Home made ballistic concrete

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748

748

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I have been doing some small scale experiments to determine what individual items or addtives can be added to concrete to make it more damage resistant compared to a control sample with no modification.
And surface treatment that can be applied to existing concrete.

The concrete used is just quikcrete 4,000psi mix, with the recommended amout of water.

All samples are 11.7x11.7 square and 1.75 inches thick and left in the forms for 3 days and left to cure for a month.
I selected this test size and 22mag test gun as a universal standard that is cheap to test and should scale up.
Because I don't know what you are trying to build, what your local building code's are, I don't know what the design your engineer signed off on looks like. I don't know if you are just trying to fill in a concrete block wall voids, if you constructed the forms your self and have added mesh or if you called in a concrete truck and can only add in some fiber before they pour.
These improvements can be used on anything from a tornado shelter to a tornado proof house.
I'm just trying to find a few options to make a better structure or maybe just a better concrete counter top.
I noticed most people's idea of a test is just shoot a wall. Well that really doesn't tell you any kind of useful information.

The test gun is a bolt action 22mag with a 20 inch barrel from about 2 feet away, striking perpendicular.

Larger thicker samples and bigger guns just cost exponentially more and tell me the exact same thing.
At some point I will make larger samples and hit them with larger center fire rounds, but not today.

So far what I have found is most additives and mix modifications do nothing.
Going out of your way to remove air is a waste of time. I tested vacuum and vibration concrete, which helps remove air, these samples did worse than the control.
I also tested polymer strength booster. It helped a little. But at a cost of an additional $150 per cubic yard it's not worth it.
I am about to test fumed silica. But I believe that it's results will be a lot like the polymer strength booster, a lot of added cost for a minimum improvement.

The 2 things I tested that seemed to help a lot was any kind of chopped fiber and any kind of mesh, even plastic mesh.

Plastic mesh should cost about $7 per layer, per yard for a 4 inch wall and allowed my samples to take twice as many rounds before failing over the control.
Stucco mesh just under the strike face did even better. The stucco mesh retained the material that had been blasted loose, and normally would have been blasted away, held it in place and disrupted incoming rounds. A very unexpected result.
The stucco mesh costs about $25 per layer, per yard in a 4 inch wall. Good news is you only need one layer, the much cheaper $7 per yard plastic mesh performed just as well in back side and internal layer tests.

Chopped fiber should cost less than $20 per yard and dramatically increased damage resistance.

Since the reduced air entrapment samples failed so bad I am going to try to increase air entrapment. I just made a sample with the equivalent of 1 pound of Styrofoam beads to 1 yard of concrete.
Each pound of Styrofoam per yard should increase air entrapment by nearly 1%.
The added cost of Styrofoam is between $20 to $50 per 1%, per yard. A chemical air aid addtive should be cheaper.

In the next few days I want to do a 4,000psi and 5,000psi control sample shoot out and see if the added cost of going to 5,000psi concrete makes a difference.

Shredded rubber added to the mix, because why not?

I have super plasticizer to test, it allows you to make concrete with less water, less water makes stronger concrete.
For an added cost of $20 per yard I should test it.

Any other addtives or mix modification recommendations?
 
Good morning. Interesting idea, and I always love an experiment.

A word about concrete: Most the peculiarities of concrete structure design stem from the combination of very high modulus (it's stiff) and brittleness (low strain to fracture). In common parlance, it's fragile relative to its compression strength and by convention we ignore its tension strength because of it's tendency to fracture.

I believe that what you're referring to as 'chopped fiber' is what I usually specified as Fiber Mesh. That should show improvement by bridging the shock fractures, see here for a summary. Even better will be steel fiber reinforcement, here and here, but if you thought the polymer was expensive. . .

SuperP, to increase strength by reducing water, and the 5kpsi mix, might help. I don't know what those changes do to brittleness, so I can't predict where you'll end up, but I have the feeling that brittleness is more important than strength in an impact/shock application. You already demonstrated that air-entrainment degrades, probably by increasing available crush volume and allowing damage to propagate further.

