TECHBRIEF Achieving a High Level of 

Smoothness in Concrete 

Pavements without 

Sacrificing Long-Term 

Performance

FHWA Contact: Peter Kopac, HRDI-11, 202–493–3151

This document is a technical summary of the report Achieving

a High Level of Smoothness in Concrete Pavements without 

Sacrificing Long-Term Performance, FHWA-HRT-05-068, that

will be published by the Federal Highway Administration in

summer 2005.

Introduction

For a portland cement concrete (PCC) pavement, it is important to

achieve both a high level of smoothness during construction as

well as a satisfactory long-term performance. It is not acceptable

to construct a pavement with a high initial smoothness that will

give poor long-term performance. Smoothness measurements

for construction acceptance are usually performed shortly after

paving is completed, using either a profilograph or a lightweight

inertial profiler. However, it is unclear whether the smoothness of

a pavement measured immediately after it is paved truly reflects

the initial smoothness of the pavement because the smoothness

can undergo changes over the short term (e.g., within 3 months)

due to curling or warping effects. In other words, a pavement can

have a very high smoothness immediately after construction, followed by a decrease in smoothness over a short time period because of changes in slab shape that occur with curling and warping. This research project was performed to:

• Assess whether high initial smoothness translates into better

long-term performance. 

• Identify design features and material properties in PCC 

pavements that can cause an initially smooth pavement to

exhibit detrimental long-term performance.

• Provide guidance on adjustments that can be made to materials properties, design features, and construction procedures

in order to avoid these detrimental effects. 

• Investigate early age changes in smoothness of 

PCC pavements.

• Provide recommendations and guidelines regarding 

smoothness testing.

Research, Development, and

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

www.tfhrc.gov

The Concrete Pavement Technology

Program (CPTP) is an integrated,

national effort to improve the long-term

performance and cost-effectiveness of

concrete pavements. Managed by the

Federal Highway Administration

through partnerships with State highway agencies, industry, and academia,

the CPTP’s primary goals are to reduce

congestion, reduce costs, improve performance, and foster innovation. The

program is designed to produce userfriendly software, procedures, methods,

guidelines, and other tools for use in

materials selection, mix design, pavement design, construction, and rehabilitation of concrete pavements.
The roughness data collected

from the Long-Term Pavement

Performance (LTPP) GPS-3 experimental jointed plain concrete (JPC) test sections were

used to study the roughness

progression of JPC sections.

The changes in smoothness of

the test sections were evaluated to determine what effect the

mix design properties, material

properties, and design features

have on pavement performance. The change in smoothness that occurs over the short

term on JPC pavements was investigated by collecting profile

data on test sections established on new PCC pavements

in five projects. The test sections were profiled 1 day, 3

days, 7 days, and 3 months

after paving. The main findings

from this study are described in

the following sections.

Value of Building

Smoother Pavements

The roughness progression

plots for JPC pavements in

the LTPP GPS-3 experiment

showed a parallel pattern in

roughness progression. The

experiment showed that

pavements that are built

smoother retain their smoothness over a longer period

than those that are built less

smooth. Hence, pavements

that are built smoother provide a longer service life and

provide road users a better

ride quality.

Effect of Design

Features on

Smoothness of JPC

Pavements

• Construction of nondoweled

pavements in freezing regions is not recommended

because in this type of climate, they have shown poor

performance from a roughness point of view. 

• Some nondoweled pavements have shown a high increase in upward slab curvature over time. These

pavements have a high

amount of faulting. Many of

these pavements are showing other distress. Factors associated with higher

amounts of slab curling over

time are high values of freezing index, coefficient of thermal expansion, and PCC elastic modulus. Higher values of

the following factors were associated with lower curvature: mean annual temperature, annual precipitation,

number of wet days per year,

and slab thickness. To prevent upward slab curvature,

it is recommended that dowels are used for all pavements constructed in freezing areas. 

