twenty-five years of performance - a …docs.trb.org/prp/13-1036.pdf · has validated idot’s...

TWENTY-FIVE YEARS OF PERFORMANCE - A VALIDATION OF ILLINOIS’

MECHANISTIC-EMPIRICAL PAVEMENT DESIGN ON US 20 AND US 50

Juan David Pava

Word Count = 7,207

Springfield, Illinois

August 1, 2012

TRB 2013 Annual Meeting Paper revised from original submittal.

Juan D. Pava i

ABSTRACT

In the summer of 1986, the Illinois Department of Transportation (IDOT) built four demonstration

sections to validate the proposed mechanistically-based pavement design procedures under development

by the University of Illinois. Multiple variables were taken into consideration in order to determine a

valid correlation between pavement design inputs and pavement performance.

After 25 years of service, these sections have provided great value to IDOT in the development of

pavement design procedures, policies and standards, and in general a better understanding of the

mechanics of pavement performance. The knowledge acquired from the four sections supports IDOT’s

practice in the use of performance graded binders, joint spacing in jointed concrete pavements, jointed

concrete and full-depth hot-mix asphalt pavement thickness design, and subgrade selection. This study

has validated IDOT’s mechanistic pavement design procedure, proving that the theory behind the 1986

design was correct. Since then, these sections and extensive laboratory testing and investigation have

allowed IDOT to further refine the mechanistic pavement design procedure to include more accurate

material properties.

In addition to improving design procedures, having 25 years of data and observing the

deterioration and rehabilitation of certain sections have allowed IDOT to fine tune the maintenance

models used for pavement type selection between flexible and rigid alternatives.


Juan D. Pava ii

ACKNOWLEDGEMENTS

The author gratefully thanks the contribution of the following people without whose help and support this

paper would have not been possible: David Lippert, Amy Schutzbach, and LaDonna Rowden for their

help with the scope of the project Michael Brownlee, Joe Vespa, Charles Wienrank, and David Lass, for

their assistance in data collection, analysis and for providing historical information; and Amy Schutzbach

and LaDonna Rowden for their guidance and assistance in this paper.

DISCLAIMER

The contents of this paper reflect the views of the author, who is responsible for the facts and accuracy of

the data represented in this paper. The contents do not necessarily reflect the official views or policies of

IDOT. This paper does not constitute a standard, specification, or regulation at IDOT.


Juan D. Pava iii

Table of Contents

ABSTRACT ................................................................................................................................................... i

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

DISCLAIMER .............................................................................................................................................. ii

INTRODUCTION AND HISTORICAL PERSPECTIVE ........................................................................... 1

ORIGINAL CONSTRUCTION DETAILS .................................................................................................. 1

Project 1 .................................................................................................................................................... 1

Project 2 .................................................................................................................................................... 1

Project 3 .................................................................................................................................................... 3

Project 4 .................................................................................................................................................... 3

Instrumentation ......................................................................................................................................... 6

Quality Control ......................................................................................................................................... 6

Objectives ................................................................................................................................................. 7

PERFORMANCE MONITORING .............................................................................................................. 8

Early age study .......................................................................................................................................... 8

Continuous Monitoring ............................................................................................................................. 9

Traffic Consumption ............................................................................................................................... 15

CONCLUSION ........................................................................................................................................... 16

BIBLIOGRAPHY ....................................................................................................................................... 17


Juan D. Pava 1

TWENTY-FIVE YEARS OF PERFORMANCE - A VALIDATION OF ILLINOIS’

MECHANISTIC-EMPIRICAL PAVEMENT DESIGN ON US 20 AND US 50

INTRODUCTION AND HISTORICAL PERSPECTIVE

For several decades the Illinois Department of Transportation (IDOT) used the empirically-based design

procedure developed from the American Association of State Highway Officials (AASHO) Road Test

conducted in Illinois in 1959 and 1960. Limitations of these empirical design procedures became apparent

with the development of new and improved materials, cross sections, and construction technologies not

used in the AASHO Road Test (Thompson & Gomez, 1983). In order to progress to the next generation

of pavement design, IDOT decided to build four demonstration sections to validate a proposed

mechanistically-based design procedure under development by the University of Illinois (Thompson &

Cation, 1986) (Zollinger & Barenberg, 1989).

