Long-term performance of granular bases including the effect of wet-dry cycles on inverted base pavement performance

GEORGIA DOT RESEARCH PROJECT 15-10
FINAL REPORT
LONG-TERM PERFORMANCE OF GRANULAR BASES INCLUDING THE EFFECT OF WET-DRY
CYCLES ON INVERTED BASE PAVEMENT PERFORMANCE
OFFICE OF RESEARCH 15 KENNEDY DRIVE
FOREST PARK, GA 30297-2534

.

GDOT Research Project No. 15-10 Final Report
Long-Term Performance of Granular Bases Including the Effect of Wet-Dry Cycles on Inverted Base Pavement Performance
By J. David Frost, Ph.D., P.E.
Principal Investigator Georgia Institute of Technology
Contract with Georgia Department of Transportation
In cooperation with U.S. Department of Transportation Federal Highway Administration
June 2017
The contents of this report reflect the views of the author(s) who is (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 Georgia Department of Transportation or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.

TECHNICAL REPORT STANDARD TITLE PAGE

1.Report No.: FHWA-GA-17-1510

2. Government Accession No.: 3. Recipient's Catalog No.:

4. Title and Subtitle: Long-Term Performance of Granular Bases Including the Effect of Wet-Dry Cycles on Inverted Base Performance

5. Report Date: June 2017
6. Performing Organization Code:

7. Author(s): Dr. J. David Frost, Ph.D., P.E.

8. Performing Organ. Report No.: 15-10

9. Performing Organization Name and Address: Georgia Institute of Technology School of Civil and Environmental
Engineering 790 Atlantic Drive Atlanta, GA 30318
12. Sponsoring Agency Name and Address: Georgia Department of Transportation Office of Research 15 Kennedy Drive Forest Park, GA 30297-2534

10. Work Unit No.:
11. Contract or Grant No.: 0011820
13. Type of Report and Period Covered: Final; July 2015-May 2017
14. Sponsoring Agency Code:

15. Supplementary Notes:

Prepared in cooperation with the U.S. Department of Transportation, Federal Highway

Administration.

16. Abstract:

The main objective of this study was to advance the understanding of alternative pavement

designs. In particular, potential techniques such as inverted base pavements (IBP) have

increased the importance of granular aggregate bases (GAB) in pavement structures. While

extensive research has been conducted on the resilient behavior of GAB's, their long-term

behavior has not been give much attention, particularly under near-surface stress-moisture

conditions prevalent in inverted base pavements. This project involved a series of preliminary

tasks aimed at establishing a working framework for future studies on IBP and included: (i)

investigations of alternative laboratory approaches to study the effect of wet-dry cycles on

permanent deformation; (ii) field studies of the performance of existing IBP test sections using

imaging techniques to establish a baseline for future performance measurements; (iii)

development and initial testing of an apparatus for laboratory investigation of the "slushing"

compaction technique; and (iv) promotion of IBP as a construction alternative.

17. Key Words:

18. Distribution Statement:

Inverted base pavements, wet-dry cycles,

pavement distress, "slushing" compaction

technique

19. Security Classification (of this report):
Unclassified Form DOT 1700.7 (8-69)

20. Security Classification (of this page):
Unclassified

21. Number of Pages:
108

22. Price:

GDOT Final Report on Granular Bases
TABLE OF CONTENTS
TABLE OF CONTENTS................................................................................................... iv LIST OF TABLES .............................................................................................................. v LIST OF FIGURES ............................................................................................................ v EXECUTIVE SUMMARY ............................................................................................. viii ACKNOWLEDGEMENTS ................................................................................................ x 1. INTRODUCTION ....................................................................................................... 1
1.1. Objectives ......................................................................................................... 1 1.2. Report Organization ......................................................................................... 1 2. WORK PLAN.............................................................................................................. 3 2.1. Laboratory Investigation of Effect of Wet-Dry Cycles on Permanent
Deformation...................................................................................................... 3 2.1.1. Material Characterization .......................................................................... 3 2.1.2. Effect of Moisture-Stress Cycles on GAB ................................................ 6 2.2. Pavement Evaluations for Establishing a Pavement Condition Baseline....... 15 2.2.1. Morgan County Quarry Access Road ..................................................... 16 2.2.2. LaGrange By-Pass Road ......................................................................... 22 2.3. Laboratory Investigation of Slushing Technique ........................................... 30 2.3.1. Apparatus Development .......................................................................... 30 2.3.2. Preliminary Simulations .......................................................................... 36 2.4. Promotion of Inverted Base Pavements as a Construction Alternative.......... 39 3. CONCLUSIONS AND RECOMMENDATIONS .................................................... 40 4. REFERENCES .......................................................................................................... 42
APPENDIX A Morgan County Quarry Road Field Measurements Report APPENDIX B LaGrange By-Pass Road Field Measurements Report APPENDIX C Inverted Base Pavement Presentation Materials
iv

GDOT Final Report on Granular Bases
LIST OF TABLES Table 1: Sieve analysis results on GAB.............................................................................. 4 Table 2: PUMA Tests loading stages.................................................................................. 8 Table 3: PUMA test results................................................................................................. 9 Table 4: CBR testing program .......................................................................................... 13
LIST OF FIGURES Figure 1: Grain size analysis for GAB material used for study. ......................................... 5 Figure 2: Proctor compaction curve obtained using the Modified method. ....................... 6 Figure 3: (a) Typical test apparatus showing the loading frame and specimen-mold, (b)
screen capture of data monitoring software .................................................................. 8 Figure 4: Stages of PUMA test (a) Sample preparation, (b) testing in loading frame and
(c) specimen after test showing dismantled mold......................................................... 9 Figure 5: Plots showing evolution of permanent deformation and stiffness modulus with
loading cycles.............................................................................................................. 10 Figure 6: Stiffness modulus versus axial stress for all three tested specimens................. 11 Figure 7: CBR stress versus penetration for four tested specimens.................................. 14 Figure 8: CBR estimated at 0.2" of penetration for four tested specimens ...................... 14 Figure 9: Selected pictures of CBR tested specimens ...................................................... 15 Figure 23: Comparison between conventional and inverted base pavement systems
[Papadopoulos, 2014] ................................................................................................. 32 Figure 24: Crushing versus Slushing action in achieving maximum density ................... 32 Figure 25: Schematic showing various components involved in testing process ............. 33 Figure 26: CAD rendering showing concept-design of slushing setup ............................ 34 Figure 27: Photographs of slushing device ....................................................................... 34
v

GDOT Final Report on Granular Bases Figure 28: Grain size distribution curve for GAB material used in slushing test............. 36 Figure 29: Horizontal load-cell readings for all cycles of compaction............................. 37 Figure 30: Photographs from pilot test ............................................................................. 38
vi

GDOT Final Report on Granular Bases
EXECUTIVE SUMMARY In recent years, the Georgia Department of Transportation (GDOT) has sought to advance the understanding of alternative pavement designs. In particular, evaluation of potential techniques such as inverted base pavements (IBP) have increased the importance of granular aggregate bases (GAB) in pavement structures. While extensive research has been conducted on the resilient behavior of GAB's, their long-term behavior has not been give as much attention, particularly under near-surface stress-moisture conditions prevalent in inverted base pavements. This project involved a series of preliminary tasks aimed at establishing a working framework for future studies on IBP and included: (i) investigations of alternative laboratory approaches to study the effect of wet-dry cycles on permanent deformation; (ii) field studies of the performance of existing IBP test sections using imaging techniques to establish a baseline for future performance measurements; (iii) development and initial testing of an apparatus for laboratory investigation of the "slushing" compaction technique; and (iv) promotion of IBP as a construction alternative.
Based on this study, a number of important insights have been observed and form the basis for a framework for future studies:
a) The Precision Unbound Material Analyzer (PUMA) tests reiterated the huge significance of the molding water content on the performance of the aggregate layer system. Specimens molded wet of the optimum water content showed lower stiffness moduli (up to 50%) and larger plastic deformations (up to 3 times larger) compared to specimen molded closer (and dryer) to the optimum water content. The increased permanent deformation in wetter conditions is potentially reflective vii

GDOT Final Report on Granular Bases
of fines-migration within the specimen in an attempt to achieve an optimized loadbearing particle matrix and also results in a higher matrix stiffness. Repeated cycles of wetting drying gradually deteriorates the particle matrix as was evident from the CBR test results.
b) Preliminary laboratory simulations of the slushing technique clearly showed the ejection of fine particles at the surface of the aggregate layer along with excess water. This establishes the effectiveness of the laboratory system towards simulating the slushing construction process as followed in the field, while enabling close control over testing conditions and electronic measurements of various metrics to quantify the improvements potentially achievable using this novel technique.
c) Combining the insights from the PUMA apparatus and the "slushing" compaction apparatus, a base layer that is compacted, within a reasonable range, close to the maximum modified-proctor dry density and optimum water content, followed by implementation of the slushing process to further enhance the stiffness of the system would potentially achieve a significant improvement in resiliency of the system. Moreover, this improvement would be achieved by minimizing void space in the unbound aggregate layer while minimizing crushing of aggregate particles, which is otherwise expected to occur with conventional high-energy lowlubrication compaction techniques.
viii

GDOT Final Report on Granular Bases
d) The field studies undertaken as part of this project to quantitatively evaluate pavement distress and rutting at the two existing locations of inverted base pavement test sections have provided both valuable information on the relative performance of the conventional and alternative pavement sections as well as critical quantitative baseline data so that future pavement distress surveys can be quantitatively compared to the baseline data. The field measurements provided clear evidence of the significantly better performance achievable with alternative pavement structures such as inverted base pavements.
e) The interest shown through both attendance as well as active engagement in discussion at both the Special Session at the TRB 2016 Annual Meeting on "Inverted Pavement Performance" and the subsequent webinar on "Inverted Pavements", both of which were organized by the AFP70 Mineral Aggregates subcommittee, and in which the PI participated as a speaker, provided strong evidence in the significant interest that exists nationwide amongst state DOT's for alternative pavement structures. GDOT has been playing an important lead technical role in these efforts.
ix

GDOT Final Report on Granular Bases
ACKNOWLEDGEMENTS A number of individuals made important contributions in the course of this study and to the findings presented herein.
Dr. Mark Wayne and Mr. Andres Peralta of Tensar International and Dr. Jayhyun Kwon of Kennesaw State University (formerly of Tensar International) provided valuable insights and assistance in the use of the PUMA device which is located in the laboratory of Tensar International.
Dr. James Tsai, Ms. Yiching Wu and Mr. Geoffrey Price of Georgia Tech conducted the pavement distress data collection and analysis using the Georgia Tech sensing vehicle. The assistance of Mr. Jim Maxwell (Martin Marietta) in coordinating access to the Morgan County Quarry Road and providing safety support there as well as Mr. Dwane Lewis (GDOT) in coordinating access and safety at the LaGrange Bypass site is gratefully acknowledged.
The efforts of Mr. Rick Boudreau (Boudreau Engineering) in coordinating both the TRB AFP70 Mineral Aggregates Sub-committee Special session and in organizing the TRB webinar on Inverted Base Pavements was most valuable. In addition, the roles of Messrs. Boudreau and Kevin Vaughn (Vulcan Materials) as co-presenters, along with the project PI, of the TRB webinar are acknowledged.
Finally, the support and assistance of Mr. David Jared and Ms. Gretel Sims of GDOT at various stages of the project are sincerely acknowledged and appreciated.
x

GDOT Final Report on Granular Bases
1. INTRODUCTION 1.1. Objectives GDOT has been actively engaged in the study of alternative pavement structures, and more specifically inverted base pavement structures, for more than 15 years. This has involved: (i) participation in the design, construction and monitoring of full scale test sections where the performance of conventional as well as alternative pavement structures could be directly compared (Morgan County Quarry Access Road and LaGrange By-pass Road (Pegasus Parkway); and (ii) support of research studies at Georgia Tech that led to two Ph.D. theses (Cortes, 2010 and Papadopoulos, 2014) and associated publications on the topic. To continue to promote the national conversation on this important subject, GDOT funded an additional one-year study to advance insights through a series of preliminary tasks aimed at establishing a working framework for future studies on IBP that included: (i) investigations of alternative laboratory approaches to study the effect of wet-dry cycles on permanent deformation; (ii) field studies of the performance of existing IBP test sections using imaging techniques to establish a baseline for future performance measurements; (iii) development and initial testing of an apparatus for laboratory investigation of the "slushing" compaction technique; and (iv) promotion of IBP as a construction alternative. This report summarizes the findings of this one-year project.
1.2. Report Organization The report is organized as a series of summary sections with additional detailed supporting materials included in appendices, as appropriate.
1

GDOT Final Report on Granular Bases
Section 2.1 summarizes a laboratory study conducted to assess the modulus and deformation behavior of pavement materials under multiple cycles of loading using a new apparatus called the "Precision Unbound Material Analyzer (PUMA) device. A parallel series of CBR tests were also conducted and are presented in Section 2.1. The significance of the work presented in this section is that it illustrates the potential for this new apparatus and test method to provide important insight into the performance of pavement structures under controlled conditions including wet-dry cycles.
Section 2.2 summarizes the results of two field studies conducted to quantify the pavement distress and rutting at two test sections that had both conventional as well as inverted base pavement sections. The field work and subsequent analysis was conducted using a vehicle developed at Georgia Tech with support from GDOT and others over the past decade. The importance of the work presented in this section is that its provides the first quantitative summary of pavement cracking and rutting conditions at both the Morgan County Quarry Access Road and the La Grange By-pass Road (Pegasus Parkway) and can serve as a critical baseline for future similar measurements at these test sections.
Section 2.3 summarizes the design, fabrication and initial testing of a new apparatus to simulate the "slushing" compaction technique in the laboratory under controlled conditions. The importance of the developments described in this section are that they provide the opportunity to study, under controlled conditions, the evolution of the microstructure of GAB during application of the "slushing" compaction technique. The technique is known to provide for superior performance of pavement structures but the specific mechanisms why are not understood yet.
2

GDOT Final Report on Granular Bases
Section 2.4 summarizes several important educational efforts which are based on the previous studies that GDOT participated in and/or supported and provide a significant portion of the basis by which inverted base pavement structures are recognized for their technical merit. The importance of the efforts summarized in this section are that they clearly identify GDOT as a leader in the search for alternative pavement structures. Aside from the specific summaries presented in Sections 2.1 to 2.4 of the report, several appendices to the report provide detailed complementary information as follows. Appendix A includes the full report for the Morgan County Access Road pavement measurement study. Appendix B includes the full report for the LaGrange By-pass Road pavement measurement study. Appendix C includes copies of the presentation materials used at the 2016 TRB AFP70 Special Session on "Inverted Base Pavement Performance" and the 2016 TRB webinar of "Inverted Pavements".
2. WORK PLAN 2.1. Laboratory Investigation of Effect of Wet-Dry Cycles on Permanent Deformation 2.1.1. Material Characterization Granular aggregate base (GAB) material used for the study was collected from Norcross, Georgia and the following geotechnical laboratory tests were run to characterize the material.
3

GDOT Final Report on Granular Bases

Grain Size Distribution Grain size distribution for the GAB material was obtained by conducting sieve analysis tests (as per ASTM D422) over two trials; the results are shown in Figure 1. The GAB was checked to satisfy GDOT gradation requirements (represented by dashed lines) for aggregate materials to be used as base material in pavements, as conveyed by the particle distribution curves in Figure 1.

The GAB material was visually classified as a well-graded mixture of predominantly gravel and sand, containing angular gray-colored coarse particles and non-plastic finer particles. Table 1 presents the parameters pertaining to the gradation curve, indicating the well-graded nature of the GAB material.

Table 1: Sieve analysis results on GAB

USCS Classification Percentage Fines (%)
Coefficient of Uniformity, CU Coefficient of Curvature, CC

GW (well-graded gravel) 7 - 7.5
70 90 0.51 0.76

4

GDOT Final Report on Granular Bases

FINES 100

SAND

GRAVEL

Fine

Medium Course

Fine

Course

80

GAB-Norcross-Trial1

GAB-Norcross-Trial2

GDOT-min
60
GDOT-max

40

% Finer by Weight

20

0 0.001

0.010

0.100

1.000

Grain Diameter (mm)

10.000

100.000

Figure 1: Grain size analysis for GAB material used for study. Modified Proctor Compaction Curve
The specific gravity (GS) of the GAB material was first computed as per ASTM D854, and estimated to be 2.737. A modified proctor test (ASTM D1557-12) was conducted at four sample water-contents to assess the moisture-density relationship of the material. The sample was sieved through a ASTM " sieve prior to compaction in the proctor mold to minimize particle-boundary interactions and edge-effects. This sample adjustment was then accounted for by using the correction method stated in ASTM 4718-87. Figure-2 present the compaction curve for the GAB material, where the dashes lines represents the modified sample (excluding " and bigger particles) and the solid line represents the

5

GDOT Final Report on Granular Bases

correction for coarse-fraction adjustment. The red-dashed line is the zero-air void line which denotes a state of complete water saturation in the material.
Maximum dry density and optimum water content values were estimated to be 148 pcf and 4.5% respectively, which are typical for GAB material.

