[ckelloug]

Rockingjess,

There are various bits of information in this thread about such things but I don't think there's a good answer here for you yet.

Given the problem that you mentioned, I would imagine that buying a piece of this material would be a lot easier and less costly than the amount of setup it will take to do an adequate job of making your own piece out of epoxy and aggregate:

http://www.fireslate.com/pages/home.cfm

If you have more specifics, post them and perhaps someone will be able to provide you some more information.

Regards,

Cameron

[lgalla]

Cameron,Wollastanite appears to be a good filler as its aspect ratio provides re -inforcement but at the expence of hardness.4.5 on the Mohs scale.
Double that for mica flakes whose aspect ratio appears to re-inforce,but it has extreme softness.2.5 on the Mohs scale.
From your extensive research,in your opinion are spherical and smooth rounded aggregate best?I assume smooth aggregates will entrap less air and help de-gassing.Sharp angular aggregate will have an aspect ratio to provide re-inforcment,but concentrate stresses to the points,possibly causing micro cracking.Spheres tend to arrest micro craking.
Thanks for all the time you spend on the issues.
Larry

[gerryv]

I've not followed the whole thread, it's long, but if it hasn't already been mentioned you might want to check out a product called "Ductal", a super concrete. - Gerry

[ckelloug]

Gerryv,

The ductal product you sent the link on is interesting and has properties similar to the E/G product we are researching making and in some cases better properties. It is a commercial product and I would assume it is expensive. I didn't get a sense of the vibration damping qualities from my perusal of the spec sheet. This is however one of the first engineered concrete products I've seen that starts to incorporate materials science instead of brute force pour and test techniques.

We're trying to make an inexpensive epoxy composite out of cheaply available materials so this isn't what we're doing but it's a good read none-the-less.

Thanks for the post.

[PlasticWorker]

As you may have noticed from ckellong's link to Firestone, most if not all concrete counter tops are made from a fairly standard concrete / water mixture. You can make your own if you are so inclined.
Make a mold from plywood pre laminated with melamine or "formica". Two inches is a good thickness.
Use dry colors to make a shade you like.
Use as little water as possible. Acrylic bonding agent also helps the strength.
Tamp and screed the the mixture into the mold.
After it cures for a week, demold and turn right side up. Scrub the surface. after it drys, seal with a concrete sealer. ( It will get darker).

Sorry to all of the on topic posters, just trying to help.

[greybeard]

Gerryv,

The ductal product you sent the link on is interesting and has properties similar to the E/G product we are researching making and in some cases better properties. It is a commercial product and I would assume it is expensive. I didn't get a sense of the vibration damping qualities from my perusal of the spec sheet. This is however one of the first engineered concrete products I've seen that starts to incorporate materials science instead of brute force pour and test techniques.

We're trying to make an inexpensive epoxy composite out of cheaply available materials so this isn't what we're doing but it's a good read none-the-less.

Thanks for the post.

I've just read one of their technical library articles published in 2002 which gives an interesting description of the way they've developed an increase in the "toughness" and "strength" of high performance concretes, (I thought they meant the same till I read the article !), by working on all the components.
Although the product is very different from what is being attempted here, the difference between the traditional idea of a concrete mix and what they have developed is quite remarkable - out go large aggregates, in come fibers of various types, for example, - and while it's dangerous to argue by analogy, it does suggest that there might be lessons to be learned, and radical new ideas to be discussed and tried.
And the emphasis has to be on "tried"......

John

[ckelloug]

Greybeard,

Fibers are another very valid method of reinforcement. I saw that the main ductal product was reinforced with metal fibers. The governing equation for fibers is different and the required chemistry to get good adhesion might be different but they are very much composites. The aerospace industry has a lot of fiber composite experience and there is a lot of research in epoxy-fiber composites.

The 1 second intro to fibers is that they must be longer than a critical length which is about an inch for carbon and glass fibers to be used to maximum effect. I don't know the critical lengths for metals off the top of my head. Materials can be made with either short or long fibers and a piece made with short fibers that are parallel but not a single piece can be 95% as strong as a piece that is made with solid fibers in it. For randomly orinted fibers, the piece is 1/5th as strong as a piece made with full length fibers.

The principles behind epoxy carbon fiber and epoxy glass fiber are well documented in books in any university library. I don't really know how they compare in vibration damping performance but I do suspect the cost is higher.

Regards,
Cameron

[ckelloug]

Materials have a number of properties which have similar sounding names and have a goal of confusing people. The following all are distinctive material properties.