The construction of the four sections began in the summer of 1986. Projects 1 and 2 are sections

of US 20, northeast of Freeport, Illinois, in Stephenson County. Projects 3 and 4 are part of US 50,

between Lebanon and Carlyle, Illinois, in St. Clair and Clinton Counties. Figure 1 shows the location of

all four projects. Multiple variables were taken into consideration in order to determine a valid correlation

between pavement design inputs and pavement performance. The demonstration projects were established

in an experimental feature work plan entitled “Evaluating Pavement Design Procedures.”

This paper presents a compendium of technical data about the four projects built, major

reconstruction and maintenance events, their significance to the state, and an analysis of their behavior

throughout time based on field surveys, instrumentation data, and site and laboratory testing.

ORIGINAL CONSTRUCTION DETAILS

Project 1

This project is located on US 20, originally known as FA 401, northeast of Freeport, Illinois in

Stephenson County. Project 1 was built under contract 40463; this contract consisted of 3.8 miles of full-

depth hot-mix asphalt (HMA) pavement. The cross section was a 13-inch HMA pavement containing two

different types of asphalt binder; Section A, beginning at Henderson Road and extending 1.65 miles west,

was constructed with AC-10, which is similar to Performance Graded (PG) 58-22 asphalt binder; Section

B, beginning at Henderson Road and extending 2.15 miles east, was constructed with AC-20, which is

similar to PG 64-22. The main objective of this Project was to evaluate the influence of asphalt binder

viscosity on pavement performance.

Project 2

This project is adjacent to Project 1 on US 20. This project was built under contract 40455 and consisted

of 2.8 miles of Portland cement concrete (PCC) pavement. The cross section is a 10-inch PCC slab on

top of a 4-inch Cement Aggregate Mixture (CAM) II stabilized subbase. This section includes four

different designs as follows:

1. 40-foot jointed reinforced concrete pavement (Sections D and G4)

2. 20-foot jointed plain concrete pavement with dowels (Sections C and F)

3. 15-foot jointed plain concrete pavement with dowels (Sections E and H)


Juan D. Pava 2

FIGURE 1 Location of projects 1 through 4.


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4. Hinge-jointed concrete pavement with three different hinge-joint designs (A1, A2, and B).

a. Design A1 consists of 20-foot joints with alternating tie bars and dowels (Section G1).

b. Design A2 has the same configuration as Design A1, but it includes full-width pavement

fabric for reinforcement (Section G2).

c. Design B consists of 13.3-foot joints with the pattern of a doweled joint followed by two

tied joints (Section G3).

Figure 2 shows the layout of Project 2. Figure 3 shows the three different hinge-joint

configurations.

FIGURE 2 Project 2 layout.

Note 1: three 400-ft hinge-jointed sections. G1 = Design A1; G2 =Design A2; G3 =Design B.

Project 3

This project is located on US 50, between Lebanon, Illinois, and the Sugar Creek Bridge, in St. Clair and

Clinton Counties. This project was built under contracts 40448 (St. Clair County) and 40315 (Clinton

County). These contracts consisted of 7.5 miles of full-depth HMA pavement with cross section

thicknesses of 9.5, 11, and 12.5 inches to evaluate the effects of pavement thickness on performance. The

primary cross section design for this project is an 11-inch full-depth HMA pavement over a lime-

modified subgrade with underdrains. Sections were also built with and without lime-modified subgrade

and with and without underdrains to evaluate the significance of each component in the design. Figure 4

shows the layout of this project.

