Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, parking lots, and airports. Asphalt concrete consists of asphalt (used as a binder) mixed with mineral aggregate and then laid down in layers and compacted. Asphalt concrete was refined and enhanced to its current state by Belgian inventor and U.S. immigrant Edward de Smedt.[2] It is increasingly being used as the core of embankment dams.[3] It is commonly called simply asphalt,[4] blacktop, or paving (particularly in North America). The terms "asphalt (or asphaltic) concrete", "bituminous asphalt concrete", and "bituminous mixture" are typically used only in engineering and construction documents and literature. The abbreviation "AC" is sometimes used for "asphalt concrete" but can also denote "asphalt content" or "asphalt cement", referring to the liquid asphalt portion of a bituminous mixture. Asphalt concrete pavements are often called just "asphalt" by laypersons who tend to associate the term "concrete" with Portland cement concrete only. The engineering definition of concrete is any composite material composed of mineral aggregate glued together with a binder, whether that binder is Portland cement, asphalt or even epoxy.

Contents [hide] 1 Mixture formulations 2 Performance characteristics 3 Asphalt concrete degradation and restoration 3.1 Prevention and repair of degradation 4 Recycling 5 See also 6 References 7 External links

Mixture formulations[edit]

As shown in this cross-section, many older roadways are smoothed by applying a thin layer of asphalt concrete to the existing portland cement concrete.
Mixing of asphalt and aggregate is accomplished in one of several ways: Hot mix asphalt concrete (commonly abbreviated as HMAC or HMA) is produced by heating the asphalt binder to decrease its viscosity, and drying the aggregate to remove moisture from it prior to mixing. Mixing is generally performed with the aggregate at about 300 °F (roughly 150 °C) for virgin asphalt and 330 °F (166 °C) for polymer modified asphalt, and the asphalt cement at 200 °F (95 °C). Paving and compaction must be performed while the asphalt is sufficiently hot. In many countries paving is restricted to summer months because in winter the compacted base will cool the asphalt too much before it is able to be packed to the required density. HMAC is the form of asphalt concrete most commonly used on high traffic pavements such as those on major highways, racetracks and airfields. Superpave, short for "superior performing asphalt pavement," is a pavement system designed to provide longer lasting roadways. Key components of the system are careful selection of binders and aggregates, volumetric proportioning of ingredients, and evaluation of the finished product. Warm mix asphalt concrete (commonly abbreviated as WMA) is produced by adding either zeolites, waxes, asphalt emulsions, or sometimes even water to the asphalt binder prior to mixing. This allows significantly lower mixing and laying temperatures and results in lower consumption of fossil fuels, thus releasing less carbon dioxide, aerosols and vapors. Not only are working conditions improved, but the lower laying-temperature also leads to more rapid availability of the surface for use, which is important for construction sites with critical time schedules. The usage of these