[walter]

woo-hoo!! #1502 :cheers:


O wait.. I need to report some problems


I was mixing E/G for the column of my Harbor Freight bench top drill and noticed something weird.

I will call it the "Lava effect". It's really annoying and affects the aggregate packing theories discussed here- to the point that it renders them useless. I'm sure I've had this problem before, but didn't make the connection (apparently, I am a moron). Plus, I've been using a lot of zeeospheres.. They change the flow and distort the overall picture.

The problem has to do with epoxy viscosity- aggregates are not really wetting - they're suspended in it like flies in the honey. How do you wet&compact flies in the honey? I'm serious!

Anyway...
This particular mix looked like thick volcanic lava- Lava with rocks floating on the surface. Impossible to mix and compact. Very fine aggregate seems to maximize the effect, which takes place at 15-20% epoxy content. Closer to 20% really.

So I'm going for 10% epoxy mix, but at 20% it turns into lava and I can't even move the stick. I'd say the air entrapment is the least of my problems at the moment?

But enough with this (chair)

So where's the party???
_

[ckelloug]

Walter,

Let's add Mixture rheology (flow characteristics) to the criteria list.

By flies suspended in honey, do you mean that the aggregate are sitting in the epoxy but they aren't wetting?

If so, this is a manifestation of the comment I made a few posts back about "type 2 voids". Such a mixture will be less strong than solid epoxy with no aggregate according to the rule of mixtures.

I'm going to post the criteria list in the index thread and then edit the post as changes occur.

--Cameron

[rancherbill]

I have been lurking for the last 850 posts.

I have two questions.

Some one told me that the only bumb question was one that wasn't asked. So here's my ?smart? questions.



Is there some type of surfactant that can be added to the epoxy, or to pre-treat the granite, to break down surface tension to reduce the voids in the mixture?



My son has a an "awesome" sound system in his car. I am impressed with the amount of mechanical enerrgy that is generated by these speakers as they make sound.

Is it reasonable to harness this energy to aid in compacting, degassing, void filling etc etc? Mechanical compaction has previously been mentioned with concrete vibrators. Speakers would be infinitely adjustable. I'm sure the guys in the electronics forums could design a simple wave form generator that that would allow for adjustement of frequency and amplitude. They would probably do it for a heartfelt attaboy.


Bill

[greybeard]

Walter - could you post a typical mixture that produced this effect ?
It sounds so different from anything you've done before.
Also any chance of a photo

Rancherbill - Hi Bill. I suspect that the "de-airing agents" that Cameron has mentioned might be something along the lines of a surfactant. I'm only familiar with their use in water based systems, but I'm sure there must be other, non-aqueous ones.

I think someone touched on the loudspeaker idea before. I can see that any vibrational energy source might be used. The difficulty lies in designing it to "couple" the energy to the mixture.

John

[Eson]

rancherbill: That wouldnt be very hard at all. Just connect a oscilloscope to the amplifier. But i think you need a very large subwoofer to be able to generate those 'slow' (for a speaker) and heavy bangs. Well i guess it depends on how large the mould is also.

Walter: If you mix the largest aggregates in the pure epoxy first you should be fine. And if you know a little about baking you should know that if you have too much flour you just knead the dough harder, try that.

[ckelloug]

Hi Bill,

Your comments are definitely on the right track in terms of vibration and surfactants. I suspect that the amplitude required might be staggering to use speakers; but for pure amusement value, look at Ling Dynamic Systems http://www.lds-group.com/

The company I work for rented time on some of these speakers which were 8ft in diameter and 10 feet high and capable of driving single hz type frequencies in the kilowatts!

I think sposl posted using a speaker for vibration back in <A href="http://www.cnczone.com/forums/showpost.php?p=280729&postcount=738">post 738</A>

The bonding and deairing agents are definitely like surfectants and there is a wide body of knowledge of using them to get epoxy to stick to stuff.

I just need to get my shop done to start testing some of the parameters involving them since nobody else is doing it.

