[greybeard]

If you have a uniform filler ie just one material of a single size, the possibility of uniform packing rather than random packing is high. This will allow crack propagation very easily along the plane of the packing.
The whole point of a mixed size aggregate is to force any micro crack that is trying to grow through the material to keep changing direction.
Each time it does so, it loses energy, and eventualy stops, so no macro crack appears.
I'll try and find a book I have with a title something like "Why materials are strong", possibly by David Pye. Good explanations about engineering qualities of reinforced materials.
John

[hansa]

WTF are you guys making??? :O :O :O

[lgalla]

WTF are you guys making??? :O :O :O

Hansa we are making choclate carmel cookie bars for machine bases.

[walter]

Larry's right. Here are the latest samples:

[victorf]

Consider a slab of granite. Find a custom countertop builder and check out their inventory. I live in a small town in upstate New York and there are at least two locations that have ample supplies of granite in various thicknesses and color. A bit pricy, but they will cut it to any size on their CNC machine. I have seen slabs up to 10' x 6' and 2" in thickness. This stuff comes in a uniformly polished condition. Check it out!

Just my two cents!

Vic

[Geof]

...I'll try and find a book I have with a title something like "Why materials are strong", possibly by David Pye. Good explanations about engineering qualities of reinforced materials.
John

Not by Pye, authored by J. E. Gordon: "The New Science of Strong Materials or Why You Don't Fall Through the Floor".

Also same author: "Structures or Why Things Don't Fall Down".

Quite old now but well worth reading.

[greybeard]

Geoff you beat me to it. Having discovered my copy had vanished I've just searched it on Amazon and found the details you've just posted. So I'm in for another copy as it was an essential part of my technological education

Regards
John

ps David Pye (designer)was another influence on me about the same time, hence the link in the old grey cells.

[Geof]

Slightly younger grey cells win again:banana:

It also helps having both books within arms reach on my desk. Along with:

"Metals in the Service of Man" by William Alexander and Arthur Street. Well worth reading even for people who are fanatics about composites .

[greybeard]

Geoff - if it's in front of you, there is a reference to a fairly universal maximum % solid filler that is still mixable/pourable, if memory serves, which may be relevant to the current discussion. In fact lots of useful data on building aircraft carriers out of sawdust and ice etc. All good stuff.
John

[ger21]

In fact lots of useful data on building aircraft carriers out of sawdust and ice etc. All good stuff.
John

A few years ago, while on vacation in the canadian rockies, we spent a few nights in a little cabin on a lake. At the bottom of the lake, is the prototype of your ship.

http://www.canadacool.com/COOLFACTS/...ftCarrier.html

[Geof]

Geoff - if it's in front of you, there is a reference to a fairly universal maximum % solid filler that is still mixable/pourable, if memory serves, which may be relevant to the current discussion. In fact lots of useful data on building aircraft carriers out of sawdust and ice etc. All good stuff.
John

You mean page 165 in the chapter on Composite Materials? Where..... Geoffrey Pyke showed that adding 2% ordinary paper pulp to water before freezing greatly improved the properties of ice.....

But this does not mention anything about the maximum wood fibre concentration for mixing. My own recollection, I can't remember from where, is that wood pulp above about 6% in water becomes unmanageable; the slurry is too thick to do anything with. But this is not relevant to the epoxy/rock situation. Wood fibres swell in water and also the water molecules sort of stick to them. This lowers the free water volume and effectively makes the water coated fiber concentration higher. This type of interaction is not present with the epoxy.

[greybeard]

I had at the back of my mind a figure of 15% solids in liquid( might be the other way round 15% liquid in solids) becomes too thick to stir, and that this was a general observation of whatever the mixture was. I thought it was in that book. The example of quicksand was cited.
John
ps thanks for the Habbakuk link

[Geof]

I had at the back of my mind a figure of 15% solids in liquid( might be the other way round 15% liquid in solids) becomes too thick to stir, and that this was a general observation of whatever the mixture was. I thought it was in that book. The example of quicksand was cited.
John

Okay I read in a bit more detail (my machine is still boring holes so I am also being productive.) I was wrong about the 6%, Gordon says anything above 2% fibers in water becomes too thick to pump. Above this you have to go the fiberglas route; pack the fibers as tight as possible then saturate them as much as possible with the resin.

