The use of milling machines to remove worn out asphalt surfaces that have completed their service life allows for a very cost-effective way to restore a roadway surface to a “like new” condition. The so-called mill-and-fill approach to pavement repairs dramatically reduces the amount of time a roadway needs to be tied up as a work zone with all of the related traffic delays and safety concerns. Milling machines grind out the worn out asphalt then transfer the material to a haul truck for delivery back to the asphalt plant for recycling into new mixes. Much of the grade and slope is restored as part of this process. Meanwhile, immediately behind the milling machine, pavers can replace the removed material with fresh mix and have it compacted and turned back over to traffic in a very short period of time. Another advantage in addition to the short construction time, restoration of grade and slope and ability to reuse the milled up asphalt is the ability to maintain a constant pavement elevation to keep bridge clearances and guardrail tolerances in check. Without question the mill-and-fill technique for asphalt pavement restoration is one of the great advantages of paving with HMA.
The primary group of private companies that comprise the membership of the Virginia Asphalt Association are asphalt producers. These companies have the asphalt plants that make the HMA products used by customers and they also provide paving services for the DOTs, local and federal government, commercial and other users of HMA. Over 95% of the HMA placed in Virginia are produced by the VAA’s asphalt contractor member companies. Other transportation related company categories that benefit from membership in the VAA include:
Stone Mastic Asphalt (SMA) is a relatively new (to Virginia and the U.S.) asphalt mix that is proving to be a superior paving material for high traffic roadways such as interstates and primaries. The mix contains a high percentage of coarser aggregate that is more cubical in shape and has a higher percentage of liquid asphalt binder. It provides a strong stone skeleton with good stone on stone contact to increase stability. Mineral filler and fibers are added to create a stiff mortar that when combined with the liquid asphalt helps lock the aggregates together. The mix was first developed in Europe and has been proven to provide a very tough and stable pavement that is virtually rut-proof and lasts much longer than conventional asphalt mixes. The first SMA placed in Virginia was on I-95 between Washington, D.C. and Richmond in 1993. Since then, the use of SMA on interstates and primary roads has steadily increased with about 360,000 tons scheduled to be put down this year. The mix is especially well suited as an overlay over PCC pavements that are in poor condition. Additional advantages of SMA from its “grainy”surface texture include a quieter ride and reduced rainfall induced water over-spray that improves windshield visibility for the traveling public. The mix is about 20-30% more expensive than conventional asphalt mixes but its long life, lower maintenance costs and other advantages make it a worthwhile investment for Virginia Roadways.
There are a large number of driveway paving companies available to choose from in most areas of Virginia. Picking one that does good work can sometimes be a challenge. We get numerous complaints at the association offices about shoddy work done by contractors in placing asphalt driveways. Since most if not all of these companies are not members of the Virginia Asphalt Association, we have little influence on the quality of their work. The best approach to take to line up a good driveway paving contractor is to check on their record of complaints at the Better Business Bureau or Consumer Affairs Office. Poor driveway paving companies will usually leave a trail of evidence at these watchdog agencies. You should also investigate similar work performed recently by the contractor if possible.You can also contact one of our member asphalt producers from your area (LINK To Member List) and get some company names of reputable driveway paving contractors.
Asphalt emulsions used to seal pavements are typically asphalt based. Coal tar, a derivative of the coal processing industry can also be used although asphalt emulsions are most commonly used. Coal tar based sealers can be somewhat more effective in areas where lighter fraction petroleum products may drip onto the surface of the HMA. An example of this would be where poorly maintained cars or equipment with oil leaks regularly drip their liquids onto the pavement in the same areas. Coal tar is more affective in repelling these drippings and preventing softening of the asphalt pavement. Typical application rates for sealers is about 0.05-0.1 gals./sq.yard. Latex modifiers and sand can also be added to enhance the sealer’s effectiveness and allow a thicker application rate. Concentrated sealing product labels will usually specify the amount of dilution with water necessary for different applications.
Some urban intersections with heavy pavement loadings from trucks and buses that slow down, stop, start and turn in a relatively small area at stop signs and traffic lights are very prone to rutting, pushing and shoving of the mix if the pavement structure and mix type are not suitable for the stresses being applied. Existing intersections that repeatedly rut after a short time following repairs often need to have a “forensic” examination done to determine the cause of the pavement failure. This involves cutting a slice out of the problem area pavement (down to the subgrade) toallow a visual analysis of the failed area.A determination can then be made as to whether the pavement deformation goes all the way through the asphalt and base down to the subgrade or whether only the surface layer is affected. If the problem is limited to the surface layer, it is indicative that the mix type or design is not adequate for the loadings being applied. The remedy would then be to replace the surface layer with a tougher mix that has a VDOT specified “D” or “E” designation. Conversely, if the deformation penetrates through the entire pavement structure, the repairs must go all the way to subgrade with adequate structure and mix type being provided. Any observed drainage or water related problems should also be corrected at that time. A properly designed and constructed asphalt pavement will not rut, push or shove even in the most highly stressed intersections.
Concrete pavement construction is a difficult and time consuming process. Although the concrete industry purports to be able to quickly place concrete with state of the art pavers and cure it rapidly with new mix additives, the fact remains that it is much more time consuming than paving with HMA. Continuously reinforced concrete pavements require the careful placement of steel within the slab matrix area and jointed pavements require cutting expansion joints. These and other issues result in far more time spent by contractors in the construction zone. HMA placement, on the other hand, causes few traffic disruptions with paving equipment in and out of the construction zone in a very short period of time. With today’s heavy traffic problems, getting the work done quickly and efficiently while still providing high quality pavements is of great benefit to owners and the traveling public.
Asphalt mix must be delivered to the jobsite while it is still very hot, typically at least 250º F. Most driveway paving contractors do not produce their own mix and buy HMA from larger highway contractors that have asphalt plants. As a result, mix can be picked up at an asphalt plant that may not be close to the driveway’s location. The contractor may also let the truck loaded with HMA sit around for a period of time while the driveway area is being prepared for the asphalt placement. This can result in an unacceptable drop in mix temperature for proper placement and compaction. A poorly constructed driveway is often the end result of the mix being placed after it has gotten too cool. One way to help avoid this problem is to have a minimum mix temperature at time of placement be part of the contractual agreement with the contractor.
Design engineers looking for value in choosing a pavement type for heavy duty (thicker) applications should review information now available on roads paved with HMA that can last indefinitely. These pavements, called “perpetual pavements”, having at least 8 inches of HMA thickness placed along with good construction practices and proper drainage virtually never need reconstruction. Once in place, only the surface layers are subject to damage over time and can be milled off and replaced with the renewed surface providing a smooth, undamaged pavement for many years. There is no need for replacement or repair of the lower layers in the pavement structure. This results in huge cost savings over the long haul for owners and results in minimal traffic disruptions that would otherwise result from reconstruction activities.
One of the important facts about HMA is that it is 100% recyclable and can be used over and over again. In Virginia, most asphalt mixes specified for use on roadways allow up to 20% of the material to be recycled HMA. HMA used as a base material can have over 25% recycled asphalt pavement (RAP). The use of RAP in HMA provides a number of benefits: