Asphalt concrete
Asphalt concrete is a composite material. It is commonly used to build roads, parking lots, airports, and embankment dams. Asphalt mixtures have been used in making pavements since the beginning of the twentieth century. It is made up of mineral aggregate bound together with asphalt. The process was made by Edward De Smedt.
Asphalt mixtures
Mixing of asphalt and aggregate is done in one of several ways:
Hot-mix asphalt concrete (commonly abbreviated as HMA)
This is made by heating the asphalt binder to make it less viscous, and drying the aggregate to remove moisture from it before mixing it. Mixing is done at about 300 degF (roughly 150 degC) for virgin asphalt and 330 degF (166 degC) for polymer modified asphalt, and the asphalt cement at 200 degF (95 degC). HMA is used on roads with lots of traffic.
Warm-mix asphalt concrete (commonly abbreviated as WMA)
This is made by adding either zeolites, waxes, asphalt emulsions, or sometimes even water to the asphalt binder before mixing. It is good for the environment because small amounts of fossil fuels are used to make them. It also releases less carbon dioxide into the air. In 2012, a survey of producers that made asphalt in the US found that nearly 25% of asphalt made was warm mix.
Cold-mix asphalt concrete
This is made by emulsifying the asphalt in water. It is done with an emulsifying agent before mixing. While it is emulsified, the asphalt is less viscous. The emulsion will break after enough water evaporates from it. Cold mix is commonly used on roads with less traffic.
References
Building materials
Road transport