They are seen and used everyday, yet they are hardly noticed, perhaps because they are beneath our feet. They are pavements or road surfaces, the durable surface materials laid down in areas for traffic from either vehicles or humans. They are inevitable for areas like US and Canada where road transport is very frequent.

So, why are pavements constructed?

USES OF PAVEMENTS

1. The reason why roads don’t just randomly break apart and cause disastrous accidents, is because they are paved. The materials of which pavements are constituted are stiffer than the material upon which they are placed, called in situ material, thus pavements assist this material in supporting loads with the most minimal cracks or deformation.

2. The reason cars ride comfortably on the road, without busting tires or causing much friction is all thanks to pavements. Pavement material can be maintained much easier than in-situ material.

3. Do you sometimes wonder what would happen if our roads were muddy, and then it rained? You don’t want to imagine that. Pavements are the reason moisture from rain is quickly eliminated from roads and problems such as mud puddles don’t arise.

In fact, some pavements made with porous asphalt help with surface water treatment.

4. Again, pavements help prevent more accidents than you could imagine. If roads were as smooth as ice rinks, surely cars would skid into each other and the woods more frequently (you sure know what happens when it snows, right?). So, pavements sure deserve more credit than we give them.

TYPES OF PAVEMENTS

Basically, there are two kinds of pavements: flexible and rigid pavements. But before we delve into elaborating them, let’s briefly discuss unpaved roads.

UNPAVED ROADS

A typical unpaved pathway These are roads without paved surfaces. They include dirt roads, gravel roads, etc. About 33% of all roads in the US are unpaved.

RIGID PAVEMENTS

Rigid pavement

These are pavements made with Portland Cement Concrete (PCC), which could either be plain, reinforced or pressured. They may or may not incorporate the component layers of stabilized or non-stabilized granular materials.

Cracks on a rigid pavement

Roads made with rigid pavements are usually very stiff because of the PCC, and as such, these pavements do not flex or bend to bear the weight of traffic loads.

FLEXIBLE PAVEMENTS

Flexible/asphalt pavement

These are pavements made basically of asphalt. Sometimes, there are referred to as bituminous pavements. You probably are familiar with this kind of pavement because 95 percent of all US paved roads are comprised of flexible pavements.

Flexible pavements sometimes incorporate underlying layers of granular materials on the subgrade, and sometimes they don’t. The reason they are called flexible is because the total pavement structure is constructed to bear traffic loads by bending or flexing. Flexible pavements are not laid with reinforcements, and they are designed based on the load distributing feature of the component layers.

When traffic load rests on this kind of pavement, some of the compressive stresses are transferred to the lower layers by grain transfer through the contact points of the granular structure. However, the pavements surface bears the maximum vertical compressive stress directly. Flexible pavements are able to distribute the stress to a large area of the pavement in the shape of a truncated cone and consequently, the lower layers bear little stress.

This means that the pavement is constructed in various layers and the topmost layer, because it bears the highest compressive stress, must be the strongest and constructed with the best materials.

HOT MIX ASPHALT

This is a bituminous concrete made from a combination of crushed aggregate and paving grade asphalt. It defers from the regular bituminous products because of the materials it consists of, asphalt and crushed aggregate.

Also,the design methods of the mixture and the mixing temperature used in producing it puts it on a class of its own. It’s called “hot mix” because of the elevated mixing temperature for its production. Sometimes, it is called other names, including blacktop, bitumen, asphalt, asphalt concrete (AC).

Paving grade asphalt has been widely used for roadway surfaces all over the world since the early 1900’s, and so far, it has proved to be a safe and efficient pavement application product. It is refined specially for roadway paving applications, never exceeding 350F for its mixing temperature.

The kind of pavements engineers and other construction personnel decide on using for roadway construction, depends largely on the kind of traffic load the roadway is expected to carry. Obviously, considering the number of US roads constructed with flexible pavements, they definitely have the greater advantage over rigid pavements.

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