites. As mentioned, the SCDOT

GAB compact specification is 100% of AASHTO T 180 (Method D). Kentucky, Ohio,

and Kansas reported using strip test to determine density requirements for granular

base materials.

Table 2.8 SHA Compaction Standards

State Name Compaction SpecificationMaine 95% AASHTO T 180 C or D, and corrected by Adjustment Chart

Illinois 100% AASHTO T 99 and corrected by AASHTO T 224

Washington 95% WSDOT Test Method

Alaska 98% AASHTO T 180 D

Indiana 100% AASHTO T 99

New

Hampshire

95% AASHTO T 99

Utah 97% AASHTO T 180 D

+/-2% optimum water content

Wisconsin AASHTO T 99 C, (replacement of the fraction)

Grading requirements for percent passing the No. 4 and No. 200 sieves for 8 SHAs

are compared in Table 2.9. Note that all SHAs have a passing No.4 sieve limit above

50%. The maximum reported limit for material passing the No. 200 sieve is 12%.

Table 2.9 Grading Requirements for No. 4 and No. 200 Sieves

State Name Percent PassingNo. 4 Sieve No. 200 Sieve

Low Limit High Limit Low Limit High Limit

Delaware 20 50 N/A N/AWashington 25 N/A N/A N/A

Florida 35 60 0 10

Tennessee 35 55 N/A N/A

Alaska 30 60 0 6

Nebraska N/A 93 N/A 3

New Hampshire 25 52 0 12

South Carolina 30 50 0 12

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Question 3. b) Research reports or summaries of internal investigations related to

unbound aggregate base course thickness for flexible pavement construction.

Little information was obtained from the survey responses about research activities

directly related to unbound aggregate base course thickness. Reported investigations

included the following: Kansas reported investigating aggregate base course

drainability; Iowa reported a study to establish layer coefficients for some localmaterials; Georgia reported construction of a test section that includes 12-inch UGAB

lifts.

In 1996, a study (Kimley-Horn and Associates, Inc., 1996) was conducted to evaluate

the feasibility of compacting unbound GAB lifts thicker than permitted by the North

Carolina DOT. Study test results demonstrated that 10 and 12 in. lifts of GAB were

successfully placed and compacted, and the required gradation, density, and water

content were maintained throughout the entire depth of the compact lift.

A similar investigation was conducted by ICAR researchers (John, et al., 1998). Five

full-scale test sections were constructed using a variety of material types and single

lift thicknesses ranging from 12 to 21. Density and shear wave velocity weremeasured using nuclear density gauge and spectral analysis of surface waves

techniques. Their findings indicated that density in excess of 100 percent of maximum

as determined by AASHTO T 180 can be achieved for thicknesses of up to 21 using

standard compact equipment.

Related Technical Information

Characterization of Unbound Granular Materials

Resilient Modulus

Resilient modulus, RM , is the fundamental material property used to characterize the

quality of subgrade and UGAB materials. Resilient modulus is the elastic modulus

based on the recoverable (resilient) strain under repeated loads.MR is expressed as:

r

dRM

=

where

d = the applied deviator stress; 31 =d ; r = resilient strain.

MR was introduced in the 1986 AASHTO flexible pavement design procedures and isa key input property for the mechanistic-empirical pavement design procedures

proposed in NCHRP Project 1-37A (2002). For older AASHTO flexible pavement

design procedures, resilient modulus of granular base material can be correlated to

layer coefficient a2.

Appendix L of AASHTO Guide for Design of Pavement Structures (1993) lists four

approaches for determining design resilient modulus. The four approaches are 1)

laboratory testing (repeated load triaxial testing), 2) estimation by correlation to other

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test results or physical properties, 3) nondestructive testing (NDT) ofin situ materials,

and 4) determination from original design and construction data.

Triaxial Test

Laboratory repeated load triaxial tests have been widely used to determine resilient

modulus and permanent deformation characteristics of unbound granular materials. Inthis test, cylindrical specimens are subjected to a series of load pulses applied with a

distinct rest period, simulating the stresses caused by multiple wheels moving over the

pavement. A constant all-around confining pressure applied on the specimen

simulates the in situ lateral stresses. The total recoverable axial deformation response

of the specimen caused by the stress pulses is used to calculate resilient modulus.

There have been several triaxial test methods presented by AASHTO, ASTM, and the

SHRP LTPP program for measuring RM of soils and unbound granular materials.

NCHRP Project 1-28, Laboratory Determination of Resilient Modulus for Flexible

Pavement Design, completed in 1997, produced yet another set of testing procedures

for RM determination of unbound materials. In order to harmonize these testing

methods, a recommended method was developed in NCHRP Project 1-28A

Harmonized Test Methods for Laboratory Determination of Resilient Modulus for

Flexible Pavement Design. This test protocol is reported to reduce testing variability

and the time required to complete testing.

Despite improvements made over the years, there are uncertainties as well as

limitations associated with triaxial testing. A study by Ke et al. (2000) showed that

reproducing the in situ internal structure of granular materials with current laboratory

specimen preparation techniques is not possible because of sample disturbance and

differences in aggregate orientation, moisture content, and level of compaction.

