Watershape Consultant and Aquatic Designer Paolo Benedetti discusses the proper placement of reinforcement steel within concrete slabs and the requirements of ACI 318.
Steel Reinforcement - Where does it go?
The reinforcing steel in most slabs-on-grade are installed in the improper location.
Welded Wire Reinforcement (WWR) is frequently placed underneath the concrete, directly on the sand or gravel sub-base.
Deformed bars (commonly known as "rebar") is often times placed too low in the slab to be provided sufficient protection.
Sheer Laziness
The improper placement of the reinforcement, whether WWR or rebars, is almost always due to the laziness of the concrete company.
The American Concrete Institute (ACI) has published standards regarding the placement of the reinforcement within "slabs-on-grade." These very standards have been adopted by almost every building code in the United States. Yet, incorrect installations occur every day by the thousands.
ACI 318-11 specifies that the reinforcement must be placed and supported to prevent deflection or displacement during placement of the concrete.
Many concrete contractors are lazy, and place the reinforcement directly upon the sub-base. Then during the placement of the wet concrete, they attempt to lift the reinforcement up into the concrete with a hook. This process is called "hooking." But as they walk through the wet concrete with their boots, they press the reinforcement back down to the bottom of the slab. The final result is an unreinforced concrete slab.
Sliced Too Thin
The American Concrete Institute (ACI) 318-11 (2011), section 7.7.1 specifies certain slab thickness (dependent upon the thickness of the reinforcement used).
It specifies 3 INCHES of concrete between the earth side (regardless if it is soil, sand, gravel, rock or protected by plastic) and 1.5 inches of top coverage for #5 bars (5/8 inch) and smaller. Thicker bars may require even greater coverage - 2 inches of coverage for #6-#18 sized bars.
Remember when determining slab thickness that the bars cross each other - resulting in steel TWICE as thick as a single bar.
Therefore, if you are using #4 bars as reinforcement in your slab, you would have a minimum 5.5 inch slab (3 inches + 0.5 inch steel + 0.5 inch steel + 1.5 inches).
Using wire WWR is difficult, because you cannot maintain the required placement of the reinforcement within the slab - it bends & deforms too much as it is walked on.
Paolo Benedetti, Aquatic Artist, Watershape Consultant, Swimming Pool Expert Witness - Construction Defects
You may contact Paolo Benedetti at: info@aquatictechnology.com or 408-776-8220
© Aquatic Technology Pool and Spa, 2013.
All rights reserved.
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Steel Reinforcement - Where does it go?
The reinforcing steel in most slabs-on-grade are installed in the improper location.
Welded Wire Reinforcement (WWR) is frequently placed underneath the concrete, directly on the sand or gravel sub-base.
Deformed bars (commonly known as "rebar") is often times placed too low in the slab to be provided sufficient protection.
Sheer Laziness
The improper placement of the reinforcement, whether WWR or rebars, is almost always due to the laziness of the concrete company.
The American Concrete Institute (ACI) has published standards regarding the placement of the reinforcement within "slabs-on-grade." These very standards have been adopted by almost every building code in the United States. Yet, incorrect installations occur every day by the thousands.
ACI 318-11 specifies that the reinforcement must be placed and supported to prevent deflection or displacement during placement of the concrete.
Many concrete contractors are lazy, and place the reinforcement directly upon the sub-base. Then during the placement of the wet concrete, they attempt to lift the reinforcement up into the concrete with a hook. This process is called "hooking." But as they walk through the wet concrete with their boots, they press the reinforcement back down to the bottom of the slab. The final result is an unreinforced concrete slab.
Sliced Too Thin
The American Concrete Institute (ACI) 318-11 (2011), section 7.7.1 specifies certain slab thickness (dependent upon the thickness of the reinforcement used).
It specifies 3 INCHES of concrete between the earth side (regardless if it is soil, sand, gravel, rock or protected by plastic) and 1.5 inches of top coverage for #5 bars (5/8 inch) and smaller. Thicker bars may require even greater coverage - 2 inches of coverage for #6-#18 sized bars.
Remember when determining slab thickness that the bars cross each other - resulting in steel TWICE as thick as a single bar.
Therefore, if you are using #4 bars as reinforcement in your slab, you would have a minimum 5.5 inch slab (3 inches + 0.5 inch steel + 0.5 inch steel + 1.5 inches).
Using wire WWR is difficult, because you cannot maintain the required placement of the reinforcement within the slab - it bends & deforms too much as it is walked on.
Paolo Benedetti, Aquatic Artist, Watershape Consultant, Swimming Pool Expert Witness - Construction Defects
You may contact Paolo Benedetti at: info@aquatictechnology.com or 408-776-8220
© Aquatic Technology Pool and Spa, 2013.
All rights reserved.
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If you want to ask a question of Paolo Benedetti, you may email him at: info@aquatictechnology.com