Road Construction - How to build a road

27 October 2014

How to build a road - a guide to road construction.

Paved road surfaces provide a means for vehicles to move along without sinking into the mud due to the concentrated weight through tyres.

The earth is removed down to the desired level to begin laying the road. This point is called the ‘sub-grade’. The sub-grade is the ground below the road layers which is exposed once the ground has been dug out. Please see diagram below for road layering.

The next layer is called the ‘sub-base’. The sub-base should be laid as soon as possible after final stripping to prevent damage from rain or sun baking which could cause surface cracks.

The most commonly used material for the sub-bases is an unbound material made from crushed rock, crushed slag, crushed concrete or recycled aggregates. The range of material size within this layer means that once compacted, it will resist further movement and avoid sinking over time.

The road is compacted by a ‘Roller’. Rollers are heavy road construction machines used for compressing the sub-base layer and asphalt layers. Asphalt rollers are used hot and therefore create flexible asphalt pavements. To prevent them from causing damage to the new asphalt surface, they must not come to a halt during the compacting operation.

In order to build a far stronger road adding a couple of layers of sub-base would be ideal.

The next layer is called the ‘binding layer’ and involves laying down rolled asphalt. At this point in order to have a road with optimum strength you would add ‘geotextile’. This is a geogrid designed with small aperture for drainage which is extremely important for countries with a rainy season. It is a flexible membrane that is made from glass fibre strands and is then polymer bitumen coated to allow it to bond well with your final ‘surface layer’. You can get more information on geotextile and geogrid here. Geogrid can also be laid below the sub-base layer to avoid the sub-grade aggregate sinking away into the earth.

A final layer of hot rolled asphalt is placed on the road. This is made with asphalt cement content with crushed rock, slag or gravel added. Normal thickness is 40mm with 20mm coated chippings rolled into the surface providing better skid resistance.

Using the above method and products your roads will last much longer than normal and require much less maintenance.

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