Control Joints In Concrete Slab On Metal Deck

Cracks will generally occur over supporting beams in the negative moment regions.

Control joints in concrete slab on metal deck.

Both of these types of joints while very different help take stress off of the concrete slab. Plan out your control joint spacing 24 36 times the depth of your concrete slab always cut off of your corners as soon as possible because this is usually the first place cracking starts the depth of your concrete joints should be 25 of the depth of your slab. Control joints running perpendicular to the corrugations can be spaced at intervals of 15 to 25 times the thickness of the concrete. Contraction control joints are placed in concrete slabs to control random cracking.

Control joints are most effective in slabs which can slide on a smooth base as drying shrinkage progresses. When shrinkage is restrained by contact with supporting soils granular fill adjoining structures or reinforcement within the concrete tensile stresses develop within the concrete section. Thomas ryan advocates a similar design intent. A fresh concrete mixture is a fluid plastic mass that can be molded into virtually any shape but as the material hardens there is a reduction in volume or shrinkage.

He recommends using no contraction joints allowing random cracks to form and patching only those that affect the. Ryan indicates that contraction joints in concrete slabs on metal decks are of little value and that cracking between joints is inevitable. Concrete slabs on metal decks are usually built with reinforcement and should not contain control joints. The topping containing welded wire fabric should not have control joints either.

Control joints are planned cracks which allow for movements caused by temperature changes and drying shrinkage. Concrete control joints should be no less than of the total thickness of the slab 1 deep for a 4 thick pour and placed no less than 2 3 times in feet the thickness in inches of the slab 8 12 feet apart for a 4 thick pour. For this reason control joints parallel to the corrugations will not be successful. Find a local concrete contractor to help with your project.

Let the cracks occur and control the crack width by using reinforcing steel. Concrete repair restoration concrete art surface preparation vol. In other words if the concrete does crack you want to have an active role in deciding where it will crack and that it will crack in a straight line instead of randomly. Control your concrete cracks written by stacey enesey klemenc on july 4 2006.

You can create control joints in concrete while pouring the concrete or you can wait until the slab has cured just enough so it won t chip when you cut into it.