Dry Density (pcf)

165.0 160.0 155.0 150.0 145.0 140.0 135.0 130.0 125.0 120.0
0

Modified Proctor - GAB-Norcross

ZAV Line ModProc-Uncorr ModProc-Corr

2

4

6

8

10

12

Moisture Content (%)

Figure 2: Proctor compaction curve obtained using the Modified method. 2.1.2. Effect of Moisture-Stress Cycles on GAB In order to quantify the effect of moisture-content and wet-dry cycles on the resiliency of the compacted granular-base-matrix, a series of tests were conducted using the Precision Unbound Material Analyzer and the California Bearing Ratio methods.

This section details the experiments conducted to characterize the performance of the compacted GAB specimens to moisture-stress changes, with focus on stiffness modulus

6

GDOT Final Report on Granular Bases
and permanent deformation. These objectives were achieved using the following two testing programs:
Precision Unbound Material Analyzer (PUMA) tests to study evolution of stiffness modulus and permanent deformation over multiple loading cycles and at varying compaction water contents.
California Bearing Ratio tests to quantify the effect of wetting and drying cycles on samples molded at the same water content
Precision Unbound Material Analyzer (PUMA) Tests Method: The PUMA is a new laboratory testing technique designed specifically for testing modulus and deformation behavior of pavement materials under multiple loading cycles. This method efficiently captures the unbound nature of the insitu road-base layer by using a flexible mold for the specimen [Brown, 2013]. The flexible wall is composed of eight curved wall segments, which are circularly arranged to form the mold, and a rubber-lined steel band is inserted around the mold to measure the horizontal strain experienced within the specimen. The horizontal strain in the specimen increases with increasing axial loads thus simulating the responsive nature of unbound pavements. The GAB test specimen was prepared in the 6"-tall by 6"-diameter using the modified method (5 layers with 56 blows/layer), and tested in a UTM loading frame as indicated in Figure 3. High frequency cyclic load was applied over thousands of cycles and the vertical-deformation at the surface is continuously monitored using two displacement transducers.
7

GDOT Final Report on Granular Bases

Figure 3: (a) Typical test apparatus showing the loading frame and specimen-mold, (b) screen capture of data monitoring software
PUMA tests were conducted on specimens molded at three water contents, i.e. 3, 6 and 9% to assess the effect of water content on multiple loading cycles. Each sample was subjected to loading stages as per Table 2. Photographs from various stages of a typical test are presented in Figure 4.

Table 2: PUMA Tests loading stages

Stage No. Stress (psf)

Stage I Stage II Stage III Stage IV

418 (20 kPa) 835 (40 kPa) 1671 (80 kPa) 3342 (160 kPa)

Frequency (Hz) 10 10 10 10

No of Cycles
1000 1000 1000 1000

8

GDOT Final Report on Granular Bases

Figure 4: Stages of PUMA test (a) Sample preparation, (b) testing in loading frame and (c) specimen after test showing dismantled mold
Results: Results from the PUMA tests conducted on compacted GAB specimens are shown below. In general, higher permanent deformation and smaller stiffness modulus was observed for samples molded at water contents wet of optimum (wopt= 4.5%). Both parameters increased at higher axial stresses, with most of the increase occurring over the first few hundred cycles followed by a more steady rate of increase as seen in Figure 5.

Table 3: PUMA test results

Test Measured Stiffness Stiffness Perm Def Perm

No. WC (%) Mod (MPa) Mod (tsf) (mm) Def (in)

1

3

248.0

2589.3

2.89

0.114

2

6

137.4

1434.7

7.68

0.302

3

9

133.3

1392.0

7.43

0.293

9

GDOT Final Report on Granular Bases

Permanent Def (mm)

Permanent Def at various water contents

10 8 6 4 2 0 0

3% WC 6% WC 9% WC
1000

2000
Cycle No

3000

4000

Stiffnes Mod (Pa)

Stiffness Modulus

3.00E+08 2.50E+08 2.00E+08 1.50E+08 1.00E+08 5.00E+07 0.00E+00
0

3% WC 6% WC 9% WC
1000 2000 3000 4000
Cycle No

Figure 5: Plots showing evolution of permanent deformation and stiffness modulus with loading cycles
These observations can be categorized and analyzed in three parts as follows.

Effect of Axial Stress:

o The GAB specimen almost instantly responds to a higher applied vertical stresses by accommodating deformation as well as mobilizing the additional stiffness required to resist the extra applied stress. Figure 6 shows a linear trend in the mobilized stiffness versus applied axial stress.

10

GDOT Final Report on Granular Bases

o Since the PUMA tests is a drained loading scenario with discrete wall elements, the additional deformation can be a combination of expulsion of void pockets through the mold walls (resulting in a tighter and stiffer particle matrix) as well as the radial expansion experienced by the specimen.

Stiffness Mod (Pa)

3.00E+08 2.50E+08 2.00E+08 1.50E+08 1.00E+08 5.00E+07 0.00E+00
0

Stiffness Modulus vs Axial Stress

3% WC

6% WC

9% WC

40

80

120

160

Axial Stress

Figure 6: Stiffness modulus versus axial stress for all three tested specimens Effect of Loading Cycles:

o Deformation curve in Figure 5(a) shows a plateau towards the second half of each loading stage, indicating the resiliency of the particle-system in supporting the applied load (from a soil mechanics perspective, the GAB reaches an over-consolidated state in the latter cycles). In other words, most of the plastic strain occurs in the first few hundred cycles until additional stiffness is mobilized by the specimen.

11

GDOT Final Report on Granular Bases
Effect of Water Content:
o Specimens compacted on the dry side of optimum generally tend to show greater stiffness moduli than specimens compacted wet of optimum, as is seen in these scenarios.
o There isn't much variation in the behavior of the 6 and 9% compacted specimens as both of these are wet of optimum, and considering the GAB material is a free-draining material, the excess water in the 9% specimen just flows out. It should be noted that water was indeed observed to being expelled while the test was in progress confirming the open drainage along the walls.
California Bearing Ratio Method: The California Bearing Ratio (CBR) is one of the oldest and most common engineering parameters used to characterize the stiffness of pavement base and subgrade material. CBR tests are conducted as per ASTM D1883-14, on compacted GAB specimens subjected to varying cycles of wetting and drying. This would allow the assessment of the effects of moisture-cycles on the resiliency of the compacted pavement base layer.
Four samples, with maximum-particle-size once again reduced to -inch to mitigate edgeeffects, were prepared in a 6-inch mold by compacting using the Modified-proctor method. These samples were subjected to 0, 1, 2 and 4 cycles of wetting-drying (shown in Table 4), with each cycle corresponding to 2 days of complete soaking in a water tub followed by 2 days of oven-drying. All CBR tests were conducted on soaked specimens. Swell
12

GDOT Final Report on Granular Bases

measurements on initial tests indicated no swell upon soaking (as expected), and hence are not presented in this report.

Table 4: CBR testing program

Soaking Stage

Specimen 1

Wet

Cycle0

Specimen 2 Wet

Dry

Wet

Cycle1

Specimen 3 Wet

Dry

Wet

Dry

Wet

Cycle2

Specimen 4 Wet

Dry

Wet

Dry

Wet

Dry

Wet

Dry

Wet

Cycle4

Results: The observed behavior of resistance to penetration for all four tested specimens is presented in Figure 7. The degradation in stiffness caused by wet-dry cycles is apparent, which is also exacerbated at larger strains. Although traditionally CBR stress-penetration curves are concave-upwards in shape, the initial convex shape observed herein can be attributed to a softer upper crust, loosened by water seepage/expulsion during the wet/dry cycles. Figure 8 shows the expected gradual reduction in 0.2"-CBR values (i.e. the CBR estimated at 0.2" penetration) for the four specimens. The 0.2"-CBR was selected for comparison over the 0.1"-CBR to get a more representative value of resistance after overcoming the surface irregularities caused by wet/dry cycles.

13

GDOT Final Report on Granular Bases

CBR- Stress-Penetration Curves
2500

CBR-C0

CBR-C1

2000

CBR-C2

CBR-C4

1500

Stress (psi)

1000

500

0

0

0.1

0.2

0.3

0.4

0.5

0.6

Penetration (in)

Figure 7: CBR stress versus penetration for four tested specimens

CBR (%)

CBR variation

90.0

80.0

70.0

60.0

50.0

40.0

30.0

.2" CBR

20.0

10.0

0.0

C0

C1

C2

C4

Cycle Id

Figure 8: CBR estimated at 0.2" of penetration for four tested specimens The loss in stiffness observed with wet-dry cycles can be attributed to sample disturbance caused by water forming flow channels through the specimen, which disturbs any previously-formed load-bearing contacts/chains among particles. Also, the CBR test involves penetration at the surface, which is also probably the zone that is most affected by moisture cycles being an open boundary. This is depicted in the pictures in Figure 9, showing some of the specimens that were tested. A stark contrast can be identified in the visibility of coarse aggregates at the surface in the C4 specimen relative to C1 and C0

14

GDOT Final Report on Granular Bases
specimens, which is probably, in part a result of dislodgement of surrounding finer particles over the course of the wet-dry cycles.

(a) Sample being soaked (b) C0 specimen

(c) C1 specimen

(d) C4 specimen

Figure 9: Selected pictures of CBR tested specimens

2.2. Pavement Evaluations for Establishing a Pavement Condition Baseline Full-scale test sections provide for comprehensive evaluation of the relative performance of alternative pavement systems.

15

GDOT Final Report on Granular Bases
2.2.1. Morgan County Quarry Access Road Three test sections with different pavement designs were constructed on an entrance road to the Martin-Marietta Morgan Quarry in Morgan County, Georgia in 2001. The three test sections were 1) conventional pavement), 2) South African inverted pavement, and 3) Georgia inverted pavement. Although a visual inspection was conducted in 2006, there has been no pavement surface distress condition evaluation conducted on these three test sections. The objectives of this study are to 1) critically evaluate the pavement condition of these three test sections using quantitative measures defined in the Pavement Condition Evaluation System (PACES) by the Georgia Department of Transportation (GDOT) (GDOT, 1993) and 2) establish a quantitative baseline for future deterioration analysis. Full details of the site, the data collection method, data processing steps and data analysis are presented in Appendix A.
For the Morgan County quarry access road, the measurements from the 2016 study were compared with falling weight deflectometer (FWD) test results conducted in 2007, along with previous rutting measurements obtained in 2003 and 2006 (Lewis et al.,2012) to identify any potential performance trends.
Figure 10 shows that FWD test deflection readings along the test section. Higher deflections were noted towards the entrance between Sta. 0 and Sta. 300, while the South African and Georgia pavements showed very low deflections, indicative of stiff pavement layers.
16

GDOT Final Report on Granular Bases
Figure 10. FWD Test Deflections conducted in Nov 2007 (after Lewis et al., 2012) Figure 11, 12 and 13 present rutting depth measurements obtained in 2003, 2006 and 2016 respectively. The section between Sta. 0 and Sta. 300 near the highway intersection indicated high rutting behavior in the 2003 and 2006 data and consequently is understood to have undergone repairs at some stage prior to the 2016 measurements, which explains the lower readings in the 2016 study at that location. Meanwhile, the rest of the conventional pavement section seems to indicate gradual rutting increases and thus deterioration. The South African and Georgia sections are performing remarkably well after 16 years of operation. Based on the 2016 data, there may be slightly lesser rutting in the South African IBP than the Georgia IBP section, but additional measurements with the
17

GDOT Final Report on Granular Bases
laser scanning technology after an additional period of service life would be required to confirm this.

Conventional

South African

Georgia

Figure 11. Rutting measurements in 2003

Conventional

South African

Georgia

Figure 12. Rutting measurements in 2006

Conventional

South African

Georgia

Figure 13. Rutting measurements in 2016 As indicated in the FWD measurements from 2007, the conventional section shows greater distress in various modes of cracking like load and block cracking as well. Figures 14 and
18

GDOT Final Report on Granular Bases
15 show Load cracking in the eastbound direction being noticeably greater in severity (levels 3 and 4) than the westbound lane, likely due to the greater stresses from loaded haul-trucks coming out of the quarry. The South African section indicates slightly better resistance to load cracking in the eastbound lane (Figure 15), while both, South African and Georgia IBP sections are clearly performing better than the conventional section in both lanes. Similarly, Figure 16 shows Block cracking being slightly severe in the conventional section where FWD deflections were the greatest, while the South African and Georgia IBP sections performed comparably better.

Conventional

South African

Georgia

Figure 14. Load Cracking measurements in the Westbound lane (2016 measurements)

19

Conventional

GDOT Final Report on Granular Bases

South African

Georgia

Figure 15. Load Cracking measurements in the Eastbound lane (2016 measurements)

Conventional

South African

Georgia

Figure 16. Block Cracking measurements (2016 measurements)
Primary observations from the Morgan County Quarry Access Road study are noted below. Data collection was conducted on April 8, 2016. The data was processed using developed algorithms and a manual review to extract distress information for every 100-ft segment. Two segments (marked at +0 ft. ~ +100 ft. and +100 ft. ~ +200 ft.) near the entrance and two segments (marked at +500 ft. ~ +600 ft. and +700 ft. ~ +800 ft.) near the crossroad, were excluded from further analysis because the stop-and-go traffic pattern in these segments had significant impact on the conditions. The pavement condition on the three test sections is summarized as follows:
20

GDOT Final Report on Granular Bases
The conventional section had diverse conditions with ratings ranging from 61 to 85. The average rating is about 75 after 15 years in service. Rutting, Level 1 block cracking, and severe load cracking (Levels 2 and 3) was observed on this section. Level 1 load cracking ranging from 15% to 65% was observed in the outbound lane where the loaded trucks travel, while lesser load cracking was observed in the inbound lane. Similarly, rutting in the outbound lane is higher than in the inbound lane. Thus, the average rating (71.7) in the outbound lane is significantly lower than the rating (77.8) in the inbound lane.
Both inverted pavement sections performed better than the conventional section. The average ratings in the South African and Georgia sections were 81.4 and 83.3, respectively. Only Level 1 load cracking (not severe), block cracking, and minor rutting was observed in these two sections.
It is noted that the South African section had a lower rating (81.4) than the Georgia section (83.3). The difference between the inbound lane and outbound lane is smaller, compared to the other two sections. There was very limited rutting observed on the South African section in both directions, except for two segments in the outbound lane.
The Georgia inverted pavement section performed similar to the South African section. The average ratings were 85.5 and 81 in the inbound lane and outbound lane, respectively. Cracking in the Georgia section was limited to Level 1 load cracking (20% to 45%) and Level 1 block cracking (15% to 65%). It is noted that rutting (1/16 in. 2/16 in.) was observed on all segments in the outbound lane.
21

GDOT Final Report on Granular Bases
In all three sections, the condition in the outbound lane was worse than in the inbound lane because of the loaded trucks traveling in the outbound lane. Significant difference (more than 6 points in rating) can be observed on the conventional section, while the South African section has the least difference in both directions. This may imply the slushing technique could help in the stiffness of GAB. Further investigation (e.g., FWD) is needed to study the stiffness of each section.
2.2.2. LaGrange ByPass Road GDOT built a 3,400-ft long IP test section on Pegasus Parkway in LaGrange, Georgia. The construction began in January 2008 and was completed in April 2009 (Cortes & Santamarina, 2011). Detailed data (including laboratory and field tests on the subgrade, the cement-treated base, the asphalt concrete, etc.) before, during, and after construction were collected to gain a better understanding of the internal behavior and performance of this pavement structure. Despite the detailed information collected at this site, there has not been any survey conducted on this test section to quantitatively evaluate its performance since it opened to traffic in 2009. The objectives of this study are to 1) critically evaluate the pavement condition of this test section using quantitative measures defined in the Pavement Condition Evaluation System (PACES) developed by the Georgia Department of Transportation (GDOT, 2007), and 2) establish quantitative baseline condition data for future deterioration analysis. With these objectives in mind, a condition evaluation was performed on the outside lanes (both Eastbound and Westbound lanes) of the test section.
22

GDOT Final Report on Granular Bases
Full details of the site, the data collection method, data processing steps and data analysis are presented in Appendix B. Resilient Modulus (Mr) of subgrade soil can be estimated using correlations with dynamic cone penetration rate as shown in the equation below that was developed by George and Uddin (2000).
, where PR is the dynamic cone penetration rate, dry is the dry unit weight, LL is the liquid limit, wc is the water content, and ai are fitting parameters. Based on an extensive field and laboratory study conducted at the LaGrange Bypass test section, Cortes (2010) estimated the mean Mr to be 250 MPa with a standard deviation of 100 MPa. The resilient modulus was measured at various stations along the test section as shown in Figure 17 below, where Sta. 280+00 and Sta. 314+00 represent the extent of the Inverted Base pavement (IBP) section. The mean and one-standard deviation lines are also presented in Figure 17. From the graph, the major outliers are observed to be between Sta. 298+00 and Sta. 300+00 (weak subgrade) and between Sta. 303+00 and Sta. 305+00 (strong subgrade).
23

GDOT Final Report on Granular Bases
Figure 17. Resilient Modulus estimated from DCP penetration rate Since in-situ moisture, density and porosity are some of the critical soil properties that affect resilient modulus and the quality of the subgrade material, Figure 18 presents plots of these properties along the test section (Cortes, 2010). There appears to be a correlation in the above-mentioned sections of pavement, i.e. Sta. 298+00 and Sta. 300+00 (weak subgrade) and Sta. 303+00 to Sta. 305+00.between resilient modulus and dry density (direct correlation), porosity (inverse correlation) and water content (inverse correlation). This confirms the merit of the resilient modulus values derived from dynamic cone penetrometer tests. Following the 2016 study conducted by the Georgia Tech team to quantify the cracking of the pavement, a comparison of the observations from this study with the information from Figures 17 and 18 was made. The section between Sta. 298+00 and Sta. 300+00 indicates low PACES ratings and high load cracking as shown in Figures 19 and 20. Sta. 303+00 to Sta. 305+00 shows relatively better performance.
24

GDOT Final Report on Granular Bases
Figure 18. Soil properties measured along the pavement test section Other regions of interest, i.e. between Sta. 280+00 to Sta. 292+00 and Sta. 305+00 to Sta. 315+00, are highlighted in the orange ellipse in Figures 17 to 21. These regions exhibit a somewhat lower resilient modulus, lower density, higher porosity, higher liquid limit and
25

GDOT Final Report on Granular Bases
higher water content values (Figures 17 and 18), and likely, as a consequence, lower PACES ratings and relatively high load and block cracking as seen in Figures 19 to 21.

