best practices for placement of asphalt- rubber...
TRANSCRIPT
Kyle MooreGranite Construction
Phone: 760) 775-7500Email:
Best Practices For Placement of Asphalt-Rubber Pavements
Presentation Overview
• Design Considerations from Contractor’s Perspective
• Field Production of AR Binders• Issues with Field Blending
Processes• Performance of AR Mixes• Conclusions
Asphalt Rubber History• Developed in 1960’s by City of
Phoenix Engineer• Referred to as the “wet process” or
McDonald Process• Large amount of crumb rubber used
as a Binder Modifier• Needs constant agitation
Asphalt Rubber80 % Asphalt
20 % Ground Tire Rubber
PRODUCTS AND PROCESSES IN THE PUBLIC DOMAIN
Minus No. 10 mesh is used; free of wire and other
contaminants; up to 0.5%
fiber.
Crumb rubber
Ground tire rubber is typically received in 2,000 pound “Supersacks”.
Virgin Asphalt
Cement Tank
Crumb Rubber Hopper Blender
Asphalt Rubber blend Tank
Auger
Agitation Systems
Maintaining Heat and Agitation is Key
Rubber Is Loaded into Weigh Hopper
The Rubber is weighed by the Hopper’s load cells.
An aerial view of a portable Asphalt-RubberPlant setup at a Hotplant.
BLENDER
Hotplant
AR BLEND TANK
VIRGIN AC TANKRUBBER STAGING AREA
Meter / Pump is interlocked with Hotplant
Rotational viscosity test - “Haake” Test
SOME CONCERNS WITH FIELD BLENDING PROCESSES
• Limited Production Rate for hotplant• High Shear Blenders allow higher
production• Sustainable rate of production is
usually between 20 and 30 liquid tons per hour
• Elevated heat at plant - safety• End of project cleanout
AR Paving is done with conventional paving techniques.
• Virgin Asphalt Temp: >375° F• Binder Temperature: 375 ° - 425° F• Aggregate Temperature: <325° F• Breakdown Roller: 290 ° F• Ambient/Surface Temp: >55°F RHMA-G
Successful AR Production is about Heat Management
PLACING AC WITH AR BINDERS
• Don’t pave in the cold but AR performs well in the cold
• No use of pneumatic rollers– “Rubber picks up Rubber”
• Elevated mix temperature is not solution
• Use of limewater in some areas
Asphalt Rubber mixes for applications requiring hand work requires attention to detail.
Issues to consider
Contractor’s Cost Issues• Small Projects = Larger UNIT Costs
– Fixed mobilization– Fixed daily costs
• Rubber Plant may limit Production Rate
Asphalt Rubber Myths• The Contractor needs
specialized equipment• Viscosity testing
procedure is standardized
• Blend Design consistency
• Nuclear Oven Results variability
Some Days Are
Better Than
Others
When It All Goes Wrong
• Plant Breakdowns
• Limited Shelf Life
• Last Day Cutoff
Elements of a successful AR Project
• Experienced Binder Designer• Experienced Mix Designer• Blender / Hot Plant Compatibility
(Electronics)• On-site contractor quality control• Knowledgeable Agency inspection• Common Sense
Common Sense Best Practices• Tarp loads• Shorten windrows when paving with
bellys• Keep rollers close• Weather forecast
– Wind– Long range outlook
• Nighttime temperatures
Constructability vs. Performance
Performance in Indio, CA
Asphalt-Rubber Asphaltic Concrete offers excellentcolor contrast for striping and marking.
The Environmental Card
Lincoln, Nebraska
Interstate 10 near Odessa, Texas
CONCLUSIONS
AR mixes resist reflective crackingGap graded and open graded mixes
perform wellConstructability and unique field
issues must be dealt withUpfront costs hamper widespread
usageNoise mitigation may be part of future
Summary• Asphalt Rubber is
construction friendly
• AR is quiet, smooth, long lasting and an environmental winner
Questions?
“I know you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant.”
---Alan Greenspan