Regards,

Cameron

[walter]

Guys, focus.. It's not the mix- it's the epoxy. I stopped heating it and this is the result. Didn't notice it before because I was heating everything since day one! Heat gunning the epoxy,mix, oven roasting aggregates, ect. But I did away with it because it's cumbersome and good for sampling not the real work. I mean how are you going to work that out with large pours: the epoxy is 40min but you need to raise the temp- every 10deg C halves the pot life. The amount of heat needed will shorten the pot life to 40sec! But you need 20min to mix/wet the aggregates. Are you going to put the mixer in your kitchen oven? And mix 100lb mould 5lb at a time?

My 80deg epoxy turns into thick honey at 15-20%. At 80deg ambient.

It's like flies in a honey jar- doesn't matter which size flies you put there first. hello!- you've got flies in the honey! No amount vibration will make it work, think about it

All these packing theories will work with air or water matrix. Any more viscosity than that and you can put any aggregate sizes you want- won't make any difference. That's why I stopped using scale to weight and proportion aggregates. Makes no difference.

That's why the big manufacturers are using water like resins. Boy, am I slow or what (chair)

[ckelloug]

Walter,

Do you have a picture of what happened and an approximate list of ingredients? I can visualize that it didn't work by your colorful description and the use of the (chair) very well but I can't visualize precisely what actually happened.

Knowing what exactly happened is a first step in fixing it.

--Cameron

[Geof]

Guys, focus.. It's not the mix- it's the epoxy. I stopped heating it and this is the result.... Didn't notice it before because I was heating everything since day one! Heat gunning the epoxy,mix, oven roasting aggregates, ect. But I did away with it because it's cumbersome and good for sampling not the real work......

I suggest putting some consideration into making the heating non cumbersome based on the thought that if you have low viscosity epoxy you may be able to mix in an almost conventional concrete mixer. This could be applicable to your real work volumes.

How about aggregate first into the mixer, rumble away with a tiger torch playing on the outside. Need I say you must use a steel drum mixer not one of the polyethylene drum type I have seen . Then pour in the epoxy mix and then into the mould. The vacuum treatment could possibly be done in the mixer as well. Just an end cap with a rotating seal to the vacuum line. Slap the cap on, turn on the vacuum, no clamps are needed it stays there.

[ckelloug]

The rotating seal in Geof's post could be accomplished by a hydraulic fitting according to one of the epoxy manufacturer's tips and tricks pages. Like StepperMoney mentioned in the dark ages, the flow properties during mixing may be improved by vibration.

Generally, smaller aggregates are more likely to cause the honey problem. I'll work on understanding Rheology (flow characteristics) next since that seems to be the need. The PC concrete guys have a whole set of stuff they add for rheology so it stands to reason that there's a set just like that for epoxy.

I'm strongly considering buying de Larrard's book too.
--Cameron

[walter]

Good suggestion Geof!

But I think I want to go one step further and eliminate heating entirely.

Nothing happened really.. The mix is in the drill column and working well. No fixing necessary

I just had another ah-ha! moment, that's all. Another piece of the puzzle fell into place.
I'm very happy now.

[greybeard]

The rotating seal in Geof's post could be accomplished by a hydraulic fitting according to one of the epoxy manufacturer's tips and tricks pages. Like StepperMoney mentioned in the dark ages, the flow properties during mixing may be improved by vibration.

Generally, smaller aggregates are more likely to cause the honey problem. I'll work on understanding Rheology (flow characteristics) next since that seems to be the need. The PC concrete guys have a whole set of stuff they add for rheology so it stands to reason that there's a set just like that for epoxy.

I'm strongly considering buying de Larrard's book too.
--Cameron

I see the deLarrard book is about £100 on Amazon.co.uk at the moment.

It just so happens that I've recently acquired an old cement mixer, but the thought of putting it under vac is somewhat mind bending.

Re my recent thought of a testing jig for samples, what about this idea. It incorporates a laser pointer with a "Greybeard's double mirror deflection multiplier" as a standard fitting.
I'm hoping that a measurable movement of the laser beam could be detected even with a fairly small weight on the sample. It assumes a x 10 multiplication of the beam deflection, and an optical beam length of about 6 feet, ie bench to ceiling.

