Need to modify mix to make it more flowable

[StoneMaker]

I have this mix,
1 Cubic yard
Portland Cement Type 1 846 pounds
Concrete Sand 1100 pounds
#57 Crushed Limestone 1700 pounds
Water 267 pounds
Air 3%
HRWR (as needed)42 ounces
Retarder (as needed)21 ounces
W/C Ratio 0.32
PVA macrofibers 96 ounces
PVA microfibers 48 ounces

This is for casting concrete spheres. The fewer voids and bugholes I have will lead to less labor and more predictable finished weights. I got a viscosity modifying admixture, Visctrol from Euclid Chemical, and did two batches. At a dosing of 2 oz per 100 pounds of cement I didn't notice any change. The second time I probably used a dosing of 6 oz per 100 pounds of cement and didn't notice any change in the flowablity. The only difference I noticed was no bleed water at the top of the mold, which is a big advantage for me.

How can I modify this to still maintain a high level of strength, but have a very flowable mixture? I don't know if I want true SCC, but something close would be nice.

 

[JedClampett]

There's better concrete technologists on this forum than me, but why such a low W/C? What strength are you trying to obtain? I see a 7000 psi plus mix there. I'd reduce the cement, add some flyash, and increase the W/C to .4.
But I'm not sure anything is going to eliminate bugholes.

 

[concretemasonry]

Since this is apparently casting in a plant, has vibration (unidirectional, directional or random) been considered for the spheres you make? That may affect the air content.

Do you have any options for different sand gradations? Type III cement could be a helpful tool.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[TehMightyEngineer]

I'm not a mix designer but I'd agree with concretemasonry above, sounds like you need to increase the vibration of the concrete.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[msquared48]

What about super-plasticizers?

Mike McCann, PE, SE (WA)

 

[concretemasonry]

"Super Plasticizers" are not usually used in plant operations because there are better options for plant produced products since accuracy of batching and materials are available. These products usually require a standard of appearance/smoothness that are beyond field use products or wet mixes. - The shape of the product and stripping is a big factor, but 8,000 to 12,000 are obtainable on a routine basis for simpler shapes.

For use in the field and the usual batching equipment super plasticizers are they way to go.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

Agree with JC....drop the cement content, increase the W/C to 0.40 or 0.45. Cut the fiber dosage as well....keep to 1% of volume max. You could also increase the air content to around 5%. That will increase workability.

 

[BigH]

I see that you are not using any air entrainment agent . . . this will also help workability.

 

[StoneMaker]

"What strength are you trying to obtain? I see a 7000 psi plus mix there. I'd reduce the cement, add some flyash, and increase the W/C to .4. "
The paper describing the mix had it listed at a touch over 10,000 psi, if 50% slag cement is used. I want something as strong as possible. I make atlas stones which are used in strongman contests and dropped repeatedly, I don't want them cracking. I have searched for supplemental cementing materials and all I can find in small quantities is silia fume. This is just a small business I run out of my garage.

"Since this is apparently casting in a plant, has vibration (unidirectional, directional or random) been considered for the spheres you make? That may affect the air content.
Do you have any options for different sand gradations?"
I do this out of my garage and all I have is a palm sander to vibrate the outside of the mold. A dedicated concrete vibrator is unaffordable at this time. Regarding sand gradations, I haven't looked much into this. Off the top of my head I know I have easy access to concrete sand and sand meant for children's sandboxes.

"What about super-plasticizers? "
I use a one at just over the maximum suggested ration,12 oz per 100 pounds of cement.

Thanks for the suggestions, I will mix up a few small doses with less cement and varying W/C ratios and see how they work. I appreciate the feedback.

 

[TehMightyEngineer]

A palm sander might be sufficient but a small pencil vibrator can be bought for as low as $90:

http://www.harborfreight.com/power-...s/3-4-quarter-hp-concrete-vibrator-34923.html

This will go a long way toward removing tapped air from your concrete and result in a much better product.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com