Karasahin et al. (1993) demonstrated stress conditions in a triaxial cell are different

from those in pavement structures due to inherent equipment flaws. The minorprinciple stress in a triaxial cell is kept constant during testing while both major and

minor principle stresses are cycled under wheel loadings. In addition, inherent

instrumentation flaws create uncertainty in the measurement of sample deformation.

Darter et al. (1995) reported that because of the complexity of repeated load triaxial

tests, most SHAs do not routinely measure resilient modulus using triaxial testing but

rather estimate resilient modulus from experience or by correlation equations

developed from physical properties or CBR test results.

CBR Test

The California Bearing Ratio (CBR) test was introduced in 1929 by Jim Porterworking as Soils Engineer for the state of California (Brown S. F., 1997). This test is

used to quantify the quality of compacted soil, soil-aggregate combinations, and

aggregate base materials using a numerical value of CBR. In this well-known test

(AASHTO Test Method T 193), a CBR value is computed from piston force and

piston penetration measurements.

There are a number of empirical equations to correlate CBR value to resilient

modulus of unbound base or subgrade materials. Heukelom and Klomp (1962)

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proposed a well-known correlation using dynamic compaction and in situ resilient

modulus and CBR values. The correlation can be expressed as:

R(psi) = 1500 CBR

The coefficient 1500 can vary from 750 to 3000. Available data indicate that the

Heukelom and Klomp equation provides acceptableMR predictions for fine-grained

soils and fine sands with CBR values less than about 20 (Huang, 2004). Materials

with CBR values higher than 25 often have theirR

values overestimated.

Another correlation for subgrade soil was proposed by Powell et al. (1984). This

correlation was primarily developed from data relating modulus measured by wave

propagation to in situ CBR results. The correlation is:

R(psi) = 2550 CBR0.64

The CBR test measures penetration resistance and thus provides an indirect

measurement of undrained shear strength. Pavement materials generally function at

stress levels within the elastic range. The CBR test provides no information about

material resilience. Brown et al. (1987) states that resilient modulus is not a simple

function of CBR. But, nevertheless, partially due to its simplicity and well-acceptance

among pavement engineers, the CBR test is widely used to evaluate the strength of

paving materials, and to correlate to resilient modulus.

Falling Weight Deflectometer (FWD)

The FWD has become a popular device for nondestructive measurement of load-

displacement behavior of constructed pavement structures or pavement layers. The

device may be van-integrated, mounted on a trailer, or hand-portable. The FWD test

involves applying a dynamic load on the pavement surface through a circular metal

plate. By varying the drop height and weight, a range of peak impact forces can be

produced to simulate actual traffic loads. Sensors are used to measure load-deflection

history at the center of the plate and deflection history at several radial distances from

the plate. The measured deflected shape of the pavement surface under peak impact

load is called the deflection basin. Pavement surface temperature can also be

measured using an infrared temperature sensor.

Measured load-deflection information is often used in back-analysis procedures for

the purpose of computing in situ moduli of the various pavement layers. There are

two basic types of backcalculation models. One involves numerous iterations of a

linear or nonlinear elastic analysis program. The other involves matching themeasured deflection basin to a number of previously calculated deflection basins. A

static pavement response model is usually used in the backcalculation procedure

without considering the inertial effects. This simplification was investigated by Tam

and Brown (1989), whose work indicated the inertial effects were generally

insignificant and static modeling can provide reasonable solutions.

Different testing and analysis procedures may produce different results. Research

conducted by Rauhut and Jordahl (1992) showed that the coefficient of variation

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(COV) of backcalculated modulus values ranged from 13% to 67% for four Strategic

Highway Research Program sections. Collop et al. (2001) performed statistical

analysis ofin situ pavement moduli backcalculated from FWD tests. The study

indicated that although backcalculated mean modulus values of the asphalt layer were

determined to an accuracy of 25% and a confidence level of 95% with a relatively

small sample size, for base layers a rather larger number of samples was required to

achieve the same accuracy and confidence level. Johnson and Baus (1993)investigated a number of basin-matching backcalculation programs. They indicated

those programs tend to underestimate the modulus of the unbound base course and

overestimate the modulus of the asphalt concrete-bound top layer and the subgrade.

Other Testing Techniques

Wave propagation techniques have also been used for the determination ofin situ

modulus of subgrade and pavement materials. Dynamic Cone Penetrometer (DCP)

testing can be used to determine in situ layer thickness and penetration resistance.

Penetration resistance can be correlated to in situ modulus.

Plate load tests have been used on flexible pavement components for design orevaluation purposes. The loading plate is also used in the Falling Weight

Deflectometer (FWD) testing to simulate dynamic wheel load on highway pavements.

Advantages of plate tests include 1) the magnitude of load and the state of stress

caused by the load reasonably approximate those in highway pavement structures, and

2) tested materials are eitherin situ or can be constructed in a way that approximates

the in situ internal structure of pavement materials. Konrad and Lachance (2001)

performed DCP and plate load tests to evaluate base and subbase materials. The

results indicated a good correlation can be found between modulus inferred from the

plate load tests and the penetration tests. In this project, cyclic and static plate load

tests were conducted to access permanent deformation resistance and resilient

modulus of the unbound granular base materials.

