FLEXIBLE PAVEMENT FOR THE TRAFFIC CONDITIONS

Designing a Fully Flexible Pavement for the Traffic Conditions



Designing a Fully Flexible Pavement for the Traffic Conditions

Introduction

Flexible pavements are so named because the total pavement structure deflects, or flexes, under loading. A flexible pavement structure is typically composed of several layers of material. Each layer receives the loads from the above layer, spreads them out, then passes on these loads to the next layer below. Thus, the further down in the pavement structure a particular layer is, the less load (in terms of force per area) it must carry . In order to take maximum advantage of this property, material layers are usually arranged in order of descending load bearing capacity with the highest load bearing capacity material (and most expensive) on the top and the lowest load bearing capacity material (and least expensive) on the bottom. This section describes the typical flexible pavement structure consisting of:

* Surface course. This is the top layer and the layer that comes in contact with traffic. It may be composed of one or several different HMA sublayers.

* Base course. This is the layer directly below the HMA layer and generally consists of aggregate (either stabilized or unstabilized).

* Subbase course. This is the layer (or layers) under the base layer. A subbase is not always needed.

After describing these basic elements, this section then discusses subsurface drainage and perpetual pavements.

The flexible pavement structure is composed of several layers of material. Each layer receives the loads above the layer, extending it, then passes these charges to the next lower layer. Therefore, the layer below the pavement structure gets fewer loads. To take full advantage of this property, the layers are generally arranged in descending order of capacity, so the top layer will be the one with the largest payload of material (and most expensive) and more low carrying capacity of material (and cheaper) anger at the bottom.

Highway pavements consist primarily of carefully proportioned and blended aggregates in such proportions as to form a dense and durable mass held together by an optimum amount of cementing material. The latter may be portland cement, which is the basis of the rigid pavement, or a bituminous cement, generally asphaltic, which is the basis of the flexible pavement. Rigid pavements usually contain calculated amounts of reinforcing steel and are, in effect, structures with sufficient internal strength to maintain grade and alignment despite minor ...