The L.A. abrasion test values offer information on the performance of the aggregate in use. This test reveals how asphalt and concrete aggregates withstand wear and strain over time. The American Association of State Highway and Transportation Officials (AASHTO) publishes annual requirements for minimum performance standards for asphalt and concrete pavements. These guidelines are called "Marks" or "Abrasions". AASHTO Marks for asphalt pavements include: lane marking equipment, line striping, and guide lines. Concrete marks consist of: roughness, hole depth, and rebar spacing.
Lane markings are used to define lanes, indicate turns, and provide other necessary information about the road surface. They are made out of colored asphalt or concrete, which can be painted onto the pavement directly or placed into grooves cut into the surface. Line striping is a single color band running down the center of a highway between the white edge lines. It is usually black with red edges, but any other color combination is possible. Guide lines are white bands laid out along the side of the road to help drivers stay within their lanes. They are used by law enforcement officials to mark traffic accidents and other incidents that may require caution. The holes drilled into the pavement during the marking process are typically 2 inches (50 mm) deep and 3/4 inch (19 mm) wide.
The quantity of absorbed asphalt is subtracted from the total amount of asphalt to compute the effective asphalt content. The absorptiveness of an aggregate is obviously a significant factor in determining a mixture's asphalt content. The more absorbent the aggregate, the greater its effect on reducing the effective asphalt content of the mix.
Effective Asphalt Content = Total Amount Of Aggregate - Absorbed Asphalt
For example, if 100 pounds of asphalt were used in a road construction project and 25 pounds were absorbed by the rock (i.e., no longer available for use), then the effective asphalt content would be 75 pounds. This means that the total amount of asphalt that can be used in the mix is reduced by 25 percent because it was lost to absorption into the rock.
As another example, if the same 100-pound batch of asphalt were used in the mix but this time only 10 pounds were absorbed, then the effective asphalt content would be 90 pounds. In other words, there is now enough asphalt left over after absorption to fill 90 pounds of the void created by the absorption process.
The effectiveness of any particular type of aggregate in reducing the effective asphalt content of the mix depends on how much asphalt it absorbs.
Sand, gravel, crushed stone, slag, or rock dust are examples of aggregates (or mineral aggregates). To construct pavements, properly chosen and graded aggregates are combined with the cementing medium asphalt. The primary load-bearing components of an asphalt-concrete pavement are aggregates. Other ingredients such as superplasticizers, antistripping agents, air-entraining agents, and fiber additives may be included to improve certain properties of the resulting pavement.
Asphalt is a mixture of bitumen, which is a type of petroleum product, and aggregate. Bitumen is a thick, sticky substance found in crude oil that can be converted into plastic sheets for use in road construction. Asphalt emulsions, which are mixtures of water and asphalt, are also used in some applications because they reduce surface cracking during freezing and thawing cycles. Asphalt mixes can also include polymers, foam, fibers, and other additives to improve performance.
The two main types of asphalt are blacktop and chipseal. Blacktop is a dark colored, homogeneous mix of bitumen and coarse aggregate (rock) that's applied over a smooth concrete surface to form a durable protective coating. Chipseal is similar to blacktop, but with fine aggregate instead of coarse.
They account for 90 to 95 percent of the overall weight and 75 to 85 percent of the total volume of the combination. Asphalt is the binding agent that holds the aggregate together and gives the pavement its protective coating. Cement is the second most important ingredient, contributing about 5 percent of the material's weight and 15 percent of its volume.
Asphalt is a sticky substance made from crude oil or natural gas that is mixed with hot rocks (600 degrees Fahrenheit or 371 degrees Celsius) to form tar. This black sticky mass is then cooled down and crushed to make it workable for vehicles. Pavement asphalts can be classified as petroleum-based or synthetic. Petroleum-based asphalts are made from the distillation product of crude oil, which contains many ingredients including polycyclic aromatic hydrocarbons (PAHs), heterocyclic compounds, sulfur-containing chemicals, nitrogen-containing chemicals, and metals. Synthetic asphalts are made from petroleum products such as straight-run asphalt bitumen that has been modified by adding various types of materials such as plasticizers, extenders, and fillers to make them softer and more flexible.
Modern road construction uses asphalt mixtures containing 40 to 50 percent asphalt by weight.