[lgalla]

Walter,
Good job at the summaries.You seem to have the best knowledge and best memories of 700 posts.Did we not decide against concrete 600 posts ago?Can you refresh specs, E/Gvs concrete?Creep,Thermal expansion,etc?It is lots of work and you deserve THANKS.I am in a different time Zone.Got Jet lag.
Thanks again
Larry

[lgalla]

Walter
As usual you are ahead of me on posting.BTW German beers are great.:cheers: You know how I am constantly walking with my head down looking at the concrete curbs and sidewalks observing the cracks.I missed seeing a crack and tripped and fell.Thank God I had a few to many German beers
and damage to my body was minimal.:cheers: :cheers: If the sidewalks were E/Q or E/G this cracking would not occur and make our streets save.
Larry

[walter]

Last night I came across an epoxy used for coating rebar..

I was just getting to that part. If I have to coat it- might as well do it with 4" chunk of E/Q and be done with it...

But I think it's individual choice at this point. I'm glad people are working on the problem, enjoying the discussion and I'm sure we'll be seeing some cool stuff here.

EDIT: Larry, hope you're having fun in Germany
Cheers!

[ahlbebuck]

Walter

To avoid the voids left by dehydration, so called super plastisisers are added to reduce the water/cement ratio - which drastically improves strength as well.

Other admixtures are used to prevent shrinkage - as is typical in certain grout applications where grout is injected into spaces left by jacking up beams, etc.

Concrete has no tensile strength, therefore reinforcing is needed in the form of rebar, steel fibre, pre/post stressing.

In the real world a little rust on rebar is good as long as it is brushed to remove loose particals before casting - improves the binding ability. If vibration / compaction is correctly applied during casting, steel will be coated sufficiently and oxygen will not reach the rebar. Rusty rebar is only a problem when badly cracked concrete allows water penetration. However a common way to avoid this is to zinc galvanise the rebar.

IGALLA

Thermal expansion and contraction of concrete is very, very small over short distances (as our machine frames would be) Typical expansion joints in concrete walls are spaced at around 6m intervals.

If you feel safer with polymer - use it. As I mentioned earlier I certainly cannot justify the use of it in my case due to cost / availability. In most cases polymer would be superior - I just feel happy that I could get acceptable results from concrete.

What to do with a 2000 pound cracked slab? Break it up and fill in that hole in the ground that has bothered you for while!

I'm gonna go with concrete and I will report back to this group what movement I can measure with a micrometer!

regards

Neil

[lgalla]

Neil thanks for joining the discussion.I agree if you are comfortable with polymers that is the way to go.If you know concrete,it may be better or a least cost effective.Since E/Q and concrete are similar mixes,can you answer the question about vibration frequency?
If you totally seal a concrete slab with epoxy,will it result in greator stability?
Thanks
Larry

[ahlbebuck]

Larry

I would seal the concrete after 3 months or so when the hydration process in concrete is practically completed.

Vibration of concrete is tricky - its a function of particle size distribution, water/cement ratio and measured slump (slump is determined by placing a sample of the mix in a cone shaped mould of known height, removing the mould and measuring the amount that the sample "collapses")

The normal trend is to over vibrate - when you see a watery cement slush appear on top of your pour, stop vibrating - you are now causing aggregate separation.

A good way to compact the concrete is to manually poke it with a piece of rebar to make sure voids are filled and to remove entrapped air pockets. After some vigorous poking you can lay in with the vibrator.

That last sentence sound like it belongs on a porn forum.

regards

Neil

[jsage]

Hilarious. I usually pick up on things like that. Missed it completely. ; )

I think we're going to owe you a case of epoxy but what's your thought on aggregate sizing. My conception is improves compressive strength due to the larger solids versus interstitual spaces? But doesn't do much beyond that, thus the need for rebar?

[ahlbebuck]

JSAGE

Aggregate sizing is graded to increase the overall density and reduce the amount of cement used in concrete. An even spread in particle size is good. Large particles are good, rounded aggregate is good. Good spread for stone will start at around 6mm crusher dust, through 13mm, 19mm, 25mm, 32mm.

Sand should be graded from around 250 micron to 3mm.

Below 250 micron certain admixtures will "fill the gaps"

When using large stone, make sure it is not cracked and weathered - this could cause it to crack up within the concrete and weaken the overall compressive strength.

Another important factor is to make sure that acidic material is avoided - granites tend to cause problems in this way. However chemical composition will be affected by location, so in your area you should find a neutral PH stone type.

As I stated earlier, concrete is assumed to have zero tensile strength and therefore the use of rebar. The last number of years we extensively use post tensioning to place the concrete under greater compressive loading and to take up the tension requirements.

