147950-FinalReport

Effectiveness of Thin Hot Mix Asphalt Overlay on

Pavement Ride and Condition Performance

Final Report

Eddie Y. Chou, D. Datta, H. Pulugurta The University of Toledo

Prepared in Cooperation with Mileage vs. Actual Service Life Distribution of all Terminated Thin Overlay Projects

in General System

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Actual Service Life (in Years)

Mile

age

The Ohio Department of Transportation Office of Research and Development Statewide PCR Family Curves - Priority System

Line of Threshold PCR

50556065707580859095

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Age (in Years)

PCR

Minor Rehab Thin Overlay and The US Department of Transportation

Federal Highway Administration State Job Number 147950

April 2008

1. Report No. FHWA/OH-2008/4

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

5. Report Date April 2008

4. Title and subtitle Effectiveness of Thin Hot Mix Asphalt Overlay on Pavement Ride and Condition Performance 6. Performing Organization Code

8. Performing Organization Report No. 7. Author(s) Eddie Chou, Debargha Datta, Haricharan Pulugurta

10. Work Unit No. (TRAIS)

11. Contract or Grant No. 147950

9. Performing Organization Name and Address University of Toledo Department of Civil Engineering Toledo, OH 43606-3390

13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Ohio Department of Transportation 1980 West Broad Street Columbus, Ohio 43223

14. Sponsoring Agency Code

15. Supplementary Notes 16. Abstract

The objectives of this study were: 1) To determine the cost effectiveness of thin hot mix asphalt (HMA) overlays as a maintenance technique; 2) To determine under what conditions a thin overlay would be suitable; 3) To determine the timing of constructing a thin overlay to maximize its benefits; and 4) To develop a prototype aggregate source information system to correlate aggregate source quality to pavement performance. Performance data for thin overlays constructed by ODOT since 1990 were collected to study the cost-effectiveness of thin overlay. The average thin overlay project cost is about 40% of the average minor rehabilitation project cost for the Priority System, and approximately 60% for the General System pavements. In contrast, the average service life of a thin overlay is generally more than 70% of that of a minor rehabilitation. Therefore, most of the thin overlays are deemed cost effective. Thin overlay projects that are not cost effective tend to be those performed on very poor pavements, and with insufficient thickness. Thin overlays are most likely to be cost effective if the existing pavements PCR score is between 70 and 90 for Priority System, and between 65 and 80 for General System pavements. A prototype aggregate source GIS system was developed. Higher aggregate soundness loss is shown to correlate with higher pavement deterioration rate. A thin HMA overlay is generally a cost-effective maintenance treatment. Employed properly, thin overlay provides a relatively low cost alternative in preserving and extending the service life of the existing pavement.

17. Key Words Thin HMA Overlay, Cost Effectiveness, Aggregate Source GIS system

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

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages 149

22. Price

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

Effectiveness of Thin Hot Mix Asphalt Overlay on Pavement Ride and Condition Performance

Final Report

State Job No. 14795 (0)

Principal Investigator: Eddie Y. Chou

Coauthors: Debargha Datta, Haricharan Pulugurta

The University of Toledo

Prepared in Cooperation with

The Ohio Department of Transportation

and

The U. S. Department of Transportation

Federal Highway Administration

April 2008

DISCLAIMER

The contents of this report reflect the views of the author who is responsible for the facts and

the accuracy of the data presented herein. The contents do not necessarily reflect the official

views or policies of the Ohio Department of Transportation or the Federal Highway

Administration. This report does not constitute a standard, specification, or regulation.

iii

ACKNOWLEDGMENTS

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

Highway Administration for sponsoring this study.

The researchers also would like to thank the technical liaisons of this project: Mr. Roger

Green, Mr. Aric Morse, Mr. Jeff Wigdhal, and Mr. Andrew Williams for their helpful

assistance during this study. Mr. Emil Marginean provided updated pavement condition data,

and Mr. Adam Au provided pavement construction cost data. Without their assistance, this

study would not have been completed.

The assistance provided by Dr. Joseph Tack, a former graduate research assistant at the

University of Toledo, during the first phase of this study is also appreciated.

iv

TABLE OF CONTENTS

Page

List of Figures ................................................................................................................ vi

List of Tables .................................................................................................................. viii

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

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

Objective of Research .................................................................................................... 3

General Description of Research ................................................................................... 3

Findings of the Research Effort ..................................................................................... 15

Conclusions and Recommendations .............................................................................. 77

Implementation Plan ...................................................................................................... 80

Appendix A: References ............................................................................................... A1

Appendix B: Thin Overlay Failure Mode District Survey Results .............................. B1

Appendix C: Cost Data of Recent Projects ................................................................. C1

Appendix D: List of Priority System Thin Overlay Projects Included in Analysis...... D1

Appendix E: List of General System Thin Overlay Sections Included for Analysis .. E1

Appendix F: ODOT Aggregate Source Information System User Manual ................. F1

v

LIST OF FIGURES

Figure 1: Benefit of a Thin Overlay ................................................................................... 9

Figure 2: Extension of Service Life Due to a Thin Overlay............................................... 11

Figure 3: Average Distress Levels Prior to and 8 Years after Thin Overlay...................... 18

Figure 4: Actual Service Lives Distribution of Terminated Thin Overlay Projects........... 22

Figure 5: Actual Service Life as a Function of Pavement Type......................................... 23

Figure 6: Average Service Life of Terminated Thin Overlays in Each District................. 24

Figure 7: Terminal PCR of Terminated Thin Overlay Projects in Each District ............... 25

Figure 8: Average Performance Trends of Minor Rehabilitation and Thin Overlay ......... 27

Figure 9: Time Extension (t) of Thin Overlays on Priority System ................................... 28

Figure 10: Time Extension (t) of Thin Overlays on General System................................... 29

Figure 11: Definition of Thin Overlay Performance ............................................................ 30

Figure 12: Effect of Existing Pavement Condition on Thin Overlay Performance.............. 31

Figure 13: Prior PCR Range in Each District....................................................................... 33

Figure 14: Average Thin Overlay Performance in each District .......................................... 34

Figure 15: Effect of Snowfall on General System Thin Overlay Performance.................... 36

Figure 16: Proportions of Thin Overlay Thickness in Each District .................................... 37

Figure 17: Effect of Overlay Thickness on Thin Overlay Performance............................... 38

Figure 18: Effect of Traffic Loading on Thin Overlay Performance ................................... 39

Figure 19: Average Performance as a Function of Year of Construction ............................ 41

Figure 20: Definition of Thin Overlay Benefit..................................................................... 42

Figure 21: Average Performance and Benefit as a Function of Prior PCR.......................... 43

Figure 22: Average Performance and Benefit as a Function of Prior Cracking Deduct ...... 44

Figure 23: Average Ride Quality Deterioration Trend of Thin Overlay .............................. 46

Figure 24: Average Benefit of Thin Overlay and Minor Rehabilitation in Each District .... 49

Figure 25: Cost Effective by the Time-Extension Method but Not-Cost Effective by the

Performance Area Method .................................................................................. 51

Figure 26: Not Cost Effective by the Time-Extension Method but Cost Effective by

Performance Area Method .................................................................................. 51

Figure 27: Not Cost Effective by Either Method ................................................................. 52

vi

Figure 28: Cost Effective by Both Methods......................................................................... 52

Figure 29: Average Benefit-Cost Ratio of Thin Overlays in Each Districts ........................ 53

Figure 30: CE and NCE Mileage by Year of Construction.................................................. 55

Figure 31: Cost Effectiveness of 1994-2002 Thin Overlays in Each District ...................... 56

Figure 32: Cost Effectiveness as a Function of the Ratio Thin Overlay Cost versus Minor

Rehabilitation Cost.............................................................................................. 57

Figure 33: Cost Effectiveness as a Function of Pavement Type .......................................... 59

Figure 34: Cost Effectiveness as a Function of Prior PCR................................................... 60

Figure 35: Determination of the Optimal Prior PCR Range Using the ROC Method ......... 61

Figure 36: Proportion of Each Parameter within Cost Effective and Not Cost Effective

Priority System Thin Overlays............................................................................ 63

Figure 37: Proportion of Each Parameter within Cost Effective and Not Cost Effective

General System Thin Overlay............................................................................. 64