I think the shredded rubber is interesting, but there's a risk that the large difference in modulus between the concrete and the rubber will weaken the matrix, not strengthen it. Finding a way to bond the concrete to the rubber would fix that, but I can't think of one.
 
I have wanted to test chopped steel fiber. But it looks like if I want any I have to make it from scrap cable I have laying around.
Then I can make enough to do a large project.

If chopped steel cable is more expensive than polymer booster then it's going to have to be ruled out in favor of everything else that has shown good improvement.

If I take the chopped fiber and mesh, use it make some kind of structure then I am looking at adding a cost around $50 to $80 per yard in fiber and meshes.
Then $70 to $120 if I get real fancy and use meshes, fibers, super plasticizer and possibly Styrofoam beads if I find they give a positive test result.
The price also largely depends on how cheaply you can get bulk addtive ingredients and how thick you cast the walls.

I am expecting the Styrofoam beads air air entrapment and to do like you said, limiting the damage to a smaller area.
 
748

Well done sir and a very interesting experiment! Please update whenever you've completed another round of testing and keep up the good work!
 
Next rounds of test will be in a few days.
Just a sample with added fumed silica, which I expect to fail exactly like a control. Some old timer mix, where took standard 6 sack per yard mix and converted it to 7 sack mix by adding more portland cement and my first 5,000psi crack resistant "pro-finish" sample. This 5000psi mix appears to have water reducer already in it, chopped nylon fiber and a lot less sand than standard mix.
 
Crushed rubber is pretty amazing in range construction but I don't think it will do well when mixed in concrete. Fiberglass would probably work well... and there's ample old boats laying around.
 
I have already destroyed 4 control samples made with 4,000psi concrete. Their failures were surprising consistent.

Today I poured a 5,000psi fiber free sample, using the store bought 5,000psi pro-finish mix. My hypothesis is this is the ideal basic mix and should be the modern equivalent of "military 7 sack mix" where the military used 7 sacks of Portland cement per yard to build fortifications and what not.
The price difference between standard 3,000psi concrete and 5,000psi concrete the military likes to use is 40% higher, due to the increased amount of Portland cement.

Then took some 4,000psi mix and added sand and chunky gravel to it to bring it down to what I believe should be a 3,000psi mix should look like.
I want to do comparisons between 3,000psi, 4,000psi and 5,000psi naked concrete mix samples.
I will probably also build up my own 3,000psi mix from seperate bags of Portland cement, sand and gravel to also test. 3,000psi is the cheapest and most commonly mixed for residential use.

Then poured a second 4,000psi mix sample made with double fibers, using chopped nylon and chopped fiberglass. The instructions recommend 1lb of one fiber or the other per yard. I used the equivalent of adding 1lb of each fiber to a yard.

Does anyone care to see pictures?
I have taken lots of pictures of the testing process.
 
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HB wrote:
I don't think it [crushed rubber] will do well when mixed in concrete.
Click to expand...

I suspect you are correct, but composite materials are funny things and it has only been in the last decade or two that we've started to get both the mathematical models and the computing power to do a job analyzing them, so the whole field is still in its comparative infancy.
 
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748 wrote:
Any other addtives [sic] or mix modification recommendations?
Click to expand...

Are you varying aggregate size?

Are you simply looking for the best ballistic performance against pistol and rifle rounds? Or are you looking for overall resistance to any kind of concussive force? Also, are you looking to minimize weight or is that not a consideration?

Also, I have only seen it in videos prepared by vendors - so I take it with a grain of salt - but spray on coatings (kind of like the stuff they spray on beds of pickup trucks) can apparently add considerable resistance to shattering and penetration concrete structures. That might be something to investigate. After all, if a three inch thick wall of concrete covered over with spray-on bedliner performs better than six inches of uncoated concrete, then the thinner wall may be more economical to build.