Project 4

This project is located on US 50 from St. Rose Road to IL 127. Project 4 consisted of 9.7 miles of PCC

pavement on a 4-inch thick CAM II stabilized subbase and was built under two contracts. Contract 40317

consisted of 4.0 miles of continuously reinforced concrete pavement (CRCP) with thicknesses of 7.5, 8.5,

and 9.5 inches to evaluate the effects of concrete pavement thickness on performance. Contract 40456

consisted of 5.7 miles of jointed PCC pavement which includes 4 different designs:

1. 40-foot jointed reinforced concrete pavement.

2. 20-foot jointed plain concrete pavement with dowels.

3. 15-foot jointed plain concrete pavement with dowels.

4. Hinge-jointed concrete pavement with the same designs used in Project 2.

All jointed pavement designs were constructed with thicknesses of 7, 8, or 9 inches. Figure 5 shows

the layout of this project.


Juan D. Pava 4

FIGURE 3 Hinge-joint panel designs.


Juan D. Pava 5




Juan D. Pava 6

Instrumentation

Several types of gauges were installed throughout all four projects in order to evaluate the response of the

pavement to loading, freeze-thaw, and other weather events. Strain gauges were installed in the concrete

sections to verify theoretical strains due to wheel loads. Detailed information regarding the

instrumentation of the four projects is available in IDOT Physical Research Report (PRR) No. 112 (Reed

& Schutzbach, 1993) (Reed & Schutzbach, 1993).

Quality Control

Prior to construction, a thorough soil investigation was conducted to determine the Illinois Bearing Ratio

(IBR; similar to California Bearing Ratio) of each section. Subgrade stability measurements were

acquired using nuclear density gauges. Mix designs for the flexible and rigid sections were designed

according to the IDOT specifications. Since these two projects were part of the first full-depth, full-

quality sections constructed in the state, both full-depth HMA projects complied with IDOT’s Special

Provision for Bituminous Concrete Overlay on Interstate Highways (Illinois Department of

Transportation, 1985) (Illinois Department of Transportation, 1985). Mixture designs for Projects 1 and 3

are shown in Table 1.

TABLE 1 Hot-Mix Asphalt Design Data

Test Surface Binder

Specification Project 1 Project 3 Specification Project 1 Project 3

Gradation, %

passing

1” -- 100 100 100

3/4” 100 100 100 82-100 98 92

1/2” 90-100 99 100 50-82 73 68

3/8” 66-100 89 99 -- 56 56

#4 24-65 53 58 24-50 40 38

#8 16-48 33 36 16-36 30 30

#16 10-32 26 26 10-25 23 23

#30 -- 21 18 -- 18 15

#50 4-15 13 11 4-12 11 8

#100 3-10 8 7 3-9 7 5

#200 2-6 4.9 5.5 2-6 4.0 3.5

Asphalt, % of

total mix 3-9 5.7 7.1 3-9 4.7 5.3

Air Voids % 3-5 4.0 5.0 3-5 5.0 4.8

Voids in the

mineral

aggregate, %

15 Min 14.6 16.0 14 Min 14.0 14.9

Marshall

stability, lbs. 2000 Min 2425 2345 2000 Min 2630 2140

Marshall Flow,

1/100” 8-16 7.2 8.2 8-16 8.2 8.8

Tensile

Strength Ratio -- 0.50 -- 0.76 0.73

-- Denotes No Specification


Juan D. Pava 7

All of the mix designs were developed using the Marshall Design Procedure (The Asphalt

Institute, 1979, March) (The Asphalt Institute, 1979, March). The only production results that were not

within the specified design parameters were the air voids in the surface mix using AC-20 binder in Project

1. The average air void content for production was 2.3 percent, compared to the specified 4.0 percent.

This problem was not identified until after production was completed. Cores taken during production of

Project 1 showed the air voids were within the acceptable range. All other production test results

complied with the specifications.

There were two PCC designs for the rigid sections, one for Project 2 and one for Project 4.

Table 2 shows the breakdown of each concrete mix design.

TABLE 2 Concrete Design Data

Ingredient Quantity, Pounds

Project 2 Project 4

Cement 455 575

Fly Ash 120 --

CA – 07 1967 1890

FA – 01 1036 1123

Water 259 249.9

Total 3837 3837.9

Flexural strength measurements were determined for these mixes at 3-, 7-, 14-, 28-, and 90-days.