Figure 38: Location of Aggregate Quarries in Ohio............................................................. 67

Figure 39: Aggregate Source Information System Structure ............................................... 67

Figure 40: Relating Source Aggregate Test Data to a Pavement Project ............................. 68

Figure 41: Average Soundness Loss of Gravel (1994-2005) ............................................... 70

Figure 42: Average Abrasion Loss of Gravel (1994-2005) ................................................. 70

Figure 43: Average Soundness Loss of Limestone (1994-2005) ........................................ 71

Figure 44: Average Abrasion Loss of Limestone (1994-2005) ........................................... 71

Figure 45: Average Soundness Loss of both Limestone and Gravel (1994-2005) .............. 72

Figure 46: PCR Slope versus Abrasion Loss for District 2 and 3) ...................................... 73

Figure 47: PCR Slope versus Soundness Loss for District 2 and 3) .................................... 73

Figure 48: Soundness Loss vs. Pavement Condition Distribution Map for District 2 and 3)

............................................................................................................................. 74

vii

LIST OF TABLES

Table 1: Existing Cost-Effective Analysis Methods ......................................................... 6

Table 2: Thin Overlay Projects Constructed During 1990-2002 ...................................... 8

Table 3: Median Deducts 8 Years after Thin Overlay in Each District ............................ 17

Table 4: Number of Thin Overlay Sections in Various Prior PCR Ranges ...................... 32

Table 5: Number of Thin Overlay Sections in Different Traffic Loading Levels ............ 35

Table 6: Thin Overlay Projects Constructed during 1994-2002 ....................................... 40

Table 7: Percent of Cost Effective Mileage versus Prior PCR and Thickness.................. 62

Table 8: Summary of Soundness and Abrasion Losses of Different Aggregates ............. 69

Table 9: Estimated RMSE of Different Interpolation Methods Applied on

Soundness Loss of Aggregates ........................................................................... 75

Table 10: Estimated RMSE of Different Interpolation Methods Applied on

Abrasion Loss of Aggregates .............................................................................. 76

viii

The Ohio Department of Transportation Office of Research & Development Executive Summary Report

Effectiveness of Thin Hot Mix Asphalt Overlay on

Pavement Ride and Condition Performance

Start Date: February 1, 2002 Duration: 76 months Completion Date: May 31, 2008 Report Date: February 1, 2008 State Job Number: 14795 Report Number: FHWA/OH-2008/4 Funding: $244,530 Principle Investigators:

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

ODOT Contacts:

Technical: Roger Green Aric Morse Office of Pavement Engineering 614-995-5993 614-995-5994 Administrative: Monique R. Evans, P.E. Administrator, R&D 614-728-6048

For copies of this final report go to

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

Ohio Department of Transportation Office of Research & Development

1980 West Broad Street Columbus, OH 43223

Problem A thin (2 inches or less) hot mix asphalt (HMA) overlay is one of the maintenance techniques performed on asphalt-surfaced pavements to extend the service life of the existing pavement. Thin overlays protect the pavement structure, reduce the rate of pavement deterioration, correct surface deficiencies, reduce permeability, and improve the ride quality. Milling may be performed prior to the thin overlay to remove deteriorated surface materials. A study of Ohios experience on thin overlay performance was initiated to determine the cost effectiveness of thin HMA overlay as a maintenance technique, and to develop criteria for selecting pavement candidates suitable for receiving thin overlay treatment.

Objectives

1. To determine the cost effectiveness of using thin hot mix asphalt overlays as a maintenance technique.

2. To determine under what circumstances a thin hot mix overlay would be suitable.

3. To determine the timing of constructing a thin overlay to maximize its benefits.

An addendum to the original study adds the following objective: 4. To develop a prototype aggregate source

information system to correlate aggregate source quality to pavement performance.

Description The study was divided into two phases. During Phase I, the researchers in collaboration with ODOT gathered performance data for all thin overlay projects constructed since 1990 on both Priority and General system pavements. The performance data gathered were used in Phase II to study the effectiveness of thin overlay as influenced by climate, existing pavement condition, overlay thickness, traffic loading, and other parameters. As a result of a concurrent research study on pavement forecasting models, predicted pavement conditions became available. This allowed more recent thin overlay projects without a long history of performance data to be included in the study. The performance of a thin overlay is measured in terms of the area under the PCR versus age curve, whereas the benefit of a thin overlay is defined as that part of the performance due solely to the thin overlay, i.e., total performance subtracting the residual performance of the existing pavement. The cost effectiveness of a thin overlay is determined by comparing the cost per unit area of benefit versus that of a typical minor rehabilitation.

Findings

The performance of a thin overlay

increases with better existing pavement condition, less annual snowfall amount, and increased overlay thickness. Thin overlays on flexible pavements perform better than those on composite pavements, as thin overlays are more effective in addressing rutting distress, but less effective in eradicating cracking distresses, such as transverse, longitudinal or reflective cracking. The

benefits of a thin overlay include improvements in both pavement condition and ride quality. The benefits decrease if the existing pavement is still in excellent condition. Based on the cost data from recent projects, the average thin overlay project cost is only about 40% of the average minor rehabilitation project cost for the Priority System, and approximately 60% for the General System pavements. However, the average service life of a thin overlay is generally above 70% of the average service life of a comparable minor rehabilitation. As a result, a majority of the thin overlays are deemed cost effective. Thin overlay projects that are not cost effective tend to be those performed on very poor pavements, and with insufficient thickness. Thin overlays are most likely to be cost effective if the existing pavements PCR score is between 70 and 90 for Priority System, and between 65 and 80 for General System pavements.

A prototype aggregate source information system has been developed. Higher aggregate soundness loss is shown to correlate with higher pavement deterioration rate, based on data from Districts 2 and 3.

Conclusions & Recommendations

A thin hot mix asphalt overlay is, in general, a cost-effective maintenance treatment. The most important criteria for selecting pavement candidates suitable for receiving thin overlay treatment are existing distress conditions and pavement type. Employed properly, thin overlay provides a relatively low cost alternative in preserving and extending the service life of the existing pavement network.

Implementation Potential The criteria developed in this study can be used by ODOT to select candidate pavements most suitable to receive thin overlay treatment to obtain the maximum benefit. The aggregate source information system developed can also be used readily.

II

INTRODUCTION

Many transportation agencies in charge of maintaining pavement networks have recognized the

importance of allocating a portion of their budgets to prolong the service life of existing

pavements through preventive maintenance measures, instead of just rehabilitated those

pavements that have already failed. It has been said that one dollar invested in preventive

maintenance at the appropriate time in the life of a pavement can save $3 to $4 dollars in future

rehabilitation costs (Geoffrey, 1996). In light of the rapid increases in highway construction

costs due to escalating fuel costs and inflation, prudent use of the cost-effective maintenance

treatments should be a vital part of the overall strategy to preserve the existing highway

infrastructure.

The Federal Highway Administration (FHWA) has encouraged transportation agencies at all

levels to implement preventive maintenance programs by allowing federal funds to be used for

maintenance treatments when it can be demonstrated that such maintenance treatments are cost-

effective methods of extending pavement life.

A thin (2 inches or less) hot mix asphalt (HMA) overlay is one of the maintenance techniques

performed on asphalt-surfaced pavements to extend the service life of the existing pavement.

Thin overlays protect the pavement structure, reduce the rate of pavement deterioration, correct

surface deficiencies, reduce permeability, and improve the ride quality. Milling may be

performed prior to the thin overlay to remove deteriorated surface materials.

A study was initiated by ODOT to determine whether or not thin HMA overlay is a cost

effective maintenance technique based on Ohios experience. The study also aims to determine

the criteria for selecting suitable candidate pavement sections for thin overlay treatment, and to

determine the appropriate timing of treatment in order to maximize the benefit.

Background

There are a number of preventative maintenance techniques, all of which focus on preserving a

pavements structure by alleviating functional deficiencies without significantly affecting the

structural capacity of a pavement. HMA thin overlay is generally the highest level of

preventive maintenance treatment performed on asphalt surfaced pavements.

