[brunog]

Cameroun,
Is there a specific sample size required to do compression tests?

Bruno

[lgalla]

Walter ,quote"I used the Cabot Carbon Black substitute. It was somewhat difficult to mix, so basically I've overdone it. (chair)

I looked back at your pictures and saw you had some furnace black and Monarch 800 in the background.I have used Monarch 800 in the past and it works well.Did you use the other stuff?There is 57 or more varieties of carbon black.Rather than a huge tec explanation:Carbon black comes in many forms depending on application such as pigment for tires,paints,inks,dyes,EPOXY,etc.Some may have dispering additives such as oil which may affect cure.
I have used tons in mixes with no curing problems,but in our case I would only use enough to make it black as to much will make the mix thixotrop.Same goes for fumed silica.It will thicken the mix too much and reduce the aggregate ratios.
Larry

[lgalla]

WilliamD on the sister thread "polymer concrete tests"is beating the E/G with a hammer.

[ckelloug]

Brunog

Here is a web site I found that does compression tests of plastic materials:

http://www.ptli.com/testlopedia/test...ssion-d695.asp

They list their specimen sizes for the ASTM tests. I had the impression that bigger samples were used but my impression is for concrete and I imagine it's a different test.

--Cameron

[ckelloug]

Igalla,

Whacking it with a hammer is a start. If it shatters under the weight of a machinist's hammer, that would qualify as bad. Weighing the hammer and measuring the drop height might be a touch better. Squishing it in a press with a load cell would be awesome. I asked for a quote for doing tests of Young's modulus on samples from the lab I referenced in my above post.

Another possibility would be to make some E/G bars maybe a foot long and about an inch square and load them with about 100 pounds exactly in the middle with a jig and record the deflection. The length between the supports in the jig and the size of the bars would need to be extremely accurate as they are raised to the third and fourth power respectively in the deflection calculation.

[HBFixedGear]

Beware air of air pockets. This site deals in normal precast concrete but one would assume the machanics would be very similar.

http://www.precast.org/publications/...nVibration.htm


There are a raft of companies making concrete vibrators for air removal DeWalt and makita even make hand held versions.

B

[lgalla]

WilliamD is bashing E/G with a hammer and finding it industrucatble with thick epoxy,straight sand and high epoxy ratios.Correct me if I am wrong,but speed3317 and sposl or sandi are finding their material brittle.An assumption is 8to12% epoxy ratios and coarse aggregates are difficult to wet out and have lots of entrapped air,resulting in brittle composites.Correct vibration is necessary for the low ratios.10% epoxy is a thick paste and normal concrete vibrators may not be up to the task.
Larry

[romihs]

WilliamD is bashing E/G with a hammer and finding it industrucatble with thick epoxy,straight sand and high epoxy ratios.Correct me if I am wrong,but speed3317 and sposl or sandi are finding their material brittle.An assumption is 8to12% epoxy ratios and coarse aggregates are difficult to wet out and have lots of entrapped air,resulting in brittle composites.Correct vibration is necessary for the low ratios.10% epoxy is a thick paste and normal concrete vibrators may not be up to the task.
Larry

Hello all,

The 8% mix was rather porous, while the 12% mix came out much better. Also, the 12% brick weighs 25% more than a brick of similar size made of 8% E/Q, implying that the 12% mix compacted better than the 8% mix.

I noticed that two of the 8% bricks which where leaning one on top of the other had 'dented' each other. They were lying on the table for several weeks. This just goes to show how plastic the epoxy is. I don't expect that this will happen to the 12% mix as easily... I hope not!!
This got me thinking of ways to test the samples too......

Testing has come to a halt... No time, still shopping around for a scale, working on the vibration table, ....

Regards

Sandi

[ckelloug]

I just got off the phone with Dan Callahan, an applications engineer for Carbon Black from Cabot Corporation. He was exceedingly helpful and agreed to send me a sample of Monarch 120 and Monarch 800. Perhaps we should consider Cabot as our "official" Carbon Black Supplier.