Sta.280+00

Sta.314+00

Figure 19. PACES Rating showing sections of interest (2016 measurements)

Sta.280+00

Sta.314+00

Figure 20. Load Cracking showing sections of interest (2016 measurements)

Sta.280+00

Sta.314+00

Figure 21. Block Cracking showing sections of interest (2016 measurements) 26

GDOT Final Report on Granular Bases
While the graphs do not indicate a definitive correlation at this stage between soil properties and observed behavior, they do indicate a possible dependency and identifies areas-of-interest to be closely monitored in the future as the pavement continues in use. Figure 22 presents the rutting depths as measured in the 2016 study conducted using laser scanning technology. Considering ruts have a larger areal footprint than other modes of distress, they tend to develop over prolonged deterioration in a pavement zone and the current 7-year operation cycle for this test section does not indicate any stand-out trends.

Sta.280+00

Sta.314+00

Sta.280+00

Sta.314+00
Figure 22. Rutting depth measurements made in 2016

27

GDOT Final Report on Granular Bases
While there is not a clear trend in rutting behavior along the pavement section, the left wheel path (near the center-line of the road) in both directions shows greater rutting than the right wheel path. Additional field distress measurements after an additional period of service life are recommended to enable performance to be monitored.
After processing these data for cracking and rutting information, the distress information for every 100 feet was aggregated. From this data, the PACES score was determined according to GDOT specifications. The scores indicate that since being opened to traffic in 2009, the IP section has performed well:
The test section has performed well with an overall average rating of 94.7 after 7 years of service. Of the 64 segments (34 in each direction), only 6 segments had a rating less than 90. This is especially notable when considering, on average, Georgia's pavements reach a rating of 70 in 10.6 years.
Overall, the test section showed limited and low-severity (Level 1) load cracking and block/transverse cracking and moderate rutting. The average extent for load cracking and block cracking is approximately 5.4% and 1.5%, respectively. Of the 68 segments (34 in each direction), 28 segments exhibited load cracking (ranging from 5% to 45%), while only 14 segments exhibited block cracking (ranging from 5% to 20%).
The load cracking was distributed differently in the EB and WB lanes. For the EB lane, the load cracking was observed only on the first half of the test section (between the 2+00 and 19+00 marks). The segments approaching the 16+00-ft to 19+00-ft marks from the EB direction had significantly higher cracking than the 28

GDOT Final Report on Granular Bases
other segments. This higher presence of cracking may be attributed to the horizontal curve in a downhill grade from the 16+00-ft to 19+00-ft marks. For the WB lane, the load cracking was observed across the length of the test section with the segments near the west side (the 32+00 to 34+00 marks) showing the highest extent of load cracking. This may be attributed to the vehicle dynamic loading when moving from the bridge to the IP section. The WB lane exhibited more block/transverse cracking than the EB lane. Only two segments in the EB lane exhibited blocking cracking, while 12 segments in the WB lane were reported with block cracking. This may be attributed to the heavy truck loads in the WB lane. Moderate rutting was measured on the test section; in general, the WB lane had more rutting than the EB lane. The average rutting in the EB lane and WB lane was approximately 2/16 in. and 3/16 in., respectively. A 3/16 in. of rutting was reported between the 13+00-ft and 19+00-ft marks in the EB lane, where the load cracking was also high. Further study is needed to determine the causes of higher rates of rutting and cracking in these segments. It is noted that the rut depth in the left wheel path (inside wheel path) was higher than that in the right wheel path (outside wheel path) in both EB and WB lanes. Further analysis needs to be done to assess the potential causes.
Using sensing technology, the cracking and rutting information for all 100-ft segments was fully captured. Through thorough analysis, the current condition of cracking and rutting for the IP section has been established. The test section has performed well after 7 years of
29

GDOT Final Report on Granular Bases
service; however, the segments with higher rates of cracking and rutting need to be monitored and studied. With this baseline information, in-depth analysis on crack deterioration can be performed in the future to assess changes in crack characteristics, such as length, width, and depth. In addition, the growth of rutting in terms of both depth and length can be analyzed to determine any problems in base or surface layers. Through this analysis, the performance of the IP section can be analyzed over time to evaluate how well this new pavement structure performs in comparison to a conventional asphalt pavement structure.
2.3. Laboratory Investigation of Slushing Technique 2.3.1. Apparatus Development The need for better grasp of unbound granular material in pavement applications is especially important in light of the emergence of new and alternative pavement designs such as inverted-base pavements. This study aimed to supplement the field-observations supporting the superior long-term performance of inverted-base sections relative to the conventional sections at two test sections in Georgia, with laboratory simulations to replicate the underlying mechanisms. To this end, the current study also served to lay the groundwork for an extensive study on inverted base pavements in the near future by including the design and fabrication of a laboratory bench-scale setup to simulate the `slushing' technique, which has been reported to further enhance the density of the packed granular base.
The slushing process is applied to the unbound aggregate base layer (UAB) of inverted base pavements, represented by the GAB layer in Figure 23, which also schematically
30

GDOT Final Report on Granular Bases
presents the differences between a conventional flexible pavement and an inverted base pavement structure. Since the UAB layer in an inverted base pavement plays a greater structural role in load-distribution, it is critical to achieve the right composition of particles and minimize voids. Slushing helps achieve this by retroactively removing excess fine particles from an already-placed UAB layer, as opposed to traditionally adopted repeated rolling which leads to particle crushing and is detrimental to the integrity of the pavement in the long term (Figure 24). The seepage action of water through the compacted UAB layer is critical to the slushing process, as explained below.
This technique involves the following steps during compaction of the unbound aggregate base layer:
A cement-treated base layer is compacted to ensure a stiff, low-permeability layer to support the overlying UAB layer.
UAB layer is placed and compacted until it exhibits no (or very little) movement under the weight of a heavy roller.
The next stage is the slushing process which involves multiple passes by a water truck, a heavy smooth-drum roller and a pneumatic rubber-tired roller, in that sequence. This combination allows the water to seep into the UAB layer and immediately being expelled back to the surface under the action of the following two rollers, while eliminating any excess air pockets and fine particles. Visually, this is observed as air bubbles and fine sediments at the surface indicating the slushing process is underway. This expelled water is removed from the pavement. 31

GDOT Final Report on Granular Bases At the end of the slushing stage, indicated by expulsion of clear water at the surface,
the UAB layer should contain lesser percentage of voids than pre-slushing and an optimum ratio of coarse to fine particles, ensuring higher stiffness and durability. The cleaned surface is allowed to dry completely and then dry-rolled before applying the tack-coat for asphalt placement.
Figure 23: Comparison between conventional and inverted base pavement systems [Papadopoulos, 2014]
Figure 24: Crushing versus Slushing action in achieving maximum density Method: The `Slushing' setup was designed as shown in the schematic below (Figure 25) and incorporated the following features:
32

GDOT Final Report on Granular Bases Two sets of rollers of to each act as steel and rubber-tired wheels. Varying stiffness
was captured by using rubber sleeves of different hardness (90A Urethane for harder roller and 60A Vinyl for softer roller) Roller weight to be controlled using dead weights hanging independently off rollers One directional compaction, capability to retract rollers to origin while elevated from the soil surface to prevent reversal of rolling stresses Ability to be speed-controlled and position controlled (micro-controller driven) Instrumented to measure and record horizontal load, speed and number of cycles Water sprinkler system to spray water at a controlled rate as desired Figures 26 and 27 show some additional schematics and photos of the device.
Figure 25: Schematic showing various components involved in testing process 33

GDOT Final Report on Granular Bases Figure 26: CAD rendering showing concept-design of slushing setup
Figure 27: Photographs of slushing device 34

GDOT Final Report on Granular Bases
Test Parameters: The gradation of GAB material was modified so as to remove the coarser particles greater than inches (to scale for reduction in the laboratory roller size as well as make any subsequent core-sampling easier) as shown in Figure 28. GAB was manually compacted during the initial placement stage in four lifts of one-inch thickness. The gab material is mixed to optimum water content (6.5%) prior to placement. This test was run in the following stages, with gradually increasing rolling stress to prevent soil `bowing':
Stage I: Surface Preparation: Low stress passes (20 lbs on each roller) to create even surface
Stage II: Conventional Compaction-I: Moderate stress (36 and 31 lbs on each roller) passes
Stage III: Conventional Compaction-II: High stress passes (55 and 40 lbs on each roller)
Stage IV: Slushing: Similar stresses as above but accompanied by water spraying in one direction
35

GDOT Final Report on Granular Bases
Figure 28: Grain size distribution curve for GAB material used in slushing test
2.3.2. Preliminary Simulations The objective of this section of the study was to primarily develop a working apparatus to simulate slushing and conduct a pilot test to qualitatively observe slushing mechanisms. The following paragraphs present the result from the pilot test. Figure 29 presents the horizontal load resistance recorded by the load cell while pushing the rollers in the forward direction. Stages I-IV comprised of one, five, five and 34 passes respectively. The varying vertical stresses on rollers for four aforementioned stages of compaction can be clearly distinguished. The default speed of rolling was set to 0.33 in/s (actuator speed 75). Horizontal drag increases upon introduction of water which explains the higher load measurements for Stage IV as seen in Figure 29. The orange-colored passes were conducted at higher speeds of 0.44 in/s (actuator speed 100) and 0.66 in/s (actuator
36

GDOT Final Report on Granular Bases speed 150), which is causing the even-higher load readings compared to the previous cycles of Stage IV. Another interesting observation, which should be closely monitored for future tests is the bell-shaped load curve, with the load reading dropping in the second half of the slushing stage. This is noticed in Stage IV at all three speeds.
Figure 29: Horizontal load-cell readings for all cycles of compaction Some photographs from the test are shown below in Figure 30. It should be mentioned that while air bubbles and fine particles were ejected at all across the surface, the water carrying these ejected particles was subsequently pushed to the side of the box by the following pass of the rollers. Therefore, the photos below indicate greater accumulation of fine particles along the edges of the box, as seen in Figure 30(f), (g) and (h).
37

GDOT Final Report on Granular Bases

(a) GAB placement and manual compaction

(b) Commencement of stage I compaction

(c) GAB surface pre-slushing

(d) Slushing stage underway

(e) Slushing stage in progress

(f) Fines being ejected to sides of roller

(g) GAB surface after slushing

(h) GAB surface after slushing

Figure 30: Photographs from pilot test

38

GDOT Final Report on Granular Bases
2.4. Promotion of Inverted Base Pavements as a Construction Alternative As a result of the significant role that GDOT has played over the past 15 years in
evaluating alternative pavement systems and in particular inverted base pavements, it also has a critical role to play in sharing the insights gained through the various studies it has participated in and in many cases led. For example, the inverted pavement test sections at the Morgan County Quarry Access Road and the LaGrange By-pass Road are amongst the best documented test sections in the country and thus performance evaluations of these test sections can provided critical evidence of the relative performance of conventional and alternative pavement systems.
To fulfill this role of promoting inverted base pavements as an alternative pavement system, several activities were undertaken as part of this project as follows:
The project PI presented a lecture at a special session organized at the 2016 TRB Annual meeting in Washington D.C. on Inverted Base Pavements by AFP70 Mineral Aggregates sub-committee. The title of the lecture was "Performance Assessment of Inverted Pavement Test Sections". The special session was attended by more than 60 individuals including representatives from more than 20 state DOT's.
The project PI was one of three lecturers who delivered a TRB webinar organized in July 2016 on "Inverted Pavements" by AFP70 Mineral Aggregates subcommittee. The webinar was attended by more than 300 participants with registered participants from 39 state DOT's.
39

GDOT Final Report on Granular Bases
3. CONCLUSIONS AND RECOMMENDATIONS Based on this study, a number of important insights have been observed and form the
basis for a framework for future studies:
a) The PUMA tests reiterated the huge significance of the molding water content on the performance of the aggregate layer system. Specimens molded wet of the optimum water content showed lower stiffness moduli (up to 50%) and larger plastic deformations (up to 3 times larger) compared to specimen molded closer (and dryer) to the optimum water content. The increased permanent deformation in wetter conditions is potentially reflective of fines-migration within the specimen in an attempt to achieve an optimized load-bearing particle matrix and also results in a higher matrix stiffness. Repeated cycles of wetting drying gradually deteriorates the particle matrix as was evident from the CBR test results.
b) Preliminary laboratory simulations of the slushing technique clearly showed the ejection of fine particles at the surface of the aggregate layer along with excess water. This establishes the effectiveness of the laboratory system towards simulating the slushing construction process as followed in the field, while enabling close control over testing conditions and electronic measurements of various metrics to quantify the improvements potentially achievable using this novel technique.
c) Combining the insights from the PUMA apparatus and the "slushing" compaction apparatus, a base layer that is compacted, within a reasonable range, close to the
40

GDOT Final Report on Granular Bases
maximum modified-proctor dry density and optimum water content, followed by implementation of the slushing process to further enhance the stiffness of the system would potentially achieve a significant improvement in resiliency of the system. Moreover, this improvement would be achieved by minimizing void space in the unbound aggregate layer while minimizing crushing of aggregate particles, which is otherwise expected to occur with conventional high-energy lowlubrication compaction techniques.
d) The field studies undertaken as part of this project to quantitatively evaluate pavement distress and rutting at the two locations of existing inverted base pavement test sections have provided both valuable information on the relative performance of the conventional and alternative pavement sections as well as critical quantitative baseline data so that future pavement distress surveys can be quantitatively compared to the baseline data. The field measurements provided clear evidence of the significantly better performance achievable with alternative pavement structures such as inverted base pavements.
e) The interest shown through both attendance as well as active engagement in discussion at both the Special Session at the TRB 2016 Annual Meeting and the subsequent webinar, on Inverted Base Pavements" both of which were organized by the AFP70 Mineral Aggregates sub-committee provided clear evidence of the strong interest that exists nationwide amongst state DOT's for alternative pavement structures. GDOT has been playing an important lead technical role in these efforts. 41

GDOT Final Report on Granular Bases
4. REFERENCES ASTM (2009), "D6913-04 Standard Test Method for Particle-Size Distribution of Soils
Using Sieve Analysis", ASTM International, West Conshohocken, PA. ASTM (2015), "D1557-12 Standard Test Method for Laboratory Compaction
Characteristics of Soil Using Modified Effort (56,000 ft-lbs/ft3 (2,700 KN-m/m))", ASTM International, West Conshohocken, PA. ASTM (2015), "D1883-14 Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils", ASTM International, West Conshohocken, PA. Alba, L.J. (1993). "Laboratory Determination of Resilient Modulus of Granular Materials for Flexible Pavement Design." Ph.D. Thesis, Georgia Institute of Technology, Atlanta. Brown, S.F., Thom N.H. (2013). "Recent Developments in Pavement Foundation Design", Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris. Cooper Technologies. Precision Unbound Material Analyzer, Manufactures Brochure, Website url: http://cooper.co.uk/wp-content/uploads/downloads/2013/08/PUMAPrecision-Unbound-Material-Analyser-Cooper.pdf Cortes, D.D., (2010), "Inverted Base Pavements Structures", Ph.D. Thesis, Georgia Institute of Technology, Atlanta. Lewis, D.E., Ledford, K., Georges, T., Jared, D.M. (2012), "Construction and Performance of Inverted Pavements in Georgia", Transportation Research Board 91st Annual Meeting, 12-1872. Papadopoulos, E. (2014). "Performance of Unbound Aggregate Bases and Implications for Inverted Base Pavements." Ph.D. Thesis, Georgia Institute of Technology, Atlanta.
42

GDOT Final Report on Granular Bases
APPENDIX A Morgan County Quarry Access Road Field
Measurements Report

Morgan County Pavement Condition Evaluation Report Yiching Wu. Yichang Tsai, Geoffrey Price
1. Scope and Objective Three test sections with different pavement designs were constructed on an entrance road to the Martin-Marietta Morgan Quarry in Morgan County, Georgia in 2001. The three test sections were 1) conventional pavement), 2) South African inverted pavement, and 3) Georgia inverted pavement. Although a visual inspection was conducted in 2006, there has been no pavement condition evaluation conducted on these three test sections. The objectives of this study are to 1) critically evaluate the pavement condition of these three test sections using quantitative measures defined in the Pavement Condition Evaluation System (PACES) by the Georgia Department of Transportation (GDOT) (GDOT, 1993) and 2) establish a quantitative baseline for future deterioration analysis.
2. Site Description The three test sections together are approximately 1,800 ft. on a private entrance road to the Martin-Marietta Morgan Quarry located near I-20, Exit 121 off the 7-Island Road in Madison, GA. Figure 1 shows the location of the test sections. This entrance road is used by empty haul trucks entering the quarry and loaded trucks leaving the quarry. In addition, there is an unpaved crossroad intersecting with the entrance road.
Figure 1. Site location.