The Long Term Pavement Performance (LTPP) program of the Federal Highway

Administration (FHWA) included a Specific Pavement Study-3 (SPS-3), which focused on

studying the effectiveness of various maintenance treatments. The treatments studied include

crack sealing, chip seal, slurry seal, and thin overlays. The goal of the SPS-3 was to determine

the life expectancy and timing of treatment applications. However, none of the 81 SPS-3

project sites are located in Ohio.

Thin HMA overlays have been performed by many transportation agencies with varying

success. A recent AASHTO questionnaire study indicates that out of the 25 States that have

used thin HMA overlays, 11 reported less than satisfactory results. The reported problems with

thin HMA overlays include de-lamination, reflective cracking, poor friction, low durability,

excessive permeability, and maintenance problems once failure starts.

An NCHRP survey (Geoffrey, 1996) showed that thin overlays generally have a service life of

between 5 and 8 years, but actual service life reported by the states ranges from as short as 2

years to as long as 10 years. The service lives vary significantly due to differences in

specifications, materials, thickness, treatment timing, traffic loading, and climatic conditions.

ODOTs Pavement Preventive Maintenance Guideline estimates that pavements that are

structurally sound, due to a recent minor or major rehabilitation, and are treated with a thin

HMA overlay are expected to last 8 to 12 years.

A study based on the performance experience of thin HMA overlays constructed in Ohio is

warranted, in order to determine the cost-effectiveness of thin overlays as a maintenance

treatment.

2

OBJECTIVE OF THE RESEARCH

The objectives of this study were:

1. To determine the cost effectiveness of using thin (2 inches or less) hot mix asphalt overlays

as a maintenance technique based on performance experience in Ohio;

2. To determine under what circumstances a thin hot mix overlay would be suitable; and

3. To determine the timing of constructing a thin overlay in order to maximize its benefits.

An addendum to the original study adds the following objective:

4. To develop a prototype aggregate source information system to analyze aggregate quality

data based on its source location, and to correlate quarry aggregate test data to pavement

performance.

GENERAL DESCRIPTION OF RESEARCH

To accomplish the above listed objectives, the study was divided into two phases. Phase I was

to collect thin overlay project performance data and to determine whether or not a sufficient

number of preventive maintenance thin overlay projects and corresponding condition data were

available to support the subsequent analysis. Phase II was to determine the cost-effectiveness

of thin overlay treatment as a maintenance treatment and to develop criteria for selecting

candidate pavements and the timing of construction in order to maximize the benefit of a thin

overlay.

The following tasks were performed:

Phase I

Task 1: Review of the Literature and Survey of District Maintenance Engineers

Task 2: Collection of Thin Overlay Project Performance Data in Ohio

Task 3: Preparation of the Interim Report

3

Phase II

Task 4: Evaluation of Cost Effectiveness

Task 5: Determination of Treatment Criteria

Task 6: Development of a Prototype Aggregate Source Information System

Task 7: Preparation of the Draft Final Report

Task 1: Literature Review and Survey of District Maintenance Engineers

Literature Review

A review of the existing literature on effectiveness of thin overlays was performed. The cost

effectiveness of thin overlay as a maintenance technique has been studied by a number of

researchers. Most of the recent studies were based on data from the LTPP SPS-3 experiments.

The major findings of the literature review are summarized below.

Geoffrey (1996) in NCHRP Synthesis 223 used a questionnaire survey of 60 transportation

agencies and published information to summarize the cost-effectiveness experiences of

preventive maintenance treatments. The report concluded that one dollar invested in preventive

maintenance at the appropriate time in the life of a pavement could save $3 to $4 in future

rehabilitation costs. The most cost-effective pavement management strategy is to perform

preventive maintenance activities on the better-rated pavements first and then fund the

rehabilitation of the poorer-rated pavements. The worst-first funding strategy is the least cost-

effective.

According to the survey responses contained in the Synthesis, for the State of Ohio, the typical

pavement age at the time of first thin overlay (years) was 9-10 years, and the typical life span

of a thin overlay was 9-10 years. The cost per lane mile was $25,000-$49,999, and the

observed increase in pavement life was 7-8 years.

Eltahan et al, (1999) studied the effectiveness of maintenance treatments of flexible pavements

based on data from 28 of the 81 SPS-3 projects located in the Southern region, which includes

Alabama, Arkansas, Florida, Mississippi, Okalahoma, Tennessee, and Texas. Their study

4

showed that the original condition of a pavement before maintenance treatment has a major

impact on the life expectancy of the treatment. For thin overlays, the median life expectancy

was 7.5, 7.3, and 2.5 years when the original condition was good, fair, and poor, respectively.

The median benefit of the thin overlay, defined as the number of years added to the median life

expectancy due to the thin overlay as compared to that of the control sections (i.e., without

treatment), was 2, 4.8, and 2.5 years when the original condition was good, fair, and poor,

respectively. They concluded that applying maintenance to sections with a poor condition

increases the risk of failure by 2 to 4 times. They also found chip seal to outperform thin

overlay, slurry seal, and crack seal in controlling the reappearance of distresses.

Hall et al. (2003) used the entire data set from SPS-3 experiment to assess the relative

performance of different maintenance treatments for flexible pavements. Thin overlays were

found to be the most effective treatment, followed by chip seals and slurry seals, in addressing

roughness, rutting, and cracking.

Chen et al. (2003) studied 14 SPS-3 sites located in Texas. The study concluded that chip seal

was the most effective treatment in most cases. However, thin overlay was the most effective

treatment in addressing rutting problems, and should be used on high traffic routes where

rutting is a major concern. They also concluded that the timing for preventive maintenance is

very important.

Based on the same subset of the SPS-3 data, Chang et al. (2005) determined the cost

effectiveness of various maintenance treatments by considering the cost of treatments. They

concluded that chip seal was the most cost effective treatment, as the cost of thin overlay was

the highest among all preventive maintenance treatments.

Several different methods to quantify the cost-effectiveness of preventive maintenance have

been described in the literature. Table 1 shows a summary of these methods. Hicks et al.

(1997 and 1999) proposed a process for selecting the most effective maintenance treatment for

flexible pavements based on a decision matrix. The timing of the treatment and user delay cost

were added to the consideration.

5

Table 1: Existing Cost-Effective Analysis Methods (from Hicks, et al. 1999)

Method Requirements Output

Life-cycle costing Interest rates Inflation rates Analysis period Unit cost for treatment Estimated life of treatment

The equivalent annual cost for each proposed treatment

Cost-Effectiveness analysis

Pavement performance curve

Area under the performance curve is equivalent to effectiveness

Equivalent annual cost

Cost of equipment, man power, materials

Unit cost per expected life of treatment

Longevity cost index

Treatment unit cost Present value of unit cost

over life of treatment Traffic loading Life of the treatment

Relates present value of cost of treatment to life and traffic

The life-cycle costing method requires interest and inflation rates as input and its result is

highly sensitive to these values. Actual values of interest and inflation rates (or the difference

of the two, called discount rate) fluctuate with time, and the appropriate values to be used for

evaluating public projects are not yet universally agreed upon. The longevity cost index

method also requires interest and inflation rates to determine the present value of future cost.

Therefore, these two methods were not selected for the current study.

The cost effectiveness method uses area under the pavement performance curve (PCR-Year) as

the measure for effectiveness. The performance histories of past thin overlay projects

constructed in Ohio have been collected and are available in the ODOT pavement database.

Therefore, this method can be used in the current study.

The equivalent annual cost (EAC) method is relatively straight forward. The EAC can be

calculated as:

years , treatmentof life expected

treatmentofcost unit =EAC (1)

6

In this study, the cost-effectiveness analysis and the equivalent annual cost methods were

selected to evaluate the cost-effectiveness of thin-overlay treatment.

Survey of District Maintenance Engineers

Telephone interviews were conducted to survey the District Maintenance Engineers in Ohio

regarding thin overlay performance in each District. The purpose was to gather the experience

of thin treatment through out Ohio, and to identify the specific distresses, related to traffic

loading or climate, observed in various Districts. The results are reported in the findings

section, along with the actual distress type and level information based on the measured

pavement condition rating (PCR) data in the ODOT pavement database.