Dan suggests Monarch 120 due to the higher particle size over Monarch 800 as it will be easier to disperse into the mixture with the ad-hoc mixing methods that we have. He suggests that Monarch 800 has much smaller particles and will tend to not disperse thoroughly in the mix with ad-hoc mixing methods leading to surface defects. He suggests using a media mill like a shot mill or a ball mill to grind up the carbon black and disperse it thoroughly. I told him we would be mixing sonically using 6khz (as the patents we have read described) and he thought it might work.

Dan said that we could expect to see greater viscosity and stiffness of our epoxy composites along with lower flexibility at the cost of some impact strength. AKA, it should improve Young's modulus and decrease creep but hurt Charpy and Izod tests. Carbon Black will also increase the viscosity of the uncured epoxy.

As lgalla said, an epoxy mixture with carbon black or silica fume is thixotropic and will almost surely need an appropriate vibration solution to keep it flowing. With the size of the particles, it will probably need to be much higher frequency than a concrete vibrator (I don't have any data though). It might be worth mixing some carbon black and epoxy resin without hardener and seeing if we can figure out how much carbon black is required to make the mix thixotropic and what vibration is necessary in terms of amplitude and frequency to get it moving.

Finally, I saw these guys who make relatively sane looking epoxy metering equipment and also sell not completely outrageous scales although Salter electronic food scales from Williams Sonoma and other sources aren't bad.

See http://www.michaelengineering.com/index.htm

[lgalla]

Cameron thanks for your research.
I would not bother using carbon black as a filler,only a pigment which would be less than 1% and not thicken the mix.
Some observations:WilliamD has unbreakable samples using only sand and thick epoxy at 25%.The 8to12% ratios are breaking.Why?William is getting a better mix with less air.An 8% mix will be so dry there is not enough epoxy to glue it together.I am not discounting low resin ratios,but to be good mixes proper vibration is necessary.
From Sandi's last post:
I noticed that two of the 8% bricks which where leaning one on top of the other had 'dented' each other. They were lying on the table for several weeks. This just goes to show how plastic the epoxy is. I don't expect that this will happen to the 12% mix as easily... I hope not!!
Sandi this made me think.At 8%there is so little epoxy between the aggregates it will slow the cure.The epoxy is micro thin and crosslinking will be a long time.Lets say you have an epoxy with a pot life of 35 minutes and brush a thin layer.It may not cure in 12 to 24 hrs.The thin layer cannot produce enough self heat to cure in a reasionable time.
Solutions:
Lets say you have 35minute pot life.
Mix A&B for 6or7 minutes
Leave it for 10 minutes to allow for crosslinking to start.We call this "Sweating"
Add carbon black or other pigment at this time.
Next add the larger aggregates first then the fines.
Then pour,vibrate,vacuum or whatever.
At 20 minutes the reaction should be started and will cure better
Larry

[ckelloug]

I am beginning to think that these slabs will have to be cured in an oven or with heat lamps. One of the epoxy vendors I was looking at suggested that approximately never was the cure time for the low viscosity epoxy below 80F (weeks). I must say however that I am a systems engineer, not an epoxy guy like Larry so I'm strictly making my observations based on book learning, not experience.

As for carbon black, it may not be appropriate in all cases. I would point out however that silica fume and carbon black strengthen the mixture by a different mechanism than large aggregates and thus provide additional strength beyond what is possible with large aggregate alone.

They are dispersion hardeners, not fillers like aggregate. In ordinary concrete, materials of this class are called pozzolans and they are used in heavily engineered ultra-high-strength concretes. Such nano-scale materials as carbon black and silica fume may be hard to work with and perhaps not appropriate for the home shop environment but they are inexpensive and represent a strength improvement in addition to the other things we can do if we can figure out how to incorporate them into the recipe in a usefully.

Finally, I've started on the interface for my java application for beam strengths. My initial application is slated to solve the Beam deflection equation in the case of no shear.