A relatively new device called the Soil Stiffness Gauge (SSG, a.k.a. GeoGauge)

measures material stiffness (modulus of subgrade reaction or stress-strain modulus)

directly using steady-state vibrations. In this project, engineering properties of

unbound granular base materials were evaluated using the SSG.

Factors that Influence Resilient Modulus of Unbound Granular MaterialsThe resilient modulus of granular materials is not a constant stiffness property but

depends upon various factors including stress state, water content, dry density, and

gradation. (Seed, 1967; Thompson, 1969; Hicks and Monismith, 1971; etc.). Lekarp

et al. (2000) illustrated that the effect of stress level on the resilient behavior is the

most significant factor.

Stress level of GAB materials in base courses primarily depends on base layer

location within the pavement structure, layer thickness, and wheel load magnitude.

Granular materials are known to exhibit nonlinear behaviors under traffic load. Uzan

(1992) introduced a universal model, applicable to all types of unbound paving

materials ranging from very plastic clays to clean granular bases. This model was

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used in the NCHRP Project 1-28A on the development of a harmonized RM test

protocol. This model, also known as 31 KK model, can be represented as:

32

1( ) ( 1)KK oct

R a

a a

M K PP P

= +

where

RM = resilient modulus; aP = atmospheric pressure to normalize stresses and

modulus; 1K , 2K , 3K = regression constants, dependent on material type and physical

properties and are obtained from regression analysis; = stress invariant, or the sum

of the three principle stresses; oct = octahedral shear stress, which can be expressed

as:

2 2 2 1/ 2

1 2 2 3 3 1

1(( ) ( ) ( ) )

3oct

= + +

Octahedral shear stress is equal to deviator stress when the stress condition of

granular materials in a triaxial test or under real traffic loads has an axis of symmetry.

A study by Lekarp et al. (2000) demonstrated that RM of granular materials increases

with increasing confining stress and sum of principal stresses. The influence of

octahedral stress is minimal.

For granular materials, it is known thatMR increases with a decrease in moisture

content and an increase in density. Hicks and Monismith (1971) used triaxial tests to

evaluate the influence of water content, dry density, and confining stress. Their

findings indicated a steady decrease of RM with increasing degree of saturation up to

optimum water content and decreasing dry density. Numerous other investigationsconfirm these findings.

A study by Hicks and Monismith (1971) showed the influence of gradation was not

well defined for two types of aggregate materials. For one material, the resilient

modulus increases as the percentage passing No. 200 sieve increased, while for

another material, the opposite trend was observed. Shaw (1980) studied the effect of

aggregate grading using triaxial test results. A comparison was made between 40-mm

maximum size broadly graded granular material and a 3-mm single-sized stone from

the same source. The broadly graded material was found to be stiffer than the single-

size stone. Thom (1988) conducted a series of repeated load tests on 10-mm

maximum sized crushed dolomitic limestone and found high stiffnesses for uniformly

graded materials, but broadly graded materials showed higher shear strengths. Kamalet al. (1993) compared the mechanical behavior of six gradings of unbound granular

materials. Testing results showed the effect of the percentage passing the No. 4 sieve

on resilient modulus and permanent strain was not defined. Santha (1994) studied the

effects of the physical properties of 15 granular materials on the resilient modulus. It

was found that RM decreased slightly with increasing percent passing the No.40 sieve.

Rahim and George (2004) investigated the relevance of soil index properties in

resilient modulus for Mississippi soils. A result of this study was a proposed

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correlation equation that indicates RM decreases with increasing percent passing the

No. 200 sieve. A review of the literature suggests that the percent passing the No. 4

and No. 200 sieves may be important influencing factors for well-graded granular

materials, but their influence on resilient modulus is not well defined and likely

material-specific.

Permanent Deformation Resistance

Permanent deformation characteristics of unbound granular materials are important

for flexible pavement performance. AASHO Road Test findings indicated a major

part of rutting occurred inside the base and subbase layers. Another finding was that

rutting in the wheel path was primarily caused by lateral movements of pavement

materials instead of material densification. A study by Thompson and Smith (1990),

confirmed by other researchers, showed that permanent deformation under repeated

load application may provide a more definite evaluation of pavement materials than

resilient modulus in some cases.

Repeated load tests, typically as an extension of the resilient modulus tests, have often

been used to determine permanent deformation of pavement materials. The testsusually involve applying loading applications of up to 100,000 repetitions and

recording permanent deformation at a number of designated cycles. Compared to

resilient behavior characterization, fewer models have been developed to describe

permanent deformation of pavement materials. Gidel and Horny (2001) suggest the

following reasons:

1. Permanent deformation tests are expensive and time consuming. Permanentdeformation is strongly dependent on stress history. Only one stress level is

generally applied on each specimen per test; a large number of tests (at least ten

each involving a large number of cycles) is therefore necessary to investigate how

stress levels affect permanent deformation.

