Control Joints in Concrete Walkways

Function of Control Joints

• Control joints are cut into the surface to control cracks in the concrete. Cracking in concrete placed on the ground is inevitable because heating and cooling isn't uniform over the surface, but a crack will go to the joint and then run along with it. Controlling the cracks keeps the pavement structure strong. Walkways don't require as many joints as they have; dummy joints are added for aesthetic effect.

Control Joint Installation

• Control joints can be tooled or sawn. Tool while the surface is being finished; cutting the joints with a saw should be done when the concrete is set enough not to be damaged, generally 12 to 24 hours after finishing. If left too long, the concrete may crack as the joints are being cut. Control joints are cut about 1 inch deep; all the reinforcing has to be cut too. Filler material isn't necessary for control joints.

Spacing Requirements

• For structural reasons, space joints no more than two to three times the thickness of the concrete. Concrete thickness for walkways is typically 4 inches, so ideally joints are spaced about 10 to 12 feet apart. If joints are spaced wider than 10 to 12 feet, a control joint should be added down the center. Control joints should be evenly spaced, not staggered or offset. Avoid joints at corners with acute angles.

Control Joint Layout

• Apart from the minimum spacing required for control joints, there is design flexibility for spacing. Joint patterns create visual rhythm in the landscape that can contribute to the character of the site, so plan their location carefully. Space control joints at intervals equal to the width of the pavement. They should be as square as possible but radial in curves. Joint placement is especially noticeable around significant spaces, such as entrances, changes in direction and steps.