John

[ckelloug]

Greybeard,

That testing jig is awesome and a sight to behold. You might need a hundred kilograms of weight or so for it if we can get out of this mode where looking at a sample causes it to self destruct. I needed another book on amazon so I clicked buy for it and a used copy of de Larrard's book before I chickened out.

www.asminternational.org is having a special on composite materials and plastics handbooks under their clearance section. I bought one of those too. I don't know whether or not it is helpful but for the $25.00 US price, it sounds like a steal. I think it is one revision out of date but that's 10 times the information I had before. asm used to be the american society of metals and they're one of the engineering societies that compiles materials data.

Gotta hit the library for rheology books and journals this weekend. Too bad I have a real job which I also have to do.

Really, good job on the testing jig!!! I've left some notes in a scribbled on copy of your diagram about making the standard jig from ASTM D790 but a library trip to xerox the equivalent ISO standard may not hurt.

--Cameron

[jkeyser14]

If vibration is needed to remove trapped air bubbles, speakers will indeed work very well. I recently visited a company that used speakers to test large metal parts in order to find their resonant frequencies. It didn't take a large amount of power, as the noise was bearable w/o ear protection (but I wouldn't sit there for a long time w/o it).

They used about 30 4" speakers to make a bed below a stand which the part was attached to at one end. A function generator along with several amplifiers was as complex as the setup got. The speakers put out enough power that when the part hit resonance, the tip would vibrate with a suprising amplitude.

I really can't say much more about it than that, but whoever mentioned the speaker idea for vibrations, it is possible, and if done properly, it would work.

[walter]

Here's something tasty


Quote"I myself have visited the monster polymer concrete/ epoxy granite thread (1500+ replies as of today) ... and well, no one is even close to doing what Dwayne has shown except for some German guys, and one US company that tipped their hat, but disappeared.. In fact, the closest anyone has come is filling their RF45 base and column with epoxy granite/quartz. It's mind boggling the amount of research and discussion from some seemingly intelligent folks but nothing to show for it. It does however bring up and point out how it could take Dwayne some many months to perfect things."


Hey Cameron.. Is that the same "Dwayne" who is buying premixed kits complete with resin from Accures for $0.85 a pound?


http://www.cnczone.com/forums/showpo...&postcount=385


http://www.cnczone.com/forums/showpo...1&postcount=10
_

[ckelloug]

According to someone from the HSM board, yes, it's the same Dewayne Harlow who posted back in the early days of the thread who I hear is buying materials if not parts from Accures. How he does it is unimportant, his product is as great as I can understand it to be without having one.

Is making our own E/G the easiest solution, no. Is it interesting, yes. Will it work? Eventually. Might it be better than the commercial solutions once the parameters are understood? Maybe.

This is a relatively hard problem that is close to state of the art materials science since progress in epoxy aggregate formulations seems to have stagnated 30 years ago after they discovered that between fire resistance and cost that E/G was not the next material for constructing buildings. It involves materials science, chemistry, rheology and the associated testing. It's a miracle that a random group on the internet has come this far.

I know I'll be here on this thread working at least until I have reproducible samples that exceed 2ksi flexural strength and a recipe to do so.

From the pictures that were posted of the German effort, they have parts, but the ultimate strength and modulus of the parts is not as high as I think it can go. The pictures I've seen of thick epoxy and uniform aggregate seem very much like the guess and check approach of PC concrete which has been stagnant but successful over that century and is only now having the mold broken to pardon the pun.

Cheers to all who read and post here,

Cameron

[lgalla]

Oh,OH More reading,sorry,but this deals with steel tubes with E/G to up the properties.Search Google for CFT,concrete filled tubes.
or[ epoxy concrete filled tubes earthquake resistance]
A copy:environmental concerns, it is now obvious that the evolvement and application of advanced composite structural materials to complement conventional construction materials is a necessity for sustainable construction. This study seeks alternative fill materials (polymer-based) to the much-limited cement concrete used in concrete-filled steel tubular structures. Polymers have been successfully used in other industries and are known to be much lighter, possess high tensile strength, durable and resistant to aggressive environments. Findings of this study relating to elasto-plastic characteristics of polymer concrete filled steel composite beams subjected to uniform bending highlight the enormous increase in stiffness, strength and ductility of the composite beams, over the empty steel tube. Moreover, polymer based materials were noted to present a wide array of properties that could be tailored to meet specific design requirements, e.g. ductility based design or strength based design.End
As Cameron stated,E/G has stagniated for 30 years as of cost,but earthquake resistance is a booming industry.Does this relate to what we are trying?I don't know,but our machines may be earthquake proof.
Larry
Cameron thanks for post#1498