2. It is difficult to predict field rut depth from laboratory test results. In flexiblepavements the material has a very complex loading history (initial phase of

pavement construction, highly varied traffic loading, variations in climatic

conditions) which is extremely difficult to simulate under laboratory testing

conditions.

Barksdale (1972) conducted repeated load triaxial tests with an average of 100,000

load applications on different granular materials. The load ramped up to the peak

value and then back to the trough value in a period of 0.1 second with a 1.9 second

period of no load separating the load applications. It was suggested that a reasonable

range of load repetition is from 100,000 to 1,000,000. From this work a qualitative

rutting index was defined to evaluate pavement performance. A relationship betweendeformation and load applications was suggested as:

)log()(1 NbaNp

+=

where

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N= number of load cycles; )(1 Np

= permanent axial strain at Nth number of cycles;

a and b are regression parameters.

The Barksdale study showed that permanent deformations were highly dependent onthe applied load and increased when confining pressure decreased and deviator stressincreased. The effect of density on the permanent deformation was also investigated.An increase of permanent axial strain of about 185% was observed when the materialwas compacted at 95 % instead of 100 % of maximum compaction density.(AASHTO T 99).

Diyaljee and Raymond (1982) developed an equation using regression methods topredict the permanent deformation under long term repeated loading using staticstress-strain data and a minimum number of cycles of repetitive load test data. Basedon their results on Conteau Dolomite railroad ballast data from other researchers, anequation for cohesionless materials was proposed:

mexpNBeN =)(1

where

B = value of strain at X= 0 for the first cycle; X = the ratio of the repeated deviatorstress to the failure deviator stress under static loading; n, m = regression parameter.

An example expression for subgrade sand with 35 kPa of confining pressure would be

4.07 0.12

10.004p xe N =

A study by Sweere (1990) on granular materials showed that a log-log approach is

appropriate for a large number of cycles:

1log( ( )) log( )p N a b N = +

Sweeres model is essentially the same as the power model proposed by Monismith in1975 (Monismith et al., 1975) though the later was based on a silty clay with a LL =35 and PI = 15. The Monismith model can be expressed as:

1

p baN =

One major finding of the Monismith study was that the exponent b depends only on

soil type. The tested soils had a b parameter between 0.154 to 0.332 and an a parameter between 0.0467 and 39.5. The effect of factors such as applied stresshistory and moisture content are included into parametera.

An asymptotic model proposed by Hornych and Paute (1993) for unbound granularmaterials is:

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1 1[1 ( ) ] (100)100

p B pNA = +

This model assumes that permanent strain approaches a finite limit asNtends towardsinfinity.

Other models relate permanent deformation to applied stresses. Representatives arethose by Hyde (1974) and Lekarp et al. (1998). A model proposed by Hyde (1974)can be expressed as:

1

3

p qa

=

Lekarp et al. (1998) used the repeated load triaxial equipment to test five differentgranular materials. A model that relates permanent axial strain to stress path length

and stress level was proposed as:

1

max

0

( )( )

/

p

ref bN q

aL P p

=

where

)(1 refp

N is the accumulated permanent axial strain at a given number of cycles; L is

the length of the stress path in kPa; a and b are regression parameters; 0Pis a

reference stress and is equal to 1 kPa.

Lekarp showed that the accumulation rate of permanent strain would eventually reachzero, if the stress ratio was low. However, at high stress ratios the accumulation ofpermanent strain was more progressive, indicating that a threshold stress ratio mustexist above which accumulation of permanent strain will cause failure. This thresholdstress ratio is called the shakedown limit.

Beside the number of load repetitions and stress level, the influence of gradation onpermanent deformation may be important. Kamal et al. (1993) conducted laboratoryand full-scale tests on unbound granular materials with 8 different gradations. Thepercent passing the No. 4 sieve varied from approximately 13% to 60%. The results

indicated the rut depth was more than twice as great for the open-graded materials asfor the well-graded materials. A study by Barksdale et al. (1997) shows permanentdeformation of crushed granite gneiss with 16% fines content was more than twicethat for 10% fines content (see Fig. 2.5). Similar results were found by Belt andRyynanen (1997). The Belt and Ryynanen study also showed that open-graded orwell-graded unbound granular materials do not necessarily behave as well in realpavement structures as would be expected based on repeated load triaxial test results.This is said to be because the rotation of principal stress directions during real traffic

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loading conditions, which significantly influences the permanent deformationbehavior of unbound granular materials.

Fig. 2.5 Influence of Number of Load Repetitions and Material Quality on PermanentDeformation (Barksdale et al. (1997))

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CHAPTER 3

LABORATORY PLATE LOAD TESTING PROGRAM

Introduction

Seven GAB materials were tested in the laboratory with compacted layer thickness of 6,9, and 12 inches. Table 3.1 lists the material types, sources, and abbreviations used in this

report. Crushed Granite (CGr), Crushed Marble-schist (CMs), and Crushed Limestone

(CL) are commonly used in South Carolina to construct base courses. Modified crushed

granite and marble-schist are those with additional material passing the No. 4 sieve.

