Road construction

Road construction is a branch of civil engineering that uses engineering techniques to design, build and maintain pavements and upper layers of transportation routes. These routes can be made of unbound materials such as soil and gravel and more commonly asphalt or concrete.

Design

Road design consists of two technical aspects:

• geometrical road design: design of the line management of the road, including environmental issues.
• structural road design: design of the body of the road
• road safety: design of the safety features of and next to a road

Besides these two technical sides of the design, planning and juridical issues are important.

Construction

The construction of a road usually starts with the preparation of the construction area in order to build up the pavement. Removal of earth and rock by digging or blasting, construction of embankments, bridges and tunnels, and removal of vegetation (this may involve deforestation) are often needed. A variety of road building equipment is employed in road building.

Once these activities are completed, the construction of the pavement begins by compaction of the native soil, known as the subgrade. Weak soils may also be stabilized with additives such as portland cement and quicklime, or dug out and replaced with imported soils.

Then a base course consisting of gravel or crushed stone is usually placed on the subgrade and compacted. Depending on the road type, different kinds of layers are build on top of the base course, e.g. asphalt concrete or portland cement concrete. Unbound materials such as soil or gravel are put on low-stressed roads such as farm tracks and country lanes. Roads made of asphalt or concrete provide a smooth and high-friction surface and strengthen the pavement structure by spreading out the vehicle loads applied to the subgrade and are therefore used for high-stressed roads.

Maintenance

Like all structures, roads wear out over time. This effect is primarily due to accumulated damage from vehicles, however environmental effects such as frost heaves, thermal cracking and oxidation often contribute. According to a series of experiments carried out in the late 1950s, called the AASHO Road Test, it was empirically determined that the effective damage done to the road is roughly proportional to the 4th power of axle weight, that's why trucks are considered to be the main cause of pavement deterioration.

Maintenance of a road can be divided in several types, from fixing small failures to a complete reconstruction of the road. Usually, road building equipment is used to replace the top material layers and to rebuild them.