Why Does Concrete Crack? Are Cracks Bad?

Concrete is the most durable product you can use for the paving of parking lots, driveways, roadways, bridges and more. But all concrete cracks. To minimize large cracks, proper installation and maintenance play a huge part in the lifespan of your concrete driveway or parking area.

Proper Installation Required

To minimize cracking, concrete must be installed on a uniform, compacted, well-drained base. If not, when excess water in the soil under the concrete freezes and thaws, it heaves slightly and displaces the concrete above it, leaving it susceptible to large cracks when heavy vehicles drive on it.

If the concrete is placed in extreme temperatures (both hot and cold) or not protected from rain and wind, it may not cure properly and be susceptible to defects. Concrete can be installed in any weather condition providing the proper hot weather or cold weather protections are being used.

Joints Provide "Give"

The pavement should be jointed to control cracking and allow for normal contraction during extreme temperatures. The joint layout, compatible with the contractor's paving method and equipment, should be submitted to the architect or engineer for approval prior to construction. Additionally, longitudinal and transverse spacing should be at regular intervals.  Concrete panels should be as square as possible. Individual spacing can be adjusted to meet catch basin and manhole castings perpendicularly. The suggested joint spacing for exterior concrete is 2 times the slab thickness, from inches to feet. For example, if you have a 4-inch concrete slab, the maximum joint spacing should be no greater than 8 feet. (6" slab < 12') with a maximum allowable joint spacing of 15 feet.

Contraction joints may be made by sawing, tooling, or installing an approved insert to a minimum depth of 25% of the slab thickness. Sawed joints should be cut as soon as possible without raveling the concrete. Joints should be continuous across the slab and must extend completely through the curb. Joints do not need to be sealed and give the concrete a controlled way to move with expansion and time.

Maintenance Can Reduce Cracks

Taking care of your concrete will also help minimize cracks and extend its life. The first year is critical for protecting the life of your concrete drive or parking area. Here are some basic tips:

• Don't drive on your concrete until it has reached opening to traffic strength (via a compressive strength test) or at least two or three days.
• Don't allow water to be trapped beneath the slab. Check your home's downspouts to make sure excess water is being drained away from the pavement.
• Do not apply deicing chemicals for snow or ice removal the first winter. Use sand if extra traction is needed. After the first winter, use only sodium chloride (rock salt).
• Keep snow and ice cleared from the concrete, particularly during the first winter.
• Never use deicers that contain magnesium chloride, calcium chloride, ammonium sulfate, or ammonium nitrate. These products will cause concrete to deteriorate.
• Apply a penetrating sealer about 30 days after your concrete is installed when the surface is dry and temperatures are above 55 degrees (NOTE: you may need to remove excess curing compound residue by powerwashing prior to applying a sealer). Reapply the sealer as recommended by the manufacturer, usually every 5-7 years.