Fiber Reinforced Concrete vs. others

[Kevin Cole]

Hi all:

I've been hanging out here quite a bit over the last few weeks, reading up on the discussions and trying to immerse myself in the concrete countertop segment of the industry. The information found here is very enlightening and I'm learing a lot (thanks to all of you). One thing I am curious about, though, is what types of concrete are most prevalent in countertops. It seems that GFRC is becoming more popular and has some real advantages, but it is really difficult to find any information on what percentage of concrete countertop manufacturers are working with fiber reinforced concrete vs. other types. I would love to hear your opinions on what percentage of tops being done are fiber reinforced -- 25%? More? Less?

Thanks,

Kevin
[e-mail]

[jschuler]

Kevin,

You will find, all of us are using different forms of fiber reinforced concrete. Although I do not do conventional GFRC, I still use substantial fiber loading....PVA and AR Glass. You will find, most that have been doing this for some time....have seen the light on fiber reinforcement, related to what we do.

[Kevin Cole]

Thanks for the input. Maybe the question then should be GFRC vs. other types of reinforcement in general?

[jschuler]

Kevin,

conventional GFRC...with a sort of spray coat and the high glass fiber back mix....hence Glass Fiber Reinforced Concrete?

Or, since I use Glass fiber....it technically is still considered Glass Fiber Reinforced?

Just trying to get a better feel for your question. Although we use a combination of fibers....in my shop we are using AR Glass fibers....either the 13H Nippons or the AntiCrak HP. We still use heavy loads in the back mix.....but technically...I think what we do is still considered more of a wet cast.

I guess the question comes back to all of us....what do we consider GFRC?

[Jim Ralston URBAN CONCRETE DESIGN]

PCI Recommended practice for GFRC.

Chapter 1 - 1.1-1.2-1.7

Fiber-Reinforced Comcrete

PCA Design and controll of concrete addmixtures.

Chapter 15 page 193.

jschuler said:

Kevin,
conventional GFRC...with a sort of spray coat and the high glass fiber back mix....hence Glass Fiber Reinforced Concrete?
Or, since I use Glass fiber....it technically is still considered Glass Fiber Reinforced?

Just trying to get a better feel for your question. Although we use a combination of fibers....in my shop we are using AR Glass fibers....either the 13H Nippons or the AntiCrak HP. We still use heavy loads in the back mix.....but technically...I think what we do is still considered more of a wet cast.

I guess the question comes back to all of us....what do we consider GFRC?

[Dave McVey]

To me, GFRC is the replacement of large aggragate with glass fiber to form a matrix. When you look in my mix bucket you will know it's GFRC. It's thick with fiber. The fiber IS the aggragate not just some re-inforcement. If you go lite on the fiber, you bascily just have grout.

[Dave McVey]

I have added a new GFRC poll above.

[Alla Linetsky]

Kevin, I use a castable gfrc mix - this means a fibre-heavy, self-consolidating mix going right on the face of the mold. No sprayed premix - too messy and time-consuming for my liking. The drawback of this method is that you cannot do a heavy aggregate-exposed grind - the fibres begin to show.

For very complex shapes, and always around sink openings, I will use ladder wire as well - but you have to be careful and use a non-shrinking cement paste if you're going to put steel into a gfrc piece. If you're using conventional cement, you must use a shrinkage reducer, or else use a CSA cement blend. If these terms are not clear to you, please do some research before attempting to make countertops.

[jschuler]

Alla,

What is your current fiber load with your SC mix? Which fibers and % content?

I just finished some pieces about 1% loading....came out very nice. I added .25 grams of the BASF defoamer....Russell Vaughn sent me....1390 I think...I will look again. But, the pieces came out without 1 flaw.....very very nice. Personally a bit too nice, a bit Corian looking and feeling. But, it is nice to see such perfection, and absolute lack of pins.

[Alla Linetsky]

Jon, I use 19 mm AR fibres from NEGA at about 3% loading of total dry ingredients weight. This is still below NEGA recommendations, but I just can't imagine stuffing more fibres into the mix. I've completely given up on PVA - they make the mix totally unworkable. And 19 mm is far superior to 13 mm.

The BASF defoamer is simply dilute tri-butyl phosphate - that's what the rep tells me. I use 2 tsp of the real stuff per 150 lb batch.

[jschuler]

You are mixing that amount into the total mix...then using more of a wet casting technique?

No issues with fibers seen in the face?

[Kevin Cole]

I checked out the poll and with 25 people participating, the result shows that 80% use GFRC. I was under the impression, from talking with some well known concrete countertop manufacturers and suppliers, that the percentage for the general population of this segment of the countertop market was much lower. Do you think 80% is representative, or do you think that this is skewed for one reason or another? Perhaps those manufacturers that took part in the poll or are members of this site are more likely to work with GFRC?

Kevin

[Alla Linetsky]

Jon, yes, I use the fibre mix in a wet casting technique. We just don't grind to expose aggregate, and the fibres don't show through. On rare occasions, when we've been a little slow in placing our rocket fuel of a mix, and we try to place concrete that has started to stiffen up, we can get fibres on the surface. But by now I've learned my lesson, and if the mix has begun to set up, we don't put it on the face.

Kevin, I think that you are correct in that there is a selection bias on this forum. When it started, it was billed as a gfrc-oriented forum, so it naturally attracted people who were already doing gfrc or wanted to start. I was in the latter group when I joined it, and shortly afterwards, I made the jump to gfrc. I don't know of anyone who has tried gfrc and has gone back to conventional wet-casting with steel reinforcement.