Many municipalities, including the Virgin Islands, struggle to decide whether to construct their roads with concrete or asphalt. The Portland Concrete Association promotes concrete as the road construction material of choice; the National Asphalt Pavement Association advocates for asphalt. Further, many individuals and other agencies promote concrete roads as being stronger than asphalt.
Well, the choice is not so clear-cut. There are pros and cons to both options.
Pros, cons of concrete
Concrete is a composite of cement, sand (fine aggregate), gravel (coarse aggregate) and water. Some special mixes may contain admixtures, which vary set times and so on.
The pros of concrete as a road building material include the following: a longer lifespan of around 30 years on average; less maintenance; a longer interval time between full replacement; and a cheaper repair cost.
The cons of concrete include a longer installation and construction process; a higher initial construction cost; less pavement flexibility; a more difficult maintenance and repair process; and a noisier ride for motorists.
Pros, cons of asphalt
Asphalt, or asphalt concrete, is a composite mixture of a bituminous material (binder), sand and gravel. Additionally, it is a flexible pavement made up of several layers: subgrade, subbase, base and surface course.
The pros of asphalt include a lower initial construction cost; easier maintenance and repair; more flexible pavement; quicker construction time; and a smoother, quieter ride.
The cons include a shorter lifespan of 15-20 years on average; a higher maintenance and repair cost; and more required maintenance and repair.
Carrying capacity
There is a common belief that concrete pavement is stronger than asphalt pavement. This belief takes root because comparisons are not usually made on equivalent designs. In general, the traffic carrying ability of asphalt and concrete pavement is approximately the same for each inch of pavement thickness if the structural number (empirical strength value assigned to a particular material, known as “SN”) of both concrete and asphalt cross sections are equal.
For example, assuming that the SN for a 3,000 PSI concrete pavement cross section is three per inch of thickness and the SN for a dense graded asphalt pavement cross section is also three per inch of thickness, the load carrying ability for, say, a six-inch-thick concrete and asphalt pavement would be the same. Therefore, concrete and asphalt pavements with equal SN will have the same traffic carrying ability with equal pavement thickness.
Mixed-use roads
Typically, other locales, like the United States, have the following road classifications: arterial, collector and local (residential). In many of these locales, there are restrictions on what wheel loads can use what roads. However, in the Virgin Islands, the roads are mixed use and are being used by cars, light trucks, heavy trucks, construction equipment and so on. Consequently, the roads must be designed, constructed and maintained to safely carry the heaviest wheel load that will use them. This will help mitigate premature road failure.
Drainage
One of the contributing factors of premature road failure in the VI is poor drainage, which is caused by improper cross sloping, settling water, undersized drainage pipes and box culverts, clogged pipes and ghuts, poor drain maintenance, restricted flow in roadside ditches and so on. Further, during extensive and prolonged rain events, the roads may temporarily serve as a drainage conveyance system. Nonetheless, the drainage system must be designed and constructed so that runoff can be quickly moved off the roads.
Finally, whether the roads are constructed of concrete or asphalt, they must be properly designed, constructed and maintained to meet the transportation needs of the territory.
The choice of road type comes down to preference. Further, roads must be religiously maintained to 1) extend and attain design life; 2) retard premature road failure; 3) extend time interval for full replacement; 4) reduce maintenance and operations cost; 5) improve serviceability; and 6) reduce vehicle owners’ operating cost. Moreover, a world-class road network is vital for continued economic growth, development and sustainability.