Asphalt is the smooth, quiet, durable and sustainable surfacing material that has been around for hundreds of years. Today's asphalt is a scientifically designed product. It is rut, shoving and crack resistant. It is the most recycled material in the world.
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Slurry Seals
A slurry seal is a mixture of emulsified asphalt, water, well-graded fine aggregate and mineral filler that has a creamy fluid-like appearance when applied. Slurry seals are used to fill existing pavement surface defects as either a prefatory treatment for other maintenance treatments or as a wearing course. Microsurfacing is an advanced form of slurry seal that uses the same basic ingredients (emulsified asphalt, water, fine aggregate and mineral filler) and combines them with advanced polymer additives.
KAPA Pavement Note on Slurry Seals
Slurry seals are not recommended for at least the first 6 months after a new pavement is placed. Covering a new pavement too quickly with a slurry seal may not allow the underlying pavement surface adequate time to set and harden.
Bituminous Surface Treatments (BST)
A bituminous surface treatment, also known as a chip seal, is a thin protective wearing surface that is applied to a pavement or base course. BSTs can provide all of the following:
A waterproof layer to protect the underlying pavement.
Increased skid resistance.
A fill for existing cracks or raveled surfaces.
An anti-glare surface during wet weather and an increased reflective surface for night driving.
KAPA Pavement Note on BSTs
Bituminous surface treatments are used in Kansas primarily as a maintenance or pavement preservation technique. Seal coats, slurrys, micro-surfacing and ultra-thin HMA wearing courses are used. Seal coats and micro-surfacing are generally used where aging and oxidation has caused surface deterioration and cracking, but the pavement is still structurally sound or as a temporary fix until a more permanent cure for structural deficiencies can be done. Seal coats and micro-surfacing are also used to provide better friction and skid resistance when needed. Micro-surfacing can also be used to fill ruts up to about ½”. Slurrys are also used for these purposes, but are more commonly used to level and seal transverse cracks that have rolled down or as strip seals over centerline joints and widening unit cracks. Seal coats, slurrys and micro-surfacing are best constructed in warm, dry summer weather. Ultra-thin HMA wearing courses 1” or less in thickness are used when some minor additional structural support is desired in addition to leveling and sealing the pavement, and can be successfully applied in a wider range of temperatures.
Non-Structural Overlays
Non-structural overlays do not involve extensive structural design. Non-structural overlays are generally thin surface overlays of 0.5 - 1.5 inches that are used to (NAPA, 1995):
Improve ride smoothness.
Correct surface defects.
Improve safety characteristics such as skid resistance and drainage.
Enhance appearance.
Reduce road-tire noise.
A loose classification of non-structural overlays can be done based on traffic characteristics (NAPA, 1995):
Light volume/residential traffic. The primary objective in light traffic areas is to retard asphalt binder aging of the underlying pavement. Since heavy traffic loads are not of great concern, overlays are generally less stiff (resulting in a more workable mix, increased durability and flexibility and a potential for the overlay to reheal under traffic) and use smaller-sized aggregates.
Heavy, high-speed traffic. The primary objective in heavy, high-speed traffic areas is to prevent rutting and provide good friction. Because of this, overlays typically use larger angular aggregate and more durable mixes such as SMA or OGFC.
Rehabilitation/Maintenance
The Asphalt Story
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