The modern use of asphalt for road and street construction began in the late 1800s and grew rapidly with the emerging automobile industry. Since that time, asphalt technology has made giant strides so that today the equipment and techniques used to build asphalt pavement structures are highly sophisticated.
Asphalt Concrete is a composite material commonly used in construction of roads, highways, airports, parking lots, and many other types of pavement. It is commonly called simply asphalt or blacktop. The terms “asphalt concrete”, “bituminous asphalt concrete” and the abbreviation “AC” are typically used only in engineering and construction documents and technical literature where the 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. To the layperson Asphalt Concrete pavements is most often called just “asphalt“.
Asphalt Technology Disciplines
Asphalt Technology is the study of asphalt mixes, properties and performance and can be divided into three primary disciplines;
Asphalt Mix Types
An asphalt concrete mixture must be designed, produced and placed in order to obtain the following desirable mix properties: 1) Stability, 2) Durability, 3)Impermeability, 4)Workability, 5) Flexibility, 6) Fatigue Resistance, and 7) Skid Resistance. Asphalt/Asphalt Concrete mixes are designed for specific functions, characteristics, attributes, performance, location and function in the pavement structure. For example, asphalt surface mixes have an entirely different function in the pavement structure than base asphalt mixes and are therefore designed differently.
Surface Asphalt mixes – The “roof” over the pavement’s structural layers and are designed to be long lasting, sacrificial (designed to wear out first, protecting the underlying layers). At some point (typically 12-15 years or more after placement) they are removed by cold-planing (commonly called milling) and replaced with a new surface. Different performance characteristics in terms of surface durability, tire wear, braking efficiency and roadway noise, can also be achieved depending on application, desired function and performance.
Base Mixes – The structural strength element of the asphalt pavement system and are designed for maximum strength, distributing the wheel loads over the subbase and subgrade. Because they are protected by the asphalt “roof” (surface) the appropriate asphalt base mixes performance can be achieved economically.
Different kinds of Asphalt Concrete
To be able to provide the best performance to different sectors, a large variety of asphalt mixes can be offered. Due to the different requirements e.g. a road needs to fulfill (high traffic, tough weather conditions etc) the respective mix used needs to have an sufficient stiffness and resistance to deformation in order to cope with the applied pressure from vehicle wheels on the one hand, yet on the other hand, the need to have an adequate flexural strength to resist cracking caused by the varying pressures exerted on them. Moreover, good workability during application is essential in order to ensure that they can be fully compacted to achieve optimum durability.
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