I plan for the following options initially as they are easy to do:

Given Force at beam center , beam length, material, and either side length of square beam or diameter of round beam: solve for deflection

Given Force, beam length, deflection, solve for side length of square beam and diameter of round beam

Given beam length, acceptable deflection, side length of square beam or diameter, solve for maximum load at beam center.

If anybody has any suggestions for other functions for the application, I'd love to hear them.

--Cameron

[brunog]

Thanks to Walter<s photos, I made this gizmo from a 5/8-11 allthread coupling, 1 1/2" long threaded rod, flat washers and regular nut.

I have attached it to a 1hp 3450RPM 110V motor I had salvaged from a pool pump.

Let me know what you guys think of this oddball item.

best regards

Bruno

[brunog]

I get kicked out of my posts all the time!!!

Based on Walter's vibrating pot photos, I made the gizmo on the prior post with a 5/8-11 allthread coupling, 5/8-11 nut, flatt washers and a 1 1/2" piece of threaded rod.
The only parts missin to it are 3 10-32 set screws to prevent the assembly from falling apart.

Bruno

[lerman]

I would be concerned about the life of the motor bearings when driving an unbalanced load. I'm sure the bearings weren't designed for that.

Ken

[jkeyser14]

Has anyone considered using Garnet (SiO4) instead of granite (SiO2)?

Here's the deal: It's an abrasive used for waterjet cutting, costs $.25 a pound, and has sharp corners. However, after the abrasive is used, it's usually scooped out of the tank and thrown out. Some people dry it and reuse it, but it severely affects cutting time because the sharp corners become rounded during cutting.

So if you find a local place w/ a water jet, and wait till they clean out their tanks, they will most likely give you used abrassive for free since it means that they don't have to pay to have it hauled away. This would lower your costs to that of epoxy. Also, garnet is pretty dense, weighing in at about 140 lbs per cubic foot.

[walter]

Looking good Bruno! That should give you some good vibrations..

I went a step further and plugged it into a rheostat. All I need now is another motor with another rheostat, so I can work both sides of the mold. Crossing frequencies should be fun.


Cameron,
Did you get the test lab price quote? What are we looking for, tension/compression, density? Any other tests?


Larry,
Small particle theory sounds interesting. My size 40 fine quartz has average particle size of 2.8 micron. Could this be the ticket?

[romihs]

Cameron thanks for your research.

From Sandi's last post:
I noticed that two of the 8% bricks which where leaning one on top of the other had 'dented' each other. They were lying on the table for several weeks. This just goes to show how plastic the epoxy is. I don't expect that this will happen to the 12% mix as easily... I hope not!!
Sandi this made me think.At 8%there is so little epoxy between the aggregates it will slow the cure.The epoxy is micro thin and crosslinking will be a long time.Lets say you have an epoxy with a pot life of 35 minutes and brush a thin layer.It may not cure in 12 to 24 hrs.The thin layer cannot produce enough self heat to cure in a reasionable time.

Larry

Larry,

The epoxy I use (I should rather say the hardener) is a very slow curing one.. Here you will see the data on the epoxy and hardener (EPH294) I have used.

If your theory is correct, I would have to wait months for this to cure fully at room temp.
I have as yet to post-cure the experiments I have made.

Thanks for the feedback.

Regards

Sandi

[ckelloug]

Walter,

I didn't get the test lab quote yet. I will have to use that obsolete communication system favored by Industry: the telephone and call them tomorrow. Ideally, tensile and compressive strength and tensile and compressive moduli are all things we want to know. If we know the moduli then we can predict the deflections in machines built with our composites. The ultimate strengths will let us know how much load parts will take before breaking. Since you guys doing the experimental work are making large samples, I'd say that a food scale and a ruler will do just fine for density measurements.

Precise measurements are only worth investing in if we think it is possible to repeat what was done and make more of the same material tested. Good notes on what has been done will be very helpful when the time comes to formally test recipes.

In a composite beam without reinforcement like rebar etc, we will ultimately be limited by the tensile strength of the material.