Table 3.1 Materials Tested in the Laboratory

Material Type Source Abbreviation

Crushed Granite Vulcan Materials Company, Columbia Quarry CGr A

Modified Crushed Granite Vulcan Materials Company, Columbia Quarry MCGr A

Crushed Marine Limestone Martin Marietta Aggregates, Berkeley Quarry CL

Crushed Granite Martin Marietta Aggregates, Jefferson Quarry CGr B

Modified Crushed Granite Martin Marietta Aggregates, Jefferson Quarry MCGr B

Crushed Marble-schist Vulcan Materials Company, Blacksburg Quarry CMs

Modified Marble-schist Vulcan Materials Company, Blacksburg Quarry MCMs

Throughout the testing program, test conditions were designed to simulate in-service

conditions of stress levels, moisture, and density. Sample preparation followed, as closely

as possible, standard methods and procedures of sample splitting, handling, compaction,

and moisture control. Laboratory testing apparatus and equipment were carefully

maintained and calibrated in accordance with manufacturers manuals. The FWD is

maintained by SCDOT technicians.

Laboratory Testing Program

Test Pit and Plate Load Apparatus

To provide control over material gradations, water content, and construction, full-scale

laboratory pavement models were constructed in a concrete test pit housed in the

Department of Civil and Environmental Engineering laboratory facility at the University

of South Carolina.

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A schematic plan view of the laboratory test pit is shown in Fig. 3.1. Test apparatus and

cross-section of the test pit are illustrated in Fig. 3.2. The test pit was 13 feet by 10 feet in

plan. Plate tests were performed with a MTS Axial-Torsion Test System capable of

applying an axial load of 50,000 pounds at a frequency range of 0 to 1000 Hz. Plate

deflections were measured by three linear variable differential transformers (LVDTs).The

LVDTs were mounted on two reference beams and were placed equally apart on a 17.8 in.

diameter metal plate. The metal plate had the same diameter as the large plate used for

FWD testing. Load was measured by a load cell aligned collinearly with a hydraulic

actuator.

Deflection and load data were collected to a computer through a high speed digital/analog

data acquisition system. An initial attempt had been made to simulate flexible plate

conditions by gluing a rubber pad from a Dynatest FWD to the bottom of the metal plate.

Initial experiments using the rubber pad showed that deformations of the rubber pad itself

dominated total deflection. Therefore the pad was removed and a rigid plate was used. To

insure proper contact between the rigid metal plate and the base layer, a thin hydrostone

membrane was applied to the contacting area.

Fig. 3.1 Schematic Plan View of the Laboratory Test Pit

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Fig. 3.2 Cross Section of the Laboratory Test Pit and Plate Test Apparatus

Materials for Laboratory Testing

Subgrade

The subgrade material was an in-place sand for general geotechnical testing purposes.

The thickness of the sand subgrade layer is approximately 10 feet. The sand is underlain

by a permeable gravel deposit. The gradation curve for the sandy subgrade material is

shown in Fig. 3.3. According to the ASTM soil classification it is medium sand.

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0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10

Particle Size mm-log

PercentPassing

Subgrade

Fig. 3.3 Subgrade Sand Gradation Curve

Base Materials

All of the base (GAB) materials tested in the laboratory were fabricated by the quarries

identified in Table 3.1. The materials were shipped then stored in containers at the testing

facility. Sieve analysis and moisture-density tests were performed on each GAB material.Gradation results are shown in Table 3.2 and Fig. 3.4.

Table 3.2 Gradations of the Macadam and Limestone GAB Materials

Sieve

Designation

Percentage by Weight Passing

CGr A MCGr A CL CGr B MCGr B CMs MCMs

2" 100 100 100 100 100 100 100

1 1/2" 100 100 97 100 100 100 100

1" 96 90 87 93 98 95 93

1/2" 71 80 72 68 86 68 68

No. 4 45 55 52 47 64 40 46

No. 30 19 35 36 23 32 17 13

No. 200 6 8 16 7 5 3 2

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0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Particle Size mm-log

PercentPassing

CGr A

MCGr A

CL

CGr B

MCGr B

CMs

MCMs

* Density (pcf)

** Optimum water content (%)

Fig. 3.4 Gradation Curves for GAB Materials

Moisture-density tests were performed in accordance with AASHTO T 180 (Method D).

Results are shown in Fig. 3.5 and Table 3.3. Fig. 3.5 shows that dry densities are not

particularly sensitive to changes in compaction water content. Table 3.3 shows that the

difference in maximum dry densities for modified and unmodified materials is not

remarkable, especially for crushed granite.

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115

120

125

130

135

140

145

150

155

160

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Water Content (%)

DryDensity(pcf)

CGr A MCGr A

CL CGr B

MCGr B MCMs

CMs

Fig. 3.5 Dry Density vs. Water Content for GAB Materials (AASHTO T 180 D)

Table 3.3 Optimum Moisture Content and Maximum Density

Material Optimum Water Content (%) Maximum Dry Density (pcf)

AASHTO T 180 (Method D)

CGr A 5 138

MCGr A 5 137

CL 10 124

CGr B 6 133MCGr B 6 133

CMs 5 153

MCMs 5 150

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Placement and Test Procedures

An electric Wacker compactor was used to compact the in-place subgrade. In situ CBR

and static plate loading tests were performed to determine its elasticity and strength

characteristics. Prior to placement of the granular material, the subgrade surface was

leveled.

