The term “asphalt concrete” refers to a composite material used to pave roads, streets, parking lots, and airports. In the states, it is also known as blacktop, pavement, or simply, asphalt; but in Great Britain and parts of Europe, it is known as tarmac or bitumen macadam. Asphalt concrete (AC) mostly consists of mineral aggregates that are bound by liquid asphalt and laid and compacted in layers. The abbreviation “AC” generally stands for asphalt concrete, but can also signify “asphalt content” or “asphalt cement” in regards to the liquid asphalt portion of the material. And in the engineering and construction industries, AC is commonly referred to as asphaltic concrete or bituminous asphalt concrete.
Asphalt and Aggregate Mixes
There are many methods to mixing asphalt and aggregate materials. Depending on its application, examples of such mixes include hot asphalt concrete, warm mix asphalt concrete, cold mix asphalt concrete, cut-back asphalt concrete, mastic asphalt concrete, and natural asphalt concrete. Take a look below for a brief overview of each mixture formulation for asphalt and aggregate materials.
Hot Asphalt Concrete (HMCA) – Asphalt binder is heated to decrease viscosity, and prior to mixture, the aggregate is dried to remove any moisture. Depending on the type of asphalt used (either polymer-modified or virgin), mixing temperatures range between 300 and 330 degrees Fahrenheit (150-166 &;C). This mixture is used most often for high-traffic pavement such as interstates, racetracks, airfield landing strips, and more. But it is also used as an environmental liner for reservoirs, ponds, and landfills.
Warm Asphalt Concrete (WMA) – It is produced by adding certain materials to the asphalt binder prior to mixing, such as waxes, asphalt emulsions, zeolites, and occasionally water. This formulation provides lower laying and mixing temperatures. This results in reduced fossil fuel consumption, which in turn releases less vapors, aerosols, and carbon dioxide.
Cold Asphalt Concrete – It is produced by emulsifying asphalt in a mixture of cleanser and water prior to mixing. This makes the mixture less viscous and easier to manipulate. It is commonly used to patch holes and cracks on low-traffic pavements.
Cut-Back Asphalt Concrete – Asphalt binder is dissolved in kerosene (or some other light version of petroleum) prior to mixing. Just like cold asphalt concrete, this makes the mixture less viscous and easier to work with. With the growing concerns of VOC’s, cut-back AC has been mostly replaced by asphalt emulsions.
Mastic Asphalt Concrete – Also called “sheet asphalt”, is produced by heating oxidized, hard-grade, blown bitumen in a mixer until thick. Then aggregate mix is added to it.
Natural Asphalt Concrete – Produced from bituminous rock. Bituminous rock is found only in certain parts of the world where the surface of porous sedimentary rock has been permeated with upwelling bitumen.