Secret Tunnel/Garage Update #4

WELL I'M SHOCKED..........And very Pleased.

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#colinfurze #tunnel #secret #update

[MuchColinFurze]

Well i'm Surprised, Pleased and comforted by that discovery. What do you think, is it what you expected?

[bryanlu]

I suspect the plastic sheet is acting as a kind of humidity trap for moisture, particularly when you consider the heat differential between the cool metal and the dirt/earth. The concrete likely does a better job of sealing against the metal, preventing moisture from entering underground. I'm all for this.

[lukemartin]

I’m a bridge engineer. We use uncoated structural steel all the time for weathering steel superstructures and driven steel piles. Depending on the environment (coastal areas, corrosive soils, etc.), you can count on a certain thickness of section loss. However, as long as the steel isn’t disturbed, the outer layer of rust will protect the material beneath. Because you’ve encased all your steel in concrete, you’ve got nothing to worry about.

[sebastianlarsen]

I'm a constructions expert and I've been working with steel for about 6000 years. When building the pyramids we ran into some weathering issues when it started raining frogs, but if you stay clear of god's wrath you should be in the clear. Hope that helps.

[johnlee]

Fellow engineer here and newcomer to this 2nd channel - This is fantastic! On the front of rust control, put the steel directly in contact with the concrete and have the moisture barrier agsinst the dirt. Your conclusion about alkilinity and rust corrosion is 100% correct!

[HMB]

Hi Colin, I’m a civil engineer. If you are going to use plastic it’s better to put it between the concrete and the soil than between the concrete and the steel.
If you put the plastic between the steel and concrete it will essentially trap moisture between the two which will marginally accelerate rusting.
If it’s between the concrete and the soil it will prevent water from getting to the concrete and seeping in through any cracks that you won’t be able to see.

In other words the ideal solution would be to line the hole with the plastic before pouring the concrete in but it should be fine if you didn’t

Alternatively you could use the more expensive option and use hydrophobic concrete

[Rulez]

Structural engineer here, its recommended to use the vapor barrier sheets on the dirt side, so you would put up the sheets against the earth, the concrete goes in between it and the tunnel steel. Great project!

[robbzelf]

I'm a NDT engineer (non destructive testing) and you can get a ultrasonic wall thickness measurement set for not to much money with which you can always check for corrosion on your backwall. The wall thickness itself is a give away as well. Asume you measure around 4.1 for new steel (factory over thickness). But you can also see if a backwall is corroded on your echoes (asuming you pick a ultrasonic wall thickness set that shows you echo's and not just a number. Love the channel!!!

[glynnepritchard]

Hi Colin, dam and tunnel engineer here - As others have said (so I wont go into too much detail) and you stated, the concrete will protect the steel due to passivation. Providing the concrete doesnt crack you will not have an problems. Looking at the ground conditions, you are basing your structure on rock and so teh chance of deformation is low, reducing the possibilities of cracking plus you seem to have compacted the concrete properly during construction. However, you may still encounter shrinkage cracks over time. I do not know your mix ratios supplied by the batching plant, so can not comment on the longevity of the concrete. Dont use the plastic sheet, you want steel to concrete connection for a number of reasons but this is a difficult format in which to explain why. For the interior, if you want to keep it mill scale just spray oil and wipe down. I presume that you are using a humidifier in the tunnels?

[mygardenofthings]

Hi mate, if you speak to your local concrete supplier ask them about concrete additives they can add to your batch. You can get a totally waterproof concrete mix that they use in construction on projects that are affected by water like bridges, foundations to protect the reinforcement. This may solve the problem at a much lower cost. They should have brochures with typical ranges of different mixes to help you choose the right one👍

[MrFlamel]

Structural engineer here, if you use a moisture barrier, it is best to attach it to the earth side of the concrete so that the water is never going to interact with the concert. If you want to use a sacrificial anode, it is pretty easy to install. You basically just attach it to the steel wall and power. Cost a couple of bucks a year to operate, but not much. But in general you can say that 1mm of Steal can hold about 10 years of normal rust activity, so in your case potentially more.

