Concrete chunks for fire pit?

I had planned on putting in a fire pit next year since I don't need it until then (actually, I hoped to do it this year but *everything* is taking longer this year than expected and I expected it to take a long time...), but I have family visiting next month and I thought it would be a fun project to do together rain or shine.

I have a mix of big and small rocks and I plan to use the big ones as primary construction and thought I'd fill in the gaps with the smaller rocks and old concrete chunks. I thought I better ask the collective permies mind if it's safe to heat concrete that way, if it's a bad idea for practical reasons, etc.

Basically is there anything I need to know before I just jump right in?

Concrete tends to crack and degrade under direct, intense heat. That's the only thing that comes to mind. High density concrete holds up longer. Low density concrete (like cinder blocks) breaks down more quickly. It doesn't take much of a heat shield to protect it, if it's nice decorative stuff. If it's just old chunks, what does it matter? My 2c.

I've had a fire pit circle of cinder blocks for 10 years, about five feet in diameter. Had some nice bon-fires. Works just fine. The only safety issue is watchin' your crocks don't get too hot.

Sonja Draven wrote:I had planned on putting in a fire pit next year since I don't need it until then (actually, I hoped to do it this year but *everything* is taking longer this year than expected and I expected it to take a long time...), but I have family visiting next month and I thought it would be a fun project to do together rain or shine.

I have a mix of big and small rocks and I plan to use the big ones as primary construction and thought I'd fill in the gaps with the smaller rocks and old concrete chunks. I thought I better ask the collective permies mind if it's safe to heat concrete that way, if it's a bad idea for practical reasons, etc.

Basically is there anything I need to know before I just jump right in?

Concrete can suffer "explosive spalling" if it is heated rapidly.

Thank you all for responding!

Dave, I looked that up and it definitely seems like it's a factor for camp fires as they can easily get up to 1200+ degrees and exploding can occur at 1000. Not something I want to risk, so I'll use the concrete for something else.