Asphalt concrete – Wikipedia, the free encyclopedia

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.

Mixing of asphalt and aggregate is accomplished in one of several ways:

Asphalt concrete pavementsespecially those at airfieldsare sometimes called tarmac for historical reasons, although they do not contain tar and are not constructed using the macadam process.

A variety of specialty asphalt concrete mixtures have been developed to meet specific needs, such as stone-matrix asphalt, which is designed to ensure a very strong wearing surface, or porous asphalt pavements, which are permeable and allow water to drain through the pavement for controlling stormwater.

Asphalt concrete has different performance characteristics in terms of surface durability, tire wear, braking efficiency and roadway noise. The appropriate asphalt performance characteristic is obtained by the traffic level amount in categories A,B,C,D,E, and friction coarse (FC-5). Asphalt concrete generates less roadway noise than Portland cement concrete surfacing, and is typically less noisy than chip seal surfaces.[6][7]

Tire noise effects are amplified at higher operating speeds. Noise is generated through the conversion of kinetic energy to sound waves. The idea that highway design could be influenced by acoustical engineering considerations including selection of surface paving types arose in the early 1970s.[8][9]

Asphalt deterioration can include crocodile cracking, potholes, upheaval, raveling, bleeding, rutting, shoving, stripping, and grade depressions. In cold climates, freezing of the groundwater underneath can crack asphalt even in one winter (by frost heaving). Filling the cracks with bitumen can temporarily fix the cracks, but only proper construction, i.e. compaction and drainage, can slow this process.

Factors that cause asphalt concrete to deteriorate over time mostly fall into one of three categories: construction quality, environmental factors and traffic loads. Often, damage results from combinations of factors in all three categories.

Read this article:
Asphalt concrete - Wikipedia, the free encyclopedia