Control Joints In Concrete Slab On Metal Deck

An article published in concrete construction august 1999 called let it crack by j.

Control joints in concrete slab on metal deck.

Control joints are most effective in slabs which can slide on a smooth base as drying shrinkage progresses. Concrete slabs on metal decks are usually built with reinforcement and should not contain control joints. Contraction control joints are placed in concrete slabs to control random cracking. Control joints are planned cracks which allow for movements caused by temperature changes and drying shrinkage.

Let the cracks occur and control the crack width by using reinforcing steel. Control your concrete cracks written by stacey enesey klemenc on july 4 2006. Grooving tools made of bronze or heavy gauge stainless steel are used for scoring freshly poured concrete and cost just 25 to 35. 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.

Ryan indicates that contraction joints in concrete slabs on metal decks are of little value and that cracking between joints is inevitable. Control joints running perpendicular to the corrugations can be spaced at intervals of 15 to 25 times the thickness of the concrete. 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. For this reason control joints parallel to the corrugations will not be successful.

Find a local concrete contractor to help with your project. The topping containing welded wire fabric should not have control joints either. 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. 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.

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. Cracks will generally occur over supporting beams in the negative moment regions. Concrete repair restoration concrete art surface preparation vol. 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.

Thomas ryan advocates a similar design intent.