Poraver - is this new?

Recently, I visited UT Tyler engineering department to view a concrete canoe. It was very interesting, and the faculty and students were very generous with their time and willingness to discuss the project.

There is an annual competition for undergrad engineering students to construct concrete canoes. This competition has been going on for some years; twenty-five I think someone said. The students typically perform a study of various concrete mixes, testing of samples, and a stress model of the boat. Each team decides their own strategy, so approaches vary. The competition includes a presentation of their engineering work as well as a boat race.

There is some knowledge of concrete boat building which has accumulated in this community. I will also point out that these canoes are not expected to have a long durable life which would be expected of most practical boats. Here is a link to some of their papers:
http://www.engr.wisc.edu/studentorgs/canoe/designpapers/index.htm

One item which was shared with me is Poraver. Poraver is a silica based material which is very porous.
http://www.youtube.com/watch?v=mLQE5PdCE_M
It seems that Poraver is commonly used in these competitions because of its relative low cost, and outstanding performance as an aggregate. It provides strength while reducing the weight. All of the competition canoes are produced with a concrete which weighs less than density of water (64 lbs/ft^3), usually resulting in a density of about 55 lbs/ft^3.

I would be interested in hearing of others’ experiences with this material in boat building, in particular its use in concrete matrixes for boatbuilding. I found on this forum that Richard suggested Poraver’s use with epoxy for an exhaust repair. I saw on Youtube where it has been used as a filler in building molds. These are interesting uses, and I’d like to hear about them. The use with concrete seems the most exciting however.

The porous structure and shape of the pores is particularly interesting because there is a bit of a dilemma regarding its pore shape. Poraver is widely used because it absorbs a relatively large amount of moisture, releases this moisture back to the cement reaction, and results in a light weight material. Although this material absorbs moisture, the students felt that the majority of the moisture was given up to the cement reaction relatively short term in the curing process. They did not have experimental data to quantify or backup this observation, but it might be worth further experiments.

I’d like to hear of other’s experience with this Poraver?

~ Michael

 

For some applications, it is a great material.

Examples:

making moulds of wing shapes (scale model airplanes) some laminate a couple of layers of glass over the wing, then box things up, and pour a mixture of Poraver and foaming epoxy in it. After cure, cover with a layer of thick multiaxial. Presto, a nice mould that will not twist or bend.

Making all 1500 or so panels for a building, all consisting of very irregular shapes, the exterior was laminated (with polyester and rocks, as per the designers specs). Then the irregular shape was filled woth a mixture of polyester and poraver, to make a smooth and flat rearside of the panels.

Most lightweight pourable concrete has its share of poraver in it.

Poraver, die Kugel die alles kan!

 

Herman,
Thanks for your reply. It seems that the examples of its use are broad, and light weight concrete is fairly common. I have found very little technical info on these concrete mixes however.


I've been searching the net and have found very little technical information on materials developed with this stuff. I've contacted the company trying to get some quanties for development work, so we'll see how it goes.

 

I guess the concrete mixtures are "secret" or at least not common. There are not many people mixing their own lightweight cement, I guess.

My experience is that samples are easy to get.

 

LOL, That industry does seem a little mysterious sometimes.

 

Poraver is just recycled, foamed glass.

I cannot comment on the properties within a concrete mix, but one can add it up to some 90% to epoxy, to get a extremely lightweight, but relatively strong filler. Or light structures when reinforced.

Regards
Richard

 

Thanks Richard,
That is good information.

Is that from your experience or a supplier's technical reference? What happens when you go to 95%?

 

Own experience. When over 90% it brakes, gets too brittle.

Regards
Richard

 

go to www.ic.gc.ca, and check poraver. It is interesting, and push your knowledge in the technicals. You will find all kinds of applications. Is this a product for the boat industry ?
I had throwned the idea of the come back of concrete hulls. Generally, concrete is a compression and filling material and i consider it as a transfering material. ie one should be aware at all times of its almost perfection state. Ask engineers about it, constant verifications of structures is necessary especially in corrosive environments.
Salt among others, is a constant preocupation in naval industry, the least hidden reactions is my main concern. If a material shows fatigue at the surface and you can see it right away it becomes interesting. I will study the fire resistance of this material for one of the greatest benefits of using concrete is exactly that. I am in the process of testing a product called Roxul, google it out on the web, my goal is to render epoxy more resistant to heat. No questions about it, sprinklers are essential on your island (being your boat) and if one can inbed light plastic piping material into a protective mass now your talking, will recycled glass do the job ? Don't know yet, i did research on very high temp. resistant materials in concrete, the results were interesting for a specific application. (3 x the strength and 2 x lighter ) i sold my company.
A tremendous bath of possibilities can come out of this new age concrete.

