TECHBRIEF Performance Comparison

of Pavement Rehabilitation

Strategies

FHWA Publication No.: FHWA-HRT-11-050

FHWA Contact: Larry Wiser, HRDI-30, (202) 493-3079, 

larry.wiser@dot.gov

This document is a technical summary of the Federal Highway 

Administration report, Impact of Design Features on Pavement 

Response and Performance in Rehabilitated Flexible and Rigid 

Pavements (FHWA-HRT-10-066).

Introduction

This TechBrief presents a general comparison of performance 

for rehabilitation strategies for flexible and rigid pavement. The 

impact of overlay thickness, preparation prior to overlay, and 

mix type on performance was statistically evaluated using data 

from the Long-Term Pavement Performance (LTPP) Specific 

Pavement Study (SPS)-5 and SPS-6 experiments.

LTPP SPS Experiments

LTPP developed two SPSs to provide quality data for developing improved methodologies and strategies for flexible (SPS-5) 

and rigid (SPS-6) pavement rehabilitation. Techniques commonly used in the United States and Canada were applied to 

test sections on a continuous highway site, which guaranteed 

all sections were subjected to the same climate conditions 

and traffic and were constructed under the same subgrade 

and pavement structure. The factors considered in the experiment included the type of treatment, surface condition before 

rehabilitation was completed, environmental conditions, and 

traffic loading. There were 32 sites built for SPS-5 and SPS-6: 

18 sites were rehabilitation projects over flexible pavements, 

8 were asphalt concrete (AC) over joint plain concrete 

pavements (JPCP), and 6 were over joint reinforced concrete 

pavements (JRCP). These sites were monitored for periods 

ranging from 8 to 17 years. The project factorial is presented 

in table 1.

Performance Parameter

An important step for this analysis was the selection of an 

analysis parameter that could represent pavement performance 

and provide a means for comparison between different sections and different sites. The weighted distress average (WD) 

(unit area under the distress performance curve over time) over 

the survey period was selected as the performance measure. 

WD is a measure of pavement performance relative to the 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

http://www.fhwa.dot.gov/

research/tfhrc/programs/

infrastructure/pavements/ltpp/

The Long-Term Pavement Performance 

(LTPP) program is a 20-year study of inservice pavements across North America. 

Its goal is to extend the life of highway 

pavements through various designs of 

new and rehabilitated pavement structures, using different materials and under 

different loads, environments, subgrade 

soil, and maintenance practices. LTPP was 

established under the Strategic Highway 

Research Program and is now managed 

by the Federal Highway Administration.
2

specific distress over the entire survey period, 

corresponding to the period in which performance is monitored. Moreover, it is a normalized value because it is divided by the total year 

survey period, allowing for comparisons when 

survey periods are different. It is calculated 

using the following equation:

Where Di is the distress value measured at the 

ith survey, Pi + 1 is the period (in years) between 

survey i and survey i + 1, i is the survey number 

(i = 0 is the initial distress level immediately 

after the treatment), and n is the total number 

of surveys for the section.

WD is related to pavement performance over 

the entire survey period. This concept is similar

to performance originally defined as area 

under the serviceability curve. The effect of 

variability from measurements by different 

surveyors is reduced. Most importantly, WD 

provided a parameter to compare sections with 

different survey periods.

Statistical Analysis

The major challenge for a broad comparison of 

performance is the intrinsic variability in factors 

associated with pavement performance such 

as traffic, pavement structure, and climate. 

Each site in the SPS-5 and SPS-6 experiments 

was located on a different road segment with 

different in situ and climatic conditions. As a 

result, direct comparison was not appropriate. 

The alternative to simultaneously evaluating 

the performance of each rehabilitation strategy 

in all sites in SPS-5 and SPS-6 was to use the 

Friedman test, which is a nonparametric test 

(distribution-free) used to compare observations 

repeated on the same subjects. Unlike the more 

common parametric repeated measures such 

as analysis of variance (ANOVA) or paired t-test, 

the Friedman test makes no assumptions about 

the distribution of the data (e.g., normality). 