Task 2: Collection of Thin Overlay Project Performance Data in Ohio

A list of thin overlay projects within each District was compiled. The researchers collaborated

with the Office of Pavement Engineering staff in reviewing thousands of project plans to

collect project specific data. In order to identify the thin overlay projects and the corresponding

pavement performance, the project history, pavement buildup, thickness added, pavement

condition ratings, traffic loading, and other relevant data for all twolane undivided highways

(the General and Urban systems) since 1990 were collected. Similar data for all four-lane

divided highways (the Priority system) since 1985 had been collected as part of a previous

research study. All data collected were included in the ODOT pavement management

database. This database also supports other research studies and various pavement

management activities.

Thin overlay projects constructed after 2002 are not included in this study, because these thin

overlays have not been in service long enough to accurately assess their performance. The thin

overlay projects identified and included in this study are summarized in Table 2. For the

Priority system, 194 thin overlay projects, totaling 1733.9 miles, constructed between 1990 and

2002 were included. Among these thin overlays, 135 projects, totaling 1030.2 miles, have

received a subsequent maintenance or rehabilitation treatment, and therefore these thin overlays

7

are considered as terminated. Only the terminated thin overlays have known actual service

life. The rest of the thin overlays are still in service, and their service life can only be estimated

from forecasted pavement conditions. For the General system, 1367 thin overlay projects,

totaling 9335 miles, are included in this study. Among them, 765 projects totaling 4075.2

miles are terminated projects. Each project may include multiple sections, due to

differences in existing or subsequent pavement conditions, traffic loading, county, or pavement

type.

Many of the thin overlays on the Priority system pavements were performed as preventive

maintenance treatments, while most of the thin overlays performed on the General system

pavements were not intended as preventive maintenance.

Table 2: Thin Overlay Projects Constructed During 1990-2002

Priority General

District No. of Thin

Overlay Project

Miles

No. of Thin

Overlay Project

Miles

1 9 (5) 102.4 (25.7) 150 (96) 1075.1 (541.3) 2 12 (9) 80 (53.8) 73 (42) 477.2 (214) 3 12 (11) 102.6 (90.4) 111 (69) 741.5 (359.9) 4 20 (15) 147.8 (103) 111 (59) 680.3 (254.7) 5 18 (9) 158.8 (91.4) 62 (43) 592.5 (332.3) 6 33 (22) 375.1 (226.9) 119 (79) 1079.3 (593.2) 7 17 (12) 177.9 (117.4) 250 (136) 1313.3 (607.8) 8 20 (13) 229 (122.5) 99 (62) 702.2 (353.9) 9 9 (6) 57.1 (33.5) 87 (31) 587.2 (118.1) 10 11 (6) 54.4 (18.9) 137 (64) 1036.7 (328.4) 11 15 (13) 129 (67) 136 (74) 931.3 (335.8) 12 18 (14) 119.9 (79.8) 32 (10) 118.4 (35.6)

Statewide 194 (135) 1733.9 (1030.2) 1367 (765) 9335 (4075.2)

* Numbers in parentheses are those thin overlays that have terminated.

8

Task 3: Preparation of the Interim Report

At the end of Phase I, an interim report was prepared and submitted. The report concluded that

the amount of thin overlay project data available were sufficient to support the analyses in

Phase II. It was decided by ODOT to include all thin overlay projects, whether or not they

were intended as preventive maintenance treatments, for this study.

Task 4: Evaluation of Cost Effectiveness

Two different methods were used to determine the benefit or effectiveness of thin HMA

overlay treatment. The first method uses the increased performance area under the pavement

condition rating (PCR) versus age curve due to the thin overlay as the measure of thin overlay

benefit. The second method uses the extension of a pavements service life due to a thin

overlay treatment as the measure of thin overlay benefit.

Figure 1 illustrates the performance area method, where the performance of a pavement is

measured by the area under the PCR condition versus Age curve above a terminal condition

threshold, when a major or minor rehabilitation become necessary (e.g., area A1 in the Figure

below). The benefit of a thin overlay treatment is defined as the performance area after a thin

overlay minus the residual performance of the previous treatment (i.e., area A0 is the benefit of

the thin overlay).

C 1

Figure 1: Benefit of a Thin Overlay

C

Time, Years

PCR = 60

Con

ditio

n, P

CR

0

AA 01

9

The benefit-cost ratio can be obtained by dividing the benefit by the cost of construction for

the thin overlay. The benefit cost ratio (B/C) can be calculated by:

0

1

1

0/CC

AACB = (2)

where A0 is the benefit of a thin overlay,

A1 is the performance/benefit of a typical minor rehabilitation in the same District,

C0 is the average cost of a thin overlay, and

C1 is the average cost of a typical minor rehabilitation.

When the benefit-cost ratio is greater than one, the thin overlay is deemed cost effective.

As a result of a concurrent research study on Pavement Forecasting Models, the ability to

predict pavement conditions became available during the course of this study. Therefore,

pavement performance to a specified terminal condition threshold can be predicted, which

allows many pavement sections that have not reached the terminal condition to be included in

the analysis. Furthermore, the benefit of a thin overlay can be evaluated by comparing the

performance of a pavement that received a thin overlay versus the predicted performance of the

same pavement if the thin overlay was not performed. Consequently, it is not necessary to

identify control sections with characteristics similar to the thin overlay test section, as the

same pavement section serves as both the test section and the control section.

The average cost of thin overlays and the average cost of typical minor rehabilitations were

obtained from an analysis of recently completed projects. The cost data were provided by the

Staff of the Office of Pavement Engineering.

Figure 2 illustrates the time extension method, where the benefit of an overlay is expressed as

the time extension, t, of the pavements service life.

10

Time, Years

Thin Overlay Minor / Major

Minor / Major

Pave

men

t Con

ditio

n

x3

x2

Minor / Major

x1

t

Figure 2: Extension of Service Life Due to a Thin Overlay

The extension of service life, t, due to a thin overlay as compared with no treatment can be

expressed as:

(3) 321 )( xxxt +=

where t = time extension of pavement service life due to thin overlay, in years,

x1 = age of the existing pavement at the time of thin overlay,

x2 = life span of the thin overlay (i.e., age of thin overlay when it falls below the

terminal condition threshold)

x3 = life span of the existing pavement, if no thin overlay was performed

As illustrated in Figure 2, x1 + x2 represents the total service life of a pavement section when a

thin overlay is performed, and x3 represent the predicted service life of the same pavement

section, if the thin overlay was not performed. If the thin overlay life span, x2, remains

relatively unchanged, the later it is performed during the life of an existing pavement (i.e.,

larger x1), the longer the time extension, t. However, a thin overlays life span may be

shortened if it is performed on a pavement with very poor existing condition.

11

The equivalent annual cost (EAC) of a thin overlay project can be calculated by dividing the

average unit cost per lane-mile of thin overlay by the time extension, t. The EAC of a minor

rehabilitation is calculated by dividing the average unit cost per lane-mile of a typical minor

rehabilitation by the typical minor rehabilitation life span, for example, x3. The thin overlay is

considered as cost effective if its EAC is less than the EAC of a minor rehabilitation. For

example, if the cost of a thin overlay is 60% of the cost of a minor rehabilitation, and if the

average service life of the minor rehabilitation is twelve (12) years, then the thin overlay must

extend the time to next treatment by more than seven (7) years to be cost-effective.

Task 5: Determination of Treatment Criteria

This task was to determine under what circumstances a thin HMA overlay would be more

likely to be cost-effective. The parameters that likely affect the performance and cost-

effectiveness of a thin overlay include: 1) existing pavement type, 2) pavement condition prior

to the thin overlay, 3) thickness of the overlay, 4) traffic loading, 5) climatic factors such as

snowfall amount, 6) District location, and 7) quality of the thin overlay itself, including quality

of the materials used, workmanship of construction, and time of year of the placement. Except

for the last category of parameters, where no data are readily available, the effect of each of the

above parameters on thin overlay performance, benefit, and cost-effectiveness were

investigated. The District location parameter likely encompasses a number of parameters such

as material qualities, maintenance practices, rehabilitation strategies, traffic patterns and

climate.

The criteria for selecting the candidate pavements suitable for thin HMA overlay treatment and

the optimal timing of constructing a thin overlay were also developed as part of this task. The

cost effectiveness of each thin overlay sections was determined based on the performance area

method. The criteria were developed by comparing the characteristics of the thin overlays that

were deemed cost effective with those thin overlays that were deemed not cost effective.