In addition to this, slump and air content were taken during production. Although some individual

measurements did not meet the specifications, the average values were well within the specified ranges.

Project 2 mix average/specified values were: slump of 2.2/3.0 inches, air content of 6.87/5-8%, and 14-

day flexural strength of 826/620 psi. The average/specified values for Project 4 were: slump of 2.83/3.0

inches, air content of 6.41/5-8%, and 14-day flexural strength of 827/650 psi. Detailed testing information

was also published in IDOT PRR No. 112 (Reed & Schutzbach, 1993) (Reed & Schutzbach, 1993).

Objectives

There were four main objectives in the original work plan.

1. Validate the early stage performance of the mechanistically-based design for asphalt pavement

developed by the University of Illinois by comparing Falling Weight Deflectometer (FWD)

deflections, and assess the benefits of different pavement thicknesses, use of underdrains, and use of

lime-modified subgrade.

2. Measure strains and deflections on the PCC sections; compare results to the predicted values from the

mechanistically-based design procedure; and assess the benefits of underdrains, slab thicknesses, and

joint sealing on pavement performance.

3. Evaluate the effect of different asphalt cement viscosity, AC-10 and AC-20.

4. Evaluate the effect of joint configuration in jointed PCC pavement. Three different joint spacings

were to be evaluated, 40-, 20-, and 15-feet, as well as three hinge-joint designs.


Juan D. Pava 8

PERFORMANCE MONITORING

As part of this study, the four projects have been monitored throughout their life to capture pavement

performance. Various types of monitoring have taken place including: video images, ride quality

(smoothness and rutting), condition rating surveys (CRS), and manual distress surveys. The CRS is a

factor in highway program development. This value presents an opportunity to review the highway

network, provides overall condition of the state highway system, gives input into the legislative/budgeting

processes, and allows calculation of pavement needs. CRS ratings range from 1 (complete failure) to 9

(new pavement), and a value between 5.5 and 6 generally triggers rehabilitation.

Early age study

IDOT published a five-year performance evaluation in 1993 based on surveys collected in 1990 and 1992

(Reed & Schutzbach, 1993) (Reed & Schutzbach, 1993). The findings of the five-year evaluation are

summarized as follows.

Full-depth HMA Pavements

Early studies of the sections showed the expected behavior of increased structural

performance with increased thickness. Pavement thicknesses of 9.5, 11, and 12.5 inches

were studied.

Generally higher deflections were observed in thinner pavement.

There was no clear correlation between the asphalt viscosity rating and rut or thermal

crack susceptibility at that point in time. IDOT has since transitioned from viscosity-

graded binders to performance-graded binders. AC-10 and AC-20 are comparable to

PG 58-22 and PG 64-22, respectively.

Lime modification of the soil yielded higher modulus values, providing a better

construction platform and better life of the pavement. Two of the three sections requiring

early age patching and a large percentage of the 9.5-inch pavement did not have a lime-

modified subgrade. Because of this, some of the poorer structural performance could be

attributed to the untreated subgrades.

The use of underdrains did not show a direct correlation to the distresses found in the

early studies. The conclusion was that underdrains did not have a measurable effect in

pavement performance. General performance trends at IDOT have shown the importance

of proper drainage, therefore now most pavement cross sections include underdrains.

PCC Pavement Sections

The CRC sections performed equally for the first five years for all thicknesses (7, 8, and

9 inches) that were evaluated.

In the jointed sections, the shorter panels showed better performance, but thinner slabs

also exhibited more distresses. The strain gauges also confirmed that thicker slabs

experienced lower strains.


Juan D. Pava 9

The value of underdrains was not tangible in the early stage evaluation.

Sealed longitudinal joints did help to lower the moisture levels of the subgrade.

It was clear that joint spacing played an important role in the performance of pavements.

