Lecture 4

PAVEMENT CONDITION SURVEYS

PAVEMENT CONDITION SURVEYS

There are four key measures to characterize or define the condition of pavement:

1) Roughness

2) Deflection

3) Surface distress

4) Surface friction/ skid resistance

Need for pavement Condition Surveys

Key Measures for Pavement Condition:

Roughness1) Roughness ( smoothness): irregularities in the

pavement surface that adversely affect the ride quality of a vehicle ( related to ride comfort or serviceability).

Measured by:

Present Serviceability Rating (PSR): The judgment of an observer as to the current ability of a pavement to serve the traffic it is meant to serve" (Highway Research Board, 1962)

International Roughness Index (IRI): define a characteristic of the longitudinal profile of a traveled wheeltrack and constitutes a standardized roughness measurement

Riding Comfort Index (RCI): developed by the Canadian Good Roads Associations.

Key Measures for Pavement Condition: RoughnessPresent

Serviceability Rating (PSR)

International Roughness Index

(IRI)

Key Measures for Pavement Condition:

RoughnessRiding Comfort Index form developed by the Canadian Good Roads Associations.

• Pavement distortions can generate both vertical and lateral acceleration in the vehicle.

• Vertical acceleration major contributing factor to occupant comfort and derives from longitudinal pavement profile.

• Lateral accelerations are the result of vehicle roll (side to side movement, rotation about the longitudinal axis) and yaw ( spin movement, rotation of vehicle about the vertical axis).

Equipment for roughness

survey data collection can be

categorized into the four broad

categories:

Equipment for roughness data

collectionDipstick Profilograph

Equipment for roughness Vidoes

Dipstick profiler

Profilograph

Evaluation of Pavement Structural Capacity

Basic considerations:

Purpose of evaluating structural capacity is to estimate the load-carrying capability and to predict the remaining service life of the pavement under the expected traffic conditions.

How to evaluate:

1) Monitoring or measuring some characteristic of the pavement

2) Analysis of the resulting data

3) Evaluation according to some criteria

Monitoring the Network

Structural monitoring should be done on a regular basis (e.g., annual, biannual, etc.)

Deflection of pavement surface under specified loads is the usual means for such monitoring.

The need for structural evaluation can be indicated by other types of evaluation, such as surface distress condition assessment, surface friction, etc.

Functional vs. Structural Evaluation

Both are important and they supplement rather than replace each other.

Serviceability observation below the acceptable level are one way to trigger a structural evaluation.

Rough pavement may have adequate strength and require only a level-up surface layer, or it may be structurally weak and require replacement or a thick overlay.

Destructive vs. Nondestructive

Evaluation (NDE) Destructive: physical disturbance

of the materials occurs.

Destructive methods: take samples of small-core drillings to obtain thickness and samples of the underlying material for laboratory testing.

NDE methods: measure surface deflection and pavement thickness

Pavement Destructive Evaluation

Key Measures for Pavement Condition: Deflection

2) Deflection: related to structural adequacy or capacity.

Deflection Measurement Schematic

Surface deflection is an important pavement evaluation method because the magnitude and shape of pavement deflection is a function:

1) Traffic (type and volume)

2) Pavement structural section

3) Temperature affecting the pavement structure.

4) Moisture affecting the pavement structure.

Deflection Devices All practical nondestructive evaluations of pavement structure capacity are performed with deflection measuring devices. They can be grouped into four categories:

1) Static devices: Measure pavement’s response to a static load or a single application of a slow moving load.

2) Vibratory devices: measure pavement response to a vibratory or cyclical load.

3) Impulse devices: load the pavement by dropping a known mass through a known distance and measure pavement’s response.

4) Multimode devices.

Typical NDE Deflection Devices: Static devices

Benkelman Beam*low cost, slow and labor intensive.

Typical NDE Deflection Devices: Vibratory devicesRoad Rater: varying load

magnitude (200-900 lb) and

frequency (5-80 Hz).

)

Dynaflect: light load, fixed

frequency 8 Hz. Peak 1000 lb

Typical NDE Deflection

Devices: Impulse Devices

The Falling Weight Deflectometer (FWD)

Key Measures for Pavement Condition:

Surface distress3)Surface distress: Any indication

of poor or unfavorable pavement performance or signs of impending failure; any unsatisfactory performance of a pavement short of failure" (Highway Research Board, 1970).

