When you use the streets, sidewalks and driveways in your city or town each day, do you think about what lies beneath the actual surface of the pavement? Probably not. Many people have the misconception that pavement is simply a layer of concrete or asphalt on a flattened surface. But if we dig into a well-paved street or driveway, we’ll see that this is not at all the case.
The natural surface where the pavement will be laid is known is the formation level, or the sub-grade. This level is, of course, very important. Pavers will roll it out, flatten, and harden it in preparation for the pavement installation. But it’s not concrete or asphalt that goes directly on top of this formation level. There is an intermediary level called the sub-base level — and it’s extremely important to the integrity of the pavement.
If you’re building a sidewalk or bike path — any pavement on which there will only be pedestrian traffic — the sub-base layer may not be necessary. But if you’re installing pavement on which automobiles will be driving, the sub-base layer is absolutely necessary for even distribution of weight.
So what exactly is it?
The sub-base is a layer of material installed directly on top of the sub-grade, and usually consists of either cement-bound material, or granular material such as slate or crushed stone. Professional pavers will be very careful about using quality materials during this part of the installation, as the sub-base layer is directly related to the lifespan and overall quality of the pavement.
In fact, the sub-base layer of pavement is so important that it’s no exaggeration to call it the real load-bearing layer — more so than the actual surface. A good sub-grade will effectively distribute weight of passing vehicles throughout the entire surface area of the installation, rather than allowing pressure and weight to be applied over and over to the same areas, which results in ruts.
Other key functions of a sub-base layer include drainage, and prevention of channels beneath the surface of the pavement — which will eventually lead to malformations and eventually a failure of the pavement. Good sub-base layers can also be re-used in some cases. If the concrete or asphalt has worn away, or is in very rough shape, it’s possible to remove it and apply a fresh layer directly on top of the intact sub-base layer. This is assuming, of course, that the company who installed the sub-base did things the right way.
A professional job, through and through
There really is more to professional paving than meets the eye. When a job is completed, and the concrete or asphalt is fresh and new, you might think your paver has done a good job. But appearances can be deceiving. That sub-base layer is incredibly important, and if it’s not done correctly, problems will soon become evident — and corrections could be costly. So the next time you hire someone to pave your residential driveway or commercial parking lot, be sure to remember the importance of the sub-base layer, and make sure they give you the reassurances you need!