The Deadliest Fire Pit Material?

Are concrete fire pits really dangerous? Will they explode? There’s only one way to find out!

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are concrete fire pits an explosion waiting to happen I don’t know but today I’m going to test it and find out when water boils in an open pot the steam can just Escape into the air but if you have something closed say like a can of tomato soup the steam has nowhere to go and it will continue to build pressure until the can explodes so we could think about concrete or even rocks as that tomato canned soup and does the steam get out fast enough to allow the pressure to release or does the pressure overcome and just explode it and that’s what we’re going to find out today concrete is just a combination of Co aggregate fine Aggregate and cement mixed together so it makes sense to see if rocks should actually explode and I grew up in the scouts I am a proud Eagle Scout and I always remember our troop Masters saying never put Sandstone near the fire because it will explode and the reason he was warning about Sandstone is it’s one of the most porous rocks out there and most sedimentary rocks that are formed through the compression of the sediment are very porous now I went ahead and picked up some rocks from the creek back behind the shed and I want to show you what they are and we’re going to test to see if these will actually explode so I’ve got four different types of rocks we have Sandstone mudstone Bassel and slate and now if you are a budding geologist and you think that I am wrong I could very well be because I got that directly from the chat GP app by uploading pictures and asking it what stone it is but it gave G me some very convincing reasons why each of these was that rock so we’re just going to go with that but I do have a test that I want to put these rocks through to see just how porous they are and we’re going to dunk them in water and see what happens now the fire pit that I have in my house is made out of concrete pavers and just for the record it has not blown up yet but I did grab some leftover pavers and I put them in a tub of water because we’re going to really soak those and put them on the fire later but right when I dropped them in the tub of the water immediately bubbles started coming up and that basically means that the water is infiltrating into the concrete pavers and displacing any air and it’s coming out so I want to see if the same thing happens to these rocks all right so I’m going to start with this Sandstone which is supposed to be the absolute most porous let’s just put this in there and see if any bubbles come up and I can definitely see some bubbles on the surface but uh nothing quite like what I saw on the concrete so right off the bat these rocks are definitely not as porous as the concrete is which makes sense cuz there’s a lot of air bubbles in the concrete but just for good me we are going to put these in a tub of water and we’re going to keep them there for a few hours to make sure they have completely soaked but let’s check out the mudstone oo so the mudstone definitely seems like it is taking in more water than that Sandstone maybe that wasn’t actually Sandstone who knows all right the mudstone got some promise for an explosion later all right now the Bassel now this one is supposedly a volcanic rock so I’m not sure why it is actually less porous than some of these others but let’s drop it in and see what happens yeah I see lots of bubbles on the surface but not a lot coming out ooh I can actually hear this mud Rock picking up water see if you can hear that that thing is soaking in water like crazy all right for the final one the slate and I don’t expect to see much of anything out of this one well I was totally wrong so the Slate actually had a lot of bubbles coming off it who knows maybe it’s not slate but the mudrock and the Slate were definitely soaking in a lot of water so I’m going to let these sit and I’m going to stoke up the fire we’re going to toss them on there get them up the boiling point and see what happens all right so this is our test zone this is an old fire pit that uh was here when we bought the property and as any good scout knows the best way to start a fire is with a flamethrower the fire is cooking and I’m going to start putting some rocks on there I also have my thermal camera here so looks like the fire on top there is about 470 in degre F so we should be able to get these rocks up really hot really quickly so I’m going to start putting some on there baselite that’s the Slate that’s the mud Rock and the Sandstone all right so I’m going to be chilling behind this OSB sheet and I got a little face shield and just kind of uh peek out with the thermal camera all right I’m going to try to pinpoint the Rocks here so looks like the rocks are about 150 160 we know water boils at 200 all right I just threw some more firewood on there I want to get this over 5 or 600 so the rocks can really heat up all right our fire is over 700° now so the fire has been going over a half hour now and those rocks are over 500° and so any of that water at this point is going to just be gone or it’s going to be steamed just trapped inside there and it’s not going to explode but when I went around to get a closer look the Sandstone is actually all split up so it cracked but it didn’t explode it’s what it’s called spalling spalling is when just a piece of the rock just splits off because of that pressure so it’s not like big explosion like the Tomato can so the idea that rocks are going to explode and just throw shards everywhere I don’t think that’s actually what is normally going to happen sure it probably could but even in that video from earlier the rock just kind of cracked and fell into the fire and the Sandstone same type of thing here it definitely didn’t explode and as far as the other rocks go it doesn’t look like anything happened at all all right so the next day these are all cooled down and I’ll tell you what we’re going to start with the sandstone and this is actually amazing when The Rock