concrete explodes?

Question

I'm building a backyard fireplace(?) firepit and I have some leftover concrete from a sidewalk project and anyhow I figure I make the walls of the fireplace with concrete bricks. Then I remember someone once told me that concrete explodes at high temp. Is that true? And does that rule also apply to rocks?

Answer 1

You have heard of fireplaces and barbeques exploding, but it is not from concrete, it is from concrete that has not dried completely.

If you make a fire pit or anything exposed to high heat of concrete or stone and morter, you must not use it for at *least* 1 week. This allows the moisture in the concrete to evaporate.

Think of it like this: If concrete is dry on the outside, to maybe a depth of 1/2 inch, but the concrete deeper than 1/2 inch is moist, and it is exposed to high temperature, the moisture in the concrete is going to turn to steam. Steam occupies more space than the water that it took to create the steam. Thus, kaboom!

Rocks won't explode, but if I were making a barbeque, I would make it out of high temperature fire brick, with concrete morter. I would let the concrete cure for *two weeks*, just to be on the safe side. THEN, and only then, would I make a fire in the barbecue.

Hope this helps.

Answer 2

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Answer 3

I saw some fishermen build a fire on a concrete surface for warmth one night. I heard a loud exploding sound and saw fishermen running in all directions , it was very funny. All the damage to the concrete was a small 1/4 inch deep X 4 inch round area. It sure was an attention getter though. I reasoned it to be the moisture retained in the concrete turned to steam and the resulting pressure caused the explosion.

Answer 4

With all due respect; FIRE BRICK is fired at temps, that allow similar temps in a fireplace that won't cause any reaction.

The Exlosion has less to do with the aggragates than it does with VOIDS/Air pockets. Certainly everything has a point at which it's affected by situations. The issue is that in its agitation; concrete used as mortar, or Blocks; isn't strictly solid; and has not been KILN fired to withstand certain high temps.

Another thought however; might be; HOW HOT do you intend a WOOD fire to be? Obviously/Hopefully; you won't be Burning Jet Fuel; and will have adequate ventilation/updraft/ etc.

I have CINDER BLOCK stacked; NO MORTAR; for an outdoor BBQ, and have never needed body armor when grilling.

Again, and with no offense; you could very easily find out more on the WWW in a keyword search regarding the heat versus strength issues of various substances.

Steven Wolf

Answer 5

Concrete, like river rocks, still have water and of course sand in it. When you heat the concrete, it does rapidly expand and "pop" which is the explosion. What you want is man made fire brick, which will not explode, and will last a much longer time. By the way, when I went to Navy fire fighting school in San Diego, they taught us that everything, and anything can burn. And to demonstrate, they did burn dirt, as well as concrete.

Answer 6

I agree with those who say concrete is not affected by heat. I have first hand experience. I recently built an outdoor fire pit from Sender block on two sides and the other two were already formed by existing dark larg rocks. On the third firing of the pit we heard these loud pop noises, and noticed that various sizes of sharp pieces of the rock were thrown out almost 20 feet away. Also noticed that the surface of the dark rocks turned brown and layers were crambling inside the pit. We were lucky we were not sitting directly in front of the pit or we would have been injured seriously. I learned from this blog that was lime stone reaction to heat. Nothing happened to sender blocks.

Answer 7

Concrete and fire do not go together. You'll need to have a firebrick lining to be OK.

I worked for a large plumbing company one time, where I had to fabricate copper plumbing systems on their concrete floor.

I had to be careful not to point the soldering torch directly at the floor when soldering the piping. The concret would indeed blow up and hit me in my face with really small pieces of concrete. Didn't hurt, but it was a eye safety concern.

Answer 8

ok, if you heat up trapped air and water, like whats going to be in concrete bricks out side, YES it will crack off pieces they can hurt you and burn you. sender blocks are more course and can handle higher temps. but I would say use fire brick. believe who you want about the concrete exploding. just remember,I TOLD YOU SO

Answer 9

Concrete is pourus and can contain water. When heated the steam expands and causes the concrete to pop. Its best to use firebrick where ever flame come into contact with the firebox.

Answer 10

concrete explodes