Ninety-four percent of U.S. roads are surfaced with asphalt, and there are about 18 billion tons of asphalt in place on our roads. There must be a reason for such wide spread usage. Actually, there are many reasons. It is my opinion that asphalt is truly the most adaptable and versatile paving material. Here are some of the reasons for using asphalt.
Asphalt is a marvelous engineering material. It lends itself to working in a great number of applications. It can be a load-carrying or structural component; it can be a wearing course or a waterproofing layer. It can be extremely dense or free-draining. It can be placed in thick layers to last indefinitely or it can be placed in ultra-thin overlays to preserve an existing road.
Asphalt can be and is re-used. RAP or recycled asphalt pavement has incredible value. Nearly 100 million tons of asphalt is re-used each year. The aggregate component of RAP saves resources and the asphalt can be restored to approximately its net original properties by using a compensating binder with the recovered materials. Other pavement types can only be re-used as an aggregate.
In addition to re-using RAP, asphalt mixtures routinely incorporate other scrap or waste materials, such as tire rubber, roofing shingles, glass, and other materials. An asphalt pavement can, effectively, recycle concrete through the rubblization process. Failed concrete pavements are broken down in-place and used as an aggregate base for a new asphalt pavement. This technique offers the environmental advantages of conserving aggregate and saving landfill space.
Speed of construction
Asphalt is quick to place and requires less traffic delays due to congestion or lanes being out of service. Much of the work can be done during off-peak hours, and this saves the traveling public time and money. Asphalt pavements can be opened to traffic as soon as they are compacted and cooled, while other pavement types can take days or even weeks to cure.
Asphalt pavements are quieter than other pavement types. Some asphalt mix types (OGFCs and SMAs) typically reduce noise levels by three to five decibels, which is like doubling the distance from the source of the noise. Noise barrier walls are incredibly expensive and paving with asphalt is the better choice.
Asphalt pavements are undeniably smoother. Because asphalt is smoother, some agencies hold asphalt to higher smoothness specs. The public appreciates a smooth ride, and as an added benefit, vehicles get better fuel mileage on smooth pavements.
These pavements are designed so that only the top, surface layer is renewed on a 15-year or longer cycle. The base, structural layers last indefinitely (40 years or more); hence, the name perpetual pavements. Over their lifetime, these pavements use less materials and have a lower overall life cycle cost.
If needed, asphalt can be readily repaired. These repairs can be done during off-peak travel times, often over-night, while other pavement types may require weeks for repairs or replacement.
Warm mix asphalt
New technologies have allowed asphalt mixtures to be mixed and placed at significantly lower temperatures. A 50¿ F reduction is typical and 100¿ is possible. The warm mix processes (there are numerous methodologies) save burner fuel and reduce emissions. Other observed benefits may include easier compaction, extended haul distances and/or paving seasons and higher RAP contents.
Asphalt mixtures can be designed to be free-draining. Such engineered installations can be used in storm-water management. The filtering process of these installations can improve the water quality by removing contaminants during the retention time.
Specially designed asphalt mixtures, such as Open Graded Friction Courses (OGFCs), can allow water to travel through the pavement surface layer and away from the actual riding surface. This reduces spray, decreases hydroplaning and increases skidding resistance.
Life cycle cost
At one time, asphalt had a significantly lower initial cost than other pavement types. This may not always be the case today, but asphalt stills remains the lowest overall cost paving material. When alternate bids are received, asphalt routinely wins.
I started off saying that 94 percent of our roads have asphalt surfaces. With that much volume, it is not a problem to find a qualified, competent contractor. They are out there working every day to build and preserve our roads.
With all these advantages, it is easy to see that asphalt is the obvious choice.
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