The layout of the three test sections is shown in Figure 2. The conventional pavement section, consisting of HMA on top of 8 in. of graded aggregate base (GAB), begins at the entrance at 7 Island Road and continues in the westbound (WB) (or inbound) direction for 1000 ft. This section is mostly straight with a slight horizontal curve near the entrance. A crossroad which intersects the conventional section at approximately +680 ft, is used for trucks carrying pit overburden to a waste site. These trucks weigh over 40 tons when loaded (Cortes & Santamarina, 2012). In addition, an unpaved parking area is located around +500 ft. mark in the eastbound (EB) (or outbound). The South African inverted pavement section (SAIP) is 400 ft. long (from the +1000 ft. mark to the +1400 ft. mark); it is a mostly straight stretch of roadway. The Georgia inverted pavement section (GAIP) is also 400 ft. long, and continues from the +1400 ft. mark to the +1800 ft. mark on a curved section.
Both the inverted pavement test sections (SAIP and GAIP) were constructed with 8 in. of a cement-treated base, a 6-in. layer of GAB, and a thin, 3-in. layer of HMA on the top, the only difference being the incorporation of the"slushing" technique for the SAIP section. Slushing increases the stiffness of the GAB layer by reducing the volume of voids between the aggregate particles.
Figure 2. Layout for three test sections.

3. Data Collection Georgia Tech's sensing vehicle, equipped with laser crack measurement systems (LCMS), GEO3D cameras, GPS, IMU (inertial measurement system), and DMI (distance measuring instrument), was used for collecting 3D pavement data, 2D images, and GPS data for extracting pavement distresses based on PACES (GDOT, 1993) standards. Data collection was conducted on April 8, 2016. Since there weren't any pavement marking on this private entrance road, location reference points were marked with fluorescent paint to help identify the 100-ft segment for use in a PACES survey. A diagram of the marking scheme is shown in Figure 3. After construction in 2001, nails were placed in the pavement's surface at +1000, +1400, and +1800 ft. to mark the different test designs. These were used as location references to mark the start and end of every section with paint. The center line was marked with a dashed line and a cross and the marking numbers were placed along the center line at every 100 ft. using the nails as references. The WB and EB travel lanes were then outlined with dashed lines. Once the lanes were outlined, the transition points between the different pavement designs were marked across the full lane. The marking, which took approximately 2 hours to finish, outlined the 100-ft segment for the PACES survey.
Figure 3. Layout for markings.
The Georgia Tech sensing vehicle, as shown in Figure 4, was driven at approximately 25 mph in both directions to collect the data at 5-meter intervals with each video log image corresponding to a single laser file. To facilitate better coverage of the access road, two runs of data were collected, and the run with better coverage of the marked lane was processed and analyzed.

Figure 4. Georgia Tech Sensing Vehicle.
4. Data Processing Distresses on the three test sections were extracted from the sensing data based on GDOT's PACES survey standards. PACES establishes standardized nomenclature for distresses and defines their respective severity levels and measurement methods for asphalt concrete pavement. There are ten distresses surveyed in PACES including: 1) rutting, 2) load cracking (LC), 3) block/transverse cracking (B/T), 4) reflection cracking, 5) raveling, 6) edge distress, 7) bleeding and flushing, 8) corrugation and pushing, 9) loss of pavement section, and 10) patches and potholes. Cracking (including load cracking, block cracking, and reflective cracking) is measured in a 100-ft section. A PACES rating is then computed on a scale of 0 to 100 (with 100 representing pavement with no visible distresses) based on the extent and the severity level of present distresses. As pavement condition worsens and distresses begin to appear, points are deducted, and the PACES rating drops. GDOT uses a rating of 70 for triggering the need for a thin resurfacing (1.5 in.). More information on the PACES distress types and severities can be found in Appendix A.
Cracking and rutting on each 5-m interval were first extracted using an automatic crack detection algorithm (Tsai et al., 2013) and rutting algorithm (Tsai et al., 2013) from the 3D pavement data. Cracking information, including type, severity level, and extent, in each 5-m interval was then reviewed and adjusted manually to ensure the distress information was correct. It is noted that load cracking is identified by its presence in the wheel path, as shown in Figure 5(a). However, because there are no markings on this private road, trucks are likely to travel outside of the wheel paths, as shown in Figure 5(b). Thus, adjustment was made to the cracking results to reflect the

true surface condition. Rutting was computed at approximately every 1 ft. and the 60th percentile rutting was reported for every 100 ft in each wheel path. The 60th percentile was chosen as the representative value because it appears to best reflect the manual PACES surveys conducted by GDOT. After reviewing and recording distresses on each 5-m interval, the information was then aggregated for each 100-ft segment, which is the sample unit length in PACES. Load cracking, block/transverse cracking, and rutting were the only distresses present on the test sections. A PACES rating was computed for each 100-ft segment based on the distresses. Tables 1 and 2 summarize the rating and distresses derived from the sensing data for each 100-ft segment of the inbound and outbound lane.
(a) Defined wheel path location (FDOT, 2015) (b) Need for adjusting wheel path locations Figure 5: Illustration of wheel path locations.

Table 1: PACES Summary - Inbound (WB)

Rutting (1/16") LC1 LC2 LC3 LC4 B/T PACES

LWP1 RWP2 (%) (%) (%) (%) (%) Rating

Conventional 0-1003

0

2

0 0 25 0 25 61

Pavement

100-2003 0

0

0 0 25 0 50 59

200-300 0

0 15 0 0 0 35 85

300-400 0

0 35 0 0 0 100 71

400-500 0

0 35 0 0 0 50 79

500-6003 0

0 35 0 0 0 55 79

600-700 0

0 35 10 10 0 35 72

700-8003 0

0 45 0 0 0 30 78

800-900 0

0 35 0 0 0 15 84

900-1000 0

0 40 0 0 0 60 76

South

1000-1100 0

0 30 0 0 0 35 82

African

1100-1200 0

0 55 0 0 0 10 81

Inverted

1200-1300 0

0 30 0 0 0 40 81

Pavement 1300-1400 0

0 20 0 0 0 45 83

GA Inverted 1400-1500 0

0 40 0 0 0 15 82

Pavement 1500-1600 0

0

0 0 0 0 60 89

1600-1700 0

1 25 0 0 0 25 85

1700-1800 0

0 15 0 0 0 30 86

1. LWP: left wheel path

2. RWP: right wheel path

3. Segments excluded from the comparison of three test sections.

Table 2: PACES Summary - Outbound (EB)

Rutting (1/16") LC1 LC2 LC3 LC4 B/T PACES

LWP1 RWP2 (%) (%) (%) (%) (%) Rating

Conventional 0-1003

1

1

0 0 55 0 0

50

Pavement

100-2003 1

3

0 0 65 25 0

48

200-300 0

1 15 0 15 0 35 64

300-400 0

1 35 10 0 0 60 76

400-500 0

2 25 0 10 0 20 72

500-6003 0

3

0 0 50 0 5

46

600-700 0

2 20 5 25 0 20 61

700-8003 0

3 10 5 30 0 20 56

800-900 0

1 15 10 0 0 35 80

900-1000 0

1 65 10 0 0 35 77

South

1000-1100 0

0 30 0 0 0 40 81

African

1100-1200 0

1 15 0 0 0 25 86

Inverted

1200-1300 0

1 65 0 0 0 25 78

Pavement

1300-1400 0

0 40 0 0 0 35 79

GA Inverted 1400-1500 0

2 45 0 0 0 15 78

Pavement 1500-1600 0

1 25 0 0 0 60 79

1600-1700 0

1 40 0 0 0 20 81

1700-1800 0

1 20 0 0 0 25 86

1. LWP: left wheel path

2. RWP: right wheel path

3. Segments excluded from the comparison of three test sections.

5. Data Analyses

Identification of abnormal segments

PACES ratings for each 100-ft segment in the inbound and outbound lane are shown in Figure 6

for reviewing the trend and identifying abnormal segments. The average rating of all the 38

segments is about 74.8. It is noted the ratings of the first two segments (marks +0 ft.~+100 ft.

and +100 ft.~ +200 ft. mark) close to the entrance are significantly lower than the other segments

in both directions, as shown in Figure 6. The distresses contributing to the deducts are rutting,

load cracking and block cracking. Figures 7 and 8 show the extent of load cracking and block cracking for each 100-ft segment. It is noted that the total load cracking (Levels 1-4) should not exceed 100%; block cracking is recorded separately with only the predominant severity level and should not exceed 100% as well. Severe load cracking (Levels 3 and 4) was observed on the two segments close to the entrance, as shown in Figures 7(a) and 7(b). This is due to the trucks' deceleration and acceleration when approaching the entrance. Truck braking and idling has a significant negative impact on pavement surface condition. Unlike typical load cracking residing only in the wheel paths, the load cracking in these two segments cover the entire lane, as shown in Figure 8. This suggests that loading has been applied across the entire lane and is likely the result of trucks not traveling directly in the lane marked. The distresses on these two segments do not represent the pavement condition under normal traffic patterns; thus, these two segments were excluded from further analysis. In addition, the PACES rating for the segments (between marks +500 ft.~+600 ft. and +700 ft.~+800 ft.) near a roadside parking space and the crossroad, is noticeably lower in the outbound direction. Severe cracking was observed before the roadside parking space and the crossroad, as shown in Figure 9. This may be the result of this section's experiencing more slowly moving loaded trucks due to that cross traffic. While severe cracking was observed mostly on the outbound direction between segments +500 ft.~+600 ft. and +700 ft.~+800 ft., this stretch in both directions (inbound and outbound) was excluded from further analysis.

PACES Rating

100

Conventional

South African

Georgia

90

80

70

60

50

40

30

20

10

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

Station (ft)

Outbound (EB)

Inbound (WB)

Figure 6. PACES rating in inbound and outbound lane.

Extent (%)

Conventional 120 100 80 60 40 20
0

South African

Georgia

BC LC4 LC3 LC2 LC1

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

Station (ft.) (a) Inbound lane.

120

Conventional

South African

Georgia

100

80 BC

60

LC4

40

LC3

LC2 20
LC1 0

Extent (%)

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

Station (ft.) (b) Outbound lane
Figure 7. Distresses in inbound and outbound lane.

Figure 8. Distresses near station +100 ft.
(a) Cracking near the roadside parking (b) Cracking near the cross road Figure 9. Severe load cracking near roadside parking space and the cross road.

Table 3 summarizes the PACES ratings and distresses for each test section after removing the

abnormal segments. Rutting, load cracking, and block cracking were observed on these sections.

The performance of each test section is discussed below.

Table 3. PACES summary for each test section

Conventional

South African IP

Georgia IP

Inbound Outbound Inbound Outbound Inbound Outbound

Load Cracking 1 32.5 % 29.2% 33.8% 37.5% 20 % 32.5%

2 1.7% 5.8 %

0

0

0

0

3 1.7% 8.3%

0

0

0

0

Block Cracking 1 49.2% 34.2% 32.5% 31.3% 32.5% 30%

Max Rutting (1/16") 0

2

0

1

1

2

Average Rating

77.8

71.7

81.8

81

85.5

81

Rating Range

71-85 61-80 81-83 78-86 82-89 78-86

Conventional Section The conventional section had diverse conditions with the ratings ranging from 61 to 85. The pavement condition in the outbound lane was significantly worse than the one in the inbound lane. The average rating in the inbound and outbound lane was and 77.8 and 71.7, respectively. These low ratings can be attributed to high levels of load cracking. In addition to Level 1, Level 2 and 3 load cracking was observed in some locations in the outbound lane. It is noted the load cracking can be attributed to the poor drainage or loss of edge support. In addition to load cracking, which has the most significant impact on the PACES rating for this section, Level 1 block/transverse cracking was also observed on all segments in both directions. Figures 10 and 11 show typical distresses in the conventional section with less severe load cracking and with significant high-level load cracking, respectively. Rutting was observed in the outbound lane only. The right wheel path had a rutting of 1/16 in. to 2/16 in., and the left wheel paths had no rutting measured, which means the rutting is less than (1/16" or 1.5 mm).

Figure 10. Example of typical distresses on the conventional section with less severe cracking. Figure 11. Example of typical distresses on the conventional section with severe load cracking.

South African Inverted Pavement Section The South African section had an average rating of 81.8 (inbound lane) and 81 (outbound lane). Cracking in both directions was limited to Level 1 for both load and block/transverse cracking. The extent of load cracking ranged from 15% to 65%; the segment at +1200 ft.~+1300 ft. in the outbound lane had the most load cracking. The extent of block cracking ranged from 10% to 45%. Figure 12 shows an example of the typical distresses on the South African section. The inbound lane performs slightly better than the outbound lane in terms of rating and load cracking. Approximately 33.8% of Level 1 load cracking was reported in the inbound lane, which is slightly less than the 37.5% in the outbound lane. This low severity cracking, accompanied by limited rutting, suggests that the South African section is sufficient to sustain cyclic travel of trucks, both unloaded and loaded.
Figure 12. Example of typical distresses on the South African Inverted Pavement Section Georgia Inverted Pavement Section The Georgia inverted pavement section performed like the South African section. The average rating is 85.5 (inbound lane) and 81 (outbound lane). Similar to the South African section, cracking in the Georgia section was limited to Level 1 load and Level 1 block cracking. Load cracking ranged from 0% to 45%, and block cracking ranged from 15% to 60%. Minor rutting (1/16 in. 2/16 in.) was observed on all segments in the outbound lane; the segments in the

inbound lane reported limited rutting. Figure 13 shows an example of the typical distresses on the Georgia section.
Figure 13. Example of typical distresses on the Georgia Inverted Pavement Section Figure 14 shows rutting reported on each 100-ft segment. In general, rutting was observed mainly in the outbound lane because of the trucks' heavy loads; very limited rutting was observed in the inbound lane. The segments highlighted in red circle are the ones excluded from the conventional section. Two segments (marked at +1100 ft.~+1200 ft. and +1200 ft.~+1300 ft.) in South African section had a rutting of 1/16 in. Compared to the Georgia section, the South African section had less rutting. This may imply the slushing could increase the stiffness of GAB. Further investigation, such as with a Falling Weight Deflectometer, is needed to verify the stiffness.

Max Rutting (1/16")
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

Conventional 4 3 2 1 0

South African

Georgia

Station (ft)

Inbound (WB)

Outbound (EB)

Figure 14. Max rutting for every 100-ft segments.

6. Summary In 2001, three pavement test sections, composed of conventional pavement, South African inverted pavement, and Georgia inverted pavement, were constructed on an entrance road to the Martin-Marietta Morgan Quarry in Morgan County. Since its operation, there had been no quantitative evaluation of the performance (e.g., cracking and rutting) on these test sections, although a visual inspection was conducted in 2006. This year, Georgia Tech's sensing vehicle, equipped with a laser crack measurement system (LCMS), GEO3D cameras, GPS, IMU (inertial measurement system), and DMI (distance measuring instrument), was used to collect data to quantitatively evaluate the pavement condition on these sections according to GDOT's PACES standards. Data collection was conducted on April 8, 2016. The data was processed using developed algorithms and a manual review to extract distress information for every 100-ft segment. Two segments (marked at +0 ft.~+100 ft. and +100 ft. ~+200 ft.) near the entrance and one segment (marked at +500 ft.~+600 ft. and +700 ft.~+800 ft.) near the crossroad, were excluded from further analysis because the stop-and-go traffic pattern in these segments had significant impact on the conditions. The pavement condition on the three test sections is summarized as follows:

The conventional section had diverse conditions with ratings ranging from 61 to 85. The average rating is about 75 after 15 years in service. Rutting, Level 1 block cracking, and severe load cracking (Levels 2 and 3) was observed on this section. Level 1 load cracking ranging from 15% to 65% was observed in the outbound lane where the loaded trucks travel, while lesser load cracking was observed in the inbound lane. Similarly, rutting in the outbound lane is higher than in the inbound lane. Thus, the average rating (71.7) in the outbound lane is significantly lower than the rating (77.8) in the inbound lane.
Both inverted pavement sections performed better than the conventional section. The average ratings in the South African and Georgia sections were 81.4 and 83.3, respectively. Only Level 1 load cracking (not severe), block cracking, and minor rutting was observed in these two sections.
It is noted that the South African section had a lower rating (81.4) than the Georgia section (83.3). The difference between the inbound lane and outbound lane is smaller, compared to the other two sections. There was very limited rutting observed on the South African section in both directions, except for two segments in the outbound lane.
The Georgia inverted pavement section performed similar to the South African section. The average ratings were 85.5 and 81 in the inbound lane and outbound lane, respectively. Cracking in the Georgia section was limited to Level 1 load cracking (20% to 45%) and Level 1 block cracking (15% to 65%). It is noted that rutting (1/16 in. 2/16 in.) was observed on all segments in the outbound lane.
In all three sections, the condition in the outbound lane was worse than in the inbound lane because of the loaded trucks traveling in the outbound lane. Significant difference (more than 6 points in rating) can be observed on the conventional section, while the South African section has the least difference in both directions. This may imply the slushing technique could help in the stiffness of GAB. Further investigation (e.g., FWD) is needed to study the stiffness of each section.

