Concrete, bullets, vaults and bunkers

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wacki

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We've had a few threads about concrete gunsafes, vaults, and safe rooms recently. Now I'm curious about different types of concrete.

There is this guy in WA that spend 30 years building a bunker by hand:
There are 3 ft concrete walls, using 5-bag cement (20% denser than regular cement).
Click to expand...
http://www.oneofakindhouse.com/fortress.html
Pretty amazing stuff.


But what is 5-bag cement? Anyone have any information on the various types of cement?

Also, what cement is the best for vaults and saferooms? What cement is the best against bullets? I've seen some concrete break apart vs a hammer. On the other hand there was this episode on mythbusters where they were trying to drill a hole in an abandoned military building and Adam Savage broke several concrete drill bits.
 
concrete is a mixture of sand, stone, portland cement and water.

you can increase the strength of the concrete by putting more portland cement in it.

the portland cement comes in large plastic lined paper bags (~80lbs. /bag) and is a very fine, gray powder, similar to chalk.

the mix is metered by how many bags of portland cement you add per cubic yard of concrete mixture.

if you buy readi-mix (what's delivered in the big trucks) they usually refer to the concrete mix by it's compressive strength as measured in psi.

2,500 psi concrete has been commonly used for years, but modern construction standards seem to call for 3,000 psi. concrete more and more.

Rule #1.....you must add rebar to get any tensile strength at all.

I've mixed concrete in both a wheel barrel and a small electric mixer and I'm tellin' ya, it aint no fun. I've also general contracted the building of four structures with poored concrete foundations and that aint cheep.

My hat's off to this guy, but personally, I'd rather not spend a large percentage of my time on this earth shoveling sand into a little mixer and hand digging a bunker
 
For the most part reducing water in the mix strengthens the final concrete however there is a critical mass required to get the chemical process known as hydration going. High early strength concrete will render a 3000 psi compression after it's cured. As was mentioned earlier, rebar is critical for proper structural bearing capacity.

One of the unanswered questions was how do you make a break in resistant concrete surface? Well aside from maintaining a proper mix ratio, placing multiple layers of welded wire fabric with stronger, larger pieces of rebar at reasonably close intervals will certainly add some trouble to anyone trying to get in. You could also opt for an extremely hard aggregate which would certainly heat up any cutting tools thereby defeating their edge.

The other unanswered question was how do you excavate without disturbing the top grade. Often buildings are jacked using multiple strong hydraulic jacks operating in concert with a structurally designed girder that intercepts the vertical load imposed on the soil by the buildings foundation. This is a painstaking process that is both expensive, and fraught with compromise. Large concrete pours are more economical however every bit of vertical height adds to the hydraulic pressure imposed on the forms near the bottom. All of this is possible to calculate and plan for. Of all areas of construction, form design and falsework (the stuff that holds form work up) get the least professional attention. This is truly dangerous and I can't emphasize enough how important it is to get the form system designed by someone who knows what they're doing BEFORE you order concrete!

Finally, concrete is comprised of water, aggregate, portland cement and often fly ash. Using sand as your aggregate makes mortar which is structurally weak compared to concrete.
 
Great result from all that work. I particularly like the sliding bookcase / passageway :p

The shells he found while digging are also pretty interesting.
 
My guess is 5 bag is 5000 psi cement. You can find it at any home improvment store. It is just more expensive.
 
Finally, concrete is comprised of water, aggregate, portland cement and often fly ash. Using sand as your aggregate makes mortar which is structurally weak compared to concrete.
Click to expand...

I guess the real question here then is what is the best aggregate to use?
 
The amount, as stated earlier, of cement in the mix determines the ultimate strength of the concrete. It's strength is measured in PIS to crush failure. 3000psi concrete can withstand, after a set period of cure time (I recall it is 30 days, but don't hold me to it) a load of 3000 lbs, sitting on a 1 sq. inch area without crushing. Concrete has very poor tensile strength. Tensile strength is what you get when you pull a rope. Materials are added to concrete to improve the tensile strength to allow concrete to withstand flexing without failure. Steel (re-bar) is added generally to make up 2% of the cross section of the concrete. Re-bar is textured to add to the grip that the concrete has on it. Concrete can also be made up with fiber, often Olefin, to achieve the same effect. This is called "Fiber Mesh" concrete and can be used for on-grade slabs. An example of concrete under tensile load is a suspended floor that is flexed by putting something heavy between the supports. The side that the flexing force ( a printing press for example) is applied to is under compression and the opposite side is under tensile (stretching) load. Without re-bar, the floor slab will simply not be able to resist the tensile load and fail.
 
water is critical

The post from "rockstar.esq" is the most technically correct.

The water:cement ratio is the determining factor; addition of more bags of cement is then an indirect way to effect this ratio. It is so critical, that the adsorbed water within the aggregates; sand, etc. is analysed by a lab or technical methodology, and this water is taken into the calculation of water available for chemical reaction.

The arbitrary ratio method e.g. 3:4:5 is suitable only for the lower strength grades, while the higher grades must be verified by sampling of the mix during pours, and destructive testing in a laboratory.

Placement of reinforcing is also technical, and while done with general experience by the home handy man, requires engineering analysis for structural, load bearing members where the public use is involved.

Where dense concrete is required, special aggregates such as metal are used, and of course mechanical vibration devices must be used to remove voids that occur during pours.

Proper curing provisions and times of set are required to avoid crack development which will defeat all the previous attempts to have sound, strong concrete.
 
I have seen bank vaults poured with some interesting mixtures. The modular systems use even more interesting concrete mixtures. Many of your modern day burglar rated safes use concrete as their barriers.

You can make a concrete room as strong as you want, but it's only going to be as strong as its door. For a normal gun room using a normal gun safe type vault door, your regular foundation type construction is more than enough.

If you're planning on installing a real vault or blast door, then that is a different story.
 
what i don't get is why this guy spent years and years on this bunker, only to sell it.

Were the drapes not matching?
 
More information on this please. Has anyone used high speed steel aggregate to prevent drilling into concrete?
Click to expand...

I saw metal alloy balls added to the mix to reinforce it in a local bank being built with a large below ground vault. I don't know what it would do to drilling or torching. It may be used instead of standard aggregate for density or maybe strength. There was also about ten miles of rebar in the vault section also...
 
I don't know as much about the science behind concrete mixing like many of the others here apparently do, but I do know that I've done it before and it (as previously mentioned) is just not fun at all.
 
Related.

Sorry I do not have any links or references.

Civil Defense , back when I was a brat, had publications with all sorts of plans, instructions and the like to build various types of bunkers and protections against attacks.

Cold War, and these Yellow and Black signs were everywhere.
Supplies in 55 gal drums, and we did more CD drills in school than we did Fire Drills.

Still, all sorts of ideas on converting basements, and using the in-ground storm shelters many folks here in the South had, due to tornado's.
 
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