In addition, it can be used for multiple comparisons, as is the case for the SPS-5 and SPS-6 

experiments that have multiple rehabilitation 

alternatives. The Friedman test uses the ranks 

of the data rather than their raw values to calculate the statistic. The test statistic for the 

Friedman’s test is a Chi-square with n - 1 degrees 

of freedom, where n is the number of repeated 

measures (i.e., the number of sections in each 

site of the experiment).

Performance of Rehabilitated 

Flexible Pavements

Long-term performance of rehabilitation alternatives was evaluated using WD as the parameter for ranking performance through Friedman 

ANOVA. Major distresses were evaluated, and 

the outcomes for smoothness and fatigue 

cracking are summarized in this TechBrief.

Table 1. SPS-5 and SPS-6 experiment factorial at each site.

Pavement Type Section/Treatment

SPS-5/flexible

0501: Control—No treatment

Sections Without Milling Sections With Milling

0502: Thin overlay (51 mm)—Reclaimed 

asphalt pavement (RAP)

0506: Thin overlay—Virgin mix

0503: Thick overlay (127 mm)—RAP 0507: Thick overlay—Virgin mix

0504: Thick overlay—Virgin mix 0508: Thick overlay—RAP

0505: Thin overlay—Virgin mix 0509: Thin overlay—RAP

SPS-6/JPCP and

SPS-6/JRCP

0601: Routine maintenance (control) 0605: Maximum restoration

0602: Minimum restoration 0606: Maximum restoration—102 mm 

overlay

0603: Minimum restoration—102 mm 

overlay

0607: Crack/break and seat—102 mm 

overlay

0604: Saw and seal AC over joints—

102 mm overlay

0608: Crack/break and seat—203 mm 

overlay

1 inch = 25.4 mm

(1)
3

Performance ranking based on smoothness 

long-term trends is shown in figure 1. Low ranks 

(e.g., 1) represent best performance. The bars 

represent the Friedman average ranking of 

rehabilitation strategies from all 18 sites in the 

SPS-5 experiment. Thick overlays show the best 

smoothness. There was no significant difference 

in smoothness between mix types (reclaimed 

asphalt pavement (RAP) versus virgin). Milling 

the surface prior to overlay created a statistically 

significant advantage for smoothness trends. 

The worst smoothness was observed in sections with thin overlays. Combined with thin 

overlays, milling provided a slight advantage 

over not milling, but no statistical difference 

was found. Figure 2 shows similar data for 

fatigue cracking. Thick overlays had less fatigue 

cracking than thin overlays. Virgin and RAP 

mixes had statistically equivalent cracking. 

Milling prior to overlay was shown to statistically lower fatigue cracking.

The results from the Friedman ANOVA were 

also used to develop a practical ranking of 

strategies (from best (B) to worst (W)). A 

statistical significance test was performed 

among all ranks shown in figure 1 and figure 2.

Statistically equivalent performing strategies 

were grouped in similar ranks. These ranks 

are also presented in tabular form in figure 1 

and figure 2 along with the design features of 

each strategy.

Performance of Rehabilitated Rigid 

Pavement

A similar analysis was performed for rehabilitated rigid pavement sections that are part 

of the SPS-6 experiment. Since there were 

rehabilitation strategies involving hot mix 

asphalt (HMA) overlays, and pavements were 

monitored according to their surface layer type, 

smoothness was the only distress measured. 

This was common to all surface types in 

SPS-6.

Figure 3 shows the average ranking of strategies based on smoothness for JPCP sites 

obtained from the Friedman analysis. The 

best strategy for HMA overlays of JPCP was 

crack/break and seat with an 8-inch HMA 

overlay. In addition, 4-inch overlays with minimum, maximum, and saw and seal restorations 

were the second best strategies for JPCP. The 

worst for overlay rehabilitation for JPCP was a 

4-inch overlay with crack/break. The best nonoverlay rehabilitation strategy for JPCP was 

maximum preparation followed by minimum 

preparation and control. The results for JRCP 

were different (see figure 4). The best strategies 

were an 8-inch HMA overlay with break/crack 

and 4-inch overlays with minimum, maximum, 

and crack/break. The next best overlay was a 

4-inch HMA overlay with crack/break and saw 

and seal. The non-overlay strategies of minimum and maximum preparation showed the 

same performance. The JRCP control strategy 

showed the worst smoothness performance. 