References Cortes, D. and Santamarina, J. C. (2012) "Inverted Base Pavement in LaGrange, Georgia: Characterization and Preliminary Numerical Analyses" Proceeding of the 91st Transportation Research Board Annual Meeting, Washington D.C.
GDOT. (1993). "Pavement condition evaluation system (PACES)" Georgia Department of Transportation, Office of Maintenance. Atlanta, GA.
Tsai, Y., Li, F. and Wu, Y. (2013) "A new rutting measurement method using emerging 3D linelaser-imaging system." International Journal of Pavement Research and Technology: 667.
Tsai, Y., Kaul, V., Yezzi, A. (2013) "Automating the Crack Map Detection Process for Machine Operated Crack Sealer."Automation in Construction, Vol. 31, 10-18
Florida Department of Transportation. "2015 Flexible Pavement Condition Survey Handbook. http://www.dot.state.fl.us/statematerialsoffice/administration/resources/library/publications/resea rchreports/pavement/flexiblehandbook.pdf. Accessed June 2016.

Appendix A: GDOT PACES Definitions
Load Cracking
Load cracking is a product of constant loading by vehicle tires on the pavement surface. It is present in four severity levels. At the first level, longitudinal cracks begin to form in the wheel paths with short transverse cracks spurring from the main longitudinal crack.
At severity level two, there are typically two longitudinal cracks within the wheel path. As cracks spur from the original longitudinal crack, loading causes them to connect with other longitudinal cracks. Some polygons will form from cracks in the pavement surface.
At severity level three, there are typically three or more longitudinal cracks in the wheel path. They are all connected by transverse cracks. This forms a network of polygons in the wheel path. The polygons forming on the pavement surface is indicative of the base crumbling from being unable to carry the applied loads.
At severity level four, loading has caused more damage and the polygon size has reduced. At this severity, the polygons have begun to pop out of the surface. As more polygons pop-out, potholes form from the holes left behind.
Block/Transverse Cracking
Block/Transverse cracking is a result of pavement weathering. As temperature changes, the pavement expands and contracts. This constant movement leads to cracks in the pavement surface. Block cracking is not confined to a particular area in the wheel path. At the lowest severity level, mostly transverse cracks are seen in the pavement surface. At this severity, the extent is computed as the total length in feet of all block/transverse cracks in the section. If the length of cracks exceeds 100 feet, the section is said to have 100% block/transverse cracking.

At severity two, block/transverse cracking develops definite block patterns. The cracks are typically wider than those at level one but may not be wide enough for sealing. Severity level two block/transverse cracking is measured in terms of area of coverage. Because it isn't load related, this type of cracking typically covers the entire travel lane. The extent of cracking is determined by how much of the 100-ft sample area is covered by severity level two block/transverse cracking.
At severity 3 the size of the blocks has reduced and the crack width has increased. The cracks are typically wide enough to require sealing. There may also be evidence of spalling around the cracks at this severity.

GDOT Final Report on Granular Bases
APPENDIX B LaGrange By-Pass Road Field Measurements
Report

LaGrange Bypass Inverted Pavement Condition Evaluation Report
YiChing Wu, Yi-Chang Tsai, Geoffrey Price
1. Background
An inverted pavement (IP) structure differs from a traditional asphalt construction in that the lower, supporting pavement layers are much more rigid than the upper surface layers. This type of pavement structure has shown to be more cost-effective and more resistant to traffic loading than traditional Portland Cement Concrete (PCC) and hot mix asphalt (HMA) designs (Lewis et al., 2012). Although the pace of adopting inverted pavements in the United States has been slow, the Georgia Department of Transportation (GDOT) has taken the lead in this regard by building two IP test sections to observe their actual performance under local conditions, materials, and construction practices. The first IP test section was built on a private access road at the Lafarge Building Materials quarry in Morgan County, Georgia, in 2001. Based on the good performance observed at this test site, GDOT built a 3,400-ft long IP test section on Pegasus Parkway in LaGrange, Georgia. The construction began in January 2008 and was completed in April 2009 (Cortes & Santamarina, 2011). Detailed data (including laboratory and field tests on the subgrade, the cement-treated base, the asphalt concrete, etc.) before, during, and after construction were collected to gain a better understanding of the internal behavior and performance of this pavement structure. Despite the detailed information collected at this site, there has not been any survey conducted on this test section to quantitatively evaluate its performance since it opened to traffic in 2009.
2. Scope and Objective
The objectives of this study are to 1) critically evaluate the pavement condition of this test section using quantitative measures defined in the Pavement Condition Evaluation System (PACES) developed by the Georgia Department of Transportation (GDOT, 2007), and 2) establish quantitative baseline condition data for future deterioration analysis. With these objectives in mind, a condition evaluation was performed on the outside lanes (both Eastbound and Westbound lanes) of the test section.
3. Site Description
Pegasus Parkway is a two-lane road located near the LaGrange Callaway Airport in Troup County, as shown in Figure 1a. It is an industrial parkway intended to serve the growing car manufacturing industry in Southwest Georgia. The test section is approximately 3,400-feet long between the 280+00 and 314+00 mark, as shown in Figure 1b. Jointed plain concrete pavement (JPCP) was constructed at both ends of the test section. Figure 2 shows the pavement structures for the IP test section and the PCC section. These pavement structures were designed based on the 1972 AASHTO interim pavement design guide. They were designed to sustain approximately 4.78 million trucks in a 20-year design life, which was estimated based on an

initial one-way traffic of 7,000 vehicles per day, a final one-way traffic of 11,700 vehicles at the end of design life, and 7% truck traffic (Cortes & Santamarina, 2011).

(a) Site Location

(b) Test Section Location

Figure 1. Inverted pavement test section in LaGrange, GA

Figure 2. Pavement structures for IP test section and PCC section

4. Data Collection Georgia Tech's sensing vehicle, equipped with a laser crack measurement system (LCMS), GEO3D cameras, GPS, an IMU (inertial measurement system), and a DMI (distance measuring instrument), was used for collecting 3D pavement data, 2D images, and GPS data for extracting pavement distresses based on PACES (GDOT, 1993) standards. Data collection was performed on June 30, 2016, on the outside lanes (both Eastbound and Westbound) of the test section. Prior to data collection, Dr. James Frost's research team marked the test section every 100-ft for use in a PACES survey. A diagram of the marking scheme is shown in Figure 3. A total of thirty-four, 100-ft segments were marked on the pavement. The Westbound (WB) transition point for the IP section will be referred to as the 0+00-ft mark, and the Eastbound (EB) transition point from IP to JPCP will be referred to as the 34+00-ft mark. The Georgia Tech sensing vehicle (see Figure 4), followed by a GDOT traffic control crew, was driven at approximately 30 mph on the outside lane to collect 3D pavement data, video log images, GPS data, etc. The 3D pavement data was collected at a resolution of 5-mm, 1-mm, and 0.5-mm for the x (driving direction), y (transverse direction), and z (depth) directions, respectively, with a full-lane width coverage (i.e., 12 ft). To facilitate better coverage of the access road, two runs of data were collected, and the run with less lateral movement (i.e., better coverage of the marked lane) was processed and analyzed.
Figure 3. Illustration of marking 100-ft segment
Figure 4. Georgia Tech sensing van (GTSV)

5. Data Processing
Distresses on the test section were extracted from the sensing data based on GDOT's PACES survey standards. PACES establishes standardized nomenclature for distresses and defines their respective severity levels and measurement methods for asphalt concrete pavement. There are ten distresses surveyed in PACES including: 1) rutting, 2) load cracking (LC), 3) block/transverse cracking (B/T), 4) reflection cracking, 5) raveling, 6) edge distress, 7) bleeding and flushing, 8) corrugation and pushing, 9) loss of pavement section, and 10) patches and potholes. Cracking (load cracking and block cracking) and rutting were the only distresses observed on this test section. More information on the cracking defined in PACES (types, extent and severities) can be found in Appendix A. Cracking and rutting on each 5-m interval were first extracted using an automatic crack detection algorithm (Tsai et al., 2013) and rutting algorithm (Tsai et al., 2013) from the 3D pavement data. Cracking information, including type, severity level, and extent, in each 5-m interval was then reviewed and adjusted manually to ensure the distress information was correct. Rutting was computed at approximately every 1 ft. This data was then aggregated for each 100-ft segment, which is the sample unit length in PACES. A PACES rating on a scale of 0 to 100 (with 100 representing pavement with no visible distresses) was computed for each 100-ft segment based on the extent and the severity levels of distresses present. Tables 1 and 2 summarize the rating and distresses derived from the sensing data for each 100-ft segment of the inbound and outbound lanes.

Table 1: PACES Summary (EB)

Station

Rutting (1/16")

Load Cracking Block Cracking

LWP*

RWP*

Level 1 (%)

Level 1 (%)

0-100

2

1

0

0

100-200

2

1

0

0

200-300

1

1

5

0

300-400

1

0

10

0

400-500

2

1

5

0

500-600

2

1

10

0

600-700

2

1

10

0

700-800

2

1

5

0

800-900

2

1

10

5

900-1000

1

1

0

0

1000-1100

2

2

20

0

1100-1200

2

2

5

0

1200-1300

2

1

0

0

1300-1400

3

1

5

0

1400-1500

3

1

5

0

1500-1600

3

1

0

0

1600-1700

3

2

30

0

1700-1800

3

2

15

0

1800-1900

3

2

45

0

1900-2000

2

2

0

0

2000-2100

2

2

0

0

2100-2200

2

1

0

0

2200-2300

4

1

0

0

2300-2400

4

1

0

0

2400-2500

2

1

0

0

2500-2600

2

1

0

0

2600-2700

2

1

0

0

2700-2800

2

1

0

0

2800-2900

2

1

0

0

2900-3000

2

1

0

5

3000-3100

2

1

0

0

3100-3200

2

1

0

0

3200-3300

1

2

0

0

3300-3400

1

2

0

0

Average

2.1

1.2

5.3

0.3

MIN

1

0

0

0

MAX

4

2

45

5

*LWP = Left Wheel Path

*RWP = Right Wheel Path

PACES Rating
98 98 96 94 94 92 92 94 90 100 90 94 98 94 94 98 88 91 83 98 98 98 95 95 98 98 98 98 98 96 98 98 98 98 95.3 83 100

Table 2: PACES Summary (WB)

Station

Rutting (1/16")

LWP*

RWP*

0-100

2

1

100-200

2

1

200-300

2

1

300-400

2

0

400-500

3

0

500-600

3

0

600-700

3

0

700-800

4

0

800-900

2

1

900-1000

3

0

1000-1100

3

1

1100-1200

3

1

1200-1300

3

1

1300-1400

2

2

1400-1500

2

2

1500-1600

3

1

1600-1700

3

2

1700-1800

3

2

1800-1900

3

2

1900-2000

2

1

2000-2100

3

1

2100-2200

3

1

2200-2300

3

2

2300-2400

3

2

2400-2500

3

2

2500-2600

2

2

2600-2700

3

1

2700-2800

3

0

2800-2900

4

1

2900-3000

4

2

3000-3100

4

1

3100-3200

3

1

3200-3300

2

0

3300-3400

2

0

Average

2.8

1.0

Min

2

0

Max

4

2

*LWP = Left Wheel Path

*RWP = Right Wheel Path

Load Cracking Level 1 (%)
15 10 15 5 0 0 5 5 0 0 0 0 0 5 20 0 0 0 0 0 0 0 10 5 0 15 0 0 0 0 5 0 40 35 5.6 0 40

Block Cracking Level 1 (%)
0 0 20 0 0 5 10 5 5 0 0 0 0 0 0 5 0 0 0 5 0 0 0 10 10 0 0 5 10 0 5 0 0 0 2.8 0 20

PACES Rating
91 92 85 94 98 96 94 89 96 98 98 98 98 94 90 96 98 98 98 96 98 98 92 90 94 91 98 96 91 95 89 98 85 87 94.1 85 98

6. PACES Data Analysis
PACES Rating
The test section has performed well with an overall average rating of 94.7 after 7-year of service. Of the 64 segments (34 in each direction), only 6 segments had a rating less than 90. It is noted that on average, the pavements in Georgia reach a rating of 70 in 10.6 years (Tsai et al., 2016). Based on typical pavement deterioration observed on Georgia's pavements, the test section with a rating of 94.6 can last approximately 8 more years before the rating drops to 70, which triggers the need for resurfacing. PACES ratings for each 100-ft segment in two directions (EB and WB) are shown in Figure 5. In general, the ratings in the EB are slightly higher than those in the WB. The average rating in the EB and WB directions is 95.3 and 94.1, respectively. This may be because traffic loads in the WB are heavier than those in the EB; traffic load data can be collected to better understand the pavement performance in the EB and WB lanes. The rating in the EB ranges from 83 to 100. The segments between the 16+00-ft and 20+00-ft marks had lower ratings (less than 90) compared to the other segments. The segments between the 19+00-ft and 34+00-ft marks had relatively high ratings (greater than or equal to 95) because no cracking or minimum cracking was observed on these segments. The rating in the WB lane ranges from 85 to 98. The segments with lower ratings are at the two ends of the test section (the 0+00-ft to 3+00-ft marks and the 30+00-ft to 34+00-ft marks), especially on the beginning of WB lane (30+00-ft to 34+00-ft marks) when transitioning from the bridge to the IP test section.
100 90 80 70 60 50 40 30 20 10 0

PACES Rating

0-100 100-200 200-300 300-400 400-500 500-600 600-700 700-800 800-900 900-1000 1000-1100 1100-1200 1200-1300 1300-1400 1400-1500 1500-1600 1600-1700 1700-1800 1800-1900 1900-2000 2000-2100 2100-2200 2200-2300 2300-2400 2400-2500 2500-2600 2600-2700 2700-2800 2800-2900 2900-3000 3000-3100 3100-3200 3200-3300 3300-3400

Station (ft)

EB

WB

Figure 5. PACES rating in the EB and WB

Cracking
There were only Level 1 load cracking and limited Level 1 block cracking observed on the test section. Figure 6 shows examples of the cracking observed on the test section; the cracks were 4-5 mm-wide, single-line cracks. Of the 68 segments (34 in each direction), 28 segments exhibited load cracking, while only 14 segments exhibited block cracking. This level of cracking indicates that the pavement is just beginning to deteriorate and the cracks are not extensive yet. The cracking extent values for both load and block cracking in the EB and WB lanes are shown in Figures 7a and 7b. Of the EB segments (34 segments), 14 segments exhibited load cracking (ranging from 5% to 45%) and the average extent for the entire EB lane (34 segments) is approximately 5.3%. It is noted that the load cracking was observed only on the first half of the test section (between the 2+00 and 19+00 marks); there was no load cracking on the second half of the section (between the 19+00 and 34+00 marks) where the road is in a tangent (straight) with a -3% downhill vertical grade. The segments approaching the 16+00-ft to 19+00-ft marks from the EB direction have significantly higher cracking than the other segments. This higher presence of cracking may be attributed to the horizontal curve in a downhill grade from the 16+00-ft to 19+00-ft marks. As drivers approach the horizontal curve, they will likely decelerate to safely navigate through the curve. The deceleration along the horizontal curve, especially by trucks, may partially cause the increased damage to the pavement in that area. There was minimum block cracking (approximately 0.3%) in the EB lane; only two segments were observed with 5% of block cracking. Compared to the EB lane, the WB lane segments had similar load cracking in terms of the extent and more block cracking. The average load cracking extent in the WB lane is approximately 5.9%; however, the cracks were distributed differently. The load cracking was observed across the length of the test section with the segments near the west side (the 32+00 to 34+00 marks) showing the highest extents of load cracking. This may be attributed to the vehicle's dynamic loading when moving from the bridge to the IP section. Block cracking was observed on a total of 12 segments ranging from 5% to 20%. There was no load cracking observed on the curved section (the 16+00-ft to 19+00-ft marks). This may be because the curve is an uphill grade from the WB direction. The vehicle does not need to decelerate excessively to navigate through the curve. Further analysis is needed to better understand the pavement performance with respect to roadway geometry (e.g., horizontal curve, vertical grade, and super-elevation) as well as cut/fill.
Figure 6. Examples of load cracking and block cracking observed on the test section

Extent (%)

0-100 100-200 200-300 300-400 400-500 500-600 600-700 700-800 800-900 900-1000 1000-1100 1100-1200 1200-1300 1300-1400 1400-1500 1500-1600 1600-1700 1700-1800 1800-1900 1900-2000 2000-2100 2100-2200 2200-2300 2300-2400 2400-2500 2500-2600 2600-2700 2700-2800 2800-2900 2900-3000 3000-3100 3100-3200 3200-3300 3300-3400

50 45 40 35 30 25 20 15 10
5 0

Station (ft)
(a) Cracking in the EB

Load Cracking Block Cracking

50 45 40 35 30 25 20 15 10
5 0

Extent (%)

0-100 100-200 200-300 300-400 400-500 500-600 600-700 700-800 800-900 900-1000 1000-1100 1100-1200 1200-1300 1300-1400 1400-1500 1500-1600 1600-1700 1700-1800 1800-1900 1900-2000 2000-2100 2100-2200 2200-2300 2300-2400 2400-2500 2500-2600 2600-2700 2700-2800 2800-2900 2900-3000 3000-3100 3100-3200 3200-3300 3300-3400

Station (ft)

Load Cracking Block Cracking

(b) Cracking in the WB Figure 7. Extent of Cracking in the EB and WB

Rutting
Moderate rutting was measured on the test section; the average rutting in the EB and WB lanes is approximately 2/16 in. and 3/16 in., respectively. Figure 8 shows the maximum rut depth (between left and right wheel paths) of each 100-ft segment in both the EB and WB lanes. In general, rutting in the EB lane was slightly lower than that in the WB lane. For the EB lane, only 7 segments had a rut depth greater than or equal to 3/16 in., and 6 of them were reported on the segments between the 13+00-ft and 19+00-ft marks, where there is, also, a

higher extent of load cracking. For the WB lane, however, 23 of the 34 segments exhibited rutting depths of 3/16 in. or greater. In particular, all segments between 28+00 and 31+00 showed a high rut depth (1/4 in.). It is noted that the rut depth in the left wheel path (inside wheel path) was higher than in the right wheel path (the outside wheel path) in both EB and WB lanes. Further analysis needs to be done to assess the potential causes (e.g., superelevation, cut/fill, etc.) of higher rutting in the left wheel path.
6
5
4
3
2
1
0

Max Rut Depth (1/16 in.)