GAB materials were transported from the quarry to the testing facility by SCDOT

maintenance personnel. The base materials were mixed with water as necessary to

achieve optimum moisture then covered with plastic sheeting for short-term storage prior

to placement. Just prior to placement, conventional oven drying moisture content tests

were used to confirm water contents within 1% of optimum.

A GAB material to be tested was spread and shaped in the test pit. Compaction

commenced immediately and continued without interruption until the desired level of

density was achieved. Compaction was performed using the electric Wacker in 3.0 in.

lifts. Effort had been made to ensure a leveled base surface for each lift. The thickness of

each compacted layer was carefully controlled to be within 1/4 in. tolerance. Where the

base course was deficient by more than in., such areas were scarified and re-compacted

with base material added. For each material, base layer thicknesses of 6.0 in., 9 in., and

12 in. were constructed and tested.

After compaction, a hydrostone mixture was applied to the contacting area between the

plate and the base layer. The plate was lowered on to the hydrostone and a 10 psi pressure

was applied to form a thin hydrostone membrane between the GAB and the loading plate.Curing of the membrane took approximately 3 hours. Meanwhile, the base was covered

with plastic sheeting to allow even distribution of moisture (curing) through the base

depth. Just prior to testing, the MTS and data acquisition systems were turned on,

warmed-up, and confirmed to be fully operational. The LVDTs were inspected for wear

and verticality with the metal loading plate.

Elliott et al. (1998) summarized repeated loading test configurations for various

permanent deformation studies (see Table 3.4). Table 3.4 shows load frequency variations

from 20 to 120 repetitions per minute. Previous research (Seed and Fead, 1959;

Barksdale, 1972) indicated the effect of load pulse shape has little effect on the resilientmodulus measurements. Barksdale et al. (1997) suggested the haversine load pulse as the

likely best approximation of traffic loading of base materials.

For this study, a haversine wave form was used for cyclic loading tests and a triangle

wave form was used for static loading tests. Load durations of 1 second for cyclic loading

tests and 1000 seconds for static loading tests were used.

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Table3.4

SummaryofTestConfigurationsforVariousPermanentDeformationStudies

(afterElliottetal.(1998))

Seedand

Fead

(1959)

Larew

and

Leonards

(1962)

Barksdale

(1

972)

Monismith

etal.

(1975)

Poulsen

etal.

(1979)

Lentz

(1979)

Raadand

Zeid

(1990)

Behz

adi

and

Yand

ell

(199

6)

Elliottet

al.(1998)

LoadFrequency

(repetitionsper

minute)

20

20-22

30

20

120

60

40

40

30

LoadDuration

(seconds)

0.2-0.3

3

1.4

0.1

0.1

0.1

-

0.2

0.5

0.1

RestPeriod(seconds)

2.7

1.2

1.9

2.9

0.4

-

1.3

1

1.9

No.ofApplications

(inthousands)

100

60to80

100

10or100

100

10

10

10

100

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After the curing, 100,000 cycles of haversine load with frequency of 1 Hz was applied to

the granular base layer. The cyclic loading test took approximately 28 hours. During thecyclic loading test, the base course remained covered with the plastic sheeting to maintain

the moisture of the GAB material. Subsequently, the plastic sheeting was removed and 3

repetitions of static loading tests were performed approximately every 2 days as the water

content decreased due to evaporation. Load and deflection data were recorded for thethird load application. Maximum plate pressure on the GAB material was 50 psi.

(Preliminary plate tests directly on the sandy subgrade used a maximum plate pressure of

20 psi). These maximum pressures are assumed to simulate typical stresses within typicalflexible pavement structures. A complete cycle of the tests on one GAB material required

about 2 months, including preliminary laboratory moisture-density and sieving analysis.

Prior to each cyclic loading and static loading test, SSG tests were performed on the GAB

material. SSG testing is discussed later in Chapter 5.

At the completion of testing for each GAB material, nuclear gauge tests were performed

by SCDOT personnel. Comparisons of measured density achieved in the test pit andmaximum laboratory density (as determined by AASHTO T 180 (Method D)) are given

in Table 3.5. All base materials achieved above 100% RC except the Crushed Limestone(CL), which had an RC of 97%. This might be due to Wacker malfunction when

compaction of the 12 in. crush limestone base layer was performed. Table 3.5 data

confirms that compacted density very near maximum laboratory density was achieved inthe testing pit using the Wacker compactor and 3.0 inch lifts.

