Preventing Concrete Cracks

One of the most common questions our distributors and contractors receive is regarding cracking in newly poured concrete. When installed properly, concrete is one of the most durable and long-lasting building materials available. However, it is important that contractors follow well-established guidelines with respect to concrete placement. Durable, high-strength and crack resistant concrete does not happen by accident.

WHY DOES CONCRETE CRACK?

Reason #1 - Excess water in the mix While additional water may make the concrete easier to install, this excess water also reduces the strength of the concrete. Shrinkage is the main cause of cracking. As concrete dries and hardens, it shrinks. This is due to the evaporation of excess mixing water. The wetter or soupier the concrete mix, the greater the shrinkage will be. This shrinkage causes forces in the concrete to literally pull the slab apart and create cracks. Make sure you know the allowable water for the mix and ensure a proper mix is poured.

Reason #2 - Rapid drying of the concrete Rapid drying of the slab will significantly increase the possibility of cracking. The chemical reaction which causes concrete to go from liquid to a solid state, requires water. You can make sure the necessary water is available for this reaction by adequately curing the slab. Use a concrete curing compound such as Maxcure Resin Clear to cure your concrete.

Reason #3 - Improper strength concrete poured on the job Concrete products are available in different strengths. Verify the strength of the concrete is suitable for the application.

Reason #4 - Lack of control joints Control joints help concrete crack where you want it to. The joints should be the depth of the slab and no more than 2-3 times (in feet) the thickness of the concrete (in inches). So 4” deep concrete should have joints 8-12’ apart.

Reason #5 - Concrete poured under inadequate conditions Concrete should never be poured on frozen ground. Under extreme weather conditions, pouring concrete should either be avoided or extreme weather precautions should be taken.

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