Purpose

Surface distress is frequently the cause of serviceability (i.e., ride quality)

Condition assessment is directed toward assessing the maintenance and rehabilitation needs to prevent accelerated, future distress, or to improve the pavement

Basic Considerations

Condition assessment should include a reasonable amount of details, including distress type, severity, extent and location.

An extremely wide variation exists in the manner in which the surveys are obtained, recorded, analyzed, summarized, and stored. Depends on the agency’s needs.

Surface Distress Components

Surface distress modes can be broadly classified into the following classes of factors:

1) Surface defect

2) Permanent deformation or fracture

3) Cracking

4) Patching

Procedures for Distress Survey

Define how the data is going to be used. The level of detail required in the survey should be designed to meet the needs of the identified uses. (network vs. project levels).

Define the types of distresses that will be included in the survey. This process should be made by a committee of experienced engineers familiar with local pavement conditions. Examples: highways 1~20 distress types, airfields: 19 distress types

Procedures for Distress Survey

Prepare carefully written definitions of the distress appearance, and support photograph, which should include instructions for rating the severity and measuring the extent of each distress type.

Devices: human field inspection (walking survey), or automation equipment that can supplement human observations. Complete automated system remain to be developed.

Sampling Methodology

Need to select the site and sections.

Sampling at fixed distance intervals.

Making a predetermined random selection

Survey crew pick “representative sections”

Sample size should be determined using statistical methods, based on the distress variability and the desired survey accuracy.

In practice, sample size is often determined based on the crew time available and the cost of performing the survey.

Human Field Inspection

Examples of Distress Survey Procedures

PAVER Distress Survey:

Sample unit 2,5000 +/- 1,000 sq. ft (flexible pavements, 20 +/- 8 slabs (rigid pavements)

3 levels of severity: low, medium, high

Ministry of Transportation of Ontario

Five levels of severity and extent: from very slight to very severe, from few (<10%) to throughout (>80%)

Driving a car, the rater makes 2 to 3 stops per section to examine distress type and severity

Skid Resistance

4. Surface friction/ skid resistance: the force developed when a tire that is prevented from rotating slides along the pavement surface (Highway Research Board, 1972). related to safety

Skid Resistance Directly related to micro and macro texture

of pavement surface

Involves a very complex interrelationship among pavement factors oil and water, vehicles tires, vehicle operation factors ( acceleration, deceleration, changing lanes) , pavement surface drainage and texture characteristics.

Often named as roughness, but should be distinguished from roughness used for performance measure.

It is actually an appearance of roughness at small scale

Skid Resistance Skid resistance is generally quantified

using some form of friction measurement such as a friction factor or skid number.

Friction factor (like a coefficient of friction):  f = F/L

Skid number: SN = 100(f)

where:

F= frictional resistance to motion in plane of interface

L=load perpendicular to interface

Typical Skid Numbers (from

Jayawickrama et al., 1996)

Measurement of Skid Resistance

All pavement skid resistance measurement are empirically “ verifiable by observation or experience rather than theory or pure logic”.

Results are valid only when evaluated relative to empirical base of evidence developed over time or by using standard test method.

Must follow standard methods for calibration and use of the device.

Measurement of Skid Resistance

Specification: ASTM E274, and others

Measurement device: Mu meter, for instance

Contributors to skid resistance changes include:

1) Porosity

2) Wear ( i.e. studded tires)

3) Polishing of surface aggregates

4) Rutting due to compaction, lateral , distortion or wear.

5) Bleeding or flushing of the service.

6) Contamination from rubber, oil , water, etc. `

Skid Number Variation

Skid Number Variation

Combined Measure of Pavement Quality

Why Need a Combined Measure of Pavement Quality

Pavement evaluation is generally directed toward the following objectives:

Selection of projects and treatment strategies at the network level;

Identification of specific maintenance requirements at the project level

A combined measure is of primary importance at network level to convey summary information to the public and senior administrators, who involves administrative, political, and financial decisions.

Why Need a Combined Measure of Pavement Quality

Method of Developing A Combined Index

Combined Index=

Where:

w is the weighting factor for pavement condition measure i

c is value of individual pavement condition measure i

How to determine weight

Expert opinion (Delphi methods)

Analytic hierarchical process (AHP) methods

Statistical regression analysis

References

http://classes.engr.oregonstate.edu/cce/winter2012/ce492/

http://www.ip-zev.gr/files/teaching/T3-4_Lateral_longitudinal_dynamics.pdf

http://onlinemanuals.txdot.gov/txdotmanuals/pdm/manual_notice.htm

www.pavementmanagement.org/ICMPfiles/2004078.pdf