Concrete Driveway Control Joints: An Easy Guide
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What Are Concrete Driveway Control Joints?
Concrete driveway control joints are fault lines intentionally incorporated in the slab so that the concrete may crack within the control joint. Cracking is an intrinsic part of the concrete curing process. The cracks do not compromise the structural integrity of the driveway. Control joints help make the cracks less visible as they stay within the joint.
Concrete driveways are an excellent choice for homeowners who want a durable and long-lasting driveway. However, it’s important to understand that concrete can expand and contract due to changes in temperature and moisture levels, which can lead to cracking over time.
That’s where control joints come in. Control joints are intentionally placed in the concrete slab, at regular intervals, to help control where the cracking occurs. Control joints create a weakness in the concrete slab so that the cracks occur and are mostly confined within it.
By creating these joints, you can direct the cracking to specific areas where it’s less likely to cause damage to the overall structure of the driveway.
There are 3 common types of concrete joints in a slab-on-grade. Control joints is one of them and can be created in a few different ways. The most common method is to use a jointing tool to cut a straight line into the surface of the concrete. This is done a day after the pour, when the slab has set but the curing process is still to begin.
The jointing tool creates a groove that extends about one-quarter to one-third of the depth of the concrete. The joint is typically placed at intervals of no more than 10 feet in each direction, depending on the size and shape of the driveway.
By incorporating control joints into the design of a concrete driveway, you can prevent unsightly and potentially damaging cracks from appearing over time.
Concrete driveway control joints are essential to ensure a long-lasting and structurally sound driveway.
How Far Apart Should Concrete Driveway Control Joints Be?
The rule of thumb is to have the concrete driveway control joints to be between 8’ – 12’ apart in each direction. According to Concrete Network,
Space joints (in feet) no more than 2-3 times the slab thickness (in inches)
Of course, the actual distance between control joints also depends on a few other factors. For example the size and shape of the driveway will play a significant role in determining the spacing of the control joints. A larger driveway with a more complex shape will require more control joints than a smaller, simpler driveway.
It is better to place the control joints closer than recommended rather than further than recommended. Please do keep in mind that the primary role of the control joint is to limit the shrinkage cracks within a confined, less visible area.
Shrinkage cracks occur when the concrete contracts as it cures and water evaporates. In fact, the correct name for a control joint is a “contraction joint”.
The Difference Between Control & Expansion Joints
Control joints (aka contraction joints) and expansion joints (aka isolation joints) are both very important. While they may look similar, there are some key differences between the two.
Contraction Joints (aka Control Joints) are either indented in fresh concrete (or cut with a saw the next day) to encourage shrinkage cracks to stay within the joint and not spread randomly, all over the slab surface.
Concrete develops shrinkage cracks as it cures. The water and cement in the concrete mix react to form a web-like crystalline structure that binds the aggregates. The concrete shrinks when water exits and the stress causes the concrete to crack.
Control joints create a fault line. The concrete slab thickness at the joint is less than the slab thickness. The concrete is therefore more likely to crack at the control joint when it shrinks.
Expansion Joints (aka Isolation Joints) are created using forms prior to the concrete pour. They give space for the concrete driveway to expand and contract when the temperature changes.
Expansion joints are placed wherever the new concrete driveway butts an existing slab or foundation such as the garage floor, house foundation or the curb.
Without an expansion joint the two slabs would press against each other and create unwanted stress, cracks & slab failure.
Control joints are designed to control where the shrinkage cracks can occur. Expansion joints are designed to allow space for slabs to move due to changes in temperature. They prevent stress and cracking.
Control joints are only one-quarter to one-third of the depth of the concrete. But expansion joints are as deep as the slab thickness.
Both types of joints are essential for a durable and long-lasting concrete driveway.
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Thank you very much for reading this post. I do hope you found it informative and helpful.