Within the first five years of service for Project 2, neither the 15- or 20-foot sections

exhibited any distresses, while all of the 40-foot jointed panels had at least one crack. The

hinge-jointed panels also showed good performance on these rural sections. However,

long-term monitoring in Illinois showed cracking in hinge-jointed pavements in urban

areas due to the increased presence of discontinuities; median nosing, cut-outs, side

streets, etc. In Project 4, only 5% of the 20-foot jointed slabs had cracked, while every

40-foot jointed slab was cracked. For this reason, the use of hinge-jointed design was

dropped, and in the early 1990’s IDOT’s pavement design shifted to use only jointed

plain concrete pavement with doweled 15-foot joint spacing.

Continuous Monitoring

CRS values for Projects 1 and 2 were collected every even year from 1986 until 1994 and every

odd year from 1995 until 2011. Manual field surveys were collected in 1990, 1992, 1993, 1995, 1997, and

2010. Figure 6 shows the CRS values for Projects 1 and 2 versus year. This figure shows the functional

performance of the sections throughout time. The effect of rehabilitation events is evident in the sections.

CRS rating sections are selected arbitrarily based on performance observed, pavement surface or critical

points. Consecutive sections with the same CRS values were grouped together in the following figures.

FIGURE 6 CRS values for Projects 1 and 2 versus year.

Sections A and B are HMA sections, Sections C though H are PCC sections.

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1980 1985 1990 1995 2000 2005 2010 2015

CR

S

Year

CRS vs Year US 20

A

B

C - H

Sections


Juan D. Pava 10

Project 1 was overlaid in 2007 under contract 64577. The overlay consisted of 0.75 inch of

leveling binder and 1.5 inches of Superpave HMA surface. Both the CRS and most recent field survey in

2010 showed a better performance of Section A compared to Section B due to the more flexible binder

(AC-10 vs. AC 20). For Project 2, part of Section C and the first 400 feet of Section D were reconstructed

in 2007 under contract 64577 as 15-foot jointed plain concrete with doweled joints as part of the

realignment and addition of westbound lanes. The reconstructed section did not show any distresses. The

remaining portion of Section D, 40-foot joints, showed low and medium severity cracks in every slab and

extensive patching. Sections E through G3 did not show many distresses. Section G4, 40-foot joints,

presented cracks in every slab mostly of medium severity and some high severity and a significant

percentage of the area was patched. A summary of the latest condition survey for each project is shown in

Table 3.

TABLE 3 Summary of the latest condition for Projects 1 and 2

Project Section Pavement Type Status of Pavement Condition in 2010

1

A Full-depth HMA,

AC-10,13 inches

Overlaid in 2007 with

0.75 inch leveling binder

and 1.5 inch HMA surface

19 low severity transverse

cracks

B Full-depth HMA,

AC-20, 13 inches

Overlaid in 2007 with

0.75 inch leveling binder

and 1.5 inch HMA surface

65 low severity transverse

cracks

2

C 20-foot Jointed

PCC, 10 inches

First 300 feet – Original 1 patch, 1 low severity crack

Remainder –

Reconstructed in 2007* No distress

D 40-foot Jointed

PCC, 10 Inches

First 400 feet –

Reconstructed in 2007* No distress

Remainder – Original

All 72 slabs cracked, 75% low

severity, 25% medium severity,

3% of section patched, typically

mid-panel

E 15-foot Jointed

PCC, 10 inches Original

1 low severity corner break,

4 low severity spalls

F 20-foot Jointed


10 low severity cracks,

6 medium severity cracks

G1 Hinge-joint design

A1, 10 inches Original


1 medium severity crack


A2, 10 inches Original 1 low severity crack


B, 10 inches Original


1 medium severity crack, some

spalls at hinge-joints

G4 40-foot Jointed


Cracks in every panel, mostly

medium severity, some low

severity, and 2% patching

H 15-foot Jointed


30 feet of longitudinal cracking

eastbound,1 corner break and

7 low severity transverse cracks

* Reconstruction unrelated to performance and due to facility improvement.


