Process
Ultra thin lift asphalt is a hot mix asphalt mixture consisting of paving grade asphalt and fine aggregate. The ultra thin asphalt mixture is produced at a central hot mix plant and delivered to the job site. While there are many variations, ultra thin lift asphalt is typically applied at .75" to 1.0" depth and designed as a preservation treatment to extend the service life of the existing pavement and address minor distresses. After applying the bond coat, the ultra thin lift mixture is applied using traditional paving equipment and compacted to achieve optimum density. Milling may also be required prior to application at start up joints, tie backs, on curb and gutter sections and to level areas to facilitate compaction.
Variations
Equipment Variations
Ultra thin HMA typically uses standard hot mix paving equipment. There are a few variations to the process depending on location, treatment type, design and specifics of the project.
- Bonded Wearing Course typically specifies the use of a spray paver where the tack coat application is applied directly in front of the bonded wearing course application.
- Material Transfer Vehicle (while not required) allows the paver to operate continuously without stopping, minimizes truck waiting time at the paving site and helps prevent aggregate seperation and temperature differentials.
Material Variations
4.75mm Ultra Thin Lift asphalt is a dense graded asphalt mixture sometimes referred to as a "Sand Mix". This application is typically applied at 1" depth or less on low to moderate volume roads, but is used on higher traffic volume routes in some regions. These dense graded ultra thin lift mixes have low permeability.
Bonded Wearing Course is a unique type of ultra thin lift asphalt. Bonded Wearing Course is a gap graded mixture that is applied over a heavy application of polymer modified tack coat. This treatment is more expensive than traditional ultra thin lift, but bonded wearing course is a great choice for application on PCC pavements and high traffic asphalt pavements in good condition.
OGFC (Open Graded Friction Course) is a type of ultra thin lift asphalt. OGFC's has only a small percentage of fine aggregates and a high percentage of air voids in the mixture. This mix has a higher degree of friction and reduces splashing and overspray.
- Ultra thin lift mixes are great options for use as a leveling or scratch course.
Common Combinations
- Crack Seal & Ulta Thin Lift HMA: The crack sealing will retard crack reflection in the underlying pavement and reduce water intrusion into the base.
- Chip Seal & Ultra Thin Lift HMA: The chip seal will act as an interlayer and help to delay crack reflection in the underlying pavement.
- Scrub Seal & Ultra Thin Lift HMA: The scrub seal will act as an interlayer and help to delay crack reflection in the underlying pavement. Underlying cracks are sealed reducing water intrusion into the base.
- Micro Milling & Ultra Thin Lift HMA: Micro Milling and Edge Milling may be required in certain instances. Milling allows you to tie into driveways and curb and gutter. It will also improve road profile which can help achieve the thinner application rate and facilitate compaction effort. Milling can also help maintain clearance of overhead structures and improve drainage.
- Using combination treatments extends the service life of the pavement verse a stand alone ultra thin lift asphalt and allows you to use this application on pavements with lower PCI ratings (C 55-70).
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