Reinforcement cover for concrete subjected to high heat 2

[Viper1xoc]

I'm working on the design of a concrete vent system for a firing pit used to melt various metals. Anyways, I'm trying to find something in the ACI code that speaks specifically to high heat applications in regards to rebar cover. So far I've only been able to come up with references for corrosion, chemical and nuclear facilities. I've also read through the fire resistance criteria, however, that is primarily for designing the structure to survive a fire related event and avoid collapse, but not necessarily be completely usable after the event. If anyone has any thoughts on a specific code reference that might be applicable I'd appreciate it. Thanks in advance.

 

[JAE]

Here is the committee at ACI dealing with Fire Resistance and the publication that appears to deal with "endurance":

http://www.concrete.org/bookstorenet/ProductDetail.aspx?ItemID=21689

The quote on the abstract includes this:

"Information is also given for determining the fire endurance of certain concrete members based on heat transmission criteria."

which might touch on what you are looking for.

There is also this:

http://www.concrete.org/COMMITTEES/committeehome.asp?committee_code=0000307-00

dealing with concrete chimneys - but not sure if that would even apply - just might have info on heat and rebar cover.

 

[civilperson]

Concrete is the wrong material for high temperature installation. Try steel with air cooled walls as inner liner for concrete vent.

 

[Ron]

As you will likely find in the referenced JAE gave, the amount of cover will depend on the insulative capability of the concrete to mitigate thermal strain differences at the rebar/concrete bond interface. Assuming you are looking at temperatures of 500F or so, this will yield cover on the order of 4 to 6 inches. Under normal conditions, thermal response of concrete and steel are similar. Under high temperatures, the steel tends to move more than the concrete.

Also, keep in mind that constant exposure to high temperature can cause a breakdown in the cementitious properties of portland cement. Generally it take temperatures of 600C to 800C for periods of 4 to 6 hours to do this. If your temperatures are sufficiently high, you might consider refractory cement rather than typical portland cement.