0-100 100-200 200-300 300-400 400-500 500-600 600-700 700-800 800-900 900-1000 1000-1100 1100-1200 1200-1300 1300-1400 1400-1500 1500-1600 1600-1700 1700-1800 1800-1900 1900-2000 2000-2100 2100-2200 2200-2300 2300-2400 2400-2500 2500-2600 2600-2700 2700-2800 2800-2900 2900-3000 3000-3100 3100-3200 3200-3300 3300-3400

Station (ft)

EB

WB

Figure 8. Maximum rutting in the EB and WB

7. Summary
Through the use of the Georgia Tech Sensing Van, 3D pavement and 2D video log data were collected on the section of inverted pavement on Pegasus Parkway in LaGrange, Georgia. After processing these data for cracking and rutting information, the distress information for every 100 feet was aggregated. From this data, the PACES score was determined according to GDOT specifications. The scores indicate that since being opened to traffic in 2009, the IP section has performed well:
The test section has performed well with an overall average rating of 94.7 after 7 years of service. Of the 64 segments (34 in each direction), only 6 segments had a rating less than 90. This is especially notable when considering, on average, Georgia's pavements reach a rating of 70 in 10.6 years.
Overall, the test section showed limited and low-severity (Level 1) load cracking and block/transverse cracking and moderate rutting. The average extent for load cracking and block cracking is approximately 5.4% and 1.5%, respectively. Of the 68 segments (34 in

each direction), 28 segments exhibited load cracking (ranging from 5% to 45%), while only 14 segments exhibited block cracking (ranging from 5% to 20%). The load cracking was distributed differently in the EB and WB lanes. For the EB lane, the load cracking was observed only on the first half of the test section (between the 2+00 and 19+00 marks). The segments approaching the 16+00-ft to 19+00-ft marks from the EB direction had significantly higher cracking than the other segments. This higher presence of cracking may be attributed to the horizontal curve in a downhill grade from the 16+00-ft to 19+00-ft marks. For the WB lane, the load cracking was observed across the length of the test section with the segments near the west side (the 32+00 to 34+00 marks) showing the highest extent of load cracking. This may be attributed to the vehicle dynamic loading when moving from the bridge to the IP section. The WB lane exhibited more block/transverse cracking than the EB lane. Only two segments in the EB lane exhibited blocking cracking, while 12 segments in the WB lane were reported with block cracking. This may be attributed to the heavy truck loads in the WB lane. Moderate rutting was measured on the test section; in general, the WB lane had more rutting than the EB lane. The average rutting in the EB lane and WB lane was approximately 2/16 in. and 3/16 in., respectively. A 3/16 in. of rutting was reported between the 13+00-ft and 19+00-ft marks in the EB lane, where the load cracking was also high. Further study is needed to determine the causes of higher rates of rutting and cracking in these segments. It is noted that the rut depth in the left wheel path (inside wheel path) was higher than that in the right wheel path (outside wheel path) in both EB and WB lanes. Further analysis needs to be done to assess the potential causes.
Using sensing technology, the cracking and rutting information for all 100-ft segments was fully captured. Through thorough analysis, the current condition of cracking and rutting for the IP section has been established. The test section has performed well after 7 years of service; however, the segments with higher rates of cracking and rutting need to be monitored and studied. With this baseline information, in-depth analysis on crack deterioration can be performed in the future to assess changes in crack characteristics, such as length, width, and depth. In addition, the growth of rutting in terms of both depth and length can be analyzed to determine any problems in base or surface layers. Through this analysis, the performance of the IP section can be analyzed over time to evaluate how well this new pavement structure performs in comparison to a conventional asphalt pavement structure.

References
Cortes, D. and Santamarina, C. Inverted Base Pavement in LaGrange, Georgia: Characterization and Preliminary Numerical Analyses. TRB 90st Annual meeting. 2011. http://www.dot.ga.gov/BuildSmart/research/Documents/Inverted_Base_Pavement_in_LaGrange _GA.pdf
GDOT. (2007). "Pavement condition evaluation system (PACES)" Georgia Department of Transportation, Office of Maintenance. Atlanta, GA.
Lewis, Dwane E., Keith Ledford, and E. I. T. Tanisha Georges. "Construction and Performance of Inverted Pavements in Georgia." TRB 91st Annual meeting. 2012.
Tsai, Y., Li, F., and Wu, Y. (2013) "A new rutting measurement method using emerging 3D linelaser-imaging system." International Journal of Pavement Research and Technology: 667.
Tsai, Y. and Wu, Y. (2016) "Study of Georgia's Pavement Deterioration/Life and Potential Risks of Delayed Pavement Resurfacing and Rehabilitation." Georgia Department of Transportation, Atlanta, Georgia.

GDOT Final Report on Granular Bases
APPENDIX C Inverted Base Pavement Presentation Materials

GDOT Final Report on Granular Bases
Invited seminar given at AFP70 Mineral Aggregates Sub-committee Special Session at 2016 TRB Annual Meeting
Washington D.C. Presenter: David Frost, Georgia Tech

5/7/2017

Performance Assessment of Georgia Inverted Pavement
Test Sections
David Frost, Georgia Tech
(with contributions from J. Cardosa, D. Cortes, S. Hanumasagar, D. Jared, D. Lewis,
E. Papadopoulos, C. Santamarina, J. Tsai)
January 11th 2016

The US Road System is vast and suffers from insufficient funding.

Vast network

Depleted funding Federal Funds
$2.0b

Georgia IBP

Wikipedia.org
Poor condition

$1.0b

$0.0b

GDOT

`04 `06 `08 `10 `12

Solution Sources
Innovative designs Optimal use of materials
(Adapted from Papadopoulos, 2015)

An inverted base pavement (IBP) is an innovative technology that can optimize the use of materials.

Georgia IBP

Conventional Flexible Pavement Stiffness
asphalt concrete

Inverted Base Pavement Stiffness
asphalt concrete

asphalt base

unbound aggregate base

unbound aggregate base

cement-treated base

subgrade

subgrade

Stiffness contrast between layers Granular base : close to load demand for exceptional performance
(After Papadopoulos, 2015)

South Africa has developed and utilized inverted base pavements for half a century.
Georgia IBP

Crushed stone base pavement development

Slushing

Accelerated Testing

G1 Base

G2 Crushed Stone Bases

Crusher Run

Macadam / gravel 1940 1950 1960

1970

Jooste & Sampson (2005) 1980

No Slushing Slushing after compaction

www.Vti.se

(After Papadopoulos, 2015)

Kleyn, 2012

% passing Resilient modulus [MPa] Reps. to failure [103] Deflection [mm]

Top quality unbound aggregate base is the fundamental block of IBPs.

Georgia IBP

Fines Shape

South Africa G1 base LL<25%, PI<4
flackiness (sphericity) <35%

CALTRANS base Sand Equivalent <21
N/A

GDoT GAB Sand Equivalent <20
elongated particles <10%

Density

86-88% of apparent solid density (~102% mod Proctor)

95% of CTM 231

98% mod. Proctor

100

GDoT

80

CALTRANS

G1 South Africa 60

40

20
0 0.01

1mm= 39mils

0.1

1

10 100

Grain diameter [mm]

900 Crushed stone
600
300
Gravel 0
0 100 200 300 400 mean stress p [kPa]
(After Papadopoulos, 2015)

US experience with inverted base pavements had also been long but sparse.

Georgia IBP

New Mexico (1960s) USACE (1970s) Georgia Tech (1980s) Louisiana (1990s) Morgan County GA quarry (2000s) Lagrange GA bypass (2000s) Bull Run VA highway (2010s) Pineville NC quarry (2010s)

2,000 1,500 1,000

Accelerated Testing, LA IBP

500 Conventional

pavement

0

0

1

2

3

4

5

Structural Number SN

0.9 FWD measurements

Conventional

0.6

Morgan Co

0.55 IBP-Lagrange
0.3

IBP-Morgan Co 0.21

0.27

0.0

Data from Lewis et al 2009

(Adapted from Papadopoulos, 2015)

1

5/7/2017

Georgia (led by GDoT supported activities) have continuously moved towards greater understanding of potential of IBP.

Georgia IBP

Progression of these efforts summarized within 5 Phases:

Phase I: Morgan County Quarry Test Section (2000 to present)
Phase II: LaGrange Bypass Test Section including detailed construction documentation (2008 to present)
Phase III: Multi-faceted lab testing - field testing compaction modelling study (2008 to 2015)
Phase IV: Field pavement distress and lab "slushing" simulation studies (2015 present)
Phase V: Proposed pooled-fund study on Inverted Base Pavements (solicitation posted project in planning stage)

Phase I: multiple test sections with well documented loading over 15 year period.

Georgia IBP

Seven Islands Road

Quarry Entrance Road
Station 0+50 through Station 10+00 Conventional Haul Road
Station 10+00 through Station 14+00 South African Base
Station 14+00 through Station 18+00 Georgia Base
Construction completed in 2001

Phase I: multiple test sections with well documented loading over 15 year period.

Georgia IBP

Performance Evaluation: November, 2006 853,719 ESAL's (63.5% designed life cycle)

(Data from Lewis et al.., 2009)

No rutting and no cracking of asphaltic layer observed in IBP sections even as recently as 2015

Phase II: fully documented construction project provides basis for long-term IBP performance assessment.

Georgia IBP

LaGrange By-Pass
Test section: 0.65 miles long 2 lanes PCC typical section IBP test section
Construction completed in 2009

3.

5

9.

"6

5

"

"

1

1

0

0

" 6

"6

"

"

Elevation [ft] D epth (cm) Depth (cm) D epth (cm) D epth (cm )

Phase II: fully documented construction project provides basis for long-term IBP performance assessment.

Georgia IBP

780

760
Cut 740
Cut Fill 720

700

680 Fill
660

640

280

285

290

295

300

305

310

Station

Specific Surface LL & m/c

Dry Density

GSD

P-wave Velocity

Laboratory Characterization of Subgrade
(Data from Santamarina, 2015)

Phase II: fully documented construction project provides basis for long-term IBP performance assessment.

Georgia IBP

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

(Data from Santamarina, 2015)

Extensive lab and field characterization studies for various layers

2

5/7/2017

[m/s] Stiffness

Phase III: comprehensive laboratory field

numerical study that expanded understanding

of IPB component performance.

Georgia IBP

Compaction

Lab Characterization

In situ testing

Inverted Base Pavements

Study completed in 2014

Mechanistic analysis

(After Papadopoulos, 2015)

Phase III: current laboratory methods do not

account for the complex nature of aggregate

base stiffness.

Georgia IBP

Inherent Anisotropy

Stress-Dependent Stiffness

F

Cortes 2010

Force
In-chamber compaction. Independent control of the 3
principal stresses. P-wave instrumentation in each
direction.
(After Papadopoulos, 2015)

Phase III: stress ratio has small influence on

the small-strain stiffness as long as the

material is away from failure.

Georgia IBP

Horizontal propagation x 2000 1500 1000

Isotropic Compression Triaxial Extension

500

0

0

500 1000 1500

Horizontal Stress [kPa]

Triaxial Compression

Characterization of unbound aggregate base stiffness:

Granular Bases: inherent & stress-induced anisotropy exist.

Mmax : function of normal stress

(Adapted from Papadopoulos, 2015)

Loading conditions: almost no effect on Mmax

Phase III: soil compaction is omnipresent in

most geotechnical construction and has

known impact on performance.

Georgia IBP

Inadequate compaction results

Post-placement changes in material

Pavement Interactive
Lab-field discrepancies

(Adapted from Papadopoulos, 2015)

test-llc.com



Heavyequipment.com

Phase III: an extensive lab study was conducted to assess the compaction process in terms of stiffness.

Georgia IBP

Specimens compacted using Modified Proctor (Adapted from Papadopoulos, 2015) Stress-dependent stiffness for different water contents

Piezocrystal

Signal Generator

Digital Oscilloscope

Effect of compaction on granular base stiffness:



: not sufficient to assess compaction

Granular base stiffness not affected by water content

Water content affects permanent deformation

Velocity changes reflect accumulation of deformation

Phase III: two tests were conceived to measure the stiffness of as-built aggregate bases.

Georgia IBP

Measure the stiffness of as-built unbound aggregate bases

Crosshole

Uphole

Dump Truck

Dump Truck

AC GAB
CTB

Piezopads

AC GAB
CTB

Accelerometer Actuator

Subgrade

Subgrade (After Papadopoulos, 2015)

3

5/7/2017

Phase III: successive forward simulations were conducted to determine the state of stress in the pavement.
AC GAB
CTB
Subgrade

Georgia IBP

Two setups to capture anisotropic stiffness 2 case histories

In situ GAB: anisotropic stress-dependent stiffness

Field values lab values:

1. Preconditioning

2. Compaction method (Field vs. lab)

Field-Compacted GAB: great stiffness

(Adapted from Papadopoulos, 2015)

Phase III: numerical simulations were

conducted to compare IBPs to conventional

pavements.

Georgia IBP

(Adapted from Papadopoulos, 2015)

Conventional

Inverted Base Pavement

Low structural capacity

asphalt concrete

160 mm

asphalt concrete
aggregate base GAB

25mm 150mm

aggregate base GAB

200mm

cement-treated base CTB

250mm

High structural capacity

Mechanistic analysis

asphalt concrete

190mm

asphalt concrete
aggregate base GAB

100mm 150mm

aggregate base GAB

305mm

cement-treated base CTB

300mm

Phase III: aggregate base stiffness in IBPs is

high due to the confinement provided by the

CTB.

Georgia IBP

(Adapted from Papadopoulos, 2015)

AC
190mm 305mm
85 105
130

AC 240 90
390

CTB

100mm 150mm 300mm

Tangent Vertical Young's modulus Ev (MPa)

Constitutive model: Anisotropy, stress-dependency, shear softening
Inverted base pavements: Unique load-bearing mechanism
Granular base: Underutilized in conventional pavements Great contribution in inverted base pavements
Thin asphalt layers: Potential for economic savings Caution when subjected to strong shear

Phase IV: IBP pavement surface distress study using imaging and LiDAR.

Georgia IBP

3D Laser Imaging System

Range Image

Detected Crack Map

The GDOT's Pavement Condition Evaluation System (PACES) is used for conducting the annual asphalt pavement condition surveys in Georgia. Ten different distress types and their severity levels are defined. Four of them are crack related distresses: load cracking, B/T cracking, edge distress, and reflective cracking.
(Courtesy of James Tsai)

Phase IV: IBP pavement surface distress study using imaging and LiDAR.

Georgia IBP

Load cracking is caused by repeated heavy loads and always occurs in the wheel paths:
Severity Level 1 usually starts as single longitudinal cracks in the wheel path.
Severity Level 2 has a single or double longitudinal crack with a number of 0-2 feet transverse cracks intersecting.
Severity Level 3 shows an increasing number of longitudinal and transverse cracks in the wheel paths. This level of cracking is marked by a definite, extensive pattern of small polygons.
Severity Level 4 has the definite "alligator hide" pattern but has deteriorated to the point that the small polygons are beginning to pop out.
(Courtesy of James Tsai)

(a) Severity Level 1 (b) Severity Level 2 (c) Severity Level 3 (d) Severity Level 4

Phase IV: laboratory study of slushing effect on microstructure and load transfer.
Georgia IBP

Laboratory Simulation of Slushing Study of evolution of aggregate shape, pore structure and load path during slushing

Characterization using UI Aggregate Image Analyzer

=

Recon(sbt)ruPcatrioticnleosf Real Particle and P(co)rePoStrreusctures Using Optical Microscopy, Image Mosaic and Serial Sectioning to create high-fidelity geo-structures

Numerical simulations of shortest load path and highest contact forces

4

5/7/2017

Phase V: pooled fund study to leverage current

knowledge and interest to expedite implementation

of IBP design specifications for state DOT's.