Finally, the strength ratings (i.e. 3,000 psi, 4,000 psi) are a measure of the compressive strength of the concrete when poured into a standard 6 inch diameter by 12 inch long test cylinder under laboratory conditions, aged for 28 days and then loaded until failure. Concrete poured in the field will rarely achieve these strengths. Depending on whether you are trying to resist a fast-moving projectile as opposed to a slow-moving one, you may get different results with different concrete strengths, so adding something like a 45 ACP pistol to your test protocol might get you some additional information about a different class of projectile you need to deal with.
 
I have just begun varying aggregate size, the samples with larger aggregate are still curing.

Because the price difference going from 4,000psi to 5,000psi ready mix is almost double the cost. So I mixed my own 1:1:2 (that's cement:sand:gravel) mix that should be 5,000psi using a 25% small gravel all under 3/4 inch and 75% larger chunky 1 to 1.25 inch gravel.

Surface coating do work.
To test surface coatings I go to the hardware store and buy a 12x12 inch paver. A fresh hardware store paver is severely damaged by a single 22mag hit.
I have so far only completed 1 experimental test and a few control tests to make sure they fail consistently.
Normally one shot from the 22mag causes the back side to spall. I applied a thin coating of epoxy resin to the back side and shot it. The back side was bulged but no material was blasted away. A definite result.
Eventually I will test epoxy plus fiber glass, I figure epoxy and fiber glass could be applied for well under $100 per cubic yard on a 4 inch wall which is 81 square feet.

You could minimize weight just going with thinner stronger concrete.
I found the 3,000psi concrete is 10% to 20% less dense than 4,000psi mix.
I have made a sample using Styrofoam to increase air entrapment. But it's only going to make each yard around 80 to 100lb lighter for each 1lb of Styrofoam I add.
I am testing Styrofoam to see if increased air entrapment limits the damage area.

The 45acp tends to bust chips off the surface, it doesn't do deep damage like high velocity rounds.
 
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Mythbusters set an explosive charge off near a block wall. Naked block was smashed, but block coated with truck bed liner held up enough to protect Bubba the dummy.
 
RinoLiner is some good stuff.
I'm wondering if spray foam and stucco mesh would give a decent improvement.
I have studied application of something to the surface of existing concrete a little, but thats not my main focus.
I probably will test that more later on.

At this point I'm testing control samples, adding 1 thing to the concrete and testing it. I have already ruled several things out that are expensive and don't work.
And found a few things that worked real good.

Real soon I am going to combine 2 or 3 things that have worked individually, make hybrid samples and blow them away with my 22mag
 
Take a look at Faswall or Durisol building blocks that use poured concrete as a filler. Both have integral rockwool insulation inside the block.
Similar to ICF forms but the blocks which are serve as forms are made from mineralized wood fibers. Looking at constructing an extension with it.
There are also some other liteweight blocks intended to serve as forms for walls that use other material as the binding agent for the blocks.
 
I tested my two 5,000psi mixes and there definitely is a difference.

One is old timer mix, improved 4,000psi concrete. Where I took stand 4,000psi mix, added more Portland cement and aggregate and boosted it up to what I thought would make it a 5,000psi mix.
I was assuming 4,000psi mix is about 1:2:3 to 1:3:3 ratio. I boosted it up to about a 1:1:2 ratio.

And a 5,000psi pro-finish finish fiber reinforced. But the pro-finish sample developed a big crack during curing in the middle of the sample so number of times shot before failure is irrelevant.

When the 5,000psi sample is shot with the 22mag the impact craters were noticeably shallower than 4,000psi mix. On the improved mix it still failed after 3 shots which is normal for a 4,000psi mix.
So you get less damage per shot, but still fails after the normal number of shots.
Makes me think the 5,000psi mix is harder but also more brittle.

At this point it looks like 5,000psi is the way to go if you can reinforce the concrete to counter the brittleness.

I am expecting my 5,000+psi 1:1:2 mix, preform about the same. Bullets kind of bounce off not blasting away a lot of material, but cracking apart sample after 3 or 4 shots. But 1:1:2 is expensive, I'm thinking it's at least 8 sacks per yard.
 
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748 - your project is very interesting and I look forward to your results.

