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Testing and Forming Natural Fiber Reinforced Concrete Update 2-29-12

  With Steel Fibrous Concrete we tested 4x4x14 inch bricks, and built a special machine to do that. But with your island project, they arent really applicable, because the deck Hexes are so thin, forces go in two dimensions and are much more spread out, and very thin in the third direction. So its better to just test the final results. You want it to do its job, not some other job.

True, you can make a brick and test stand, and compare numbers with published standards. However, that doesnt mean that your project will work anywhere near the same. Better too test to see if it does what you want it to do. Its more of an art than a science.

Thats why I say, turn it right-side-up, put it in the water, and walk on it. Does it hold you and your mate dancing in the sand without breaking or sinking? If so, it will probably be good. If not, the design may need changing. Thats practical. Your NFRC may need to be thicker. Your float may need to be bigger.

Start with at least one inch thick one. Test it and see if it needs stiffing.

And generally, NFRC will be fireproof. (But not always, so test it.)

NFRC floats

NFRC can also be used to make floats, but its a good idea to use Berylex (company in Missouri) additive to the Portland Cement to make it hold air properly by keeping the water out. NFRC has the quality that it can be made in any shape, but it is time consuming. Each float takes at least a week to cure.

But, you can make others in the meantime.

The Navy uses 7 sack mix Portland Cement, which is supposed to be waterproof, to protect docks and the like. If you make your NFRC without sand, it should be waterproof, if you dont leave holes in it on top.

A deck and float may be formed at the same time using a plastic garbage pail as the form. See my articles, in fact read all of them so you will have as much knowledge as I can give you.

There are a number of ways to form a NFRC float.

  1. Make a Hex upside-down as described. Make it just enough larger than the plastic trash pail you intend to use as a form for your float. The Hexes all have to be of the same size so you can hook them together in the water. And make them hook together as Ive already shown. (Side-by-side, or overlapping at the edges.) Set the plastic trash pail on the fresh NFRC float deck, with the bottom, the small end, down.

    If your fibers, are about a foot long, such as those cut from palm leaves, you should be able to wind them around the plastic trash can, overlapping each one. If your Portland Cement is just moist, not too wet, in theory you should be able to wind it all the way to the top, on the outside of the form.

    Make sure you dont leave any gaps, or the air will just leak out.

    After several days you should be able to raise the plastic pail out. The finished float, after a week, can be put in the water, right-side-up. But one by itself, when filled with air, will just fall over because its base is too small. At first just add a little air. However, when several Hexes are hooked together, you can fill the floats all the way and they will hold each other upright. In case it leaks air, you can easily plug the hole from the inside, or insert a plastic trash bag, then filled with air, and with a few rocks near the opening to keep it pointing down. Try it to see what changes you should make.

  2. Another way is to wind the NFRC around the inside of you plastic pail. Make sure the fibers overlap, and you leave no gaps. Leave a hole big enough to get your fist through easily in the bottom. Make a flap at the top for connecting to your Hex.
    1. It may allow you to make a fresh Hex, and turn your pail up-side-down, onto the Hex, and slide it off. The fresh NFRC may not sag, and may hook to the Hex ok.
    2. It may sag but still retain enough shape to make a good float.
    3. It may fall apart.
    Try it and see.

    If it doesnt work, let the pail full of NFRC (walls of the pail of course) stand until its hard. Remove the float from the form pail. Paint the flap with chemical to hook Old Portland to New Portland, and place it on a fresh Hex. When a week old, place it in the water and fill with air as with the method above.

    You may be able to mix sand in with your Portland Cement, twice as much by volume as the Cement itself. It depends on your project as to whether it is a good idea or not. You have to try it and see.

Portland Cement was originally invented for building boats. It has been used successfully for many years. But lacking tensile strength, it needs fiber. And unless its thin as in NFRC, its heavy.

Many kinds of natural fibers can be used in NFRC. Palm leave strips, old cotton clothing, pine needles, strong grasses, even old cut whiskers (theyre just slow growing.) Try what you can get free, or at least cheap. Its an art more than a science.

Plastic Floats are a good choice, because it doesnt biodegrade in either salt or fresh water. You may have to protect it from the ultraviolet rays of the Sun, however, under an island usually does that. In theory it will last for hundreds of years.

It can be hooked into an island float with bags, or NFRC.

NFRC has the advantages that the fibers can often be had for free from certain tree trimming companies. Or you can harvest it yourself, even on your island. The Portland Cement is not expensive in most places. And you can also order it over the Internet.