Georgia IBP

GDoT proposed Pooled-Fund Study 09/25/15

IBP Test Sections

Objective: To expedite the implementation of inverted base pavement design specifications for state DoT's and to make IBP a practical and reliable alternative design approach for highway pavements.

Broad Tasks: Further study of existing field cases with
detailed construction records and long-term performance monitoring data Advanced material characterization and modeling with emphasis on granular base Numerical simulation of IBP performance Relevant calibrations for design within framework of Mechanistic-Empirical Pavement design Guide (MEPDG)

Strategic Timing: Existing field cases range between
~95% and ~0% of design life thus allow broad performance assessment Ability to compare IBP and conventional pavement performance under same loading histories High interest for use of innovative designs that optimize material use within constrained budgets

Phase V: pooled fund study to leverage current

knowledge and interest to expedite implementation

of IBP design specifications for state DOT's.

Georgia IBP

GAPS in knowledge: Improved understanding of IBP component performance,
particularly of unbound granular base, through advanced material characterization and modeling Better understanding of relationship between construction and long-term performance of CTB, in particular, and IBP, in general, through continued assessment of test sections and associated numerical simulations
BARRIERS to implementation: Need for reliable framework for assessment of economics
of IBP for both construction and performance stages Need for material model calibrations and damage functions
suitable for IBP designs in MEPDG Guidelines for implementation through all phases of
design, construction and maintenance

PROPOSED POOLED-FUND STUDY CAN RESOLVE GAPS AND ELIMINATE BARRIERS TIMING IS STRATEGIC TIPPING POINT HAS BEEN REACHED - PARTNERS NEEDED

Selected References
Georgia IBP
Cortes, D. D. (2010). "Inverted Base Pavement Structures." Ph.D., Georgia Institute of Technology, Atlanta, GA. Terrell, R.G., Cox, B.R., Stokoe II, K.H., Allen, J.J., and Lewis, D. (2003). Transportation Research Record, No. 1837, pp. 50-60. Papadopoulos, E. (2014). "Performance of Unbound Aggregate Bases and Implications for Inverted Base Pavements." Ph.D., Georgia Institute of Technology, Atlanta. Cortes, D.D., Shin, H.S. and Santamarina, J.C. (2012), Numerical Simulation of Inverted Pavement Systems, ASCE J. Transportation Engineering, vol. 138, no. 12, pp. 1507-1519. Cortes, D.D. and Santamarina, J.C. (2013), Inverted Base Pavement Case History (LaGrange, Georgia): Construction, Characterization and Preliminary Numerical Analyses, International J. Pavement Engineering, International Journal of Pavement Engineering vol. 14, 463-471 Lewis, D.E. and Jared, D.M. (2012). "Construction and Performance of Inverted Pavements in Georgia." Proceedings of 91st TRB Meeting, Washington D.C., Paper # 12-1872. Papadopoulos, E., D. Cortes, and Santamarina J.C., (2015). "In Situ Assessment Of The Stress-Dependent Stiffness Of Unbound Aggregate Bases: Application In Inverted Base Pavements", International Journal Pavement Engineering., http://dx.doi.org/10.1080/10298436.2015.1022779 Papadopoulos, E. and Santamarina J.C., (2015). "Analysis Of Inverted Base Pavements With Thin Asphalt Layers", International Journal of Pavement Engineering, http://dx.doi.org/10.1080/10298436.2015.1007232 Papadopoulos, E., and Santamarina, J. C. (2014). "Optimization of Inverted Base Pavement Designs with Thin Asphalt Surfacing." Geo-Congress 2014 Technical Papers, ASCE, Atlanta, GA, 2996-3004.

Acknowledgements
GDoT Chuck Hasty David Jared Dwane Lewis Gretel Sims Supriya Kamatkar Others John Cardosa Georgene Geary Jim Maxwell Erol Tutumluer Rick Boudreau

Georgia IBP
David Painter Tom Yu Mark Wayne Georgia Tech Douglas Cortes Thymios Papadopoulos Carlos Santamarina James Tsai Andreina Etzi Alessio Contu Sangy Hanumasagar

5

GDOT Final Report on Granular Bases
Webinar organized by AFP70 Mineral Aggregates Sub-committee
Presented July, 2016 Atlanta, GA.
Presenters: Rick Boudreau, Boudreau Engineering; David Frost, Georgia Tech; and Kevin Vaughan, Vulcan Materials.

5/7/2017

Inverted Pavements
A TRB Webinar
(AFP70 Mineral Aggregates)

TRB Webinar - July 18, 2016

Inverted Pavement

1

Why now?
TRB Webinar - July 18, 2016

The IP topic was briefly reviewed in NCHRP Synthesis 445 Practices for Unbound Aggregate Pavement Layers (Erol Tutumluer, Deb Mishra and Rick Boudreau).
download from the TRB website: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp _syn_445.pdf
We received tremendous audience feedback following the TRB Webinar presented June 24, 2015 (Erol Tutumluer, Andrew Dawson, Deb Mishra and Rick Boudreau).

Inverted Pavement

2

Invited Speaker Session TRB 95th Annual Meeting
Sponsored by AFP70 Mineral Aggregates
(E. Tutumluer Chair)
Rick Boudreau (Moderator) Boudreau Engr. Kevin Vaughan Vulcan Wynand Steyn South Africa David Frost Georgia Tech Reza Ashtiani UTEP Bryce Symons N. Mexico

TRB Webinar - July 18, 2016

Inverted Pavement

3

Invited Speaker Session TRB 95th Annual Meeting
Sponsored by AFP70 Mineral Aggregates
(E. Tutumluer Chair)
Rick Boudreau (Moderator) Boudreau Engr. Kevin Vaughan Vulcan Wynand Steyn South Africa David Frost Georgia Tech Reza Ashtiani UTEP Bryce Symons N. Mexico

TRB Webinar - July 18, 2016

Inverted Pavement

4

Outline
Introduction and Background (Boudreau) Design Considerations (Frost) Construction Methods (Vaughan) Performance Assessment (Frost) Summary Comments (Boudreau)

TRB Webinar - July 18, 2016

Inverted Pavement

5

Inverted Pavement - Alias
Inverted Base Pavement (IBP) Inverted G1-Base Pavement (South Africa) Stone Interlayer Pavement (Louisiana) Upside Down Pavement Sandwich Pavement

TRB Webinar - July 18, 2016

Inverted Pavement

6

1

5/7/2017

Inverted Pavement - Defined
Alternative flexible pavement structure Relatively thin upper AC layer(s) Layered stiffness profile does not decrease
with depth Structure typically looks like this (from
bottom up):
Compacted Subgrade Cement-Treated Base (CTB w/ 2-5% cement) Unbound Aggregate Base (UAB) Relatively thin Asphalt Concrete (AC)

TRB Webinar - July 18, 2016

Inverted Pavement

7

Inverted Pavement Compared to Conventional Pavement
Conventional Pavement Section
7-8 inches AC (HMA)
8-12 inches UAB
12 inches well-compacted Subgrade Soil

TRB Webinar - July 18, 2016

Inverted Pavement

8

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section

3-4 inches AC (HMA) 7-8 inches AC (HMA)
6-10 inches UAB
8-12 inches UAB 8-12 inches CTB
12 inches well-compacted 12 inches well-comSpuacbtgerdade Soil Subgrade Soil

TRB Webinar - July 18, 2016

Inverted Pavement

9

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section

Can reach up to 25% less $ to build the inverted

compared with conventional for similar performance

3-4 inches AC (HMA) 7-8 inches AC (HMA)
6-10 inches UAB

8-12 inches UAB 8-12 inches CTB

12 inches well-compacted 12 inches well-comSpuacbtgerdade Soil Subgrade Soil

TRB Webinar - July 18, 2016

Inverted Pavement

10

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section

Can reach up to 25% less $ to build the inverted

compared with conventional for similar performance

3-4 inches AC (HMA) 7-8 inches AC (HMA)
6-10 inches UAB

$0.75

8-12 inches UAB 8-12 inches CTB

$1.00

12 inches well-compacted 12 inches well-comSpuacbtgerdade Soil Subgrade Soil

TRB Webinar - July 18, 2016

Inverted Pavement

11

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section Stiffness (layer modulus)

TRB Webinar - July 18, 2016

Inverted Pavement

12

2

5/7/2017

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section Stiffness (layer modulus)

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section Stiffness (layer modulus)

TRB Webinar - July 18, 2016

Inverted Pavement

Still trying to minimize strains

13

TRB Webinar - July 18, 2016

Inverted Pavement

14

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section

As a result of the stiff CTB layer, higher densities can be achieved in the UAB layer during installation.
This results in higher stiffness properties, and the UAB layer remains in compression.

TRB Webinar - July 18, 2016

Inverted Pavement

15

Inverted Pavement Compared to Conventional Pavement

Inverted Pavement Section

Conventional Pavement Section

1993 AASHTO Design Guide hypothetical example

E = 80,000psi ai = 0.24

E = 30,000psi ai = 0.14

TRB Webinar - July 18, 2016

Inverted Pavement

16

Improving the Chance of Success Unbound Aggregate Base (UAB) Layer
Equipment: Mixing should be accomplished by stationary plant such as a pugmill or by road mixing using a pugmill or rotary mixer. Mechanical spreaders should be utilized to avoid segregation and to achieve grade control. Suitable vibratory compaction equipment should be employed.
Mixing and Transporting: The aggregates and water should be plant mixed (stationary or roadway) to the range of optimum moisture plus 1% or minus 2% and transported to the job site so as to avoid segregation and loss of moisture.
Spreading: The material should be placed at the specified moisture content to the required thickness and cross section by an approved mechanical spreader. At the engineer's discretion, the contractor may choose to construct a 500-ft long test section to demonstrate achieving adequate compaction without particle degradation for lift thicknesses in excess of 13 in. The engineer may allow thicker lifts on the basis of the test section results.
Allen, et al. ICAR 501-5 (1998)

TRB Webinar - July 18, 2016

Inverted Pavement

17

Improving the Chance of Success Unbound Aggregate Base (UAB) Layer
Equipment: Mixing should be accomplished by stationary plant such as a pugmill or by road mixing using a pugmill or rotary mixer. Mechanical spreaders should be utilized to avoid segregation and to achieve grade control. Suitable vibratory compaction equipment should be employed.
Mixing and Transporting: The aggregates and water should be plant mixed (stationary or roadway) to the range of optimum moisture plus 1% or minus 2% and transported to the job site so as to avoid segregation and loss of moisture.
Spreading: The material should be placed at the specified moisture content to the required thickness and cross section by an approved mechanical spreader. At the engineer's discretion, the contractor may choose to construct a 500-ft long test section to demonstrate achieving adequate compaction without particle degradation for lift thicknesses in excess of 13 in. The engineer may allow thicker lifts on the basis of the test section results.
Slushing: South African method to increase packing density of layer by careful over-watering during the compaction process (slush acts as a lubricant to increase density while the slush or cream exudes to the surface).

TRB Webinar - July 18, 2016

Inverted Pavement

18

3

5/7/2017

Design ............

TRB Webinar - July 18, 2016

Inverted Pavement

19

The US Road System is vast and suffers from insufficient funding.

Vast network

Depleted funding Federal Funds

$2.0b

Wikipedia.org
Poor condition

$1.0b

$0.0b

GDOT

`04 `06 `08 `10 `12

Solution Sources
Innovative designs Optimal use of materials

TRB Webinar - July 18, 2016

Inverted Pavement

20

An inverted base pavement (IBP) is an innovative technology that can optimize the use of materials.

Conventional Flexible Pavement Stiffness
asphalt concrete
asphalt base
unbound aggregate base
subgrade

Inverted Base Pavement Stiffness
asphalt concrete
unbound aggregate base
cement-treated base
subgrade

Stiffness contrast between layers Granular base : close to load demand for exceptional performance
(After Papadopoulos, 2015)

TRB Webinar - July 18, 2016

Inverted Pavement

21

South Africa has developed and utilized inverted base pavements for half a century.

Crushed stone base pavement development

Slushing

Accelerated Testing G1 Base

No Slushing

G2 Crushed Stone Bases

Crusher Run

Macadam / gravel

1940

1950

1960

1970

1980

Jooste & Sampson (2005)

Slushing after compaction

(After Papadopoulos, 2015)

www.Vti.se

"Ping" when struck with rock hammer
Kleyn, 2012

TRB Webinar - July 18, 2016

Inverted Pavement

22

Reps. to failure [103] Deflection [mm] % passing Resilient modulus [MPa]

US experience with inverted base pavements had also been long but sparse.

New Mexico (1960s) USACE (1970s) Georgia Tech (1980s) Louisiana (1990s) Morgan County GA quarry (2000s) Lagrange GA bypass (2000s) Bull Run VA highway (2010s) Pineville NC quarry (2010s)

2,000 1,500 1,000

Accelerated Testing, LA IBP

500 Conventional pavement

0

0

1

2

3

4

5

Structural Number SN

0.9 FWD measurements

Conventional

0.6

Morgan Co

0.55

IBP-Lagrange 0.3

IBP-Morgan Co 0.21

0.27

0.0

Data from Lewis et al 2009

(Adapted from Papadopoulos, 2015)

TRB Webinar - July 18, 2016

Inverted Pavement

23

Top quality unbound aggregate base is the fundamental block of IBPs.

Fines Shape

South Africa G1 base LL<25%, PI<4
flakiness (sphericity) <35%

Density

86-88% of apparent solid density (~102% mod Proctor)

CALTRANS base Sand Equivalent <21
N/A
95% of CTM 231

GDoT GAB Sand Equivalent <20 elongated particles <10%
98% mod. Proctor

100

80

GDOT CALTRANS

60

G1 South Africa

40

20
0 0.01

1mm=

39mils

0.1

1

10 100

Grain diameter [mm]

900 Crushed stone
600
300
Gravel 0
0 100 200 300 400 mean stress p [kPa]
(After Papadopoulos, 2015)

TRB Webinar - July 18, 2016

Inverted Pavement

24

4

5/7/2017

Key component of Inverted Pavement construction is slushing technique
Slushing
Process to wash away excess fines to achieve optimum fine to coarse soil matrix Water migrates to surface by capillary action carrying excess fines

TRB Webinar - July 18, 2016

Inverted Pavement

25

Comprehensive laboratory field numerical study that expanded understanding of IPB component performance.
Compaction

Lab Characterization

In situ testing

Inverted Base Pavements

Study completed in 2014

TRB Webinar - July 18, 2016

Mechanistic analysis Inverted Pavement

(After Papadopoulos, 2015) 26

Field: fully documented construction project provides basis for long-term IBP performance assessment.

TRB Webinar - July 18, 2016

Inverted Pavement

LaGrange By-Pass
Test section: 0.65 miles long 2 lanes PCC typical section IBP test section

Construction completed in 2009

3

.

9

56

.

""

5

1

" 1

0

0

" 6

"6

"

"

27

Field: fully documented construction project provides basis for long-term IBP performance assessment.

780

760
Cut 740
Cut Fill 720

700

680 Fill
660

640

280

285

290

295

300

305

310

Station

Specific Surface LL & m/c

Elevation [ft]

GSD TRB Webinar - July 18, 2016

Dry Density P-wave Velocity

Laboratory Characterization of Subgrade
(Data from Santamarina, 2015)

Inverted Pavement

28

D epth (cm) D epth (cm) D epth (cm ) D epth (cm )
Stiffness

Field: fully documented construction project provides basis for long-term IBP performance assessment.

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

0 0 10 20 30 40 50 60 70 80 90 100

PR (mmblow -1 ) 5 10 15 20

(Data from Santamarina, 2015)

Extensive lab and field characterization studies for various layers

TRB Webinar - July 18, 2016

Inverted Pavement

29

Field and Lab: current laboratory methods do not account for the complex nature of aggregate base stiffness.

Inherent Anisotropy

Stress-Dependent Stiffness F

TRB Webinar - July 18, 2016

Cortes 2010

Force
In-chamber compaction. Independent control of the 3
principal stresses. P-wave instrumentation in
each direction. (After Papadopoulos, 2015)

Inverted Pavement

30

5

5/7/2017

Lab: stress ratio has small influence on the small-strain stiffness as long as the material is away from failure.

[m/s]

Horizontal propagation x 2000 1500 1000

Isotropic Compression Triaxial Extension

500

0

0

500 1000 1500

Horizontal Stress [kPa]

Triaxial Compression

Characterization of unbound aggregate base stiffness:

Granular Bases: inherent & stress-induced anisotropy exist.

Mmax : function of normal stress

(Adapted from Papadopoulos, 2015)

Loading conditions: almost no effect on Mmax

TRB Webinar - July 18, 2016

Inverted Pavement

31

Field and Lab: Soil compaction is omnipresent in construction and has known impact on performance.