<OL>
<LI>Tensile Strength
<LI>Tensile Modulus
<LI>Compressive Strength
<LI>Compressive Modulus
<LI>Flexural Strength
<LI>Flexural Modulus
<LI>Poisson's Ratio
<LI>Fracture Toughness
</OL>

Tensile strength is the property of a rope when you pull on both ends until it breaks.

Tensile Modulus is the ratio of the force applied per square inch to the elongation.

Compressive strength is the property of a piece of new bubblegum which represents the force it takes to see the surface crack.

Compressive modulus is the ratio of the force applied per square inch to the shrinkage in the direction of the applied force in the chunk of bubblegum.

Flexural Strength is the strength required to break a pencil in half when it is supported at the point and the eraser ends and a force is applied in the middle.

Flexural Modulus is the ratio of the force applied per square inch of cross section of the pencil to the amount that the center moves towards the desk when the force is applied.

Poisson's ratio describes the amount that the chunk of bubblegum gets wider in one direction when it is squashed in another.

Finally, fracture toughness is the material property that describes how much mechanical work it would require to cause a crack in a brittle material like glass to continue all of the way through the material and severe the piece. (Almost all the materials that we deal with on this thread are brittle except for metals).

<B>Putting the Pieces together</B>

In E/G, the fracture toughness of both the aggregate and the epoxy define what the flexural strength of the material will be.

Tensile strength is of minimal interest as most machine designs don't use tensile loading. Compressive strength is good to know but usually requires forces too high to be testable without large presses. Flexural strength, the only one that is both relatively useful and measurable is the "strength" that governs most E/G machine parts like beams and tables.

<B>Stretching: the Truth</B>

The biggest problem in making E/G metal cutting machine parts is that a beam of E/G with weight on it will sag in the middle. (All materials will sag but E/G sags more). This sagging is proportional to the flexural modulus. It is very possible to make a beam that is quite strong but sags a bit under load (not good for a machine tool but okay for a house). It is also very possible to make a beam that is much more rigid than the first beam but fails when only a few pounds of load are applied (also bad since that might free a 10hp router to fly around the shop). Flexural modulus of an E/G part is most affected by the tensile, compressive, and flexural moduli of the aggregate and the same parameters in the epoxy.

<B>The School of Hard Knocks</B>

To make epoxy granite that is difficult to break, the fracture toughness of the aggregate and the epoxy are the most important. Synthetic Fused Quartz is inferior to natural quartz which is inferior to flint which is much inferior to aluminum oxide. Brittle materials fail by cracking through rather than by stretching like chewed bubble gum where the strand becomes thinner and eventually breaks. A general trend amongst the small particle aggregate under consideration is that materials with a high fracture toughness also have a relatively high modulus.

The most important thing to remember is that smaller aggregate generally has a higher fracture toughness than larger aggregate. The general reason is this: any piece of aggregate of a given size most likely broke off of a larger piece of aggregate when a critical flaw in the larger piece reached it's griffith stress. As a result, each time an aggregate breaks under an applied load, most of the flaws for a given stress level are eliminated by the fracture and all remaining flaws in the fractured pieces have a higher griffith stress than the original piece. If this is repeated until the aggregate pieces become very small then the tiny pieces of aggregate end up being very difficult to further break.

<B>Keeping it Together</B>

All of this talk about measurements and aggregate means that it is necessary too to consider the interface between the matrix and aggregate. This is most often ignored by materials scientists because the interaction itself is mainly a chemical affair involving covalent and hydrogen bonds between the matrix, the bonding agent and the aggregate.

In general, a bonding agent such as a silane based agent works by having a chemical group with mineral properties on one end of the molecule and adhesive properties on the other end. Dow Z6040 has silica on one end and epoxy on the other for example.

Epoxy tends to be very versatile and will bond with most surfaces that have either acidic or basic chemical groups attached. The main place where this doesn't work is in long chain polymers whose regular structures do not contain chemical groups that interest the epoxy molecules.

That being said, most epoxy will stick to most aggregates as long as everything is free of contaminants. It should also be noted that most epoxy sticks to most aggregates a lot better when it has a silane with a high chemical affinity for the aggregate providing a bonding site.

<B>Putting it all together</B>

An epoxy with as high a tensile strength and as low a viscosity as practicable when mixed with an aggregate with as high a fracture toughness as practicable, combined with a bonding agent that has an epoxy ring on one end and a siloxane group on the other is likely to perform maximally well when accompanied by a dispersion hardener.

<B>Remaining hurdles</B>

The remaining hurdles in order of severity are:

<OL>
<LI>Aggregate Size Distribution
<LI>Aggregate Maxium Size
<LI>Thorough Deairing of the mixture to avoid type 2 voids
</OL>

We can tell from fracture toughness that smaller aggregate is stronger. We know from Gupta and Gamski that there is an ideal average epoxy thickness over the estimated aggregate surface areas around 30um. This leads to the possibly unwarranted assumption that particles near in size or smaller than 30 micrometers make the total epoxy required go up quickly and we know from the rule of mixtures calculation that increasing the epoxy fraction beyond this point is bad for all parameters.