Its long lasting, and can be formed into a variety of shapes. It works well in both fresh and saltwater.

The authority for Natural Fiber Reinforced Concrete (NFRC) is the Portland Cement Association at www.cement.org. But their work is for commercial cement organizations and engineers. Your NFRC island is an experiment, therefore, you are the sole one responsible, yet, your experience can be valuable to others.

You are not asking a lot of NFRC, or your skill in using it. However, you are able to do an improved job as you gain experience, and work with the materials you can obtain. You basically are building a deck, supported by various floats. Your project is subjected to weather and water conditions at your location. Please keep track of your progress, it will help you to learn, and help others too.

Keep tract of your mixtures, and change them as you go. Write the date of each NFRC project in the concrete, along with any information that will help you improve. There isnt much island-building experience I could find, so you have the freedom both of your mistakes, and your successes to learn from.

Ill offer what little experience I have, to help you, but your experience can be invaluable, even profitable.

Concrete is very tough stuff. On Wake Island in the Pacific, I saw Japanese bunkers built at the oceans edge over 20 years before. They had been pitted on the surface by the sea, but were otherwise still usable. On Saipan Island I saw various concrete buildings, built away from the sea, still usable after a half-century. Of course they still had big holes from Allied explosives, but were otherwise still in good shape, and some of them are still in use.

These structures were not fibrous, if they had been, they might have provided their occupants with much greater protection.

In 1979-80 I designed, and worked building, an earth-sheltered geodesic dome, of steel fiber reinforced concrete in Missoula, Montana. Its still providing enjoyable living today. It was so beautiful, its picture was on the cover of 3 national magazines. At one point in construction we had to bore 1 inch holes in the 4-inch thick hexes and pentagons. It took over 20 minutes for each hole using an electric jackhammer! Its tough stuff.

When finished, the home held over a million pounds of earth, and was engineered to hold another million! Yet its only 4 inches thick. It works very well.

However, the steel fiber was expensive. But to get the results we need, we dont have to buy steel. Natural fiber, even free fiber, should do the job for us. On Saipan I used coconut leaf fibers, and bound together a float made of recycled plastic bottles. It worked real well, but I suffered a stroke, and my experiment came to an end.

What I did, proved to be quite strong. Certainly much better than the plain mortar I tried for the same purpose, which, lacking fiber, it crumbled and fell off the bottles.

What do you want to do? Are you building a runway for the space shuttle? If so, I suggest you hire real engineers. But for this project, YOU are more-than-likely more than capable. Just think about what you are doing. You can do it with a little help from me!

The Island Segments I suggest are 8-foot Hex pieces. They have these qualities:

  1. Hexagonal shape
  2. 4-foot on a side, for 8 feet total at an angle. (See the illustration.)
  3. Hexes fit together to make a flat floor, or deck.
  4. They are tied together with inexpensive plastic rope.
  5. The rope is indented into the NFRC so the connection can be easily covered with sand and hidden.
  6. The upper surface is coated with sand, having been constructed up-side-down on the beach. For:
    1. Inexpensive colorization
    2. A natural sand appearance
    3. Texture
    4. Ease of repair
    5. To soak up your spilled beer!
  7. Only inch thick.
    1. Inexpensive
    2. Easily built by hand
    3. Easy to repair
  8. Relatively fast to reproduce (Yes, the concrete takes a week to harden, but it's fast and easy to make them. You can easily make many more during that week.)
  9. Handmade
  10. Need very few tools.
  11. Can be made stronger where needed.
  12. Fits any shape, even hexagonal.
  13. Inexpensive
  14. Readily available materials.
  15. Can be easily built on most beaches.
  16. Works in saltwater or fresh.
  17. Easy to mix
  18. Surface can be smooth or rough
  19. Can be colored
  20. Easily connected to other kinds of Island Segments.
  21. You can do it!
Making the Form
Take 3 10-foot 2x4s, as straight as you can find. And cut them in the middle at a 60 angle. Drill a inch hole in each piece about 1 inches from the angle cut for the screws. Measure from the cut end, 4 feet and put an easily seen pencil mark.

With a rag, wipe each piece, especially the ends, with diesel fuel or light oil, to keep the NFRC from sticking to it.

Lay it out on a sandy beach, raked flat, to make a hexagon 4 feet on a side. Measure the cross distances at 8 feet as shown in the illustration. And screw them together with 3 inch screws. Youll need 6 per hex form.

