Asphalt is a black cement like substance that is found in most crude petroleum and occurs in natural deposits in pits, lakes, and rocks. 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. Asphalt is a thermoplastic. It softens and changes to a liquid when heated and returns to a solid when cooled. Asphalt is highly durable and waterproof. It is unharmed by most acids and salts.
Asphalt is manufactured by separating 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 into asphalt or other products. By varying the refining processes, different kinds of asphalt may be obtained. Most topped crude is refined to produce asphalt cement, a semisolid asphalt used for paving.
Asphalt has many applications and is used to produce a multitude of products. The most common application of asphalt is used to pave driveways, streets, roads, highways, and airfields. It is used in the production of roofing, waterproofing, insulation materials, floor tiles, varnishes and ink as well. Asphalt coating is used to protect underground pipelines, line reservoirs, waste storage ponds, dams, and irrigation canals from corrosion.
Asphalt also known as blacktop is a natural resource most commonly used to surface driveways, streets, roads, highways, and airports. Over 90 percent of all paved roads in the United States have an asphalt surface.
Asphalt is produced in several ways. Frequently, asphalt cement (a product made by the destructive distillation of organic matter) is mixed with mineral aggregates such as crushed stone, gravel, and sand which vary in size. The largest particle is usually 3/4 inch (19 millimeters) in diameter.
The aggregates are blended, dried, and heated to approximately 300 °F (149 °C) in a paving plant at the quarry. Paddles mix the asphalt cement with the aggregates in a Pugmill Mixer. The mix contains only about 5 to 10 percent asphalt by weight. The hot asphalt or blacktop is loaded onto a truck and quickly delivered to the paving job site. A paving machine spreads the mixture evenly on the roadbed. A roller flattens it into a smooth, hard surface.
In some instances, a cold mix or patch is used to temporarily pave an area until the final surface can be applied. A cold mix can be prepared directly on the roadbed because little or no heating is required. Cold mix is a blend of asphalt cement and a light petroleum solvent (a substance that can dissolve other substances). It can also be made by blending asphalt cement with water.
Surface treatment is a procedure used to pave roads with light vehicle traffic. 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.
The liquid asphalt in blacktop needs time to harden and cure usually 6-12 months. Until the curing process is complete, the driveway will remain soft and pliable. You may walk on the new driveway immediately, but keep automobile traffic off the driveway for at least 3 full days or longer in hot temperatures. After the blacktop has cured, do not expect it to be as hard as concrete.
During the first 6-12 months while the driveway is curing, don’t park vehicles in the same spot repeatedly. 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. Automobiles starting out too fast, pulling in too quickly and just plain driving too fast will scar blacktop. Excessive weight from large heavy vehicles can depress new blacktop. Keep oil trucks, concrete trucks and any other heavy trucks off the new driveway. When storing campers or boats 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 the new driveway. Especially watch out for those pointy high heel shoes during the warm months when the driveway is new. The edges of the driveway are the weakest part 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 once the grass has been established.
The driveway blacktop will soften and harden as temperatures rise and fall. Watering down the 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 in blacktop and a high chlorine content found in some city water. Although every effort is made to avoid puddles in the driveway, some small ones are inevitable depending on the natural slope and drainage of the ground.
The driveway may look smoother in some areas than in others because of the nature of blacktop. Blacktop has various sizes of stone, sand, liquid asphalt, and other ingredients that produce a varied texture of the surface. Blacktop areas that have been hand-raked and hand-spread will have a different appearance 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 a professional evaluation and repair.
To preserve your new driveway, it is advisable to sealcoat it after it has been paved. The best time to sealcoat is 3-12 months after it has been paved and every 2-3 years thereafter. Since blacktop is naturally porous, water can seep into and through the driveway. This can cause deterioration, ridges and upheaval due to thawing and freezing temperatures. Blacktop will softened and break up by gasoline, lube oil, grease, road salts and anti-freeze that drip from cars. Sealcoating protects the blacktop as it is impervious to these harmful elements. Unsealed driveways remain porous, dry out, become rough, and breakdown much more rapidly than sealed driveways.