What is the minimum concrete cover for rebar?
Why it varies for different RCC members?
Do we really need to maintain a minimum concrete cover? Why?
It’s a confusing thing for many construction professionals who’ve just started their job.
I know, you’ve read about this on your college curriculum.
But when we start to practice on the field, we often get confused. We also can’t remember how we actually maintain the minimum concrete cover.
You don’t need to pressurize your memory.
I’ll make everything clear to you in this post.
Let’s first know…
What Is Concrete Cover for Rebar?
The distance between the surface of embedded reinforcement and the outer face of concrete of an RCC member is the concrete cover for rebar.
We often define it as concrete clear cover or minimum concrete cover in our daily construction activities.
What Is The Minimum Concrete Cover For Rebar?
The minimum concrete cover is a thickness of concrete that you must keep around each reinforcement bar in an RCC member. Less than that the reinforcement bar can be affected by weathering impact.
Why The Minimum Concrete Cover Is Very Important For Rebar?
Maintaining concrete cover for rebar is a must for the quality of construction.
The following are the reasons why we should maintain a minimum concrete cover-
- It protects reinforcement bars from bad effects of weather.
- Concrete cover acts as thermal insulation of reinforcement bars to protect it from fire.
- It provides enough embedding to reinforcement bars to enable them to be stressed without slipping.
See the image below, how the reinforcement bars have been affected due to insufficient concrete cover.
How Do We Maintain The Concrete Cover?
There are various types of material and methods used to maintain concrete cover for rebar.
Generally, we use cement mortar block.
Plastic chair and block are also used for this purpose.
But what should be the…
Minimum Concrete Cover For Rebar
The minimum concrete cover depends on the type of RCC member, Diameter of bars used in the member, and exposure condition.
It is a structural engineer’s responsibility to show the minimum concrete cover in drawings. Most of the time we find them in the structural drawing.
If found, you should follow that.
If you don’t find any instruction in the structural drawing you should follow your national building code.
Here, I’ll discuss the minimum concrete cover as specified in ACI code.
- The RCC member which is cast against the earth and exposed to earth, the concrete cover should be not less than 3 inches. The footing is an example of this kind.
- Concrete which is not cast against earth but exposed to earth or weather, the concrete cover should be –
* For #5 bar – 1½ inch * For #6 to #18 – 2 inches
- The member which is not exposed to earth or weather, the concrete cover should be not less than –
# For slab, Wall, and Joist: * For #11 and smaller bar – ¾ inch. * For bar #14 to #18 – 1½ inch. # For Beam and Column –1½ inch
If you’re confused with the above discussion, see the image below:
Although I’ve shown different concrete cover for different RCC members under different conditions, yet you should follow your national building code for minimum concrete cover for rebar.
It’s better to consult the structural designer before you go for construction any RCC member.
Or you should follow the instruction provided in the structural drawing.
Editor’s Note: This post was originally published in April 2017 and has been completely revamped and updated for accuracy and comprehensiveness.
Now Your Turn:
Which code do you follow for knowing the minimum concrete cover? Could you please share the minimum concrete cover for rebar that you apply in your day to day construction activities?
Please share in the comments below…