Table 3.5 Comparison of GAB Test Pit Density and Maximum Laboratory Density(AASHTO T 180 (Method D))

Base Material CGr A MCGr A CL CGr B MCGr B CMs MCMs

AASHTO T 180D(pcf)

138 137 124 133 133 153 150

Nuclear Gauge(pcf)

138 139 120 136 138 155 151

RelativeCompaction

100% 101% 97% 102% 104% 101% 100%

Experimental Results

Static Plate Loading and CBR Tests on Subgrade

Preliminary plate tests conducted on the sandy subgrade showed linearpressure-deflection behavior for plate pressures up to 20 psi (see sample data shown in

Fig. 3.6a). In situ CBR tests were performed on the compacted sand anticipating thatCBR values could be correlated with resilient modulus. CBR test results are shown in Fig.

3.6b. Nine CBR tests were conducted with one test at the center of the load plate and

eight other tests positioned in a uniform circular pattern 25.0 in. from the center test. The

result from one test was disregarded due to testing error and thus the results from eighttests are shown in Fig. 3.6b.

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0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

0 5 10 15 20 25

Plate Pressure (psi)

V

erticalDeflection(in.)

Subgrade

Fig. 3.6a Plate Load Test Results for the Sandy Subgrade

#1_sand*2003.xls

0

50

100

150

200

250

300

350

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Penetration (in.)

Resistance(psi)

Fig. 3.6b CBR Test Results for the Sandy Subgrade

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GAB Cyclic Plate Load Tests

Plastic behavior of the granular materials in the plate loading test was observed by

applying a repeated plate load to the surface of the compacted GAB material (maximum

plate pressure = 50 psi) and measuring the accumulation of nonrecoverable deformation

versus the number of load cycles. To assure proper seating of the loading plate, the firstfive cycles of loading were regarded pre-test seating cycles. Deflection and plate pressure

data were recorded at a frequency of 100 Hz throughout the test until 100,000 load

repetitions were applied. Fig. 3.7 shows typical results obtained from the cyclic plate loadtests.

Resilient deflections (i.e., recoverable deformations) were calculated by subtractingpermanent deformation from total deflection measured at 50 psi. Typical results are

shown in Fig. 3.8. Except for the CMs GAB, no significant change in resilient deflection

was observed as the number of cycles increased. This is especially the case after 1000cycles. As resilient deflections are inversely proportional to GAB densities, the results

appear to be in good agreement with AASHO Road Test data, which showed thatpermanent deformation is caused primarily by lateral movements of the materials instead

of material densification.

Due to fast data acquisition rate during a cyclic test, only a few hundred cycles could be

recorded at a time. This required the data collection be performed manually at regular

intervals during the 28 hours testing period. The test usually began in the late afternoonafter GAB compaction and apparatus setup, which meant overnight data collection.

During the testing program, two unavoidable schedule changes caused unsuccessful data

collection (specifically the 6 in. MCGr A and the 12 in. CGr B base tests).

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1-2000 Cyclic Loading Test Results for 6 in. CGr A Base

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Number of Cycles

VerticalDeflection(in.)

Permanent

deformation

Total

deflection

Resilient

d

eflection


0

0.02

0.04

0.06

0.08

0.1

0.12

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Number of Cycles


Permanent

deformation

Total

deflection

R

esilient

d

eflection

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0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Number of Cycles


Permanent

deformation

Total

deflection

es

ent

defle

ction

Fig. 3.7 Three Typical Cyclic Plate Load Test Results (CGr A)

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1 10 100 1000 10000 100000 1000000

Log(Number of Cycles)

ResilientDeflection(in.)

6 in. CGr A

9 in. CGr A

12 in. CGr A

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0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1 10 100 1000 10000 100000


ResilientDe

flection(in.)

9 in. MCGr A

12 in. MCGr A

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1 10 100 1000 10000 100000



6 in. CGr B

9 in. CGr B

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0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1 10 100 1000 10000 100000 1000000


ResilientDe

flection(in.)

6 in. MCGr B

9 in. MCGr B

12 in. MCGr B

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

1 10 100 1000 10000 100000 1000000



6 in. CMs

9 in. CMs

12 in. CMs

0

0.005

0.01

0.015

0.02

0.025

0.03

1 10 100 1000 10000 100000 1000000



6 in. MCMs

9 in. MCMs

12 in. MCMs

Fig. 3.8 Resilient Deflection vs Load Repetitions

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GAB Static Load Tests

At the completion of the cyclic loading test, three cycles of static loading tests were

performed. The first two load cycles were considered plate seating. Vertical deflection

and plate pressure data were recorded for the third static load repetition.

Static deflection curves for the seven GAB materials are shown in Fig. 3.9. Due to a

power surge that adversely affected data collection, the deflection data were abandoned

for one test (6 in. CGr B). Increasing layer thickness helped decrease plate deflections.The deflection curves indicate that the granular base materials exhibited stress-hardening

properties. The influence of water content is pronounced. Fig. 3.10 shows the sensitivity

of plate deflection to water content. For CGr and MCGr materials, a 1% drop in watercontent results in approximate 0.001 in. decrease in plate deflection at plate pressure of

50 psi.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0 10 20 30 40 50 60Plate Pressure (psi)

VerticalDeflection(in.

