Road Construction – Modern Methods
These roads were based on several prominent Scottish engineers’ designs with Macadam being the most popular choice.
As automobiles became more popular, the increase led to more new roads and highways being built to carry them and experience in road construction grew at a fierce rate to meet this new challenge.
The use of the refined petroleum asphalt was the norm and engineers could dictate the composition of asphalt required to meet the needs of the road surfaces such as traffic speed and volume, which varied throughout the country.
A typical method is noted below:
The surface of the excavated area is compacted and levelled. Fine sand and gravel mix is laid on top of this at a predetermined depth and compacted until no further indentations can be made. This layer acts as a vegetation inhibitor and drainage medium, drainage being one of the most important qualities in road construction.
This consists of a layer of stones and rubble, sieved to a required size and compacted using mechanized heavy roller equipment.
This is the load-bearing layer and is made up from a mix of hot asphalt mixed with a aggregate of uniform sized stone chips, once again the size being dictated by the road conditions.
This is then rolled flat using heavy roller equipment.
- 4th Layer (Final Surface)
The surface layer is known as Stone Mastic Asphalt. It is made up from different grades of small aggregate that have been previously coated in hot bitumen that acts as a binder when mixed thoroughly with hot asphalt.
The mix is then laid using a specialist machine that ensures an even spreading to the requisite thickness, leaving a slight camber from the center of the road to the edges.
Water drain gratings are inserted at the edge of the road connected to underground pots. These pots act as oily water separators, from which the water is fed to perforated drain pipes to field and ditch drains.
The pots are emptied regularly using tanker trucks with suction equipment.
1. macadam - early roadbuilding.
2. htma- properties of road surfaces.
3. docrep - road construction.