[lgalla]

De-airing agents.
Can't find this info,but if memory serves me correct.I think de-airing agents work by expanding the entrapped air forcing it to the surface.In high filler loadings this may cause more problems as the thick mix may entrap the air and expand causing type 2 voids.Anyone have info on this?
Larry

[ckelloug]

Epoxy is a minor miracle: It sticks to anything unless it involves E/G. :boxing:

Another parameter that affects whether a given mix works is a property called surface energy. I have no idea why it occurred to me to check this out but it turns out to be of major research interest in various branches of materials science. While, like everything else in the universe, it works against us and E/G a bit, it provides a very scientific explanation for walter's latest complaint about bonding problems.

Surface energy is a measure of the energy required to form a surface in a given material. The nuances of the technical definition are beyond my power right now but I can say this: The surface energy of the aggregate has to be much higher than that of the epoxy while it is liquid, otherwise, it won't wet.

For aggregate, the surface energy is(units in ergs/cm^2):

Basalt = 72.8
Granite = 48.8
Quartz = 96.6

See our friends at the aggregate research center at University of Texas for more details:
http://www.engr.utexas.edu/icar/reports/505_2.pdf

For epoxy, the surface energy increases with the amount that the epoxy has set

For at least one epoxy at 80C the number varies linearly between 33 and 44 according to the percentage of setting that has been completed according the the following swiss paper.

http://www.unifr.ch/physics/mm/polymer/4.pdf

Considering that for granite, the numbers are almost even at setting time and quartz is only about twice as high at setting time, we don't get complete wet out. It does however likely explain why there were some tests in the NIST fire sciences paper where the quartz did better than the granite.

And that ladies and gentlemen explains why bonding agents, deairing agents and or fluoro-surfactants are likely essential to make samples beyond mediocre.

The bonding and deairing agents that I have posted about work by adding siloxane molecules that form covalent and hydrogen bonds to the aggregate and in the case of dowz6040 an epoxy ring to link the other end of the molecule into the crystal matrix of the epoxy. They don't work specifically by forcing air to the surface so much as by making the affinity between the epoxy and the aggregate higher.

About 3 eons back, I mentioned that I was also interested in fluoro-surfactants like 3M novec. Seeingst that we have surface energy problems (related to surface tension) put in the high tech soap and the bonding agents.

Like all things we seem to need, from the following link, fluoro surfactants seem to cost about 300 dollars a pound. The bright spot is that each of us probably only needs a couple drops and we might be able to share a single low cost/free sample between us for our research.

I haven't read this supplier's page thoroughly but I was so glad they posted prices that I couldn't resist posting.

http://www.cytonix.com/fluoroproducts.html

Walter's old standby, the cary company, carries the 3m fluoro-surfactants. I'm not up on fluoro-surfactants at the moment.

--Cameron

[Jay C]

Here's something tasty

My point being, that despite all for the bits/bytes/ideas you guys still are debating degassing, aggregate shape, fill factors. There is one highly motivated (though I can't see exactly why ... what's in it for him) individual Cameron that has made this a mission to engineer it to the best he can. Investing both time (lots of research) and money (books, supplies). This is getting close to "rocket science, and away from the initial intent as specified by you Walter and paraphrased by me as ... DIY polymer concrete (or E/G or whatever) machines for the home hobbyist.

None of this is meant as an insult, more of an "ah, ok, I see now and can cut Dwayne some slack" type of epiphany for both myself and the guys that have ponied up some money over the past 6 months. Or in short ... this ain't easy

FWIW,
Jay