• The provision of dowels in

pavements has served its intended function by preventing faulting. If there is any

reason to believe there is

even the slightest possibility

for faulting to occur, dowels

are recommended. 

• Doweled pavements with a

joint spacing of 4.8 meters

(m) (16 feet (ft)) or less seem

to perform better than those

having a higher joint spacing. It is recommended that

States utilizing a joint spacing of greater than 4.8 m (16

ft) investigate whether using

a joint spacing of 4.8 m (16

ft) or less will give better

performance.

Effect of PCC Material

Properties on

Smoothness of JPC

Pavements

• For both doweled and nondoweled pavements, using

PCC with higher split tensile

strength (which results in a

higher flexural strength) appears to be beneficial for

long-term performance from

a roughness point of view.

• In nondoweled pavements,

generally pavements having

high elastic modulus values

(greater than 35,000 megapascals (MPa) (5 million

pounds per square inch (psi))

or pavements having a high

ratio (greater than 8000) between elastic modulus of

concrete and split tensile

strength appear to be showing high rates of increase of

roughness. These trends

were not seen for doweled

pavements.

• Evidence suggests that higher values of coarse to fine aggregate ratio in concrete results in pavements that

maintain their smoothness

over longer periods.

• A survey of State departments of transportation

(DOT) personnel and concrete industry personnel

showed no evidence suggesting that contractors have

been adjusting their mix designs to achieve higher

smoothness. The general

consensus was that no modifications have been required

in the concrete mix design to

achieve higher smoothness.
Construction

Considerations

• The construction procedures

needed to construct a smooth

PCC pavement are documented in publications prepared by

Federal Highway Administration (FHWA) (Portland Cement

Concrete Pavement Smoothness: Characteristics and Best

Practices for Construction,

Publication No. FHWA-IF-02-

025) and the American Concrete Pavement Association

(Constructing Smooth Concrete Pavements, Technical

Bulletin TB-006.0-C). Adherence to these procedures is

recommended for constructing smooth pavements.

• Analysis of data from five

projects indicated that the

smoothest pavement was

constructed in the project

where the tie bars were attached to chairs fixed to the

base. The dowel bars were

also fixed to the base in this

project. The International

Roughness Index (IRI) of the

test section established in this

project was 0.80 meters per

kilometer (m/km) (51 inches/mi). The IRI of the test sections established on the other

four projects, where the tie

bars were inserted by the

paver, were 1.11, 1.44, 0.95,

and 1.07 m/km (70, 91, 60, and

67 inches/mi). In three of the

projects, the dowels were

fixed to the base, but for the

project that had an IRI of 1.07

m/km (67 inches/mi), dowels

were inserted during the

paving process. Although fixing the tie bars to the base

prior to paving may be more

costly, these results indicate

that doing so may achieve a

smoother pavement.

Measurement of

Smoothness

• The surface of the pavement

must be clean when performing profile measurements.

Residue from the saw-cutting

operation that is present adjacent to the transverse joints

can appear as small humps

on the measured profile, and

these can affect the smoothness indices computed from

the profile data. 

• The data collected by lightweight profilers do not measure the shape of the joint accurately. Profilers from

different manufacturers are

using different methods to filter data. As a result, joints are

being measured differently.

Some profilers eliminate most

of the effect of a joint by filtering, which flattens out the profile at the joint. Nonetheless,

differences in smoothness indices between devices may

still occur between equipment

manufactured by different

manufacturers. 

• In many States, an initial sawcut is made on the pavement,

a joint reservoir is formed,

and then the joint is sealed.

Profile measurements should

not be obtained when the

joint reservoir is formed and

the joint has not yet been

sealed. At that point, data can

yield high roughness values

because the joint reservoir

appears in the profile data.

• On transverse tined surfaces,

when three repeat runs were

obtained with lightweight profilers, the difference between

the maximum and minimum

IRI of the three runs over an

approximate distance of 161

m (528 ft) typically ranged

from 0.03 to 0.06 m/km (1.9 to

3.8 inches/mi). However, in

longitudinally tined surfaces,

this value was much higher

and ranged from 0.06 to 0.09

m/km (3.8 to 5.7 inches/mi).

