Concrete Driveway Construction - Thickness, Rebar & More

Starburst Concrete Designin Yorktown Heights, NY

To ensure that your concrete driveway will look good for many years to come, there are important specifications your contractor should follow during installation. How well your driveway looks and performs long-term is largely related to the quality of workmanship and materials that go into it. To help ensure a problem-free driveway, use the following list for information about proper construction.

Placing concrete at the proper thickness

Concrete driveway thickness is the major factor (even more than the strength of the concrete) in determining structural capacity. Place concrete at a minimum thickness of 4 inches. Increasing the thickness from 4 inches to 5 inches will add approximately 20% to your concrete cost, but will also boost your driveway's load-carrying capacity nearly 50% , according to the Tennessee Concrete Association.

Also consider thickening the edges of the driveway by 1 or 2 inches to provide additional structural support in the area most likely to be subject to heavy loading. The thickened sections should extend in from the slab edge 4 to 8 inches.

Your local soil conditions and weather patterns may also require a thicker driveway slab. Contact a local driveway contractor for an expert recommendation.

Local Conditions Matter

The recommendations on this page are general guidelines. An experienced local contractor will know how to adjust these details for your specific soil, climate and more.

See our guides for driveways in your area:

• Atlanta Concrete Driveways
• Dallas Concrete Driveways
• Chicago Concrete Driveways
• Boston Concrete Driveways
• Baltimore Concrete Driveways

Rebar & wire mesh reinforcement

Using steel reinforcement will provide additional structural capacity for your driveway and is especially important if the slab will be exposed to heavy traffic. Reinforcement won't prevent cracks, but it will help hold them together if they do occur.

Concrete reinforcement can be either wire mesh or ½-inch (#4) steel rebar. Use wire mesh for driveways that are 4 to 5 inches thick, and rebar for those that are 5 inches or more. Place rebar in a grid pattern with a spacing between bars of approximately 12 inches. In either case, blocks should be used under the reinforcement to keep centered within the concrete.

Synthetic fibers have also proven to be beneficial in driveways as a way to reduce shrinkage cracks. Fibers will not provide structural reinforcement, however. (See Using Fibers for Secondary Reinforcement.)

Driveway control joints can be incorporated into a decorative pattern.

A properly prepared subgrade

Uniformity, in both soil composition and compaction, is the key to a good subgrade-one that will provide adequate support, ensure an even slab thickness, and prevent slab settlement and structural cracking. Soft spots should be removed and replaced with good material, such as gravel or crushed rock. Many western states have expansive soils. In these conditions, 2 to 8 inches of crushed rock should be used as subgrade material, depending on the degree of expansiveness. If you are unsure about the soil characteristics in your area, consult a soils engineer.

Don't allow the concrete to be placed on bone-dry subgrade, advises the Tennessee Concrete Association. Spraying the subgrade first to dampen it will prevent it from wicking water from the fresh concrete.

Vibratory plate compactors and rammers are the most common machines used for subgrade compaction of residential driveways. Click here to read more about subgrades and subbases for concrete slabs.

The correct concrete mix

Mix design will impact the performance and longevity of a concrete driveway. Read more about concrete driveway mix design to find out exactly what to ask for.

Correctly placed joints

To help prevent random cracking, control joints should be placed at a maximum spacing of 10 feet for a 4-inch-thick driveway slab. While random cracks are generally not a structural problem and will not reduce the service life of the driveway, they can be an eyesore. Also avoid joint patterns that produce rectangular or triangular sections. The depth of control joints is also critical. Your concrete installer should hand tool or sawcut them to a depth equaling one-fourth the slab thickness (or 1 inch for a 4-inch slab).

In addition to control joints, an isolation joint should be installed where the driveway meets a sidewalk, garage floor slab, and other existing pavements. Ask your contractor to provide a jointing plan as part of his written proposal.