Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, as well as the core of embankment dams. It consists of mineral aggregate bound together with asphalt, laid in layers, and compacted. Asphalt concrete is preferred in surface roads as it generates less roadway noise than a Portland cement concrete surface, and is typically less noisy than chip seal surfaces.
Asphalt concrete is commonly regarded as being 100% recyclable as very little asphalt concrete is actually disposed of in landfills.
It should be noted that mix design methods and design requirements form an essential part for all asphalt concrete mixtures. An asphalt concrete mixture must be designed, produced and properly placed in order to obtain maximum stability, durability, flexibility, fatigue and skid resistance and impermeability.
Mixture should ensure optimum stability to resist shoving and rutting under loads. At the same time it should be noted that very high stability will make pavement too stiff and therefore less durable than desired. Maximum binder content increases durability because thick binder films do not age and harden as rapidly as thin ones do. To an extent impermeability is important for durability of compacted paving mixtures as it resists the passage of air and water into or through an asphalt pavement.
Asphalt mixture produced should be such that it should be capable of being easily placed and compacted. Mixtures containing a high percentage of coarse aggregate have a tendency to segregate during handling and also may be difficult to compact. A gummy mixture is also difficult to compact. An ideal mix should provide for gradual settlements and movements in the sub-grade without cracking. An open-graded mix with high binder content is generally more flexible than a dense-graded, low binder content mix.
Most of the problems with asphalt concrete arises because of faulty mixing and by those who do not have basic knowledge about the concrete. It should always be remembered that ratio of ingredients also play as important role as quality of ingredients in asphalt concrete (for that matter in any concrete).