Because of the interaction between the laser sensor and

the longitudinal tines, the IRI

obtained on longitudinally

tined surfaces is less repeatable than that obtained on

transverse tined surfaces.

• If a profiler is used to measure

smoothness of concrete pavements, this profiler should be

certified on PCC sections. Differences in the way profilers

treat joints and tining can affect smoothness indices obtained from profile data.

Hence, certifying profilers on

asphalt surfaces and using the

profilers to measure smoothness on concrete surfaces

may not necessarily mean

that comparable data are obtained by different profilers.

Early Age Changes in

Roughness and Profile

• Testing at the five projects indicated negligible built-in

slab curling was present on

the pavement. Curvature of

slabs changed little over a

31/2-month period, and no

noticeable effect of changes

in slab curvature affecting the

IRI was noted.

• A study performed on five

projects indicated somewhat

variable results in changes

that occur in the IRI over the

first 3 months after paving. In

some projects, very little

change in IRI was noted (within ±5 percent). In some projects, changes up to ±10 percent were noted. It is unclear

whether these changes occurred because of changes in

pavement profile or whether
they were related to either

equipment effects or lateral

wander during profiling.

• For a specific profiler, no significant changes in IRI were

observed from measurements obtained when the 3-

milimeter-(mm) (0.12-inch-)

wide initial sawcut was present on the pavement and

after the joint reservoir was

sawed and sealed. Although a

significant difference was not

seen for the profilers used in

this study, differences may

nonetheless occur between

these measurements in some

profilers because of the different data filtering methods

they use.

• Based on the five projects

used in this study, it appears

that smoothness measurements can be performed at

any time within the first few

months of a pavement’s life

as long as the pavement is

clean. 

Use of Profile Data 

for Achieving Smoother

Pavements

• Usually smoothness indices

like IRI are computed for each

lane over a 161 m (528 ft)

length. The IRI for the overall

section does not provide any

information on how IRI varies

within the section or where

rough spots within the section are located. A roughness

profile of the section that

shows how the roughness is

distributed within the section

can be used to investigate the

spatial distribution of roughness and to see where rough

spots within the section are

located. The location of the

rough spots can then be correlated to the construction

process to obtain information

on a specific construction

event that occurred at that location and resulted in a high

roughness value. 

• Advanced profile analysis

techniques, such as power

spectral density (PSD) plots,

can be used to identify

whether a roughness associated with a specific repetitive

wavelength or a waveband

significantly contributes to

the roughness. Using such

procedures on projects having problems in achieving the

desired smoothness can help

troubleshoot the cause for

such problems. 

• Using roughness profiles as

well as PSD plots on profile

data collected at the start of a

paving project will indicate

whether any features in the

profile are contributing to a

high roughness. If such features are identified, they can

be corrected at the start of the

project.

Researchers—This study was performed by R.W. Perera and S.D. Kohn of Soil and Materials Engineers,

Inc., Plymouth, MI and S. Tayabji of Construction Technology Laboratories, Inc., Columbia, MD.

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

is being made to the Divisions and Resource Centers.

Availability—The report will be available in summer 2005 and may be obtained from the FHWA Product Distribution Center by e-mail to report.center@fhwa.dot.gov, by fax to 301–577–1421, or by phone to 301–577–0818.

Key Words—Concrete pavement, concrete properties, concrete mix design, pavement construction, pavement testing, pavement smoothness, pavement performance, inertial profilers, profile measurements

Notice—This TechBrief is disseminated under sponsorship of the U.S. Department of Transportation in

the interest of information exchange. The TechBrief provides a synopsis of the study’s final publication. It

does not establish policies or regulations, nor does it imply FHWA endorsement of the conclusions or recommendations. The U.S. Government assumes no liability for the contents or their use.

MAY 2005 FHWA-HRT-05-069

HRDI-11/05-05(1M800)E