Asphalt Q&A

Asphalt is a black cementlike substance that is found in most crude petroleum. It has hundreds of uses. It is used to pave streets, highways, and airfields; to make roofing, waterproofing, and insulating materials, and floor tiles; and to line reservoirs, waste storage ponds, dams, and irrigation canals. Asphalt is also used in varnish and inks. Asphalt coatings also protect underground pipelines from corrosion.

Asphalt is thermoplastic. That is, it softens and becomes a liquid when heated, and returns to a solid when cooled. Asphalt wears well, is highly waterproof, and is unharmed by most acids and salts.

Asphalt production. Asphalt is separated from crude petroleum by refining methods that also produce gasoline, kerosene, and other products. Usually, gasoline and other products with low boiling points are removed by a distillation (boiling) process. The oil that remains is commonly called topped crude. Topped crude may be used as a fuel oil, or further refined to asphalt or other products. By varying the refining processes, different kinds of asphalt may be obtained. For example, blown or oxidized asphalts are made by blowing hot air through topped crude. They are widely used for roofing, enamels, and other industrial applications. Most topped crude is refined to produce asphalt cement, a semisolid asphalt used for paving.

Asphalt also occurs in natural deposits in pits, lakes, and rocks. But only a small part of the asphalt used in the United States comes from natural deposits. Some natural deposits found in pits and lakes are pure, but most deposits have become mixed with mineral matter, water, and other substances. One of the best-known deposits is Pitch Lake on the island of Trinidad in the Caribbean Sea. Sir Walter Raleigh discovered this 114-acre (46-hectare) bed in 1595. One of the largest deposits of asphalt is in Lake Guanoco in Venezuela, near the Gulf of Paria. The deposit covers about 1,000 acres (400 hectares). Uintaite or gilsonite, a solid form of asphalt, is found in Utah and Colorado.

Paving with Asphalt

Asphalt is used mainly to pave streets, highways, and airports. Over 90 percent of all paved roads in the United States have asphalt surfaces. Blacktop is the common name for many types of asphalt paving. Asphalt pavements are made in several ways. But usually, asphalt cement is mixed with mineral aggregates, such as crushed stone, gravel, and sand. These aggregates vary in size. The largest particles are usually about 3/4 inch (19 millimeters) in diameter.

The aggregates are blended, dried, and heated to about 300 °F (149 °C) in a paving plant. Hot mixes are prepared by adding hot asphalt cement. Paddles mix the asphalt with the aggregates in a pugmill mixer. The mix contains only about 5 to 10 percent asphalt by weight.

A paving machine spreads the mixture evenly on the roadbed, and a roller flattens it into a smooth, hard pavement. Cold mixes are made with liquid asphalt. This is a blend of asphalt cement and a light petroleum solvent (a substance that can dissolve other substances). Cold mixes can also be made by carefully blending asphalt cement with water. Cold mixes often can be prepared directly on the roadbed because little or no heating is needed in their preparation.

Surface treatment is used to resurface pavements or to pave lightly traveled roads. Hot asphalt cement or liquid asphalt is sprayed evenly over the roadway surface. Mineral aggregates are then spread over the surface and rolled into the asphalt.

Asphalt Driveway Maintenance

Since the liquid asphalt in blacktop needs time to harden and cure, usually 6-12 months your driveway will remain soft and pliable until then. You may walk on your new driveway immediately, but keep automobile traffic off it for at least 3 full days and longer in hotter temperatures. Even after the blacktop has cured, do not expect it to be as hard as concrete.

Your New Blacktop will soften and harden as temperatures rise and fall. Watering down your driveway with a hose on hot days will cool and temporarily harden the blacktop. This is helpful but not mandatory. If soapsuds should appear do not be alarmed. This is a reaction between the diesel fuel found in blacktop and a high chlorine content found in some city water. Although every effort is made to avoid puddles in your driveway, some small ones are inevitable depending on the natural slope and drainage of your ground.

Automobiles starting out too fast, pulling in too quickly and just plain driving too fast scar blacktop.

During the first 6-12 months while your driveway is curing don’t park in the same spot every time. Do not turn your steering wheel back and forth when your car is not moving.

Avoid using jack stands or car ramps unless a piece of plywood is placed under them to help distribute the weight.

Excessive weight from large heavy vehicles can depress your new blacktop. Keep oil trucks, concrete trucks and any other heavy trucks off your new driveway. When storing campers for long periods of time, place a piece of plywood under the tongue jack and also under the tires.

Lawn chairs, bicycle and motorcycle kickstands exert weight on concentrated areas and will create holes and depressions in your new driveway. Especially watch out for those pointy high heels during the warm months when your driveway is new.

The edges are the weakest part of you driveway due to the lack of side support. Avoid driving on the edges since they will crack and crumble over time. We suggest building up the sides of your driveway with topsoil. This will support the edges and enhance the appearance after the grass has grown in.

Your driveway may look smoother in some areas than in others because of the makeup of blacktop. Blacktop has various sizes of stone, sand, liquid asphalt, and other ingredients that cause a varied texture of the surface. Also, blacktop areas that have been raked and spread with hand tools may appear different in texture from those spread by a machine.

Avoid gasoline, oil anti-freeze, power steering and transmission fluid spills and leaks. These will dilute the liquid asphalt in your blacktop. Any hole left by these spills should be filled with cold patch. Any hairline cracks that may have developed over the winter due to the contraction and expansion of the ground should be filled with crack filler. These products can be purchased from your local building supply store or you can call GoreCon for any repairs needed.

To preserve your new driveway, it is advisable to seal coat it after it has been paved. The best time to seal is 3-12 months after it has been paved, and every 2-3 years thereafter. Because blacktop is naturally porous, water can seep into and through the pavement. This not only causes deterioration, but also results in ridges and upheaval due to frost and freezing. Blacktop is also softened and broken up by gasoline, lube oil, grease, road salts and anti-freeze that drip from cars. Sealer protects blacktop with a coating that is impervious to these harmful elements. Unsealed driveways remain porous, dry out, become rough, and lose their life more rapidly than sealed driveways.