Transcript Training

Module 2-4
Roughness and
Surface Friction Testing
Learning Objectives
 Explain the importance of conducting
roughness and surface friction evaluations
 Describe the different types of roughness
survey methods, equipment types, and
roughness indices
 Describe the different types of friction
measuring equipment
 List the different categories of surface
texture
Learning Objectives
(continued)
 Explain the importance of measuring
surface texture as part of a surface friction
evaluation
 Describe the different types of texturemeasuring devices
 Explain the advantages of using IRI and IFI
over other indices
 Describe how roughness- and frictionrelated information influences the selection
of rehabilitation activities
Why is it important to assess
roughness and friction?
 Both affect “functional” performance
 Roughness leads to increases in:
 Vehicle operating costs
 User delay
 Accidents
 User dissatisfaction
 Friction loss leads to increases in wet
weather accidents
Roughness Surveys
Definition of Roughness
 Deviations in pavement surface that affect
ride quality
 Caused by:
 Built-in surface irregularities
 Traffic and environment
Purpose of a
Roughness Survey
 Identify areas of severe roughness
 Determine relative roughness between
projects
 Gauge benefits of various rehabilitation
activities by measuring roughness before
and after construction
Roughness Survey Types
1.Ride quality surveys (serviceability)
 Subjective method
 Simple assessment tool
2.Objective roughness surveys
 Quantitative unbiased method
 Various types of equipment are
available
Ride Quality Surveys
Serviceability
 Subjective measure of user’s perception
of pavement rideability
 Measurement scale
 Zero (very poor) to Five (very good)
 Working range: 1.5 to 4.5
 Trigger levels for rehabilitation depend on
speed and level of traffic
 Correlations with other roughness indices
Roughness Measuring
Equipment
 Response-Type Road Roughness
Measuring Systems (RTRRMS)
 Maysmeter
 PCA Roadmeter
 BPR Roughometer
 Inertial Road Profiling Systems (IRPS)
 ICC Profiler
 K.J. Law Profilometer
 South Dakota Profiler
Response-Type Road Roughness
Measuring Systems (RTRRMS)
 Measure vehicle response
 Advantages
 Low initial and operating costs
 Ease of operation
 High measuring speeds
 Disadvantages
 Output sensitive to vehicle
characteristics
 Requires frequent calibration
Response-Type Systems
Maysmeter
Inertial Road Profiling Systems
Equipment (IRPS)
 Measure actual pavement profile
 Advantages
 Relatively accurate and repeatable
profile measurements
 Used to calibrate RTRRM systems
 Disadvantages
 High capital and operating expenses
 Complexity of systems
Inertial Profiler Systems
International Roughness Index
(IRI)
 Current roughness measurement standard
 Correlates to RTRRM systems
 Scale: 0 to 20 m/km (0 to 1267 in/mi)
 2 m/km (125 in/mi) is typical break point
between rough and smooth pavements
 Standard for FHWA HPMS Database
Roughness Data Variability
 Seasonal and daily environmental effects
 Lateral positioning
 Differences in operator practice (betweenoperator variability)
 Differences between equipment devices
(between-device variability)
 Manufacturing differences
 Calibration problems
Surface Friction Testing
Definition of
Surface Friction
 Force developed at pavement-tire
interface that resists sliding
 Influenced by:
 Surface texture
 Surface drainage (cross-slope)
Purpose of a Surface
Friction Survey
 Assess safety concerns
 Hydroplaning
 Wet weather accidents
 Target testing in areas of poor surface
condition:
 Smooth macrotexture (polishing or
inadequate finishing)
 Inadequate pavement cross slope
How do you adequately assess
surface frictional characteristics?
 Historical method—Measure friction
directly (“skid number”)
 Recent research indicates that “surface
texture” MUST also be considered
What is surface texture?
 Characteristics that contribute to surface
friction
 Microtexture – Roughness of individual
pieces of aggregate
 Macrotexture
 General coarseness of pavement surface
 Formed water channels (grooving)
 Large impact on surface friction
Friction Survey Measurement
Equipment Types
 Locked-wheel testers
 Side force testers (Mu Meter, SCRIM)
 Fixed slip testers (Gripster)
 Variable slip testers (Norsemeter ROAR)
Note: These devices do NOT measure texture!
Friction Measuring Devices
Locked-Wheel Trailer
Friction Measuring Devices
Examples of Other Devices
SCRIM
(side force tester)
Mu Meter
(side force tester)
Norsemeter ROAR
(variable slip tester)
Surface Texture Measuring
Devices
 Volumetric (“Sand Patch”) method
 Outflow meter
 Circular track meter (CTMeter)
 High-speed laser-based devices
(ROSAN, most laser-based profilers)
Surface Texture Measurement
Sand Patch Method
Surface Texture Measurement
High-speed Laser-Based Devices
High-Speed Inertial
Profilers
ROSANv
International Friction Index
(IFI)
 Incorporates simultaneous measurements
of friction and macrotexture
 Speed constant (Sp)
 Friction number (F60)
 Becoming friction measurement standard
 Modern high-speed measuring equipment
measure IFI directly
Review
 Why is it important to conduct roughness
and surface friction evaluations?
 What are the two types of roughness
measuring equipment?
 What are two types of friction measuring
equipment?
 What are the three categories of surface
texture?
Review (continued)
 Why it is important to measure surface
texture as part of a surface friction
evaluation?
 What are two of the different types of
texture-measuring devices?
 What are the advantages of using IRI and
IFI (over other indices)?
 How do roughness and friction affect the
selection of rehabilitation alternatives?
Key References
 Henry, J. J. 2000. Evaluation of Pavement Friction
Characteristics. Synthesis of Highway Practice No. 291.
National Cooperative Highway Research Program,
Transportation Research Board, Washington, DC.
 Karamihas, S. M., T. D. Gillespie, R. W. Perera, and S. D.
Kohn. 1999. “Guidelines for Longitudinal Pavement
Profile Measurement.” NCHRP Report 434.
Transportation Research Board, Washington, DC.
 Ksaibati, K., R. McNamara, W. Miley, and J. Armaghani.
1999. “Pavement Roughness Data Collection and
Utilization.” Transportation Research Record 1655.
Transportation Research Board, Washington, DC.
Key References (continued)
 Sayers, M. W. and S. M. Karamihas. 1998. The Little
Book of Profiling—Basic Information about Measuring and
Interpreting Road Profiles. University of Michigan
Transportation Research Institute, Ann Arbor, MI. Web
address: www.umtri.umich.edu/erd/roughness.
 Smith, K. L., K. D. Smith, L. D. Evans, T. E. Hoerner, and
M. I. Darter. 1997. “Smoothness Specifications for
Pavements.” Web Document #1, Final Report NCHRP
Project 1-31. Transportation Research Board,
Washington, DC.
Applicable ASTM Standards
 ASTM E 274, Skid Resistance of Pavements Using a FullScale Tire
 ASTM E 965, Measuring Pavement Macrotexture Depth
Using a Volumetric Technique
 ASTM E 1845, Calculating Pavement Macrotexture Profile
Depth
 ASTM E 1859, Friction Coefficient Measurements
Between Tire and Pavement Using a Variable Slip
Technique
 ASTM E 1926, Calculating International Roughness Index
of a Pavement Surface
 ASTM E 1960, Calculating International Friction Index of a
Pavement Surface