popped it is into three pieces the piece popped up in the air turned upside down landed and balanced this is like a stonehinge or something here but this one definitely collapsed now the mudstone did shift but the mudstone actually is completely intact it did not break apart at all now now looking at the Basset the bass salt bass salt looking at the Bas salt same thing this one does not appear to have any cracks it is still completely intact and lastly the Slate same thing for this guy so the only one that had an issue was the Sandstone guess my old scout leader was right don’t use a sandstone in a fire pit so now we know that some rocks will explode under extreme heat but we need to find out what about concrete cuz that’s the whole idea here I want to build a concrete fire pit and I need to know if concrete is going to just blow apart or maybe even just get cracks under extreme heat so what I’ve done is I’ve mixed up some samples of three different types of concrete now this first one here I mixed up just out of a regular concrete this is a 5,000 PSI and put it in a little form I also used two other types of concrete to see if there’s any difference between any of them so the second one here is a fast set concrete which I would expect to perform the worst because the faster it sets the more gaps of the more porous it should be and the last one I’m going to test is a crack resistant concrete which I’m calling the no crack basically what they’ve done is added some fiberglass reinforcement in there and maybe some more additives to let that Flex so it’s going to be really interesting to see if any of these will cracked under high heat to be a little bit more scientific instead of just putting them on top of the fire pit there I want to make sure that they’re getting even heat and that we know exactly what’s happening so I set up a little test jig and we’re going to actually use the flamethrower to to test them this little test ring I think is going to work out well so I’m going to put the pieces here and I’m going to be using the torch and I have a little setup that’s going to hold it in the same spot so we can make sure that it’s being evenly heated and then I’m just going to I guess probably tape down the handle and then on the back side I have the thermal imaging camera that is looking straight at it and we’ll be able to see when that back of the rock is above the boiling point and then that way we’ll know anything inside there will have steamed or boiled off at that point now I don’t think this is going to explode but I still want to have eye protection but I’m not going to use the full face shield I’m using out my new pair of shop Shades if you’ve not seen them yet shop Shades these are from my buddy John Miki these things are awesome super clear they are scratch resistant and fog resistant and they meet all of the safety standards they also have these really cool side shields here they are light and comfortable for all day use these things are awesome if you want to check out a pair there’s a link Down Below in the description go check them out you’re going to love them they get great reviews shop Shades they’re pretty rad now let’s nuke some stuff so starting out the back of our concrete is right around 88 89 Dees fahit so we’re going to be looking for this to get over let’s call it 250 maybe 300 Dees before we call it quits but we’re just going to give it the beans and find out all right let’s crank this bad boy up and three two one oh jeez that was substantially more than I thought it would be we’re uh turning that down all right quarter crank it is Holy jimy this is going to take a minute so I want to see what we’re at on the front oh wow so we are well over 770 de which is what this Max is out at all right oh it is getting hot you can see steam coming off that top [Music] left all right I shut it off and I we went for right about 15 minutes and you can see the front of this in the middle is well over 770 de which is as high as this thermal camera goes and the backside got all the way up to 250° and uh visually I don’t see any spalling which would be pieces popping off or really any cracks so at this point I know all the water has gotten out of that and I did see steam coming off the top what I think was steam uh could have been something else could have been just smoke but I saw steam coming off so I feel like all the water boiled off and escaped because this is going to be worst case scenario we’re heating this up as quickly as possible in a fire it’s going to heat up probably much more gradually I’m going to take this bad boy off these gloves are supposed to be heat resistant up to 9 900° uh still a little little concerned those gloves did work great didn’t even burn but taking a closer look I don’t see any cracks whatsoever just some little minor surface cracks and as I carried it it was completely solid nothing was falling apart I don’t understand according to the comments in these videos I should be standing at the bottom of a crater right now but uh nothing really happened so I think maybe it’s because of the fast setting concrete is probably the most poorest of all the concretes now this 5,000 psi concrete this is definitely a lot more tightly dense and packed so maybe it’ll want to hold on to that steam just a little bit better and you know give us a good show so we’re going to set this bad boy up and put it to the test all right so we are starting right around 86 87° and we’re going to give it a quarter turn just like last time and I believe we are ready in 3 2 1 we’re going to let this go for about 15 minutes which is exactly how long the last one went all right we are at 250° we will turn it off now something very interesting happened here this one got to 250° in just over 10 minutes now this front is still let’s see here well over 770 de again I think the reason why that happened is because this high strength concrete is a lot more dense than that fast setting because first of all I mix that fast set a little dry there was a lot more air gaps in between it you can even see it on the side but this