Even though the techniques for constructing highways have kept evolving because of technology advancement and the complexity of the highway, one thing has remained unchanged. Before any highway construction, there should a well taken survey and a good subgrade preparation. In highway construction, there is always a big difference in highway construction between urban areas and rural areas. Needless to say, the former is much more complicated.
Highway construction can be broken down into several elements which have been outlined right below. It can be broken down into both commercial and technical elements. The technical elements are traffic, installation techniques, material quality and materials while the commercial elements are public concerns, legal aspects, political aspects, environmental aspects and contract understanding.
Before construction begins in earnest, it is very necessary to have the following information at hand as they are critical in taking certain decisions. The engineers need to know the quantities of water for compaction and dust control. They need to know the shoring requirements for excavation protection. If below-grade work becomes necessary, the dewatering requirements need to be known too.
A Good Preparation is Important
Before excavation begins, the major properties of the materials to be excavated should be known to determine the most suitable excavation techniques. The engineers also need to verify the existing ground conditions. After all these, the engineers can now decide the best tools and equipment for grading, excavation and material transportation. They need to find out all these to be able to give a reliable cost estimate.
The real construction begins with the separate construction of three road layers. The sub-base course, base course and the road surface are constructed one after the other. The sub-base is usually the first to be constructed. The thickness of the sub-base is generally from 4 to 16 inches thick. The sub-base course is constructed with the following materials lime, fly ash, subgrade soil or crushed stone and gravel.
The next is base course construction. The thickness of base course is also from 4 to 6 inches. However, the underlying layer properties also contribute to the thickness of the base course. The base course is usually constructed with gravel, slag or crushed stone.
The next is the surface course construction. The two major types of pavement surfaces are Portland cement concrete and hot-mix asphalt. The pavement surface course must give a smooth ride and also transfer the traffic load to other layers too. The common construction issues are joints, compaction, laydown and asphalt mix segregation.
Even though highway maintenance is not taken half as seriously as its construction, maintenance is equally as important as construction. In fact, the objective of regular maintenance is to preserve serviceability and structure and also fix little defects. A stich in time saves nine.
To be able select an appropriate maintenance plan, highway defects have to be well-defined and understood by all stakeholders. This is because the defects of rigid pavements usually differ from those identified with flexible pavements. The main objectives of highway maintenance can be summarized into the four listed below.
- To maintain road reserve
- To maintain road safety and signage
- To lengthen the structural and service lifespan of a road
- To fix pavement defects