Features

5 Major Steps to Road Construction

A quick review of the typical steps involved in construction of a road.

Updated on

August 7, 2024

A road construction site. PHOTO | COURTESY

Construction of a road involves the careful laying of soil stabilizers, asphalt, concrete, and other such materials along a predefined path.

This complex task involves paving, rehabilitation, and/or reclamation of degraded pavements into a motorable roadway.

Construction of a road can be a complex venture that requires months or even years of planning, depending on the size and type of the envisioned road.

Steps in road construction

The various processes of road construction have continued to change and differ when it comes to the type of road to be put up but the following process is designed to give a generic view of road construction using asphalt and/or concrete.

1. Planning

Road construction usually begins with planning.

This involves assessing the current and future traffic patterns and performing a cost-benefit study to ensure the road will serve its purpose.

Layout drawings, funding, legal, and environmental issues are all sorted out during this initial stage of road construction to ensure the project runs smoothly without running into financial or legal problems.

2. Setting Out

Setting out means transferring design proposals from drawings onto the ground. It demarcates the boundaries of the site, foundations, and other structural parts that might be necessary.

In most highway schemes, a series of boards are set up at intervals along the alignment or line proposed for the highway design. A profile board carrying a fixed height, sometimes referred to as a ‘traveller’, is used to check levels between profile boards on the excavated areas.

A traveller is set in the line-of-sight between two levelling boards so that it can be seen after both the before and after excavation and therefore adjustments of levels can be made.

Like in any other building process, the gradient of the profile board is measured using a line level – a short spirit level suspended on a nylon string.

The string is lifted or let down until the level of the bubble is centred.

3. Earthworks

Earthworks are the most labour-intensive works in road construction, where a grader deployed at a site will be used to remove the topsoil from the ground.

This makes up to the stage where the site is scraped and graded to expose the ground underneath, also known as the level formation.

Excavation will stop at this level, and it is where construction on the road will start.

If the strength of soils forming the subgrade below the formation level is not possible, prior testing should be conducted during excavation, to give a clear pass. Where there is poor quality in the subsoil, it can be removed or stabilized.

If the excavation cost is considered too high, then sand drains and sand wicks can be applied. Sand wicks are sand-filled below the road embankment boreholes.

These systems reduce the length that water travels in the path of a drainage way thus reducing the steam of water along its path before it breaks down water pressure, offering greater stability to the soil.

Sand drains are provided for capturing groundwater; this caters to the payment and verge leakage originating due to higher ground and fluctuation of the water table.

There should be adequate reinforcement of soil stabilization with chemicals or cement and bituminous material for all sections thickness of pavements.

This includes the complete removal of poor material which should be replaced with selected fill to ensure adequate subsoil drainage, with the subsequent compaction of the subgrade to a high dry density.

This should be done to prevent moisture from subgrade weakening. The subgrade should be covered with medium-gauge plastic sheeting or treated with a bituminous binder with a topping of sand.

4. Paving

Paving is done after the installation of the drainage system and subgrade compaction. Paving is categorized into two categories based on the project’s demand, which is either rigid or flexible.

Rigid pavements are superior in many ways: they provide higher flexural strength and a longer design life with lower maintenance costs.

On the other hand, flexible pavements are expandable and contractible; hence, they do not need to have expansion joints due to temperature variations.

i.) Rigid paving

This consists of a reinforced or unreinforced in situ concrete slab laid on top of a thin granular base course. It is the inflexibility and strength of rigid pavements that allow the dispersion of the loads and pressures over a wide area of the subgrade to reduce the potential impact.

What layers are needed to build a road?

The rigid paving, from top to bottom, consists of these layers:

Subgrade of existing soil.
60-cm crushed stone subbase course.
Polythene sheeting for the lubricous sheath.
On this a reinforced in-situ concrete paving slab, with steel fabric or re-bar, if necessary.
As appropriate, an asphalt or other topping is used.

Thus, rigid pavements are not capable of extending or contracting either through temperature or under changes in moisture.

Longitudinal and transverse joints are provided between the slabs to prevent cracking that occurs due to restrained deformation caused by temperature changes and moisture variation.

The spacing of the joints is usually determined by the temperature at which the concrete is laid, the slab thickness, the expected traffic load, and whether the slab is reinforced or not.

ii.) Flexible paving

Flexible pavements are several layers of asphalts or bituminous material overlaying the ready-made subgrade to which all the varied traffic loads are distributed.

They are thus named ‘flexible’ because the whole pavement structure bows or deflects under loading from the traffic.

The thickness of every individual layer must have the capability to distribute loads to avoid permanent deformation of the road surface.

In flexible paving, the subgrade is compacted along with the sub-base.

The sub-base course is generally filled with crushed stone or dry lean concrete and vibrated/compacted by a road roller machine.

The sub-base should not be more than 15 cm thick and is usually laid after the operation of waterproofing.

Above the subbase is the surfacing layer, which is composed of the base and the wearing course. The wearing layer is the topmost of the bituminous material and may be comparatively more substantial and stronger than the base layer.

Its thickness varies with material specifications and the expected or predicted traffic loads.

Common materials used for the wearing course include porous asphalt, hot rolled asphalt, dense bitumen tar macadam, and dense bitumen macadam.

On the other hand, the sub-layer is considerably at least 6 cm in thickness and is made up of dense bitumen macadam or asphalt laid in suitable cross-falls and gradients.

5. Quality control

After a road surface has been put in place, a series of quality tests must be done before the road construction project can be deemed complete.

This process needs monitoring so that it can be determined that the drainage, grading levels, and all other characteristics of the road are in good standing.

All the tests are done and are evident and yield positive results; the road can then only be free for use by the motorists. Most of the road pavements can be in use for a duration of up to 40 years – with major upgrade works due every decade or so.