Barring rheological considerations about the material being pourable or transferable from its container, it seems that the practical limit is probably about 60um at the low end except for dispersion hardeners and 5mm at the high end based on the handbook comment that 5mm sand generally has awful fracture toughness.

Because it is generally impossible to achieve the dense pack figure of 75% for a single size of aggregate, it is necessary to use multiple sizes. The handbooks I saw indicated that Fuller's ratio is tuned for some of the water and aggregate problems in PC concrete rather than maximum possible strength and modulus. AS a result, it appears likely (at least to me) that the best distribution will either come from further study of the NISS paper on statistical aggregate simulation or research from the rather expensive and rare book on the subject by de Larrard posted earlier.

Deairing is a simple matter of using vaccum and possibly deairing agents and people can draw their own conclusions on what works for them with the concensus seeming to be that less than 28 inches is probably ineffective and more than 29.75 inches is overkill.

Regards to all and especially John for asking the question that promulgated this post,

Cameron

[walter]

Hi everyone, just a quick update on the name change.

I wanted to start a separate "Epoxy-Granite" thread to better reflect what we're doing here, but was advised against it. Then the name change idea came up and the Moderators sort of went with it (and I appreciate that very much). They also helped us with an Index to this particular thread and made it into a Sticky. The Index will help you navigate through the main thread, find documents, pictures, etc. Please continue to post here- the other thread is for indexing purposes only.

On or off topic- it's all welcomed!
We want this to be the friendliest place on the Zone

Thanks for all the suggestions and feedback.

Cheers!
_

[lgalla]

:violin: I feel badly for quartz being outlawed as a good aggregate.Good or high quality granite is 60 or 70 % quartz.Does this also outlaw granite as a filler.Copy from a paper"
Synthetic Fused Quartz 0.7
Spinel 1.3
Chalcedony 1.3
Chert 1.4
Flint 1.4
Agate, Banded 1.8
Sapphire 2.1
Aluminum Oxide 3.9
Silicon Carbide 4.0
Silicon Nitride 4.0"
Synthetic fused quartz is basically melted quartz,or glass.Most items on the chart are gemstone minerals.You cannot walk in to a supplier and get a bag of spinel.Surfing for fracture toughness on granite produces little info.
Cast iron is full of micro cracks and the reason for damping properties.
Some machine builders use quartz as a high end aggregate.Nearly all sands and small aggregates will have high quartz content.In our case,is fracture toughness the ability to resist hammer blows or forklift bumbs.
Fracture toughness of aluinium is 36Mpa,steel50Mpa.From the Mpa's they appear to be better choices,but we know their damping sucks.Steel or alu will bend of flex to reduce fracture cracking as they are ductile.Ducile= vibration.We are attempting to reduce vibrations with extremely stiff materials.Hope someone understands my jist,I don't
Larry

[ckelloug]

Larry,

I wouldn't outlaw quartz or granite just yet. They are just more likely to crack under stress. Very similar to engineers My comments on strategy above are based on making an epoxy aggregate combination with the absolute maximal strength. Maximal strength is likely not be necessary for most E/G machine parts but I find it interesting to explore that part of the problem space because making the minimum strength material appears to have already been accomplished.

The precise characteristics for transmitting vibration are relatively complicated. From my understanding, it is a combination of the density, the damping properties of the material, and the modulus that are the main factors. As metals go, Aluminum is one of the worst. I am not sold on ductility being the prime cause of vibration transmission.

Because epoxy has a low modulus and a much higher viscous damping than metals or aggregates, even epoxy diamond would probably have good damping. Epoxy diamond would probably not do as well from a fracture toughness standpoint as say Epoxy Boron Nitride however But before I digress and get more silly. . .

I cited the mineral data for fracture toughness because it was available and depending on the exact location of the quartz quarry you are using, it may behave similar to the other materials or be sold as quartz. The paper from the minerologists called them forms of quartz.

Many of the others like garnet (for which I do not have data) as well as silicon carbide and silicon nitride are available as abrasives and thus probably cost effective on the order of quartz.

I've blithered enough on this thread lately and it's once again time to quit for the day.

--Cameron

[greybeard]

Time for a party - we've just passed the 1500 post mark, so to entertain you briefly, a link to something very silly but somehow wonderful.

http://www.youtube.com/watch?v=D2f1KEEtRyk

John

[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