Juan D. Pava 11

CRS values for Projects 3 and 4 were collected every even year from 1986 until 2010. Complete

manual field surveys were collected in 1990, 1992, 1993, and 2010, and partial surveys were collected in

1995, 1997, and 1999. Figure 7 shows the CRS values for Projects 3 and 4 by year. This figure shows the

functional performance of the sections throughout time. The effect of rehabilitation events in the sections

is apparent in this figure.

FIGURE 7 CRS values for Projects 3 and 4.

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1984 1989 1994 1999 2004 2009

CR

S

Year

CRS vs Year - Project 3 - HMA

A-B

C , D , E, H

I

J, K, L

M, MI

N

O, P

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1984 1989 1994 1999 2004 2009

CR

S

Year

CRS vs. Year - Project 4 - PCC

R - Z

AA

BA - FA

GA

HA - MA

NA

OA - RA

Sections

Sections


Juan D. Pava 12

Project 3 has received partial overlays throughout its life. In 1994, Sections A, B, J, K, L, M, and

M1 were overlaid. All of these sections were originally 9.5 inches thick. Sections A and B’s overlays

were triggered by rutting. These sections were originally constructed with AC-10 and were overlaid with

2.25 inches of recycled HMA with AC-20 binder. Sections J and K also exhibited rutting and were

overlaid with 3 inches of HMA. Sections K, M, and M1 required extensive patching prior to being

overlaid. Sections K and M were the only two sections with untreated subgrade and Sections M and M1

did not have underdrains. These sections exhibited severe stripping and were overlaid with 2.25 to 3

inches of HMA. Sections N, O, and P were overlaid in 2007 under contract 76A79. These sections

showed high occurrences of alligator cracking, raveling, block cracking, and centerline cracking in the

1999 distress survey. The CRS values ranged in the low 5’s in 2006. These sections were milled and

filled with 2.25 inches of Superpave HMA.

Sections GA through RA from Project 4 received an overlay in 2008. These sections were

overlaid under contract number 76B12. The last manual survey recorded before the overlay of these

sections dates back to 1997. In this survey, it was observed that the 40-foot jointed sections exhibited a

high number of medium- and low-severity panel cracks. Some patching was also noticed in this survey.

The 20-foot jointed and hinge-jointed sections did not show many distresses. All sections were overlaid

with 2.25 inches of HMA binder and 1.5 inches of HMA surface. The CRS values for these sections

ranged between 6.0 and 6.5 in 2006; whereas in 2008, CRS values ranged between 8.0 and 9.0. The latest

visual inspection of Project 4 took place in 2010. This survey showed a high number of medium- and

low-severity transverse cracks along the bare sections and a few low- and medium-severity transverse

cracks on the overlaid sections. These distresses were observed mainly in the 40-foot jointed sections. A

summary of the most recent condition survey for Projects 3 and 4 is summarized in Table 4 and Table 5,

respectively.

Detailed survey data was published by IDOT in PRR No. 159, Performance Monitoring of

Mechanistically Designed Pavements 2010 Data Collection (Pava, 2011, March ) (Pava, 2011, March ).


Juan D. Pava 13

TABLE 4 Latest condition of Project 3

Project Section Thickness,

Inches Binder Subgrade Underdrains Status of Pavement Condition in 2010

3

A 9.5 AC-10 LM Yes Overlaid in 1994 with 2.25 inches of HMA due

to rutting

Centerline deterioration, raveling and weathering,

and some longitudinal cracks noticed.

B 9.5 AC-10 LM Overlaid in 1994 with 2.25 inches of HMA due

to rutting

Centerline deterioration, and raveling and

weathering noticed.

C 12.5 AC-10 LM Original Low block cracking, centerline deterioration, and

raveling and weathering noticed.

D 12.5 AC-10 LM Yes Original Low block cracking, centerline deterioration, and


E 12.5 AC-20 LM Yes Original Low block cracking, centerline deterioration, and


H 12.5 AC-20 LM Original Low block cracking, centerline deterioration, and


I 9.5 AC-20 LM Yes Original Low block cracking, centerline deterioration, and


J 9.5 AC-20 LM Yes Overlaid in 1994 with 3 inches of HMA due to

rutting.