Strategies with the same ranking had statistically equivalent performances.

Conclusions

Statistical evaluation of performance of different rehabilitation strategies for flexible and 

Figure 2. Performance ranking based on fatigue 

cracking for SPS-5 experiment. Performance Ranking

8

7

6

5

4

3

2

1

0

Ranking

Milling

Material

Thickness

1(B) 1(B) 4 4 4 4 4 9(W)

No Milled Milled Milled No No Milled No X

Virgin RAP Virgin Virgin RAP Virgin RAP RAP X

Thick Thick Thick Thin Thick Thin Thin Thin X

1(B)

Performance Ranking

9

8

7

6

5

4

3

2

1

0

Ranking

Milling

Material

Thickness

1(B) 2 2 2 5 5 5 8 9(W)

Milled No Milled Milled

RAP RAP Virgin Virgin Virgin RAP Virgin RAP X

Thick Thick Thin Thick Thick Thin Thin Thin X

Milled No No X

No

Figure 1. Performance ranking based on long-term 

roughness for SPS-5 experiment.

Milled No No X
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Researchers—This study was performed by Applied Research Associates, Inc., Elkridge, MD.

Distribution—This TechBrief is being distributed according to a standard distribution. Direct 

distribution is being made to the Divisions and Resource Center.

Availability—This TechBrief may be obtained from FHWA Product Distribution Center by e-mail to 

report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at http://www.fhwa.dot.

gov/research/.

Key Words—Pavement performance, Flexible pavement, Rigid pavement, Pavement rehabilitation, 

LTPP data, Data analysis, and SPS.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no liability 

for the use of the information contained in this document. The U.S. Government does not endorse 

products or manufacturers. Trademarks or manufacturers’ names appear in this report only because 

they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides high-quality 

information to serve the Government, industry, and public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and 

integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

july 2011 FHWA-HRT-11-050

HRDi-30/07-11(1.5M)E

rigid pavements was conducted using LTPP 

SPS-5 and SPS-6 experiments. The results, 

based on statistical significance, indicate that 

thick overlays improved performance of rehabilitated flexible pavements for smoothness 

and fatigue cracking. Milling the existing HMA 

surface prior to overlay was effective in keeping 

the overlay smoother. Mix type (RAP or virgin 

HMA) did not have a statistically significant 

effect on performance. 

Smoothness performance was significantly 

improved in all JPCP and JRCP sections overlaid

with HMA. Thicker HMA overlays produced 

smoother pavements. In comparison, rigid 

pavement rehabilitation strategies without 

HMA overlay did not exhibit as smooth of a 

surface. The maximum preparation showed 

improved smoothness over minimum preparation for JPCP but not for JRCP. It must be noted 

that the construction costs would be different 

for these various rehabilitation strategies. The 

above results relate strictly to performance and 

can be used as one component of the decisionmaking process, along with cost, material 

availability, and contractor experience.

Figure 3. Performance ranking based on long-term 

roughness for SPS-6 JPCP sections. Performance Ranking

8

7

6

5

4

3

2

1

0

Ranking

Thickness

Restoration

1 2 2 5 5 5 8

8 inches 4 inches No No X

Crack/

break

Min Max Max Min X

2

4 inches 4 inches 4 inches

Crack/

break

Saw &

seal

9

Performance Ranking

8

7

6

5

4

3

2

1

0

Ranking

Thickness

Restoration

1 1 4 4 6 6 8

8 inches 4 inches No X

Crack/

break

Max Min Min X

1

4 inches 4 inches

Saw &

seal

9

Crack/

break

4 inches No

Max

Figure 4. Performance ranking based on long-term 

roughness for SPS-6 JRCP sections.