Effect of heat on concrete strength 1

[mattnorm]

I am looking to find out if extreme heat can have an adverse effect on the strength of concrete?

There will be some welding done around an anchor and there will a lot of heat transmitted to the concrete behind the 3/4" backing plate...will this affect the capacity of the anchor/concrete system?

 

[Ron]

In general, no. You can get some localized spalling if the temperature gets very high. To lose strength in concrete due to heat, it has to be held at temperatures above 600 to 800C for 3 to 4 hours.

The most common effect of heat on concrete is spalling due to moisture expanding in the pores, and carbonation of the surface, usually to a depth less than 1/8".

 

[msucog]

agreed in general. but if unsure or need additional confidence/documentation, do a field load test or two to back it up.

 

[conceng]

It is important that the welding procedure address the steel/concrete situation. I just looked at a project last week where they performed immediate concurrent fillet welds of a column to a 1" thick embedded plate. The heat expansion of the plate cracked and spalled the perimeter concrete as well as distorted the plate so it was no longer in intimate contact with the concrete.

For welding in this situation it is best to perform multiple pass fillet welds and allow sufficient cooling between passes to prevent excessive heat buildup. If necessary, each pass may be done sections at a time. With a 3/4" thick plate, I don't see a real problem with overheating the concrete if the plate is allowed to cool between passes.

Greg

 

[MultiVar]

Curious noob needs learnin': What type of anchor, exactly? CIP L-bolt? Post-installed expansion/wedge/bolt...?