Asphalt Constructions Paving is often thought of by laymen as the asphalt overlay on portland cement concrete pavements.
The term concrete is defined as “a composite material of mineral aggregates such as small stones or crushed gravel bonded together by a binder such as portland cement, asphalt or epoxy used in the construction industry for airports, parking lots, road surfaces and other such pavements”. Asphalt concrete may also be used as a roofing overlay to minimise, if not to completely eradicate, leaks and seepage.
Concreting services started with portland cement as binding material which lent it its popular etymology of “concrete” being equated to “portland cement”. As technology advanced, engineers and scientists discovered that overlaying portland cement concrete pavement with asphalt constructions paving was a much better option mainly for following reasons:
· increased surface durability thereby lengthening the pavement’s lifespan
· minimised tire wear and tear offering a smoother ride because of its softer surface
· higher braking efficiency insuring safety for motorists
· reduced “roadway noise” and better mileage efficiency
Use of blacktop, as asphalt constructions paving is otherwise known in North America, rapidly spread to other countries while being continually improved with new innovative technologies. Today, there are at least 6 asphalt concrete formulations used for different purposes and types of paving construction.
The Hot Mix Asphalt Concrete (HMA or HMAC) can withstand “heavy beating”, hence used most commonly for “highly trafficked” pavements to include airfields or airport runways, major highways and race tracks. As its name suggests, it involves heating the asphalt binder to “soften” it and mixing with properly dried aggregate at 300°F for virgin asphalt and at 330 F for polymer-treated asphalt.
Warm Mix Asphalt (WMA) Concrete is done at lower mixing temperatures due to the addition of either asphalt emulsions, waxes or zeolites consequently decreasing the use of fossil fuel. The lower laying temperature allows for faster seasoning period and thus hastening pavement’s availability for use.
Cold Mix Asphalt Concrete is used as patching material or for lesser traffic service road applications. It is a “cold” version of the HMAC involving emulsification of asphalt in water with soap.
Cut-back Asphalt Concrete is a formulation that is now seldom applied for environmental reasons as it involves use of kerosene to “soften” asphalt instead of heating.
Mastic Asphalt Concrete involves “cooking” hard asphalt in a mixer for 6-8 hours. Experienced layers hand- or machine-lay the formulation at 20-30 mm thickness on foot paths and roads and at 10 mm for flooring and roofs.
Natural Asphalt Concrete is a natural formulation resulting from the upsurge of bitumen from within porous sedimentary rocks that area found in certain parts of the earth. This is a more preferred formulation, where applicable, because of its harmlessness to the environment.
It is absurd why, in some countries, especially in the tropics where climate is moderate and favourable, roads and highways are without asphalt constructions paving, despite its positive economic implications.