One interesting idea both to improve tensile strength and to null out static deflection due to the wight of a beams is post tensioning. If some small tubes are cast into the beams below the neutral axis, one could insert some high tensile strength bolts or perhaps some music wire with the appropriate fittings after the cure running through the tubes. One could then set the beam on parallel rails on a big epoxy surface flat sitting with the ends supported on parallel rails. Using a dial indicator and a dial indicator stand, one could carefully tighten the bolts/wires in the bottom of the slab and null out static deflections resulting in a beam that is perfectly straight under the normal load conditions. Since the tension wires would only contact the ends of the beam, they should not transmit vibration unlike embedded rebar. This may be a completely stupid idea as it's a touch complex but it is similar to what is done in certain types of engineered concrete bridge spans and it can be used to fully remove static deflections.

As for small particle dispersion reinforcement, I believe 2.8 micron sand falls into the large particle category. Callister, my materials textbook suggests between .1 and .01 microns for dispersion reinforcement candidates. That pretty much leaves carbon black and silica fume. Fortunately, Cabot makes silica fume as well so I'll call my newfound apps engineer friend over there and inquire. I have no real data on dispersion hardening as it appears to be mainly black magic in determining what works for given conditions. I'm going to see what I can dig up. The Cabot engineer did say that smaller particle sizes make it more difficult to disperse the pozzolan into the matrix e.g. mix the goo.

P.S. I am an expert in severely over-engineering things so let me know if and when I have flooded the thread with an overabundance of ideas. It should also be noted that I am on sabbatical from my real job right now (so I can finish building my shop) and I am having a blast here getting the brain exercise trying to make this E/G thing work well.

[lgalla]

Sandi,WOW I have never heard of 400minute pot life.Take my previous sugestion and "Sweat it"Do a sample mix and let it sit for 200 minutes before adding aggregates.Check the temperature if it is getting hot add the aggregates.Your hardner choice needs post cure.296 would be a better choice,eg.25minute pot life.A 25 minute pot life will probably be hours with the aggregates.
Walter you have micron silica,sand,epoxy,carbon black,Zeeospheres,vibrator in the works,etc.Do you have a hammer???
Cabosil and other fumed silicas.01 micron are thixotrops which thicken the epoxy at very low ratios and the cost is high.A very low % will result in vasoline consistancy.It is designed to prevent saging on verticals.It would not allow heavy loadings of larger aggregates.Here is an example I coppied ;
Normally, Cabosil is added at a 1% to 7% proportion based on the weight of the liquid (resin, hardener, thinner) involved. Because resin and Cabosil have such different densities, weight proportions are awkward. For example, one gallon of polyester weighs 9 pounds; 7% of 9 lbs is 10 ounces, which for Cabosil is about 1.25 gallons by volume. For many situations, volumetric proportions are more convenient. A gallon of resin and a gallon of Cabosil is a 50/50 ratio by volume, but only 5% by weight. Incidentally, this 50/50 volume ratio results in a resin consistency about like vaseline. Lesser amounts yield a more liquid consistency, whereas greater amounts yield thicker pastes. The exact amount used is determined by the application. The addition of Cabosil has no effect on such properties as pot life, cure time , etc., and only affects strength to the degree that entrapped air reduced cross-sectional area.

Larry

[Geof]

Has anyone considered using Garnet (SiO4) instead of granite (SiO2)?

Here's the deal: It's an abrasive used for waterjet cutting, costs $.25 a pound, and has sharp corners. However, after the abrasive is used, it's usually scooped out of the tank and thrown out. Some people dry it and reuse it, but it severely affects cutting time because the sharp corners become rounded during cutting.

So if you find a local place w/ a water jet, and wait till they clean out their tanks, they will most likely give you used abrassive for free since it means that they don't have to pay to have it hauled away. This would lower your costs to that of epoxy. Also, garnet is pretty dense, weighing in at about 140 lbs per cubic foot.

This was suggested back in Post #200