Centerline deterioration and raveling and

weathering noticed.

K 9.5 AC-20 Overlaid in 1994 with 3 inches of HMA due to

rutting. Patching was required prior to overlay.

Centerline deterioration and raveling and

weathering noticed.

L 9.5 AC-20 LM Yes Overlaid in 1994 with 3 inches of HMA due to

rutting. Patching was required prior to overlay.

Block cracking, centerline and center of lane

deterioration, raveling and weathering noticed.

M 9.5 AC-20 LM

Overlaid in 1994 with 2.25 to 3 inches of HMA

due to stripping. Patching was required prior to

overlay.

Block cracking, centerline deterioration and


M1 9.5 AC-20

Overlaid in 1994 with 2.25 to 3 inches of HMA

due to stripping. Patching was required prior to

overlay.



N 9.5 AC-20 LM Yes Milled and Filled with 2.25 inches of HMA

overlay in 2007.



O 9.5 AC-20 LM Milled and Filled with 2.25 inches of HMA

overlay in 2007.



P 11 AC-20 LM Yes Milled and Filled with 2.25 inches of HMA

overlay in 2007.




Juan D. Pava 14

TABLE 5 Latest condition of Project 4

Project Section Thickness,

Inches

Joint

Spacing,

Feet

Under-

drains

Sealed

Joint Status of Pavement Condition in 2010

4

R 9.0

CRC

Yes Original 228 square feet of patching.

S 8.0 Yes Original 42 square feet of patching.

T 8.0 Yes Yes Original

U 8.0 Yes Original

V 8.0 Original

W 7.0 Original 792 square feet of isolated HMA Patch/OL and 2 punchouts.

X 7.0 Yes Original 2 medium severity punchouts.

Y 7.0 Yes Yes Original

Z 7.0 Yes Original

AA 9.5 20 Yes

Overlaid in 2011

with 3.75 inches of

HMA.

11 feet of low severity longitudinal cracks.

BA 9.5 40 Yes All panels showed mid-panel cracks mostly of high severity.

CA 8.5 40 Yes Yes All panels cracked, some more than once, most cracks of medium severity.

DA 8.5

HJ Yes On average 38 low severity cracks per lane were found. DB 8.5

DC 8.5

EA 8.5 40 Yes All panels cracked, some more than once, most cracks of medium severity.

FA 8.5 40 Yes Yes 76% of panels cracked, most cracks of medium severity.

GA 8.5 40

Overlaid in 2008

with 3.75 inches of

HMA.

Weathering and raveling throughout section. Few low severity transverse

cracks were recorded.

HA 8.5 40 Yes

IA 8.5 20 Yes

JA 8.5 20 Yes

KA 8.5 20 Yes Yes

Weathering and raveling throughout section. LA 8.5 20 Yes

MA 7.5 20 Yes Yes

NA 7.5 20 Yes

Weathering and raveling throughout section. Few low severity transverse

cracks were recorded.

OA 7.5 40

PA 7.5 40 Yes

QA 7.5 40 Yes Yes

RA 7.5 40 Yes


Juan D. Pava 15

Traffic Consumption

One of the subjects of interest for IDOT was the correlation between traffic consumption and pavement

performance. Design Equivalent Single Axle Loads (ESALs) were determined for each of the test

sections, assuming poor subgrade and a 20-year design life. These values were compared to actual

cumulative ESALs values for each section when the section received an overlay. Table 6 shows the actual

cumulative ESALs of each section at the time of each overlay or as of December 31, 2011 if the section

was still bare. Percent consumption is defined as the ratio of actual cumulative ESALs to 20-year design

ESALs. For the HMA sections, these data show that the fatigue algorithm used in IDOT’s original design

procedure was conservative. Later fatigue work on Illinois specific mixes (Carpenter, 2006) (Carpenter,

2006) led to adoption of a less conservative fatigue algorithm in IDOT’s current design policy (Bureau of

Materials and Physical Reseach, 2011). Pavement performance monitoring in Illinois’ network has

showed that overlay timing is predicated by environmental factors, aging, and material issues rather than

traffic consumption. These data support IDOT’s practice that there is no direct correlation between

overlay timing and traffic consumption of the section since overlays were applied at consumption levels

ranging between 60% and 500%.