Insert the blockouts for the corner holes, cut at a 60 angle to fit in the corners, made of exterior inch plywood or wafer board. They only have to be a couple inches wide, with a round plastic piece about 1 inches wide to make a rope hole in the NFRC. Screw them to the blockouts about 1 inch from the edges.

Note that 2 opposite ones have double holes, so 3 Hexes will tie properly.

Also, coat with diesel fuel.

Remember that youre building the Hex up-side-down on the beach for good reason.

Also, the local hardware store may have scraps so you don't have to buy a full sheet.

Mixing
In a 5 gallon plastic bucket, put about 5 cups of Type II Portland Cement. For this first test, mix in just enough water to make all the Portland wet, not sloppy, but wet enough you can coat your chosen fiber.

Concrete requires water to harden, but too much water will make it weak. Remember how much water you used, and write that on the Deck Piece you construct.

Fiber
I used coconut leaf fiber cut from dry coconut leaves, about a foot long and an inch wide, with the leafs bigger fiber (not biggest) down the middle. Try both dry and green fibers to see which works best. I think the dry ones will, but Im not sure.

Pine needles should also work. Especially, longer Ponderosa Pine needles. These fibers are much smaller than the coconut fibers, so you can mix them right into the Portland Cement. Whereas the longer coconut strips have to be dipped in one at a time.

Different fibers, grass or whatever, should make different NFRC, however, you may not be able to tell much difference, since your project doesnt require much. So test several natural fibers to see what will work best, especially ones you can grow in the future on your finished island.

Laying the fiber
Fibers have direction to them. If you are laying fiber strips, make sure they all go in one direction to carry the tensile force all the way across your hex. Overlap each one about 2 inches. Keep track of this overlap, write it on your hex, and vary it in different pieces.

Do this on the first layer. All running the same way, and smash it flat with a trowel. Then lay a second layer going 90 from the first layer, also all the way across the hex.

If youre using cotton, from recycled clothing, note that its already going at 90. But you still must overlap the edges, to transfer the tensile forces all they way across your Hex.

If you are using mixed, smaller fibers, just trowel on about a inch with overlapping fibers running randomly throughout the mix. Up and over the corner blockouts.

You have to do all this within 3 hours of working time, because the chemical reaction that causes hardening of the Portland Cement will be taking place, or your hex wont turn out right.

Make the edges of the form go up the 2x4 form pieces, and thicker on the edges, especially around the hole blockouts.

Floats
If youre going to tie soda bottle floats to the edges of the Hex, insert a plastic string, about 8 inches long, with a knot in the middle every foot along each edge. Then cover the knots with NFRC, but leave the string ends sticking out so you can tie the bottles to it.

In the middle of the Hex, put two walls, with the plastic bag and their round river stones trapped in the middle, as shown on the illustrations.

Or, if you are going to make your floats out of NFRC, per my previous instructions, now is the time to insert them, while the NFRC is still wet.

Admixtures
We used Berylex from Missouri. It makes Portland more dense, waterproof, and somewhat air proof. It makes new concrete stick to old concrete like you wouldnt believe. You can learn more at http://www.sturgismaterials.com/indprods/BerylexSpec.pdf. I love it!

You can also get some white bonding chemical at your hardware store.

Curing
Sit back and have a beer. Concrete takes a week to harden well. But keep it moist, by covering it with a plastic drop cloth. Especially this thin work of your project.

Testing
NFRC bends. You dont think of concrete as bending, but it does, especially NFRC. Even the big thick pieces we made with steel fiber would bend like a swimming pools diving board. It was quite a sight.

Your project should bend too. Turn the Hex over, and walk across it. It should bend in the middle without breaking. If it bends so as to touch the beach, dig a hole in the beach, to let it sag. The safety factor engineered into reinforced concrete is 50%, so your Hex piece should hold two of you or 3 if you enjoy dancing with your mate in the sand.

If all is ok, put your Hex in the water. Blow up the plastic float bag, if you need one, and then see if it will hold two of you in the water. It may not, you be the judge. You can always add more flotation, or reduce the size of your Hexes, and hook many together. But it has to float well. Also bending should not be so bad with a float in its middle.

Conclusion
Neither Dr. Hait, nor the Rocky Mountain Research Center hold any responsibility for your project. This paper is strictly educational.

Contact Dr Hait

Please write and tell me how it worked.