HomeownerHelpful Info: Outdoor Projects

Driveways – Concrete

Concrete Driveways Educational Content

The first step in replacing a concrete driveway is to break up and remove the old driveway. Then, the contractor may put down extra gravel or fill dirt to create a stronger base. This reinforced base layer should be compacted with a mechanical tamper. This step helps ensure that the new driveway will be poured on a solid foundation. The dense base layer will also be less susceptible to erosion. The contractor may add a steel reinforcement grid for strength.

With temporary forms in place, the concrete is poured and smoothed. The crew will cut control joints into the slab while the concrete is still wet. The forms are removed once the concrete hardens. The concrete curing process will start as soon as the concrete is poured and smoothed. Control joints and curing are key to the new driveway staying strong and crack-free.

You’ll be able to walk on the driveway a day or two after pouring. Approximately one week after the driveway is poured, you will be able to drive most cars on the concrete. After about one month, the driveway will be completely cured. At this point, you won’t have to worry about heavy vehicles damaging the concrete. Keep an eye on your driveway for the first several weeks after it’s poured. As concrete sets, it has a natural tendency to shrink. This can cause cracks. Control joints and the curing process let the concrete shrink while minimizing cracks.

Small, superficial cracks can be caused by a variety of factors, including the weather. Because of this, companies can’t guarantee their concrete projects against superficial cracking. Keep in mind that these small cracks are largely cosmetic. They aren’t an indication that anything is wrong with the driveway’s structure.

Larger cracks, however, may be worth a second look from your contractor. In very rare cases, the slab may need to be torn out and replaced.

Control joints. Control joints are shallow grooves cut into a concrete slab just after it’s poured. If the concrete is going to crack as it hardens and shrinks, it will usually happen at the control joints. This prevents major cracks across the surface of the concrete.

Isolation joints, also called expansion joints, separate a concrete slab from a wall or other structure. These joints are filled with a synthetic material and then sealed. Isolation joints also help prevent concrete from cracking. They do this by making space for the concrete to expand during hot weather.

Setting or curing. Concrete sets or cures through a chemical process called hydration. Water molecules and the cement mix form tiny interlocking crystals. These crystals give the concrete its strength. Concrete that isn’t cured properly may not be as strong as it’s supposed to be. It’s also more likely to crack and have structural problems.

It is important to keep the surface of the concrete wet and covered during the hardening period. Concrete that is poured in cold weather typically requires a longer curing time. Contractors often cover the surface with an insulating blanket or surround it with heaters. In hot weather, the curing period may be shorter. The contractor still needs to keep the concrete wet to prevent water evaporation in the heat.

Concrete grade is a measure of the strength of the concrete. It’s measured in pounds per square inch (psi). Generally, the higher the psi, the more weight the concrete can handle. Residential driveway concrete is usually 3,000 or 4,000 psi.

In addition to grade, the concrete’s thickness also impacts how much weight your new driveway can handle. Residential driveways should be at least four inches thick. This ensures that the driveway won’t crack when you drive on it. Greater thickness does equal extra strength. If you have a heavy truck or more than a couple of cars, ask your contractor whether a thicker driveway is better. Going up to five or six inches of concrete at certain points on the driveway might be worth the extra cost.

The curing process is one of the most important steps in a concrete job. Concrete that isn’t cured correctly can be as much as 50 percent weaker than properly cured concrete. That’s a significant difference. And while the curing process may seem time-consuming, the results are well worth it. Properly cured concrete surfaces are strong and less likely to crack or erode. They also wear better over the years.

The three most common curing methods are water curing, surface sealing, and chemical curing. The goal of all three methods is to prevent water from evaporating from the concrete as it cures. Concrete that is water cured is kept wet during the curing process. The contractor will do this by flooding the concrete, spraying it with water, or covering it with wet cloth.

Concrete surfaces can also be covered (or sealed) to keep them wet during the curing process. For this method, the contractor covers the wet concrete with heavy paper or plastic film. This cannot be done until the concrete has hardened enough that the material won’t mar the surface. In most cases, this is approximately one to two days after pouring. Chemical curing involves spraying the finished surface with a chemical that forms a thin membrane. This chemical membrane prevents the water in the concrete mix from evaporating.

Residential concrete driveways should be at least four inches thick. If they’re much thinner, they will be more likely to crack over time. The driveway should also have adequate slope and drainage. This prevents water from puddling or running down the side of the driveway. A concrete surface that doesn’t drain well is at higher risk of erosion and cracking.

Paver driveways are an attractive alternative to a plain concrete driveway. Pavers are brick-like pieces of high-density concrete. They come in different sizes, shapes, and colors. They can even mimic the look of cobblestone, brick, and slate. Concrete pavers are usually more expensive than standard concrete but less expensive than brick or natural stone. Pavers are installed individually as the top surface of a driveway or other surface. In most cases, pavers aren’t mortared in place.

Concrete installation can vary based on different soil types. In areas with expansive soil, concrete contractors use a thicker gravel base. A thick gravel base compensates for the expansive soil that shrinks and expands with changing moisture levels.

In areas with very dry soil, concrete crews dampen the soil before pouring any concrete. This prevents the soil from leaching water from the wet concrete and making it brittle.