 

Yellow Cat, thanks for the link to ic.gc.ca but my site searches did not come up with poraver.

“Is this product for the boat industry? “
It seems that Richard has used poraver in special applications in the boat industry. I believe the appeal to him was its fire resistance properties, while still being relatively light weight.

It is my impression that it is not widely used in boats.

The high compression strength and light weight along with good thermal properties are attractive enough for me to investigate it a bit further. Oh, and relatively chemically inert.

I looked at the Roxul just now, although not extensively. It seems that it has the open cell structure (fibers) and will absorb water unless it is isolated by using another material. I would be reluctant to use glass wool or mineral wool as an insulation material in boats because of this property. As far as I can tell, poraver suffers from the same unattractive property; however, it may be a little easier to encapsulate the poraver on a bead by bead basis, thus creating an effective closed cell property. I don’t think the poraver thermal stability properties will be as good as Roxul. Poraver is made in a kiln at 900C, so I suspect its temperature limit is less, while the Roxul withstands temperatures significantly greater. However if using an epoxy resin, the limit to thermal stability is likely below 900C anyway.

I agree with you that there are a lot of possibilities to come out of a new age of concrete and materials technology. Portland Cement; silica; concrete - all have very versatile chemistry, and thus opens a lot of possibilities for new developments.

What came to my mind when hearing about the poraver – light weight, high compression strength, and probably relatively good shear strength – was that of a core material for a laminate. The open cell or moisture absorption may still be an issue, but the other properties are moving in the right direction for a core material. Perhaps a new laminate of carbon fiber on a core matrix incorporating poraver.

 

Water & Cement

Here is some of what I've come up with.

A crystalline structure would seal against the penetration of water and other liquids from any direction, however concrete is not a crystalline structure. Standard cement composites have micro-cracks, capillary tracks and pores which allow water penetration.

The chemical reactions in concrete typically absorb water. This stoichiometric ratio of water to cement is well known and is often referred to as 0.21 wcr, (water weight) / (cement weight) ratio.

Capillary tracks are left in standard cement composites because an initial excess of water is required in the mix to make a workable slurry. The excess water makes a mix that can flow and move, but when water leaves by drying, it leaves the matrix riddled with capillaries. These capillaries allow water to move freely through the mix; causes the mix to dry out much more rapidly than a capillary free mix; causes the dry mix to shrink significantly after it cures; and causes the resulting composite to be weak compared to a capillary free mix. Capillaries contribute to shrinkage, weakness, and permeability.

Our goal is to stop open capillaries around the closed spherical bubbles or cells. It is true that one should avoid using excess water because of this weakening effect. However more importantly, considering the desired properties, we want to create a concrete mix that does not result in open capillaries.

First consideration is the amount of water. A 90 lb bag of Portland cement reacts with about 19 lbs of water. This corresponds to a water to cement ratio by weight of 0.21 wcr. Many people have gotten lost in the maze of trying to equate the exact water content to the reaction conditions in the cement. One big reason is that aggregates’ ability to uptake, hold, and release water is complex. The aggregates uptake and release of water is related to particle size composition and gradient, and pore volume shape and size distribution.

If you baked the sand or aggregate in an electric oven, and used oven dried aggregate in your mix, when you added a precise amount of water to the mix, a portion would be sucked right back up into the aggregate and not available for the cement reaction. Without knowing the amount of water sucked back into the aggregate you don’t know the amount available for the reaction.

The industry practice is to monitor and control water content, then judge minimal hydration conditions through consistency of mix and make adjustments in water content based on experience. The goal is to ensure an optimal amount of water to the interaction boundary between aggregate and cement. Now, just what should we consider aggregate? What role does each aggregate component play in water uptake and release?

Air bubbles are part of the mix and must be included in consideration as a component of the aggregate.

Idea #1:
It would be desirable to have closed spherical bubbles (closed cells) that stop the open capillary tracks. We would like closed cell aeration which blocks moisture intrusion instead of aiding it.

Idea #2
It would be desirable to have increased fluidity of the mix with a water amount closer to the stoichoimetric amount of 0.21 wcr. A particle size small enough to fill interstitial spaces between the larger aggregate components, form chemical bonds with the cement matrix, yet does not uptake or release water – is expected to increase fluidity of the mix.


Not sure where this is going right now, but thought I'd share in case anyone else is thinking about cement applications in boats.

 

Wow, I have never been into cement, except for some low-tech casting of concrete in my house (not even structural).

Your text does make me think. Nice.