12

Task 6: Development of a Prototype Aggregate Source Quality Information System

Aggregates comprise the basic skeleton of any flexible or concrete pavement. Therefore, the

quality of aggregates strongly influences the durability and performance of pavement. The

scope of this task was to develop a prototype aggregate source information system to reference

aggregate source and quality data geographically, and to correlate the aggregate quarry test data

to pavement performance. Available data from Districts 2 and 3 are use to developed the

prototype system. The geo-referenced aggregate source quality information can be used by the

Office of Materials Management as a pro-active tool for allocating sampling resources (i.e.,

increasing sampling in suspect areas before they become a problem) and for monitoring

aggregate quality.

The specific subtasks performed include:

Development of an ArcGIS Script for Data Entry

An ArcGIS Script was developed to allow the user to append and edit the aggregate quality

data into the database and use them for further analysis. The detailed description of the steps to

use the script is covered in Sections 3 to 6 of Appendix F.

Clipping the Grid Automatically 20 Miles from Aggregate Source

After importing the aggregate quality data into ArcGIS, the method of clipping the resulting

raster data was done using the buffer and extraction tools available in ArcGIS 9.1. The detailed

steps to accomplish this task are covered in Section 11.2 of Appendix F.

Recommendation for a Suitable Interpolation Method

Different methods are available to interpolate the aggregate test data from the quarry source

locations. The details of these methods and the steps to identify the best method are described

in Section 9 of Appendix F. The estimated root mean square error (RMSE) was used as an

13

indicator to determine the most suitable interpolation method. The method that yields the

lowest RMSE is recommended as the best method.

Analyzing the Aggregate Test Data and Correlation with Pavement Performance

Large amounts of aggregate quality test data from various quarries have been collected by

ODOT dating back many years. The two types of test data analyzed for this study are

soundness loss and abrasion loss. Using data from Districts 2 and 3, where aggregate source(s)

for each pavement project were identified through the Job Mix Formula (JMF) and the

Producer/Supplier Code information, the aggregate quality corresponding to the same time era

of construction was correlated with the subsequent pavement performance, in terms of the

average PCR drop per year. When the exact aggregate source can not be identified, aggregate

quality interpolated from nearby quarry locations was used to correlate with pavement

performance.

14

FINDINGS OF THE RESEARCH EFFORT

The findings of this study are presented in this section. They include:

I. Performance experience of thin overlay as a maintenance treatment in Ohio

District Maintenance Engineers survey results,

Summary of distresses from PCR data,

Actual service life of terminated thin overlays,

II. Cost effectiveness of thin overlays

Time extension of service life due to thin overlays,

Performance (area under the PCR-age curve) of thin overlays,

Benefit of thin overlays,

Cost analysis,

Benefit-Cost Ratio and Cost-Effectiveness Determination

III. Criteria for cost-effective thin overlay treatment and timing of construction, and

IX. Prototype aggregate source quality information system

I. Experience of Thin Overlay as a Maintenance Treatment in Ohio

District Maintenance Engineers Survey Results

The following distresses were reported by the District Maintenance Engineers as typically

failure modes of thin HMA overlays:

Reflective cracking, Random / thermal cracking, Edge cracking (only on Urban/General system pavements), Raveling, Longitudinal cold joint failures, Rutting (only on Urban/General system pavements in Districts 6 and 11), Corrugation (occasional, in hilly area with high trucks and thin overlay

thickness, reported by Districts 4, 6, 7, and 8),

De-bonding (occasional), and

15

Water in base course was identified by Districts 8 and 11 as cause of many failures.

The survey questionnaire and the detailed responses of each District Maintenance Engineer are

included in Appendix B.

Summary of Distresses from PCR Data

Based on the historic PCR and corresponding distress data contained in the ODOT Pavement

Database, the actual distresses observed for pavements that received a thin overlay treatment

between 1990 and 1998 were extracted. Table 3 shows the median deduct value of the more

significant distresses for thin overlays that were eight (8) years old in each District. Higher

deduct values correspond to a combination of higher severity and/or extent of a particular

distress. It can be seen that the type of distress and the severity of each distress vary from one

District to another. The shaded cells in Table 3 represent significant distress deducts. For the

Priority system, where the majority of pavements are composite pavements, joint reflective

cracking, raveling, rutting, and crack sealing deficiency are the major distresses. For the

General system, with predominantly flexible pavements, block and transverse cracking,

raveling, rutting, wheel track cracking, and crack sealing deficiency are the major distresses.

The effect of milling is not obvious and varies among Districts.

Figure 3(a) and 3(b) shows the average levels of the more significant distresses before and

eight (8) years after thin overlays. The vertical axis is the percentage of pavements having the

particular distress level. The horizontal axis shows the level of distress in terms of severity and

extent, ranging from NULL (not-exist) to LO (Low severity, Occasional), LF (Low severity,

Frequent), to HE (High severity, Extensive). Thin overlays are more effective in reducing

rutting distress, but less effective in eradiating cracking distresses. Figure 3(c) shows that thin

overlays that required milling had more prior cracking distresses. The average cracking

distress levels eight years after thin overlays with milling are not significantly different from

the average prior distress levels, and are comparable to that of overlays without milling. As the

milling data are not precise and the practices of milling vary among Districts, more detailed

analysis is necessary to accurately determine the effect of milling.

16

Table 3: Median Deducts 8 Years after Thin Overlay in Each District

(a) Priority System District Type of

Distress Milling 1 2 3 4 5 6 7 8 9 10 11 12 w/o 3.2 1.9 1.9 0.6 0 1.9 0 0 3.8 Intermediate

Transverse Cracking with 1.9 3.2 1.9 0 4.8 0.6 0 1.9 6.4 1.9

w/o 12 9.6 12 7.2 0 7.2 2.4 1 7.2 Joint Reflection Cracking with 12 12 7.2 12 12 7.2 0 7.2 12 9.6

w/o 3.5 2 2.4 3.0 0 3.5 0.8 1 4 Longitudinal Cracking with 3 4 1.2 1.8 5 0.8 2.5 2.4 3 2.4

w/o 3 3 3 3 0 3.0 3 3 3 Raveling

with 3 3 3 3 4.8 3 3 3 3 3 w/o 3 1.8 3 5.6 0 2.4 0 0 3

Rutting with 7 7 4.2 0 3 2.4 3 1.8 7 4.2 w/o 5 4 5 4.0 0 4.0 0 4 4 Crack

Sealing Deficiency with 5 2.5 4 0 5 5 5 5 4 5

w/o 32 25 35 30 23 22 8 12 18 30 30 ALL

with 33 37 29 11 41 24 29 27 34 31

(b) General System District Type of

Distress Milling 1 2 3 4 5 6 7 8 9 10 11 12 w/o 3.5 4.9 7 7 7 4.9 5 4.9 3.5 4.9 7 7 Block and

Transverse Cracking with 3.5 2.8 4.9 7 7 5 5 4.9 2.8 7 7

w/o 1 1.8 2.5 2.5 2.5 2.5 1.8 1 2 2.5 1.8 2.5 Edge Cracking with 1.8 1 3.5 2.5 2.5 2.5 1.8 1.8 2 1.8 1.8

w/o 2.4 3.5 3.5 3.5 2.5 2.5 3 2.5 1.8 1.4 1.8 2.5 Longitudinal Cracking with 2.5 2.5 2.5 3.5 2.5 2.5 2.5 2 1.4 2.4 2.4 1.2

w/o 3 3 3 3 3 3 3 3 3 3 3 3 Raveling

with 3 3 3 4.8 3 3 3 3 3 3 3 3 w/o 3 3 4.2 3 3 3 3 3 3 1.8 2.4 3

Rutting with 3 2.4 4.2 3 4.2 3 3 2.4 0 3 3 1.8 w/o 3 4.2 7.3 5.2 4.2 4.2 3 3 3 5.2 5.2 4.2 Wheel

Track Cracking with 3 4.2 5.2 4.8 5.2 3 3 3 5.2 4.2 5.2

w/o 4 5 5 5 5 4 5 5 4 4 5 4 Crack Sealing

Deficiency with 4 2.5 4 5 4 5 4 5 0 5 5 2.5

w/o 23 29 37 35 32 26 27 26 23 24 32 30 ALL

with 23 18 35 32 32 28 25 23 18 31 32 17

17

(a) Priority System Thin Overlays constructed between 1990 and 1998 Intermediate Transverse Cracks (Jointed Base)

