A well constructed road provides many benefits to the road user – comfort, safety, good mobility , peace of mind and provides a good driving experience and its fun!. However many road users – typically non-civil engineers rarely understands what it takes to build a good road. Most of us just see the ‘surface’ which comes in contact with motor tyres – but we don’t know what goes beneath the surface before what we actually call ‘the road’ is finished. Lets demystify it!
A road pavement typically consists of a number of layers such as base, sub base. A road pavement is the portion of the road located directly below the riding surface and above the existing natural ground. So a typical structure starting from the ground is natural ground (subgrade), above it sub base, and above it base and then the surface. All that structure constitutes a pavement. Pavements can either be rigid or flexible and in Malawi flexible pavements are the most commonly used.
A rigid pavement is where concrete is used as the surfacing material and this provides the majority of the strength of the pavement. A rigid pavement flexes very little under loading due to the concrete layer.
A flexible pavement is constructed with bituminous-treated surface or a relatively thin surface of hot-mix asphalt over one or more unbound layers resting on the subgrade. A flexible pavement deflects, or flexes under loading whereby each layer receives the traffic loads from the above layer, spreads them out, then passes on these loads to the next layer below. The strength of a flexible pavement is therefore derived from the load-distributing characteristics of a layered system designed to ultimately protect each underlying layer including the subgrade from failure.