bad boy is definitely more dense I think what’s going on here is it got hotter on the backside because the heat was able to transfer through a lot faster and that’s because the facet had a lot more gaps it a lot more porous and air is actually a great insulator against heat so with all the molecules all packed together that heat could transfer all the way through to the back which means the water left in this would have converted to steam way faster but again I don’t see any explosions I don’t see any cracks we did get a little bit of fire on that piece of wood though so uh you know that was something but I’ve got an idea there’s one thing I want to try that if it doesn’t give us an explosion I don’t know it will so it’s really interesting it makes me think maybe fastet concrete is the best solution for making a conrete fire pit because it’s going to leave all those extra air gaps in there and especially with a dry mix which is for one going to have more resistance to heat because of all the air gas and two it’s going to let that steam escape a little more easily so yeah I don’t know that’s kind of my take on it let me know what you think I’m sure there’s some disagreements to what that actually means but it also gets me thinking the fastet concrete helped resist the heat transfer really well I wonder what would happen with one with refractory cement on it and this is a sample that I made up the other day when I made these other samples and what I did was I put about an eighth of an inch of this refractory cement on there and that’s the kind of cement that you would use in a pizza oven or a kiln or a furnace and so it has an extremely high resistance for heat I’m going to put this on there and we’re going to Nuke it for 15 minutes and see how hot the back gets and what that looks like at the 10 and 15 minute Mark and if that’s an even better solution than either of these now before I put that refractory cement on there it’s worth taking a look at this one and again when you look up close there are no cracks in it other than little minor surface cracks uh you can see in the center there it’s all white from where just the extreme heat was and nothing really happened obviously with the refractory cement facing the fire we’re going to see how well this will resist the Heat versus the other ones and even with it being uh like 33% smaller this is about an inch the other ones are an inch and a half so the others are 50% bigger but this one’s 33% smaller weird huh in 3 2 1 [Music] n all right I think that’s enough this was a complete failure it only took a little over 7 minutes for the back side of that to get well over 250° now I know it is thinner and I tried to actually add some thickness onto it and it did not Bond at all so I don’t know what happened there but I tried to make it thicker it didn’t so yes I know the test is flawed but regardless I think it shows us that a thin layer of refractory cement is not a silver bullet it is not going to hold back much heat at all so I’m probably just going to not use any of that on the fire pit when I actually make it I know you guys were looking for some explosions and I am too so I’ve got one last ditch effort that if anything is going to explode it’s going to be this and that is a concrete pav that has been soaking in water that’s right I’ve had this bad boy in here for over 24 hours and this is the exact concrete block that I have at the bottom of my fire pit so we’re going to see if we just put extreme heat on this if we can make Steam fast enough that we’ll at least get a crack out of it I don’t know but let’s find out now at a bare minimum we should see all kinds of steaming we’ll see if that steam leads to anything all right here we go I’m going to crank it up a little bit too just give us a little bit extra heat so we’re going to go in three two one let’s go [Music] [Applause] [Music] now that is what I’m talking about after a full 20 minutes we got up to 250° on the backside and there are huge cracks coming through this I’m going to move this out of the way because I’m going to do something to uh try to completely destroy this in a second but I think this is a great example of what would actually happen with a concrete fire pit now this crack down here at the bottom you can see this thing just started widening up and the coolest thing was looking at it from the backside with a thermal camera you could see there was a crack already there because the heat was coming through and then it started making this like Starburst just looked like something from stranger things like it was just going to pull you into the upside down now what I will say is that this is a very old stone it’s been sitting outside for a long time so those cracks were probably pre-existing but that is what’s going to happen with concrete over a period of time with thermal expansion and contraction and expansion and contraction you will get cracks and actually I’ve got a bunch of cracks in these cinder blocks around this fire pit for that exact reason but I’m going to throw some water on here and I’m going to see if this thing just snaps in half with the shock of a cold water and the front side of this is still in the center over 600° so I’m going to throw some cold water on there we’re going to see if that split will just go all the way through I don’t think this will explode because it’s going to be like Contracting but uh I’m just going to kind of throw it from back here that is crazy how quick that evaporated off but uh even with an extremely hot concrete you throw that on there it’s not going to explosively react and tear itself apart now because none of these other ones cracked I don’t think we even need to test the crack resistant because it is just not going to crack either but it might be better in the longevity and help resist cracks over time so can rocks explode in a fire pit absolutely will concrete explode in a fire pit probably not but it will crack over time with enough heating cycle but that’s okay I’m still going to use it I’m Brad until next time get out there and build something awesome