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

(3.2)

Joint Reflection Cracks (Jointed Base)

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e (9.6)(7.2)

Longitudinal Cracking

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

(2.4)(3) (4)

Ravelling

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th Year

(3)

Perc

ent

Mile

age

Rutting

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e (7)(3)

Crack Sealing Deficiency

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th Year

(5)

Perc

ent

Mile

age

(4)(2.5)

Figure 3(a): Average Distress Levels Prior to and 8 Years after Thin Overlay

(Numbers in parenthesis indicate the corresponding deduct Value)

18

(b) General System Thin Overlays constructed between 1990 and 1998 Edge Cracking

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

(7) (10)

Longitudinal Cracking

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

(3.5/3)(5)

Ravelling

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th Year

(3)

Perc

ent

Mile

age

(6)(3)

Rutting

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th Year

Perc

ent

Mile

age

(3) (7)

Wheel Track Cracking

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

(5.25) (7.35)

Crack Sealing Deficiency

0.00

50.00

100.00

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th Year

(5)

Perc

ent

Mile

age

(4) (2.5)

Figure 3(b): Average Distress Levels Prior to and 8 Years after Thin Overlay

(Numbers in parenthesis indicate the corresponding deduct Value)

19

Intermediate Transverse Cracks (Jointed Base) - Without Milling (Priority System)

0

50

100

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

Intermediate Transverse Cracks (Jointed Base) - With Milling (Priority System)

0

50

100

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

Joint Reflection Cracks (Jointed Base) - Without Milling (Priority System)

0

50

100

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

Joint Reflection Cracks (Jointed Base) - With Milling (Priority System)

0

50

100

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th Year

Perc

ent

Mile

age

Longitudinal Cracking - Without Milling (General System)

0

50

100

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

Longitudinal Cracking - With Milling (General System)

0

50

100

NU

LL LO LF LE L MO

MF

ME M HO HF

HE H O F E

Prior8th YearPe

rcen

t M

ileag

e

Figure 3(c): Effect of Milling on Average Distress Levels Prior to and 8 Years

after Thin Overlay constructed between 1990 and 1998

20

Actual Service Life of Terminated Thin Overlay The actual service lives of terminated thin overlays, i.e., those thin overlays that have been

replaced by a subsequent minor rehabilitation or another thin overlay treatment, vary widely.

Figure 4 shows the distributions of actual service lives of thin overlays on Priority and General

Systems, respectively.

The typical actual service life of Priority system thin overlays is between 4 and 9 years, with an

average life of 6.6 years. The typical actual service life of General system thin overlays is

between 6 and 12 years, with an average life of 9.1 years.

Figure 5 shows that the actual service lives of thin overlays performed on flexible pavements

are longer than those on composite pavements. This is particularly true for Priority system thin

overlays. The median actual life of Priority system thin overlays on flexible pavements is 8

years, while on composite pavements, its 6 years.

The average actual lives of thin overlays in each District are shown in Figure 6. The average

lives for most Districts are not significantly different from the statewide average values.

Priority system thin overlays in District 9 have the longest average service life of nearly 10

years, while General system thin overlays in District 12 have the longest average life of nearly

12 years. However, comparing the actual service lives can be misleading, as the condition at

which a thin overlay is replaced can be very different. A thin overlay may be replaced at a very

poor condition resulting in a long actual service life, whereas another pavement may be

replaced at a much better condition, resulting in a shorter actual life. Therefore, the length of

actual service life may not fully reflect the performance of a thin overlay.

Figure 7 shows the terminal PCR score, i.e., the PCR score at which a thin overlay was

replaced by the next treatment, varies significantly among Districts. Statewide, the average

terminal PCR score for Priority system thin overlays is 73, and for General system thin

overlays, 69. General System thin overlays in District 12 have the lowest terminal PCR scores

of mostly below 60, indicating that the long actual service lives in this District are simply due

to not replacing the thin overlays until the pavements are in very poor condition.

21

Mileage vs. Actual Service Life Distribution of all Terminated Thin Overlay Projects in Priority System

0

20

40

60

80

100

120

140

160

180

200

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15


Mile

age

`` `

Total Miles = 1030.1 No. of Sections = 507 No. of Projects = 135 Mean () = 6.6 years STDev () = 2.7 years

(a) Priority System

Mileage vs. Actual Service Life Distribution of all Terminated Thin Overlay Projects

in General System

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17


Mile

age

Total Miles = 4075.2 No. of Sections = 1923 No. of Projects = 764 Mean () = 9.1 years STDev () = 3.0 years

(b) General System

Figure 4: Actual Service Lives Distribution of Terminated Thin Overlay Projects

22

Actual Service Life by Pavement Type in Priority System

0

2

4

6

8

10

12

14

Flexible Composite

Pavement Type

Act

ual S

ervi

ce L

ife

(a) Priority System

Actual Service Life by Pavement Type in General System

0

2

4

6

8

10

12

14

Flexible Composite

Pavement Type

Act

ual S

ervi

ce L

ife

(b) General System

Figure 5: Actual Service Life as a Function of Pavement Type

23

Thin Overlay Actual Service Life by District in Priority System

0

5

10

15

1 2 3 4 5 6 7 8 9 10 11 12Districts

Ave

rage

Act

ual S

ervi

ce L

ife(in

Yea

rs)

Priority System (a) Priority System

Thin Overlay Actual Service Life by District in General System

0

5

10

15

1 2 3 4 5 6 7 8 9 10 11 12Districts

Ave

rage

Act

ual S

ervi

ce L

ife(in

Yea

rs)

General System (b) General System

Figure 6: Average Service Life of Terminated Thin Overlays in Each District

24

Priority System Terminal PCR of Terminated Projects by District

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12District

Ter

min

al P

CR

(a) Priority System

General System Terminal PCR of Terminated Projects by District

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12District

Ter

min

al P

CR

(b) General System

Figure 7: Terminal PCR of Terminated Thin Overlay Projects in Each District

25

II. Cost Effectiveness of Thin Overlays In order to evaluate the cost effectiveness of thin overlays accurately, it is necessary to project

the thin overlay performance to a uniform terminal PCR. The terminal PCR threshold value for

Priority system pavements is 65, while the terminal PCR threshold value for General system

pavements is 60, which was raised from 55 recently. If the measured PCR deterioration trend

ends above the terminal threshold, the deterioration trend is projected to the terminal threshold,

using the Markov prediction model developed in a separate research study. The expected

service life of a pavement is defined as the time from the end of construction till the actual or

predicted PCR score falls below the threshold value.

Figure 8 shows the statewide average deterioration trends of thin overlays and minor

rehabilitation for Priority and General System pavements. Based on a terminal PCR threshold

of 65, the expected service life of a Priority System thin overlay is 9 years, while a Priority

system minor rehabilitation is expected to last 12 years. For the General System, based on a

terminal PCR threshold of 60, the expected service life of a thin overlay is 13 years, and of a

minor rehabilitation, around 14 years.

The Extension of Service Life Due to a Thin Overlay

The expected time extensions of service lives due to the performance of a thin overlay are

shown in Figures 9 and 10. Figure 9 shows that Priority System thin overlays, on average,

extend the expected service life of an existing pavement by about 7.5 years, with a standard

deviation of 3.4 years. Figure 10 shows that General System thin overlays extend the expected

service life of an existing pavement by an average of 10.7 years, with a standard deviation of

3.8 years.

The actual time extension of service lives varies widely from the average values as evidenced

by the rather high standard deviation values, and as shown in Figures 9 and 10.