If I really want to go overboard, I might post tension my frame to improve things greatly but this will add complexity to what I still believe should be a simple DIY solution.

Concrete is not all that bad - if machine manufacturers did not have to put their products on a showroom floor and transport it a few times, I believe a lot more machines would be manufactured out of concrete.

[jsage]

Wow thanks albebuck.

You have added some clarity on a number of things. One example is the concrete on the back side of the pool is sinking. You gave me an idea how to mitigate it.

I like concrete. Takes some patience though. I have about 6 types of cement/concrete mix in my garage. Precision Grout, Marble dust, fiber reinforced, type 1 white, resurfacing, quickcrete fast cure. Lot's of choices.

Regards

Mike

[Zumba]

In my application, the mix will double as a bonding agent for steel plates, so I pretty much have to use epoxy. Portland cement won't work for me.

Neil, does larger aggregate add to the strength of the structure or is only there to minimize the amount of cement/epoxy needed in the mix? If the aggregate is almost entirely sand, will it adversely affect strength in a significant way?

Thanks for your input!

[Zumba]

Oh and here's another question for you guys. Let's say you fill up a 4" square tube, 5 feet long, with E/Q.

How the heck are you going to get the air bubbles out of that fill? It's five feet deep!!

I guess that'll be my problem.... you guys with the molds will have it easier. :rainfro:

[ahlbebuck]

JSAGE

With all the modern blends of cement available its like going back to school for me - waaaay too many choices, but good, informed choices though.

ZUMBA

Larger aggregate will add to the strength purely because it is a naturally dense, strong material - exactly what we are trying to reproduce with concrete - why reinvent the wheel. Just make sure that you use graded aggregate to ensure that you fill the gaps under the large boulders.

I often argue with people who want to blast away rock in a foundation trench just to replace it with concrete - baffles my mind completely!

Using sand in large quantities will adversely affect the strength of your mix. Imagine shortbread cookies. Now add nuts to them - they definitely become harder to break. Probably not a good analogy but hey, I'm feeling peckish right now!

To remove the bubbles from the slender tube mould, why not use vacuum to remove the air after mixing the material and then slowly force it in from the bottom of the mould?

[ger21]

How the heck are you going to get the air bubbles out of that fill? It's five feet deep!!

Cap one end and use vacuum?

[walter]

Larger aggregate will add to the strength purely because it is a naturally dense, strong material

What about sand with 99.5% quartz content? Good granite has only 66% quartz, can't be stronger than pure quartz?

[ahlbebuck]

Walter

Quartz is perfect - as long as you also have the added advantage of widely graded size. Sand tends to be very single sized grains and this will be a problem in shear loads. The concrete will be brittle and will also have too much cement in the cement/aggregate ratio. Shear and compressive strength will suffer from single sized fines. Think of a bowl full of marbles - lots of empty spaces in between, all the same size - allowing no real stress absorbsion and distribution. Come to think of it - it might also not be very good for vibration damping as the concrete would be "tuned to a fixed frequency"

What would be nice is a good mix of quartzitic fines / sand and weathered quartzite from 6mm up to about 25 - 32 mm

Problem with freshly quarried quartz though is the crystal shape - there will be lots of sharp corners and protrusions that will not assist in upping the strength. What would be interesting would be getting quartz from an area where river flow has rounded the pebbles / boulders over time - this would be the ideal aggregate.

I'm suddenly getting revved up to start this project!!!

[Zumba]

Cap one end and use vacuum?

Will the bubbles from 5 feet deep actually make it up to the surface? If not, I'll probably have to apply vacuum prior to pouring. I'm thinking that most of the bubbles are created by mixing and stirring, not pouring.

Whaddayathink?

[ger21]

Pour in a foot at a time, vacuum, another foot, vacuum,...

[lgalla]

Zumba reply to"Whaddaythink"I does thinkist pre de-gassing is good as careful pours should not entrap air.Gerry is correct at one foot at a time.Resin will pool on top and sprinkling sand will suckup the excess.Your fast epoxy will smoke if done in a single pour.Take your time.I assume you are filling a steel tube.In that case the steel is the structure,E/QorE/G the vibra damp.Some bubbles should not be a problem.
Larry

[lgalla]

Neil good to have a concrete expert on board as E/Q and concrete are simmilar animals.The book on Polymer concrete frame is now 699pages of useful info.My E/G brain has cured and run out of RAM.Memory is cheap and my capicity should be re-newed to-morrow
larrty

[lgalla]

Wow 1 day without a post.I guess we are all take-in a break or holiday.Walter did you get any 635 epoxy yet?Anxious to hear your experiments.
Larry