One of the links that came up in nsco search had this at the end of the article:

"The researchers’ analysis of Roman concrete sheds light on existing modern concrete blends that have been used as more environmentally friendly partial substitutes for Portland cement, such as volcanic ash or fly ash from coal-burning power plants."
Click to expand...
(http://www.history.com/news/the-secrets-of-ancient-roman-concrete)
Click to expand...

Several years ago, there was a short-lived series about different types of home construction that were "green". These included hay bale houses with stucco finishes as well as some using concrete. In one of those episodes, they used a regular mix to which they had added some percentage of fly ash. While this caused the concrete mix to take nearly double the time to dry and cure, they also found it to be a lighter and more durable.
 
Coal fly ash is pretty interesting. It is a water reducer, flow enhancer and air aid which helps the concrete entrap more air. Kind of like a cheaper version of fumed silica.
I would test it if I could buy smaller quantities than 1 ton.

Speaking of fumed silica, I tested my fumed silica sample where I used, you guessed it, about 1lb per cubic yard and it preformed at least as well as the controls.
In my my mind I had written it off using 1lb per yard because everything I could find on using fumed silica in concrete said you need at least 5% by weight to make any difference. I used like 1/4,000th by weight.
Since I have a 1 gallon container still pretty much full of fumed silica that I have no other use for so, I will make more fumed silica samples I'm probably going to use at least 4 times as much fumed silica on the next sample.

Edit, if you search "fly ash" instead of "flyash" you get reaults. That was my problem a few months ago when I tried to find it.
 
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The force that the bullet exerts on the concrete is the rate at which the bullet is shedding momentum. Since concrete is brittle, it sheds momentum in a hurry. Anything you can do to stretch out time will proportionally reduce force.
 
Ok, having put 39 years into design and construction (to include storm-resistant sctructures in 180mph tropical storm wind zones), I'm going to quibble with some of your testing methodology.

Projectile impact loads on concrete (storm debris, bullets, etc.) create tensile loads in a given section of concrete.

Concrete gets its compressive strength by using portland cement to afix an arrangement of graded aggregate in place.

The key to compressive strength in concrete is in the strength of the aggregate--the better the rock the better the strength. In the rawest sense, this argues for fine aggregate in copious quantity, in something with sharp edges and to some dimensional standard (a true ideal aggregate would be water-washed granite-gneiss river wash--however granite does not "make" very good sand let alone gravels that can be graded for aggregate).

The other problem with use of all-fines is that the increased surface area requires more cement to make the matrix.

This is why concrete uses a range of aggregate sizes (typically driven by placement method, you need finer for pump placement than for wheelbarrow or tremie placement). If we know we can use 3/4" or 1.25" aggregate, we then need a range of finer aggregate sizes to fill in the void spaces (use less cement).

This is a long way to say not all gravel, and not all sand are the same; neither are they fungible. There are significant differences in material over rather short geographical distances. The materials suitable for engineered concrete vary for distances as small as Boston to Newport RI (or, for that matter, Fort Worth to Dallas, a similar distance).

Concrete less than 2.25-2.5" really requires really high surface compactions to have any utility. You need about 1.5" of concrete to cover rebar (the pointlessness of woven wire mesh is an entire web page of monographs). So, the first usable section of concrete ti sample is right at 3" thick with #3 or #4 bar, as that is the minimum vertical wall section possible to encounter. In real like 4" to 8" is far more likely, Even more likely is engineered concrete masonry units, which are then reinforced with non-shrinking grout or a 2800-3200 psi concrete.

Air entrainment is more for the energy efficiency of the concrete mass.

Shredded steel cable fiber has been tried, it fails in actual use due to it forming surface rust far too quickly. Portland cement will bind to the rust and not the metal, which negates the tensile strength the metal in meant to impart (it also reduces the compressive strength, too).

For bullet resistance the best addititve for concrete is actually glass-reinforced plastic composite sheets for converting a point load into a spread-out area load. The FRP panels (and their fasteners) are just not very good out-of-doors in the elements.

Even better is to have sloping & undulating surfaces the better to also change the point loading by deflection.
 
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