Uses of Asphalt in Road Construction

Asphalt road construction is multi-layered in form. The subgrade layer is itself covered by a base cover upon which is laid a final coating. Early classical base courses consisted of a handmade, packed layer which was then graveled. Later this technique of construction was replaced, on a global basis, by a flexible asphalt layer in which asphalt gravel or sand asphalt had been mixed (Ibid. 149).

Asphalt as a road construction and/or road repair solution offers design, cost and durability advantages over concrete. The following will serve to put these issues into perspective.

Asphalt products are used to produce low cost, "flexible" pavements for primarily highway and airport applications. The term "flexible" is used to distinguish this type of pavement structure from those made utilizing portland cement. The latter are termed "rigid" pavement structures. Rigid pavements are used when the application requires a high beam strength (Larson 177).

This "flexible pavement" classification may be further divided into highly flexible and marginally flexible sub-units. Assignment to one of these sub-units usually depends on whether solid or liquid asphalt material is uti

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ng" which is a relatively new phenomenon. With reflection cracking, there occurs a replication of cracks and joints which are in the underlying layers of the pavement and the foundation materials. Once this new surfacing has become fractured, further deterioration of the pavement occurs resulting in a reduction of the effectiveness and strength of the road structure thus requiring additional maintenance (Scherocman 3). This additional maintenance can be costly, especially over time. To counter the negative influences of reflection cracking, asphalt mixes have been modified through the addition of rubber additives. In most applications, the addition of typically 1.5 percent to 5 percent of a rubber material (often latex based) has proven to be most effective. Durability The individual problems arising in road construction will not be dealt with at this time. Preparation and design of an asphalt road surface will inevitably require compromise, as do most design processes. Clearly, the economic result of meeting the wide range of technical road requirements will depend on the right selection of the constituent materials as well as the budgetary restraints of the project. Fundamental to the process is, of course, choosing
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