The garage interior however is a different story as it will be exposed to way more water and salt. There you should probably put a coating of some sort on.

[teeslunk]

8 years ago u done the bunker. Time flys ❤❤🎉🎉

[HaSte]

Hey Colin,
i think the best way to deal with this situation is, to "cover" the soil walls itself with the polythene and create some kind of "pool" for the concrete. The steel gets covered directly in concrete, but the concrete itself is also protected from the moisture inside the soil and can´t soak in the water.
In germany the baseplate (groundplate) of most houses without basements are build that way.
Sorry, english is not my native language.

[MrDrakkus]

I'm a structural steel detailer, I make the drawings that steel fabricators use. We always make sure to note the areas that are in contact with concrete to not be painted. The reason is that when the paint gets scratched water will get through the crack and stay trapped there, causing it to rust faster. Plastic traps water as well, which will lead to more rust over time.

With no coating the water will run right off the steel and through the concrete. That and the chemical reaction you mentioned protects the steel surprisingly well.

[thomaspase]

Hey Colin, I'm in a non-profit association, which restores old Fortresses and bunkers from before WW1. Some of them are rearmed in WW1 and/or WW2 with corrugated iron sheeting.
We were facing a similar problem, because parts of the sheeting was directly exposed to dirt. Thus the restauration requires as minimal change as possible because of it's historical protection, we decided to cover the entire sheeting with bitumen. Now, 10 years later there is still no rust on the outer side.
Also we discovered a bunker from the early WW2 which was covered in bitumen initially. There where only two or three spots of rust, after the farmer who found the bunker hits it with his plow.

[andrewfulton]

G’day Colin, I’m a builder in Australia. We use a product called xypex which is an additive for concrete that makes it pretty much water tight. As I understand it, it’s a salt of some sort that expands when in contact with moisture and seals any micro cracks in the concrete… might be a bit of extra insurance…

[nickcapps]

Above the under ground garage, when it is finished, where will rain water go? Normally rain water settles through your grass/dirt. If you are getting rid of the dirt below, and you put plastic and concrete where water would normally settle… your front driveway area (above ground) might turn into a “bog” (very wet area) until water can drain off. So you may want to put a slight slope to the roof of your under ground garage but do it in the direction you want the water to drain to (i.e. you don’t want the water to drain toward your house). You might want to consider making concrete drain tunnels that allow the water to go from ground level to below your metal floor. That way the water can still settle into the earth and off your under ground garage roof. Your bunker didn’t have this problem because your lawn is slightly sloped away from the house. Water naturally drains behind your fence or just into the surrounding dirt/earth. That’s my thoughts. Great work, keep it up! From Florida, USA

[darthgator]

Hello Colin, fellow engineer here. I would pour the concrete right on top of the steel. Rebar reinforcements are also poured into concrete without any protection, it is the concrete that seals the metal from oxygen and stops further corrosion. There will be some water content present in the concrete for some time, but it will dry and harden over time (even submerged in water!) In big civil engineering structures they usually inspect the concrete for cracks, as these can lead to water ingress. So I would be more worried about the concrete cracking over time then the steel corroding from the inside.

[kyleb]

Love the giggidy you snook in there 😂😂😂😂

[ThinkLiveLife]

I have a degree in building construction technology.
The reason having a moisture barrier like a sheet over the metal is worse is that you are trapping any moisture between 2 impervious surfaces leaving water contact with your metal. If you were going to go that road you would want to use some sort of spray liner or closed cell foam around your metal so that it bonds to the metal and there is no room for moisture to contact the metal.
Unfortunately I can not speak intelligently about the PH interaction by contact of concrete but I feel like the PH of the moisture itself that gets into contact with the metal is what matters more. Keep in mind that concrete (unless its specially engineered to be) is not impervious and water does move through it at a very slow rate.

To the point though, With the rate of rust you are seeing over 8 years in your climate zone I wouldn't even bother addressing it.