TABLE 6 Consumption of sections at time of major rehabilitation.

Project Section Pvmnt

Type

Thickness,

Inches

Design

ESALs1

1st Rehab Future

Rehab

Dec 2011

Year ESALs1 % Cons

2 ESALs

1 % Cons

2

1 A AC-10 13 3.5 2007 3.58 102% 4.59 131%

1 B AC-20 13 5.5 2007 3.58 65% 4.59 83%

2 C,D,F,G1,G2,G4 Jointed 10 11.7 5.96 51%

2 E,G3,H Jointed 10 18 5.96 33%

3 A,B AC-10 9.5 0.5 1994 0.64 128% FY 2012 3.14 628%

3 C,D AC-10 12.5 1.9 FY 2012 3.14 165%

3 E,H,I AC-20 12.5 2.6 FY 2012 3.14 121%

3 J,K AC-20 9.5 0.7 1994 0.64 91% FY 2012 3.14 449%

3 L,M,MI AC-20 9.5 0.7 1994 0.64 91% FY 2012 3.14 449%

3 N,O AC-20 9.5 0.7 2007 2.67 381% 3.25 464%

3 P AC-20 11 1.4 2007 2.67 191% 3.25 232%

4 AA,BA Jointed 9.5 2.6 2011 3.81 147% 3.81 147%

4 CA - FA Jointed 8.5 1.5 2011 3.73 249% 3.73 249%

4 DA, DB, DC Hinged 8.5 1.9 2011 3.73 249% 3.73 196%

4 GA - LA Jointed 8.5 1.5 2008 3.25 217% 3.7 247%

4 MA - RA Jointed 7.5 0.64 2008 3.25 508% 3.7 578%

4 R CRC 9 9.4 4.3 46%

4 S,T,U,V CRC 8 4.3 4.2 98%

4 W,X,Y,Z CRC 7 1.8 4.2 233%

1 ESALs in millions

2 Percent consumption = (Actual ESALs / Design ESALs) x 100


Juan D. Pava 16

CONCLUSION

After 25 years of service, US 20 and US 50 have provided great value to IDOT in the development of

new pavement design procedures, policies, standards, and in general, a better understanding of the

mechanics of pavement performance. The knowledge acquired from the four sections supports IDOT’s

practice in multiple ways. Project 1 demonstrated the influence of asphalt binder in full-depth HMA

pavements. IDOT assumes use of a PG 64-22 for pavement design purposes and selects performance

graded binders for surface and top lift of binder depending on the traffic and the location of the project.

Projects 2 and 4 illustrated the importance of joint spacing in jointed concrete pavement performance.

Based on performance history, IDOT now constructs 15-foot dowel jointed slabs. Project 3 is evidence of

the value of correct pavement thickness and the influence of the subgrade in pavement performance.

IDOT currently requires 12 inches of improved subgrade (modified soil or aggregate) under all new

construction. This study validated IDOT’s mechanistic pavement design procedure, proving that the

theory behind the 1986 design was correct. These sections and extensive laboratory testing and

investigation have allowed IDOT to further refine the mechanistic pavement design procedure in order to

include more accurate material properties.

Additionally, having 25 years of data and observations on the deterioration and rehabilitation of

certain sections have allowed IDOT to fine tune maintenance models to improve pavement type selection

procedures.

The four projects have served IDOT as a life-sized laboratory on pavement performance. These

sections will continue to bring knowledge to IDOT in years to come by providing further understanding

of pavement performance and enhancing pavement design procedures.


Juan D. Pava 17

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