Concrete Joints Types: Quick Look at 3 Important Ones! -

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What Are the Joints in a Concrete Driveway Called?

There are three concrete joints types that are usually found in a concrete driveway. These are:

Expansion Joints (aka Isolation Joints)

Contraction Joints (aka Control Joints)
Construction Joints

What Is the Purpose of Concrete Joints Types?

The purpose of different concrete joints types is to provide space for unrestrained external or internal movement of the concrete slab, foundation or beam.

Concrete and steel are possibly the most widely used construction materials in the world. Both have high compressive strength. While steel is ductile and can handle high levels of tensile & flexural stress, concrete is brittle and cracks readily.

Construction concrete is subjected to the following types of stresses & loads, commencing from the time concrete is poured:

Shrinkage Stress: 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.

Thermal Expansion Stress: Concrete expands when temperatures rise. The thermal coefficient of expansion of concrete is small but enough to cause cracks if the slab movement is restrained.
Structural Load:

Such stresses can result in cracks if the concrete slab is restrained externally or internally.

The different concrete joints types in slabs, such as driveways, help in either containing the cracks (shrinkage) within a limited area or prevent stress (expansion) that can lead to cracks.

Specifically, each type of joint functions as under:

1. Expansion Joints (aka Isolation Joints)

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.

2. Contraction Joints (aka Control Joints)

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.

3. Construction Joints

Construction Joints can be a feature in long concrete driveways. They become necessary when the entire driveway can not be poured within a single day. Construction joints are the interruptions between two pours.

Do You Need Joints in Stamped Concrete?

Sometimes concrete driveways may be stamped for enhancing the curb appeal of a house. This is particularly true for circular or horseshoe driveways that lead up to the home front.

You may think that a stamped concrete will not need contraction (control) joints as it already has indentations. However, this is not true as the indentations are not deep enough.

Contraction (control) joints need to be at least ¼ the concrete thickness deep to be effective. A stamped concrete driveway that is 6” thick will need to have control joints that are 1 ½ “ deep.

If your stamped concrete driveway has a pattern with straight lines, such as slate, cobblestone, etc. cut the control joint along those lines as far as possible. This way the control joints become a part of the pattern.

Moreover, you still need expansion joints where the driveway meets the home foundation or any other obstruction such as a pillar or a manhole.

I do hope that this clarifies the role of different concrete joints types in a driveway.

Is Sealing Concrete Driveway Joints Necessary?

Yes, sealing concrete driveway joints is necessary to prevent water from seeping under the concrete and causing damage. Concrete expands and contracts with changes in temperature, and the expansion joints allow for this movement without cracking the concrete.

Sealing concrete driveway joints is a relatively easy process that can be done by a DIYer. The first step is to clean the joints with a wire brush to remove any dirt or debris. Then, a flexible sealant, such as polyurethane sealant, is applied to the joints.

Finally you must always apply a topical concrete sealer over the driveway.

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