Inadequate compaction results

Post-placement changes in material

Pavement Interactive
Lab-field discrepancies

test-llc.com



Heavyequipment.com

TRB Webinar - July 18, 2016

Inverted Pavement

32

Lab: an extensive lab study was conducted to assess the compaction process in terms of stiffness.

Specimens compacted using Modified Proctor (Adapted from Papadopoulos, 2015) Stress-dependent stiffness for different water contents

Piezocrystal

Signal Generator

Digital Oscilloscope

Effect of compaction on granular base stiffness:



: not sufficient to assess compaction

Granular base stiffness not affected by water content

Water content affects permanent deformation

Velocity changes reflect accumulation of deformation

TRB Webinar - July 18, 2016

Inverted Pavement

33

Field: Two new field tests were conceived to measure the stiffness of as-built aggregate bases.

Measure stiffness of as-built unbound aggregate bases

Crosshole

Uphole

Dump Truck

Dump Truck

AC GAB
CTB

Piezopads

AC GAB
CTB

Accelerometer Actuator

Subgrade

Subgrade (After Papadopoulos, 2015)

TRB Webinar - July 18, 2016

Inverted Pavement

34

Field: Successive forward simulations were conducted to determine the state of stress in the pavement.

AC GAB CTB
Subgrade

Two configurations to capture anisotropic stiffness 2 case histories

In situ GAB: anisotropic stress-dependent stiffness

Field values lab values: Due to preconditioning and compaction

method (field versus lab)

Field-Compacted GAB: great stiffness

(Adapted from Papadopoulos, 2015)

TRB Webinar - July 18, 2016

Inverted Pavement

35

Modeling: Numerical simulations were conducted to compare IBP's to conventional pavements.

Conventional

Inverted Base Pavement

Mechanistic analysis

Low structural capacity

asphalt concrete

160 mm

asphalt concrete
aggregate base GAB

aggregate base GAB

200mm

cement-treated base CTB

High structural capacity

asphalt concrete
aggregate base GAB

190mm

asphalt concrete aggregate base GAB

305mm

cement-treated base CTB

25mm 150mm 250mm
100mm 150mm 300mm

TRB Webinar - July 18, 2016

Inverted Pavement

(Adapted from Papadopoulos, 2015) 36

6

5/7/2017

Aggregate base stiffness in IBP is high due to the confinement provided by the CTB.

Constitutive model: Anisotropy, stress-dependency, shear softening
Inverted base pavements: Unique load-bearing mechanism
Granular base: Underutilized in conventional pavements Great contribution in inverted base pavements
Thin asphalt layers: Potential for economic savings Caution when subjected to strong shear

AC
190mm 305mm
85 105
130

AC

240

90

390

(Adapted from Papadopoulos, 2015) TRB Webinar - July 18, 2016

Tangent Vertical Young's modulus Ev (MPa)
Inverted Pavement

CTB

100mm 150mm 300mm
37

Construction ...........

TRB Webinar - July 18, 2016

Inverted Pavement

38

Inverted Pavement Construction

Standard construction methods may be used for most layers in an inverted pavement

Subgrade, Cement Treated Base and Asphalt may be constructed in the normal way

Unbound Aggregate Base course may take a little more effort to ensure the higher density required
South African methods vs. traditional

TRB Webinar - July 18, 2016

Inverted Pavement

39

Subgrade Construction

Generally use standard subgrade requirements

Remove/correct saturated soils, organics, unsuitable, etc.

Typical density requirements

Variety of subgrades have been used in US inverted pavements

TRB Webinar - July 18, 2016

Inverted Pavement

40

Subgrade Construction

South Africa
90% to 93% Modified Proctor
Georgia
Mixed in graded aggregate base to improve CBR to 15
New Mexico
Lime treated subgrade
Luck Stone Virginia
Standard VDOT subgrade requirements
Vulcan North Carolina
Standard NCDOT subgrade

TRB Webinar - July 18, 2016

Inverted Pavement

41

Vulcan North Carolina Subgrade

TRB Webinar - July 18, 2016

Inverted Pavement

42
7

5/7/2017

New Mexico Subgrade Construction

TRB Webinar - July 18, 2016

Inverted Pavement

43

Cement Treated Base

Can generally use traditional CTB requirements

Relatively low level of strength & cement
South Africa requires 100 to 200 psi
Pugmill or mix in place

Recommend spreader box to reduce segregation

Typical density requirements

TRB Webinar - July 18, 2016

Inverted Pavement

44

Cement Treated Base
Pugmill system works well if available

Cement Treated Base

TRB Webinar - July 18, 2016

Inverted Pavement

45

TRB Webinar - July 18, 2016

Inverted Pavement

46

Cement Treated Base
Asphalt paver used in NM for CTB
Good control over depth and segregation

Cement Treated Base

TRB Webinar - July 18, 2016

Inverted Pavement

47

TRB Webinar - July 18, 2016

Inverted Pavement

48
8

Cement Treated Base

Cement Treated Base

5/7/2017

TRB Webinar - July 18, 2016

Inverted Pavement

49

TRB Webinar - July 18, 2016

Inverted Pavement

50

Cement Treated Base

Cement Treated Base

TRB Webinar - July 18, 2016

Inverted Pavement

51

TRB Webinar - July 18, 2016

Inverted Pavement

52

Cement Treated Base

TRB Webinar - July 18, 2016

Inverted Pavement

53

Cement Treated Base
Seal with emulsified asphalt tack coat
Allow to cure for 7 days

TRB Webinar - July 18, 2016

Inverted Pavement

54
9

5/7/2017

Unbound Aggregate Base

Typical laydown
Spreader box should be required for thickness and consistency

Density requirements higher than normal

How is this achieved
South Africa requires "slushing" Will normal methods work?

TRB Webinar - July 18, 2016

Inverted Pavement

55

Unbound Aggregate Base

TRB Webinar - July 18, 2016

Inverted Pavement

56

Unbound Aggregate Base

Unbound Aggregate Base

TRB Webinar - July 18, 2016

Inverted Pavement

57

TRB Webinar - July 18, 2016

Inverted Pavement

58

Unbound Aggregate Base

TRB Webinar - July 18, 2016

Inverted Pavement

59

Slushing Process

What is slushing?
After initial compaction UAB flooded with water

Rolled at high speed to "suck" the fines out of the UAB
Fines and water act as a lubricant As they are removed, larger particles are consolidated for high
density and stiffness
Excess fines collect on top of the UAB

Excess fines broomed off

TRB Webinar - July 18, 2016

Inverted Pavement

60

10

5/7/2017

Slushing Process

No vibration High speed rolling

TRB Webinar - July 18, 2016

Inverted Pavement

Slushing Process
15 to 17 ton minimum 27 to 37 ton towards end of cycle

Fines being expelled

High speed rolling "sucking" fines from saturated layer

61

TRB Webinar - July 18, 2016

Inverted Pavement

62

Slushing Process

Slushing Process

Notice air being expelled = interlocking taking place

TRB Webinar - July 18, 2016

Inverted Pavement

63

Initial slush/fines same color as parent rock

TRB Webinar - July 18, 2016

Dried fines

Inverted Pavement

64

Slushing Process

Slushing Process

Well-knitted mosaic being exposed

Bristles of broom should just touch surface

TRB Webinar - July 18, 2016

Inverted Pavement

65

TRB Webinar - July 18, 2016

Inverted Pavement

66
11

5/7/2017

Unbound Aggregate Base
To Slush or not to Slush...that is the question First test section in Georgia saw no benefit to
slushing New Mexico specified slushing All others used traditional compaction methods
Easily achieved 102 to 103% of modified Proctor

TRB Webinar - July 18, 2016

Inverted Pavement

67

Unbound Aggregate Base

TRB Webinar - July 18, 2016

On Vulcan section, the UAB on the conventional & inverted sections compacted same time
Density on conventional: 99.8%
Density on inverted: 103.4%
86.4% of apparent

Inverted Pavement

68

Unbound Aggregate Base

Hot Mix Asphalt

Used the same compaction techniques on both
Roller operated commented that the inverted section caused more "bouncing" when compacting with vibration

Normal HMA construction in accordance with local DOT requirements
Nothing new

TRB Webinar - July 18, 2016

Inverted Pavement

69

TRB Webinar - July 18, 2016

Inverted Pavement

70

Vulcan Final Density Comparison

Inverted Layer Densities

Conventional Layer Densities

9.5mm A 9.5mm B
UAB
CTB

Required Achieved

90% of Gmm
92% of Gmm 102% of Mod. Proc. 97% of Mod. Proc.

90.8% 94.3%
103.4%
99.2%

9.5mm B 19.0mm
UAB

Required Achieved

92% of Gmm 92% of Gmm 100% of Mod. Proc.

93.2% 93.1%
99.8%

TRB Webinar - July 18, 2016

Inverted Pavement

71

Construction Summary

Subgrade standard methods
Cement Treated Base standard methods
Unbound Aggregate Base requires higher density
Standard methods have been shown to work Slushing will work, but may not be required
Asphalt Paving standard methods
QA/QC: Stiffness-based measurements vs density- based measurements
Intelligent Compaction (IC) LWD, PLT, DCP .....

TRB Webinar - July 18, 2016

Inverted Pavement

72

12

5/7/2017

Performance Assessment

TRB Webinar - July 18, 2016

Inverted Pavement

73

Test sections with well documented loading over 15 year period (Morgan County Quarry).

Seven Islands Road

Quarry Entrance Road

Station 0+50 through Station 10+00 Conventional Haul Road
Station 10+00 through Station 14+00 South African Base
Station 14+00 through Station 18+00 Georgia Base

Construction completed in 2001

TRB Webinar - July 18, 2016

Inverted Pavement

74

FWD evaluations of test sections (2009).

Performance Evaluation: 853,719 ESAL's (63.5% design life cycle)

Lewis et al., 2012

TRB Webinar - July 18, 2016

Inverted Pavement

75

Surface distress study using imaging and LiDAR (2016).

3D Laser Imaging System

Range Image

Detected Crack Map

The GDOT's Pavement Condition Evaluation System (PACES) is used for conducting the annual asphalt pavement condition surveys in Georgia.

Ten different distress types and their severity levels are defined.

Four of them are crack related distresses: load cracking, B/T cracking,

edge distress, and reflective cracking.

(Courtesy of James Tsai)

Inverted Pavement

TRB Webinar - July 18, 2016

76

Surface distress study using Imaging (2016).

Abnormal sections due to truck
braking at main exit

Abnormal sections due to truck braking at
temporary crossing

TRB Webinar - July 18, 2016

Inverted Pavement

77

Surface distress study using Imaging (2016).

Georgia Inverted

South Africa Inverted

1800'

1400'

1000'

Conventional Inbound
Outbound
0'

Fine transverse crack Transverse and longitudinal crack

Block cracking

TRB Webinar - July 18, 2016

Inverted Pavement

Alligator cracking
78

13

5/7/2017

Pavement surface distress study using imaging.

Load cracking is caused by repeated heavy loads and always occurs in the wheel paths:

Severity Level 1 usually starts as single longitudinal cracks in the wheel path.
Severity Level 2 has a single or double longitudinal crack with a number of 0-2 feet transverse cracks intersecting.
Severity Level 3 shows an increasing number of longitudinal and transverse cracks in the wheel paths. This level of cracking is marked by a definite, extensive pattern of small polygons.
Severity Level 4 has the definite "alligator hide" pattern but has deteriorated to the point that the small polygons are beginning to pop out.

(a) Severity Level 1 (b) Severity Level 2 (c) Severity Level 3 (d) Severity Level 4

(Courtesy of James Tsai)

TRB Webinar - July 18, 2016

Inverted Pavement

79

Surface distress study using imaging (2016).
Inbound

Outbound

TRB Webinar - July 18, 2016

Inverted Pavement

80

Surface distress study using imaging (2016).

Conventional Severe cracking

Conventional Less severe cracking

Load

1

Cracking

2

3

Block

1

Cracking

Max Rutting (1/8")

Average Rating

Rating Range

Conventional

Inbound

Outbound

32.5 %

25.8%

0%

5. %

0%

12.5%

52.5%

31.7%

0 79 71-85

4 68.7 43-80

South African IP

Inbound

Outbound

33.8%

37.5%

0

0

0

0

32.5%

31.3%

0 81.8 81-83

0 80.5 76-86

Georgia IP

Inbound

Outbound

20 %

32.5%

0

0

0

0

32.5%

30%

1 85.5 82-8G9A IBP

2 81.5 79-86

SA IBP

TRB Webinar - July 18, 2016

Inverted Pavement

81

Rutting study using LiDAR (2016).

Load

1

Cracking

2

3

Block

1

Cracking

Max Rutting (1/8")

Average Rating

Rating Range

Conventional

Inbound

Outbound

32.5 %

25.8%

0%

5. %

0%

12.5%

52.5%

31.7%

0 79 71-85

4 68.7 43-80

South African IP

Inbound

Outbound

33.8%

37.5%

0

0

0

0

32.5%

31.3%

0 81.8 81-83

0 80.5 76-86

Georgia IP

Inbound

Outbound

20 %

32.5%

0

0

0

0

32.5%

30%

1 85.5 82-89

2 81.5 79-86

Comparable rating for SA IBP and GA IBP far superior to conventional design.
Less rutting with SA IBP than with GA IBP possible link to benefits of slushing?

TRB Webinar - July 18, 2016

Inverted Pavement

82

Laboratory simulation study of slushing process.

Laboratory study of slushing on cracking and rutting.

Ongoing laboratory simulation study to examine evolution of aggregate shape, pore structure and load path during slushing

TRB Webinar - July 18, 2016

Inverted Pavement

83

TRB Webinar - July 18, 2016

Inverted Pavement

84
14

5/7/2017

Selected References
Cortes, D. D. (2010). "Inverted Base Pavement Structures." Ph.D., Georgia Institute of Technology, Atlanta, GA.
Terrell, R.G., Cox, B.R., Stokoe II, K.H., Allen, J.J., and Lewis, D. (2003). Transportation Research Record, No. 1837, pp. 50-60.
Papadopoulos, E. (2014). "Performance of Unbound Aggregate Bases and Implications for Inverted Base Pavements." Ph.D., Georgia Institute of Technology, Atlanta.
Cortes, D.D., Shin, H.S. and Santamarina, J.C. (2012), Numerical Simulation of Inverted Pavement Systems, ASCE J. Transportation Engineering, vol. 138, no. 12, pp. 1507-1519.
Cortes, D.D. and Santamarina, J.C. (2013), Inverted Base Pavement Case History (LaGrange, Georgia): Construction, Characterization and Preliminary Numerical Analyses, International J. Pavement Engineering, International Journal of Pavement Engineering vol. 14, 463-471
Lewis, D.E. and Jared, D.M. (2012). "Construction and Performance of Inverted Pavements in Georgia." Proceedings of 91st TRB Meeting, Washington D.C., Paper # 12-1872.
Papadopoulos, E., D. Cortes, and Santamarina J.C., (2015). "In Situ Assessment Of The Stress-Dependent Stiffness Of Unbound Aggregate Bases: Application In Inverted Base Pavements", International Journal Pavement Engineering., http://dx.doi.org/10.1080/10298436.2015.1022779
Papadopoulos, E. and Santamarina J.C., (2015). "Analysis Of Inverted Base Pavements With Thin Asphalt Layers", International Journal of Pavement Engineering, http://dx.doi.org/10.1080/10298436.2015.1007232
Papadopoulos, E., and Santamarina, J. C. (2014). "Optimization of Inverted Base Pavement Designs with Thin Asphalt Surfacing." Geo-Congress 2014 Technical Papers, ASCE, Atlanta, GA, 2996-3004.

TRB Webinar - July 18, 2016

Inverted Pavement

85

In Conclusion .............

TRB Webinar - July 18, 2016

Inverted Pavement

86

Pooled fund study to leverage current knowledge to expedite implementation of IBP design specifications for US state DOT's.

GDOT Led Pooled-Fund Study: Closing Sept 25, 2016
http://www.pooledfund.org/Details/Solicitation/1416
Objective: To expedite the implementation of inverted base pavement
design specifications for state DoT's and to make IBP a practical and reliable alternative design approach for highway pavements.

IBP Test Sections

Broad Tasks: Further study of existing field cases with detailed construction
records and long-term performance monitoring data
Advanced material characterization and modeling with emphasis on granular base Numerical simulation of IBP performance Relevant calibrations for design within framework of Mechanistic-Empirical Pavement design Guide
(MEPDG)

TRB Webinar - July 18, 2016

Inverted Pavement

87

Pooled fund study to leverage current knowledge to expedite implementation of IBP design specifications for US state DOT's.

GAPS in knowledge:
Improved understanding of IBP component performance, particularly of unbound granular base, through advanced material characterization and modeling
Better understanding of relationship between construction and long-term performance of CTB, in particular, and IBP, in general, through continued assessment of test sections and associated numerical simulations
BARRIERS to implementation:
Need for reliable framework for assessment of economics of IBP for both construction and performance stages
Need for material model calibrations and damage functions suitable for IBP designs in MEPDG
Guidelines for implementation through all phases of design, construction and maintenance
PROPOSED POOLED-FUND STUDY CAN RESOLVE GAPS AND ELIMINATE BARRIERS

TRB Webinar - July 18, 2016

Inverted Pavement

88

15