chapter 2 surface characteristics
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Chapter 2 Surface Characteristics. From… Maintenance Technical Advisory Guide (MTAG). Why are Surface Characteristics of a Pavement Important?. They are what the public notices They also affect their driving and the associated costs of driving - PowerPoint PPT PresentationTRANSCRIPT
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From… Maintenance Technical
Advisory Guide (MTAG)
Chapter 2Surface Characteristics
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Why are Surface Characteristics of a Pavement Important?
They are what the public notices They also affect their driving and the
associated costs of driving Customer satisfaction is at the heart and
soul of a successful pavement preservation program
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Surface characteristics deteriorate as the pavement wears out
Structural / FunctionalCondition
Pavement Life
Minimum Acceptable Rating
Roadway Rehabilitation
Reconstruction
Restoration (CAPM)
Preservation
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Presentation Outline
Important Surface Characteristics• Ride quality
• Surface Texture and friction
• Noise Achieving Desired Surface
Characteristics Summary
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Important Surface Characteristics
Ride quality-the public demands a smooth ride
Safety-Safety for users in terms of texture and skid resistance
Noise-Quieter pavements Durability-longer lasting treatments Aesthetics- eliminating patches and
other surface irregularities
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Timely Treatments Keep the Surface Characteristics in good condition
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Ride Quality
Definitions-deviations in the surface that affect vehicle dynamics, ride quality, and drainage. Smoothness can affect • driver safety
• fuel efficiency, and
• vehicle wear and teat Measuring smoothness Factors contributing to poor smoothness
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Ride Quality
Measuring smoothness• Several techniques have been used over the
years
• Profilographs were one of the first and still is used in California for construction quality control
• Road meters were used for many years to measure the relative smoothness of the pavement (e.g. Mays Meters). However, it is not a true measure of smoothness
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California Profilograph
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Limitations of profilographs
Operates manually so the process is slow
Cannot be used for high speed network data collection
Used primarily for construction quality control
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Vehicle instrumented with a road meter (e.g. Mays Meter)
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Limitations of Road meters
Operation dependent on the host vehicle; hence, equipment measurements were not transportable to other devices or other vehicles
Not a true measure of smoothness-actually measures the relative motion of the host vehicle in response to the smoothness of the traveled roadway
Smoothness measurements not stable over time
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Profiling equipment
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Profiling equipment
Common for network pavement data collection
Not designed for project level quality control
Measures the longitudinal profile Inertial devices most commonly used
(Dynatest Profilometer, South Dakota Profiling device)
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Profiling equipment
Operation typically requires a two person crew
One person as the driver and one person to operate the system
System calculates the roughness index in inches per mile
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Lightweight profiler
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Lightweight profiler
New generation of profilers has emerged for quality control and quality acceptance purposes
They are much smaller; however operating speeds are limited to 8-25 mph
Equipment is available from Dynatest, Ames engineering, International Cybernetics and Pathway services
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Multi Laser Profiler
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Multi Laser Profiler
Useful in monitoring large road networks at speeds from 18-75 mph
Simultaneously measures smoothness, rut depth, macro texture in both the longitudinal and transverse directions
Portable devices are also available
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Summary
Ride is an important surface characteristic
It has been measured in a variety of ways
Calibration of the ride equipment is important to get consistent results from year to year.
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Surface Texture
Definitions Measurements of
surface texture Summary
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Definitions
Includes microtexture, macrotexture, megatexture, and roughness
Texture affects friction, splash and spray, rolling resistance, and tire wear
Roughness is not normally considered a traditional component of surface texture, but it does affect ride quality and noise.
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Surface Characteristic Classifications
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Differences between Microtexture and Macrotexture
Microtexture- fine texture and is all that is usually is needed to stop under normal dry conditions
Macrotexture- intermediate texture and plays a key role in wet weather friction
Megatexture- typically a result of poor construction practices and cause vibrations in tire walls, affects ride quality and produces noise
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Macrotexture vs. Microtexture
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Techniques to Create Texture
Drag textures• Burlap dragging
• Broomed surfaces
• Turf dragging Tined textures
• Transverse
• Longitudinal Diamond grinding
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Methods to Measure Texture
Sand patch method-ASTM 365
Circular texture meter (CT meter)
Outflow time (using an outflow meter)
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Sand patch Method
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Circular Texture meter
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Outflow Meter
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Summary
Surface texture influences several tire-pavement interactions
Several methods have been used to measure texture; however the results cannot be compared directly
It is believed by many that the CT meter is the best test for predicting wet weather friction
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Surface Friction
Importance Factors affecting friction Measurement of surface friction Current practices Summary
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Importance
Good friction provides for safe roads in wet weather conditions
Water on pavements also affects splash and spray which can result in a loss of visibility
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Factors affecting Pavement Friction
Tire design and condition Micro- and macro-texture Time and seasonal effects
• Aggregate wear
• Dust and oil accumulations
• Cold climates Hydroplaning-cause by water ponding on
the surface
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Measurement of Surface Friction
Several methods have been used to obtain a number
Some of the devices used in California include;• ASTM locked wheel trailer
• British pendulum device
• Dynamic friction tester
• Caltrans test method
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Locked Wheel Trailer (ASTM E-274
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British Pendulum Tester
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Dynamic Friction Tester
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Caltrans Skid Tester (CTM 342)
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Current practices
FHWA-provides guidance to the states but recommends no minimum level of skid number
AASHTO-Guides are currently being updated to provide more specific information
SHA’s-Many agencies require a minimum skid number of 30 to 40 for speeds greater than 40 mph
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Summary
Highway safety is most important to the agency
Pavement friction usually decrease over time
Devices are available to measure surface friction
Minimum acceptable skid numbers have been set by many agencies.
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Noise
Noise is unwanted sound Pavement type and texture contribute to noise
levels Caltrans has developed a pavement advisory
guide for quiet pavements which can be found on the following website
www.dot.ca.gov/hq/oppd/pavement/qpavement.htm
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Achieving Desired Surface Characteristics for Rigid pavements
Ride and smoothness- grinding is the most effective way to improve this property
Texture and Friction- can be improved by grinding or with an overlay
Noise- Grinding and overlays will improve this surface characteristic.
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Overall Summary
Highway users are concerned with roadway surface characteristics
Highway safety is most important to the agency , but ride and noise are important to the users
Devices are available to measure all roadway surface characteristics
We can control the surface characteristics through proper design and maintenance.
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Questions