26

Statewide PCR Family Curves - Priority System


50556065707580859095

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Age (in Years)

PCR

Minor Rehab Thin Overlay

(a) Priority System

Statewide PCR Family Curves - General System


50556065707580859095

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Age (in Years)

PCR

Minor Rehab Thin Overlay

(b) General System

Figure 8: Average Performance Trends of Minor Rehabilitation and Thin Overlay

27

Distribution of x1

0

100

200

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20Time (in Years)

Mile

age No. of Sections = 820

Total Miles = 1679.85 Mean () = 8.1 years Stdev () = 6.0 years

(a) Age of Existing Pavement at the Time of Thin Overlay, x1

Distribution of x2

0

100

200

300

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (in Years)

Mile



(b) Service Life of Thin Overlay, x2

Distribution of x3

050

100150200

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 21Time (in Years)

Mile



(c) Service Life If Thin Overlay Was Not Performed, x3

Distribution of Time Extension (t)

0

100

200

300

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18Time (in Years)

Mile



(d) Time Extension, t

Figure 9: Time Extension (t) of Thin Overlays on Priority System

28

Distribution of x1

0

500

1000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (in Years)

Mile



(a) Age of Existing Pavement at the Time of Thin Overlay, x1

Distribution of x2

0200400600800

1000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Time (in Years)

Mile



(b) Service Life of Thin Overlay, x2

Distribution of x3

0200400600800

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (in Years)

Mile



(c) Service Life if Thin Overlay Was Not Performed, x3

Distribution of Time Extension (t)

0200400600800

1000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (in Years)

Mile



(d) Time Extension, t

Figure 10: Time Extension (t) of Thin Overlays on General System

29

The Performance (Area under the PCR-Age Curve) of Thin Overlay

The performance of a thin overlay is defined by the area between the PCR versus Age curve

and the terminal PCR threshold line. For example, Figure 11 shows the performance area for

an actual General System thin overlay section. The shaded area is the performance of the thin

overlay.

The performance of a thin overlay can be influenced by many parameters. One of the most

important parameters is the condition of the existing pavement prior to the thin overlay. Figure

12 shows that thin overlay performance increases with better existing pavement condition, i.e.,

higher PCR prior, especially on Priority System pavements. Table 4 shows that thin overlays

were performed on pavements with various Prior PCR scores, from below 55 to nearly 90.

Thin Overlay PerformanceCounty LUC; Route 024R; Station UP; Elog 0; Blog 1.11

60

70

80

90

100

1993 1995 1997 1999 2001 2003 2005 2007 2009 2011Year

PCR

MinorMinor (Predicted)Thin OverlayThin Overlay (Predicted)

Figure 11: Definition of Thin Overlay Performance

30

Priority System (Threshold PCR = 65) Thin Overlays PerformanceArea Under Curve Distribution

0

50

100

150

200

250

300

350

0-55 56-60 61-65 66-70 71-75 76-80 81-85 86-90

PCRPrior

Perf

orm

ance

(PC

R-Y

ear)

(a) Priority System

General System (Threshold PCR = 60) Thin Overlays PerformanceArea Under Curve Distribution

0

100

200

300

400

500

600

56-60 61-65 66-70 71-75 76-80 81-85 86-90

PCRPrior

Perf

orm

ance

(PC

R-Y

ear)

(b) General System

Figure 12: Effect of Existing Pavement Condition on Thin Overlay Performance

31

Table 4: Number of Thin Overlay Sections in Various Prior PCR Ranges

No. of Thin Overlay Sections in each Prior-PCR Range Priority 0-55 56-60 61-65 66-70 71-75 76-80 81-85 86-90

P 58 84 160 185 206 125 101 31 G 584 754 954 1136 1012 539 282 150

Figure 13 shows that PCR scores prior to thin overlays vary significantly among Districts.

Districts 1, 5 and 9 performed most of their thin overlays on pavements with an exiting PCR of

between 70 and 85. In contrast, some Districts often perform thin overlay treatments when the

prior PCR scores are below 70 or even below 60.

This high variation of prior PCR scores among Districts can be attributed to both the variation

of pavement performance and conditions among Districts and differences in District

maintenance policy. For General System thin overlays, the prior PCR scores shown in Figure

13 are similar to the terminal PCR scores shown in Figure 7 for most Districts, because thin

overlays are routinely followed by another thin overlay treatment on General System

pavements. However, the pattern is different for Priority system pavements, as thin overlays

are usually not repeated. If the thin overlays were performed as a preventive maintenance

treatment, the terminal PCR score would be lower than the PCR score; such is the case in

District 1. However, in other Districts, thin overlays were often performed as a way to

postpone the next rehabilitation, and were replaced at a relatively early age. As a result, the

terminal PCR is higher than the Prior PCR.

Thin overlays that were constructed on pavements with better existing conditions have better

performance; therefore, they likely have higher terminal PCR scores when replaced by the next

treatment, say, seven to nine years later. This becomes a positive, upward cycle for those

Districts that do not have a large backlog of poor pavements, and can afford to maintain and

rehabilitated their pavements in a timely manner.

Figure 14 shows the average thin overlay performance in each District.

32

Priority System Prior PCR by District

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12District

Prio

r PC

R

(a) Priority System

General System Prior PCR by District

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12District

Prio

r PC

R

(b) General System

Figure 13: Prior PCR Range in Each District

33

Thin Overlay Performance by DistrictAverage Area Under Curve

0

50

100

150

200

250

1 2 3 4 5 6 7 8 9 10 11 12District

Ave

rage

Per

form

ance

(PC

R-Y

ear)

Priority System - PCR Threshold = 65 (a) Priority System

Thin Overlay Performance by DistrictAverage Area Under Curve

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9 10 11 12District

Ave

rage

Per

form

ance

(PC

R-Y

ear)

General System - PCR Threshold = 55 General System - PCR Threshold = 60

(b) General System

Figure 14: Average Thin Overlay Performance in each District

34

Figure 15 shows that the amount of annual snowfall adversely affects thin overlay performance.

This climate parameter contributes, at least partially, to the above average performance in

Districts 8, 9, and 10 and the below average performance in Districts 3, 4, and 12.

The overlay performance is also influenced by overlay thickness. However, for thin overlays,

the thickness ranges only from 1 to 2 inches, with a majority of the thin overlays having a

thickness of 1.5 inches or higher. Figure 16 shows that the proportions of different thin overlay

thicknesses vary significantly among Districts. For example, on the Priority System, most of

the 1.75-inch overlays were performed by District 7. District 2 performs mostly 1.5-inch

overlays, while District 10 performs mostly 2-inch overlays.

Figure 17 shows that greater thickness corresponds to a slight increase in performance. The

effect of thickness is likely confounded with other parameters, such as the Prior PCR. As

shown, 1.75-inch Priority System thin overlays perform poorly, but they are mostly in District

7, where the median prior PCR of its Priority System thin overlay is 66, below the statewide

average.

Figure 18 shows that Priority System thin overlay performance does not appear to correlate

with traffic loadings. However, the performance of General System thin overlays decreases at

high traffic loading level of annual ESAL above 200,000 (log ESAL greater than 5.5).

Table 5 shows that most of the General System pavements are in the low to medium traffic

loading levels (log ESAL below 5.5).

Table 5: Number of Thin Overlay Sections in Different Traffic Loading Levels

No. of Pavement Sections in Each Traffic Loading Range (log ESAL) Priority

0-4.4 4.5-4.9 5.0-5.4 5.5-5.9 6.0-6.4 6.5-8.0 P 67 237 441 227 G 1323 1960 1576 590 157 12

35


0

50

100

150

200

250

300

15-21 22-28 29-35 36-42 43-99Snowfall (inches)

Perf

orm

ance

(PC

R-Y

ear)

n = 230 n = 378 n = 101 n = 84 n = 197

(a) Priority System


0

50

100

150

200

250

300

350

400

15-21 22-28 29-35 36-42 43-99Snowfall (inches)

Perf

orm

ance

(PC

R-Y

ear)

n = 1081 n = 2531 n = 1055 n = 567 n = 389

(b) General System

Figure 15: Effect of Snowfall on General System Thin Overlay Performance

36

Thickness Added-Mileage by District in Priority System

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9 10 11 12District

Mile

age

21.751.51.251

(a) Priority System

Thickness Added-Mileage by District in General System

0

200

400

600

800

1000

1200

1400

1 2 3 4 5 6 7 8 9 10 11 12District

Mile

age

21.751.51.251

(b) General System

Figure 16: Proportions of Thin Overlay Thickness in Each District

37


0

50

100

150

200

250

300

350

1.25 1.5 1.75 2Thickness Added

Perf

orm

ance

(PC

R-Y

ear)

n = 122 n = 464 n = 111 n = 222

(a) Priority System


0

50

100

150

200

250

300

350

400

450

1 1.25 1.5 1.75 2Thickness Added

Perf

orm

ance

(PC

R-Y

ear

n = 275 n = 488 n = 2077 n = 1169 n = 1513

(b) General System

Figure 17: Effect of Overlay Thickness on Thin Overlay Performance

38


0

50

100

150

200

250

300

350

5.0-5.4 5.5-5.9 6.0-6.4 6.5-8.0log(Average ESAL)

