What causes driveway cracks?
Unsightly cracks in your driveway can result from a number of factors. (Photo courtesy of Angie’s List member Joe D. of Rosemount, Minn.)
Given enough time, almost every driveway will crack when the material starts to break down and separate. But while you may find it acceptable to discover cracks in a 20-year-old driveway, cracks in a much newer one can be frustrating.
By understanding the reasons behind driveway cracks, you can take preventive and corrective measures to ensure your driveway will look like new for as long as possible.
Concrete vs. asphalt
Asphalt and concrete comprise the material in the vast majority of driveways in the United States, and both can experience cracks from the same set of causes. However, because asphalt driveways are generally set up as one long, unbroken surface, they will crack more easily than concrete surfaces, which have controlled joints interspersed throughout. Even with this propensity, when properly installed, cracks of significant size should not appear for several years.
Poorly installed base
The most common cause of cracks in driveways is an improper installation, usually in the form of a poorly constructed base or subbase. Installers will build a good driveway subbase from crushed stone. Pack it extremely tightly and then install an aggregate base and then the driveway itself over it. An improper base or subbase, usually used to save money or time on the installation, is made from a light material like sand or dirt. When this loose material gets moist, the freeze-thaw cycles will cause the material to expand and contract, putting uneven pressure on the driveway and causing it to crack.
Salt may be fine for winter traction on some surfaces, but it's brutal on concrete. The salt speeds up the thawing process of the snow, and the water will seep directly into the concrete where it will refreeze and exert pressure on the concrete's structure, eventually resulting in a crack. Use sand instead of salt on concrete in the winter. The snow will stick around, but the sand will provide traction for vehicles without ruining your driveway.
Just as the freeze-thaw cycle can cause tremendous pressure on your driveway, growing tree roots can do the exact same thing. As the roots grow, they apply uneven pressure on certain parts of the driveway and its foundation, eventually resulting in a crack in the concrete or asphalt once the pressure has built up past the material's breaking point.
Both concrete and asphalt are fairly strong materials, so you may assume that they can withstand a lot without breaking. But they are far from indestructible. Just as pressure from below can crack a driveway, pressure from above can as well. The exact amount of weight that a driveway can hold without cracking will vary based on the type of driveway material, the depth of the material, whether the material is reinforced and the overall makeup of the driveway's foundation. You can be fairly certain that anything over a few tons, or 10,000 pounds, has the chance of cracking a poorly installed residential driveway.
Preventing driveway cracks is a much better option than repairing them, for obvious reasons, but true prevention can only happen during the driveway's installation. The driveway's base is the biggest factor when it comes to excessive cracking, so choosing a professional installation over laying the material yourself or getting a friend to do it will help ensure that the material has a stable subsurface that will spread out pressure across the entire driveway. You can also choose to install root guards on the sides of the driveway to ward off growing root systems, but remember that this will make nearby trees slightly unstable as they grow.
If the installation is done correctly, the only preventive measures you need to take are the occasional sealing to keep out excess water and to avoid damaging the concrete through salt or heavy weights.