I know that there have been a few discussions about concrete, but I did a test pour and wanted to share my findings.
Bottom line is that using minimal water makes an extremely stiff mix which makes it almost unmanageable.
On this pour I used the max amount of recommended water, 5 pints. I used a concrete vibrator and mallet on the sides of a small plastic mold. Flowability of the material was virtually nonexistent. The results were less than satisfactory with voids still present and a lack of workable cream on the surface and sides of the form. Gravel still in contact with the sides of the mold in spite of malleting.
On the second pour I added a Ā½ table spoon of sugar to the water. This extends the set time of the concrete and greatly increases the flowability of the mix. Same mix, same 5 pints of water, same process:
Sugar acts as a retarding agent against the chemical reaction between the water and cement in the mix. One of the side effects is increased slump or viscosity/flowability. Sugar has no deleterious effects on the curing properties of the concrete according to my research and my test seems to bear that out.
Materials Used:
Concrete Mix: Quikrete Q-Max 50#
Sugar: .25 Ounces / Ā½ tbsp - ā 0.1% by weight of cement content in mix
Mold: Plastic Oil Drain Pan
Tools: Cement Mixer / Ā¾ HP Concrete Vibrator / Rubber Mallet / Wood Hand Float / Small Steel Hand Trowel
I would encourage others to test their mix themselves before the actual poor to eliminate surprises or regret.
The only way to really determine how good the concrete is a slump test on a wet mixā¦and a pressure test after 30 daysā¦
Concrete by visible inspection is unfortunately not very accurate.
The concrete you are making is not for holding a car up on a bridgeā¦it is counter weightā¦vibration controlā¦
Yes, adding sugar can help slow down and harden the concreteā¦I would suggest once the pour is complete you place a damp rag on the concrete and keep it damp for around 24 hours or moreā¦
Also adding liquid soap in the mixture adds air to the concrete and makes the concrete even betterā¦this is air entrainmentā¦
It would be interesting to measure the shrinkage of the concrete. If the concrete can not mantain intimate contact with the aluminum bed plates and the Y-axis frame, it cannot secure these items. A gap of 0.001 would not be acceptable. It would have to rely on the epoxy to secure the concrete to the aluminum and steel surfaces.
wellā¦you are in for shrinkage and it is not because of the cold waterā¦lolā¦
Physically, concrete that experiences a drying shrinkage of about 0.05 percent (500 millionths or 500 x 10-6) will shrink approximately 0.6 inches per 100 feet (50 mm for every 100 m). In more visual terms, that is about 2 inches for the length of a football field.
I didnāt use a slump cone, but I do know the difference between having to scoop and pack the mix into the form verses pouring, which was the difference between the 2. I didnāt need an accurate slump reading to observe the differences. The workability between the 2 was night and day.
And youāre right, a pressure test would be the only way to confirm the PSI. I do not have a Schmidt Hammer handy.
That is a very interesting test, thanks for the work! - to summarize, so far we have these hints:
adding sugar (1/2 tpsp per 50lb bag) that increased the flow and finish
liquid soap (unknown how much) to increase air entrainment
wet cloths to keep the curing concrete hydrated
use of vibration to make the mixture settle
I like the idea of some testing before committing to the ābig pourā, I plan to do that, as well as I am in a bit later batch so hopefully some more feedback will happen in the forum.
I 've made quite a bit on concrete pool block and we add in some titebond III glue into the cement mixture. It was a receipt from concrete sinks if i remember correctly. They stand up to some use and abuse.
It may work in this application ?
work add in fibre to the mix sometimes too.
there is a metal version of the fibers too.
I had a thought that using lead also may work well if the tray was shallower or it would weight 2000lbs.
The Q-Max Pro mix that I intend to use and tested is already Fibers Reinforced and Air Entrained. It also is Corrosion Resistant and has high early strength.
Another potential choice could be Countertop Mix which is designed to be cast-in-place, has plasticizers for good flowability with low water content.
Keep in mind that these other than standard mixes are quite a bit more expensive as @langmuir-daniel mentioned in another topic.
Q-Max: 3 Times the price
Countertop Mix: 4.3 times the price
Whatever choice you make, standard or not, I would advise doing at least a one bag test run to work the kinks out of your process and the workability of the material.
It seems like $150 extra bucks is a no brainer, when discussing the foundation of a $5k machine.
However, you get the same mass regardless of the sugar, liquid soap, etc. Is the less hard mix better for shock absorption maybe? What happens when you move the machine and it flexes?
Iām thinking from the perspective of tool steel, although hard, is not always being the strongest option. Not sure if that logic applies here.
fwiw Iām naive with concrete, and using it for machine bases. Iām curious what you pros think.
I think we are over thinking this. 6-8" of high strength concrete is not going to flex. As for moving the machine afterwards is why I made a steel platform to mount it to prior to pouring. Just my two cents.
I have to say the teaspoon of sugar is a great idea. Will definitely add it to my mix. I would not have believed it, till I saw the photos that JDE put up.
Per JDE recommendation I just ordered a hand held concrete vibrator. Anybody that will need it after I do my concrete is welcome to it. I will never use it again. I hate pouring concrete. Thats why I pay contractors to pour our facility concrete.
We can just send it around for you guys to use. Then ship it to the next guy.
I do believe the vibrator will make the job much easier.
I have a good sized Dewalt concrete drill with a chisel setting so it only vibrates, not rotate, so that would work to vibrate the concrete I would think.
I do concrete counter tops here and there. I use a palm sander with no paper on it to vibrate the forms. For deep pours I have a palm nailer with a rubber bumper over the magnetic nail end. They both have their place.
it will allow the concrete to have smooth sidesā¦like the picture aboveā¦
mond you the best way to set the concrete is to use a broom handleā¦steel rodā¦and just do what they call roddingā¦up and down hand motion ā¦yoiu get the ideaā¦
that is a little overkillā¦just a bitā¦
now this is the bets wayā¦
remember as noted this is a 6"-8" slab of concreteā¦if you manage to crack it by twistingā¦then you have other problems at handā¦like a very expensive boat anchor ā¦and not because the concrete crackedā¦but because you did something to crack itā¦
think of thisā¦most commercial high rises are only 5" concrete slabsā¦you park your car on 4" slabā¦the concrete from the MR1 will be around long after you ā¦
A quick substitute for a concrete vibrator is a DA sander without sand paper. Use the pad against the outside of the machine and wrap the pad with plastic and tape for direct concrete contact. Just a suggestion
