What is asphalt?
Asphalt is a dark, highly viscous liquid or semi-solid that is present in most crude petroleum. The liquid is used in road construction. Asphalt is a carefully refined residue from the distillation process of crude oils. (Do not confuse asphalt with tar. Tar comes from coal.) It is heated and used as glue for aggregate materials in road construction. The black paving you see on the road is made up of many different types of gravel and ground rocks, and held together with asphalt. That is why blacktop roads are commonly known as asphalt roads.
Rolling asphalt is the most popular method of paving roads. Rolled asphalt accounts for 80% of asphalt consumption in the US.
In places with colder, wintry climates, asphalt requires a special protective seal coating to prevent damage from cracking. Freezing temperatures and subsequent thawing cause cracks and fissures in asphalt paving.
When an asphalt services contractor is deciding how to go about paving a driveway, there are two methods the company will likely choose. Usually, any existing asphalt or pavement is ripped out and the new asphalt paving is rolled over the soil. In other situations, an aggregate of stone, sand, and gravel is laid down first as a bed for the asphalt paving. Then the contractor rolls the dark asphalt paving over this aggregate bed.
Keep in mind the time of year when you plan to hire an asphalt services contractor. This is one of the greatest factors in the successful pavement of your driveway, parking lot, or road. Here’s why:
It’s best to lay asphalt in warmer temperatures. The asphalt does not harden quickly, so there’s more time for the crew to work. Ideally, a crew will roll a layer of asphalt 1.5” thick at 70 degrees Fahrenheit.
Once conditions are right, the actual paving is a relatively quick process. The average driveway takes only 20 minutes to pave. The next step is compacting the pavement with a roller, and letting it harden as it dries.
Here are some variables to be aware of when picking a time to hire an asphalt services contractor. At 40 degrees Fahrenheit, it takes 16 minutes before 1.5” of asphalt paving hardens. At the same temperature, it takes 46 minutes before 3” of asphalt paving hardens. So you have to think about the thickness, or depth, you prefer for the asphalt paving. Thinner layers need warmer weather for a job well done. If you have to pave at temperatures below 70 degrees Fahrenheit, you may want to choose a greater thickness. That way the crew has more time to do quality work.
Also make sure you talk to your asphalt services contractor about the load you intend your asphalt paving to bare. There are special mixtures for different types of uses. For example, special mixtures of asphalt paving are designed to specifically accommodate cars or trucks, or both.
The 1993 Guide for the Design of Pavement Structures from the American Association of State Highway and Transportation Officials says that the principal factors in choosing between different types of asphalts are the intended traffic load, the kind of soil that will form the road’s bed, the area’s dominant weather patterns, any adjacent construction considerations, recycling, and cost comparisons.
Additionally, consider the performance of pavements in the area of the intended road or parking lot. Think about the conservation of the project’s materials, the energy necessary to complete the project, and the availability of local materials.
Interesting statistics: the US has more than two million miles of paved roads. 94% of these use asphalt. The asphalt paving industry employs 300,000 Americans. The breakdown of asphalt paving is 95% stone, sand, and gravel aggregate, and 5% asphalt cement petroleum product.