6" CGr A W=3.8%

6" CGr A W=3.4%6" CGr A W=2.7%

Decreasing water content

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035



6" MCGr A W=4.5%

6" MCGr A W=2.9%

6" MCGr A W=1.8%


0

0.005

0.01

0.015

0.02

0.025

0.03



9" CGr A W=4.4%

9" CGr A W=1.8%

9" CGr A W=1.2%


0

0.005

0.01

0.015

0.02

0.025

0.03



9" MCGr A W=3.4%

9" MCGr A W=2.0%

9" MCGr A W=0.9%


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0

0.005

0.01

0.015

0.02

0.025

0.03


VerticalDeflection(

in.

12" CGr A W=4.0%

12" CGr A W=2.0%

12" CGr A W=1.2%


0

0.005

0.01

0.015

0.02

0.025

0.03


VerticalDeflection(

in.

12" MCGr A W=4.0%

12" MCGr A W=2.8%

12" MCGr A W=2.0%

Decreasing water cont ent

0

0.005

0.01

0.015

0.02

0.025

0.03

0 10 20 30 40 50 60



6" CL W=11.5%

6" CL W=9.3%

6" CL W=8.1%6" CL W=6.0%


0

0.005

0.01

0.015

0.02

0.025

0 10 20 30 40 50 60



9" CL W=10.7%

9" CL W=9.9%

9" CL W=8.0%


0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02


VerticalDef

lection(in.

12" CL W=8.9%

12" CL W=5.4%

12" CL W=4.0%


0

0.005

0.01

0.015

0.02

0.025

0.03

0.035


VerticalDef

lection

(in.

6" MCGr B W=6.2%

6" MCGr B W=4.6%

6" MCGr B W=2.7%


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0

0.005

0.01

0.015

0.02

0.025

0.03


VerticalDeflection(

in.

9" CGr B W=2.0%

9" CGr B W=0.8%

9" CGr B W=0.7%


0

0.005

0.01

0.015

0.02

0.025

0.03



9" MCGr B W=6.0%

9" MCGr B W=3.0%

9" MCGr B W=1.5%


0

0.005

0.01

0.015

0.02

0.025

0.03



12" CGr B W=3.5%

12" CGr B W=3.0%

12" CGr B W=1.3%


0

0.005

0.01

0.015

0.02

0.025

0.03



12" MCGr B W=4.5%

12" MCGr B W=3.2%

12" MCGr B W=1.2%


0

0.005

0.01

0.015

0.02

0.025

0.03


Vertical

Deflection(in.

6" CMs W =4.1%

6" CMs W =3.4%

6" CMs W =2.3%


0

0.005

0.01

0.015

0.02

0.025


Vertical

Deflection(in.

6" MCMs W=4.0%

6" MCMs W=1.8%

6" MCMs W=1.5%


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0

0.005

0.01

0.015

0.02

0.025

0.03


VerticalDeflection(

in.

9" CMs W =3.0%

9" CMs W =1.6%

9" CMs W =1.5%


0

0.005

0.01

0.015

0.02

0.025


VerticalDeflection(

in.

9" MCMs W=4.0%

9" MCMs W=1.7%

9" MCMs W=1.6%


0

0.005

0.01

0.015

0.02

0.025

0.03

0 10 20 30 40 50 60



12" CMs W=3.4%

12" CMs W=1.5%12" CMs W=1.1%


0

0.005

0.01

0.015

0.02

0.025

0 10 20 30 40 50 60



12" MCMs W=3.8%

12" MCMs W=2.9%12" MCMs W=2.0%


Fig. 3.9 Static Loading Test Results

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0.015

0.02

0.025

0.03

0.035

0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0%

Water Content


MCGr A TH*=6in.

MCGr A TH=9 in.MCGr A TH=12 in.

CGr A TH=6 in.

CGr A TH=9 in.

CGr A TH=12 in.

* TH: Layer

Fig. 3.10 Static Deflection vs Water Content for MCGr A and CGr A

(Plate Pressure = 50 psi)

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CHAPTER 4

LABORATORY PLATE LOAD TEST RESULTS

Cyclic Plate Load Test Results and Analysis

From cyclic plate load tests, permanent deformations were obtained by subtracting theresilient deflections from total deformations. Permanent deformations were plotted

against the number of cycles. Log-log plots were found to describe approximately

linear relations between permanent deformation and number of cycles. The permanent

deformation at the100th

cycle was introduced into the log-log model to help data

interpretations using the following model:

)log(2))100(

log(1

1 Nbbp

p

+=

where

)100(1p

is permanent strain at the 100th

cycle;)100(1

1

p

p

is defined as the permanent

strain ratio; b is regression parameter.

Permanent strain is calculated by dividing the measured permanent deformation by

the base thickness.

Log-log plots of the permanent strain ratio against the number of cycles are shown in

Fig. 4.1. Water content values and regression lines are included as well. It should be

noted that although efforts were made to control base layer water content during eachcyclic loading test, some variations were not avoidable. Fig. 4.1 data suggest that

there is no significant difference between parameterb (slope of the trend line) for 6

in., 9 in., and 12 in. base layer thickness for any of the GAB materials tested. The

resul

spr 630_2

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