Perf

orm

ance

(PC

R-Y

ear)

n = 67 n = 237 n = 441 n = 227

(a) Priority System


0

50

100

150

200

250

300

350

400

0-4.4 4.5-4.9 5.0-5.4 5.5-5.9 6.0-6.4log(Average ESAL)

Perf

orm

ance

(PC

R-Y

ear)

n = 1323 n = 1960 n = 1576 n = 590 n = 157

(b) General System

Figure 18: Effect of Traffic Loading on Thin Overlay Performance

39

Figure 19 shows that the average statewide thin overlay performance has improved

significantly since the earlier 1990s, likely due to improved material specifications and

construction quality. The performance improvement is particularly pronounced for Priority

System thin overlays, although General System thin overlay performance has also been

improving steadily. Another reason for the dramatic improvement in the performance of thin

overlays on the Priority system could be ODOTs move to designed overlays in 1985. If the

project went through the 4-lane/Intertate rehabilitation program and received a thin overlay,

them the dynaflect measurements indicated a thin overlay was structurally ok. Pavement in bad

condition structurally would not have received a thin overlay.

Because of the significant performance improvements in recent years, only thin overlays

constructed after 1994 were included in the subsequent analysis for cost effectiveness

determination. Table 6 below shows the number of thin overlay projects and mileage

constructed between 1994 and 2002. These data were used in the subsequent analysis.

Table 6: Thin Overlay Projects Constructed during 1994-2002

Priority General No. of Thin

Overlay Project

No. of Thin

Overlay Project

District Miles Miles

1 5 77.3 80 557.3 2 5 30.7 37 232.1 3 5 47.8 60 400.6 4 9 57.4 60 389.9 5 14 102 30 310.4 6 22 285.2 74 669.4 7 12 139.6 160 810.9 8 11 161.3 53 387.8 9 3 4.3 51 293 10 8 40.8 100 842.1 11 8 76.9 91 694.4 12 12 82.7 21 85.5

Statewide 114 1105.90 817 5673.4

40

Average Performance Trend by Year of Construction in Priority System (Threshold PCR = 65)

0

50

100

150

200A

vera

ge P

erfo

rman

ce

0 1 2 3 4 5Year of Construction

(a) Priority System

Average Performance Trend by Year of Construction inGeneral System

0

50

100

150

200

250

300

350

400

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5Year of Construction

Ave

rage

Per

form

ance

General (Threshold PCR=60) General (Threshold PCR=55) (b) General System

Figure 19: Average Performance as a Function of Year of Construction

1997-1999 2000-2002 1994-1996 1991-1993

1997-1999 2000-2002 1994-1996 1991-1993

41

The Benefit of Thin Overlay

The benefit of a thin overlay may be defined as the part of the thin overlay performance area

that would not exist if not for the construction of the thin overlay. In other words, the benefit

of a thin overlay is the performance area of the thin overlay minus the residual performance

area of the existing pavement. Figure 20 illustrates the benefit of a thin overlay according to

the above definition with the shaded area represents the thin overlay benefit.

The benefit of a thin overlay is influenced by both the thin overlay performance and the timing

of thin overlay construction. As shown earlier, thin overlays that are constructed early (i.e.,

with higher prior PCR) tend to have better performance, but more of the performance area is

attributed to the residual performance of the existing pavement.

Figure 21 shows the average performance and benefit as a function of the existing pavement

condition (prior PCR). The benefit is identical to the performance when the existing pavement

condition is at or below the terminal PCR threshold. Figure 22 shows the prior cracking

deduct values adversely affect thin overlay performance and benefit.

Thin Overlay Benefit

County LUC; Route 024R; Station UP; Elog 0; Blog 1.11

60

70

80

90

100

1993 1995 1997 1999 2001 2003 2005 2007 2009 2011

Year

PCR

MinorMinor (Predicted)Thin OverlayThin Overlay (Predicted)

Figure 20: Definition of Thin Overlay Benefit

42

Thin Overlay Performance vs. Benefit in Priority System

0

50

100

150

200

250

55 60 65 70 75 80 85 90 95PCRPrior

Ave

rage

Are

a un

der

the

Cur

ve(P

CR

-Yea

r)

Benefit Performance

(a) Priority System

Thin Overlay Performance vs. Benefit for General System(Threshold PCR = 60)

0

50

100

150

200

250

300

55 60 65 70 75 80 85 90 95PCRPrior

Ave

rage

Are

a un

der

the

Cur

ve(P

CR

-Yea

r)

Benefit Performance

(b) General System

Figure 21: Average Performance and Benefit as a Function of Prior PCR

43

Thin Overlay Performance vs. Benefit in Priority System(Threshold PCR = 65)

0

50

100

150

200

250

0 5 10 15 20 25 30Prior Cracking Deduct

Ave

rage

Are

a un

der

the

Cur

ve(P

CR

-Yea

r)

Benefit Performance

(a) Priority System

Thin Overlay Performance vs. Benefit for General System(Threshold PCR = 60)

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35 40Prior Cracking Deduct

Ave

rage

Are

a un

der

the

Cur

ve(P

CR

-Yea

r)

Benefit Performance

(b) General System

Figure 22: Average Performance and Benefit as a Function of Prior Cracking Deduct

44

In addition to correcting surface deficiencies and reducing the rate of condition deterioration, a

thin overlay also improves the ride quality of the existing pavement. The ride quality of a

pavement is measured by the International Roughness Index (IRI) in inches/mile or m/km.

Higher IRI means poorer ride quality.

Figure 23 shows the average IRI values before and after a thin overlay on flexible and on

composite pavements. It can be seen from this figure that the ride condition improves (i.e., the

IRI value decreases) immediately following the thin overlay, and the ride condition gradually

deteriorates (as the IRI value gradually increases) as the thin overlay ages.

For flexible pavements in both the Priority and General Systems, the improvement of ride

quality due to a thin overlay is very significant, as it takes nearly 16 years, on average, for the

IRI of the overlaid pavement to return to the same IRI level prior to the thin overlay. For

Priority System composite pavements, the average time is less than 7 years; and for General

System composite pavements, its about 11 years.

It can be concluded that the benefit of a thin overlay, in terms of improved ride condition, is

very substantial for flexible pavements. Even for Priority System composite pavements, a thin

overlay provides, on average, nearly 7 years of ride condition improvement compared with the

ride condition before the thin overlay. Note that the average actual service life of thin overlays

on Priority System pavements is also approximately 7 years.

The benefits of condition and ride improvements are not combined in this study, as the

maintenance and rehabilitation decisions are mostly driven by the pavement condition alone,

and the two have different characteristics and units. However, the above analysis on ride

quality before and after thin overlays shows that thin overlays provide comparable

improvements to the pavement distress condition as well as ride quality.

45

Priority System

Average Prior IRI

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16 18 20

Age (in Years)

Ave

rage

IRI

Flexible Composite

(a) Priority System

General System

Average Prior IRI - Flexible

Average Prior IRI - Composite

0

20

40

60

80

100

120

140

160

180

0 2 4 6 8 10 12 14 16 18 20

Age (in Years)

Ave

rage

IRI

Flexible Composite

(b) General System

Figure 23: Average Ride Quality Deterioration Trend of Thin Overlay

46

Cost Analysis

Average Unit Cost of Thin Overlays

Thirteen (13) Priority system thin overlay projects completed between 2001 and 2007 were

included in the analysis. The average project length was 5.07 centerline miles (or 20.26 lane

miles). The overlay thicknesses were 1.5, 1.75, or 2 inches, with an average thickness of 1.65

inches. The average weighted by length unit cost was $58,856 per lane-mile (when not

weighted by length the unit cost was $64,376 per lane mile). The weighted by length unit cost

is lower than the straight average cost per mile, because shorter projects generally have higher

unit costs than longer projects.

Ninety three (93) General system thin overlay projects completed between 2003 and 2007 were

included in the analysis. The averag

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