But non of this is directly applicable to the epoxy aggregate situation. And so far quicksand has not bubbled up.

[lgalla]

RELATIONSHIPS OF CONCRETE STRENGTH TO MAXIMUM SIZE AGGREGATE
Accession Number: 00217627
Record Type: Component
Abstract: THE CONCEPT THAT CONCRETE STRENGTH IS BENEFITED BY USING THE LARGEST MAXIMUM SIZE OF AGGREGATE PRACTICABLE IS DISPROVED. IT WAS FOUND THAT MAXIMUM STRENGTHS IN BOTH FLEXURE AND COMPRESSION WERE SECURED WITH COARSE-AGGREGATE OF ABOUT 3/4 IN. MAXIMUM SIZE. USE OF COARSER AGGREGATES, IN SPITE OF REDUCTION IN MIXING WATER, CAUSES A REDUCTION IN STRENGTHS. THE CAUSE OF THIS REDUCTION OF STRENGTH WAS SOUGHT IN CONCEPTS THAT GREATER SURFACE AREA FOR BOND AND CROSS-SECTIONAL AREA TO RESIST SHEAR ARE AVAILABLE WITH THE USE OF SMALLER SIZE AGGREGATES.
Supplemental Notes: Vol 38, pp 367-385
TRIS Files: HRIS
Authors: WALKER, S ; Bloem, D L; Gaynor, R D; Gray, J E

Anyone have info on aggregate size.vs strength?I assumed the larger aggregates provided more strength,but It appears this is not so.Larger aggregate can cause cracks which are longer than with smaller aggregate.Smooth or rounded aggregate are isotropic reiforcments.The question was brought up seeing some of the guys are trying sand only.
Would a mix of fines only, have better specs than one with 1/4 and1/2" aggregate?
Here is something from one of my plastics books:
"Spheres clearly have no aspect ratio to provide reinforcement properties,but their geometry affords important advantages.
Unlike fiber with its directional strength,the spheres effects are isotropic.Photoelastic stress is concentrated at the ends of a fiber,the edges of a flake or irregular particle,but stress around a sphereare even and predictable.spheres distribute stress evenly throught the matrix"
Smooth rocks seem to be in order.
Larry

[brunog]

Check this one out
Optimization of Polymer Concrete Composites. Final Report.
http://www.fire.nist.gov/bfrlpubs/build99/art032.html you can download the full report and it's a freebee

Best regards

Bruno

[brunog]

Anyone have info on aggregate size.vs strength?I assumed the larger aggregates provided more strength,but It appears this is not so.Larger aggregate can cause cracks which are longer than with smaller aggregate.Smooth or rounded aggregate are isotropic reiforcments.The question was brought up seeing some of the guys are trying sand only.
Would a mix of fines only, have better specs than one with 1/4 and1/2" aggregate?
Larry

Larry,
Read the report on my last post, there are some graphs that state physical properties of E/G vs aggregate sizing.

Take your time in looking at them closely, it took quite a while to understand them. Maybe some of our engineer friends can point out the main results.

Regards

Bruno

[martinw]

Anyone have info on aggregate size.vs strength?I assumed the larger aggregates provided more strength,but It appears this is not so.Larger aggregate can cause cracks which are longer than with smaller aggregate.
Larry

Dear Larry,

Given my previous, and dubious posts on flatness, I think I may need to qualify this with a mighty big IMVVVHO. Anyway, here goes...

If E/G gets to the point at which it is cracking, it is way past the point at which strength is an issue.

For a rigid structure such as a CNC gantry, deflection is always going to be the killer. It is in almost all structural calculations.

Best wishes



Martin

[lgalla]

Martin the point is on my head(chair) You are right we don't want to get to the point of cracking,but I am trying to just understand or illustrate how aggreate sizing affects ultimate strength.I agree deflection on a gantry is important,but being of WIMPY type nature,I would shy away from a total E/Q gantry until more tests are done.My cautious nature at this point sees a self supporting frame work of weldments damped with E/Q.
BTW Walter what was your % on the choclate chips?
Larry Gallio,chip sweeper,Apprentice.As quoting Don Trump"youre fired"

[martinw]

Larry Gallio,chip sweeper,Apprentice."

Dude,

Best wishes

Martin

[lgalla]

Martin forgot to ask you.Did you see the posts on epoxy telescope mirror's.Looks cool to me.Any comments?
Larry