No control joints in concrete?

[wssix99]

What will happen is somewhat unpredictable.

It's only unpredictable if one isn't in command of the design. I would say that even with a proper design, the results can be somewhat "uncertain" as there is no 100% guarantee that there won't be unsightly cracks. However; with a proper design, the likelihood of a desired outcome is very high. (Certainly much higher than a guess and less expensive than over-designing a solution.)

Concrete shrinks, so cracks happen.

This is always true. Design guides call this out: "The use of reinforcement will not prevent cracking, but will actually increase crack frequency while reducing crack widths. Properly proportioned and positioned, reinforcement will limit crack widths such that the cracks will not affect slab serviceability."

^ When the 0.5% steel area ratio is used, the crack frequency becomes so high and the crack widths become so small, that they can't be detected.

 

[Vintage Veloce]

This is what ACI calls for:

"Reinforcement required for crack-width control is a function of joint spacing and slab thickness. To eliminate sawcut contraction joints, a minimum steel ratio of 0.5% (PCA 2001) of the slab cross-sectional area is recommended. The reinforcement should be located as close to the slab top surface as possible while maintaining minimum concrete coverage over the reinforcement."

I don't understand this 0.5%... how is this us to calculate the rebar spacing?

 

[joes169]

I don't understand this 0.5%... how is this us to calculate the rebar spacing?

Simply put, it means that .5% of the concrete's volume needs to be replaced by steel re-enforcement. If it seems complicated, it certainly is, as well as extremely old-fashioned, which is why it's rarely used to extend control joints.

Like I posted earlier, you can use certain macro fibers to do exactly what you're trying to accomplish for a fraction of the financial expenditure. I've personally witnessed a wharehouse floor that had control joints extended to more than 100' each way, along with intermediate column lines intersecting with no joints. It was 9 months old and no noticeable cracks. Like I said earlier, it can be done for about $25-30 per yard of concrete.........

 

[wssix99]

I don't understand this 0.5%... how is this us to calculate the rebar spacing?

It's a test of the rebar spacing.

Take the area cross sectional area of your rebar and divide it by the cross sectional area of a rectangle the size of your spacing times your slab depth. Multiply that times 100 and you get your cross sectional ratio:

Ratio (in percent)=((PI()*(r/2)^2)/s/d)*100

Where:
PI = is Pi
r = rebar diameter
s = rebar spacing
d = slab depth

As long as that Ratio is greater than 0.5, you are good.

 

[wssix99]

Simply put, it means that .5% of the concrete's volume needs to be replaced by steel re-enforcement. If it seems complicated, it certainly is

Maybe if Pi is a problem? Looks like 5th grade math, to me. ^

Like I posted earlier, you can use certain macro fibers to do exactly what you're trying to accomplish

So, do we all have to sit in suspense or do you have actual product information that you can share for these special fibers? It would be great if you could offer some specifics in what exact materials could be used to build this slab more economically.

for a fraction of the financial expenditure. I've personally witnessed a wharehouse floor that had control joints extended to more than 100' each way, along with intermediate column lines intersecting with no joints. It was 9 months old and no noticeable cracks.

There are many ways this can be done. There are even shrinkage compensating concretes on the market that can do this sort of thing without any help from reinforcement.

Can a homeowner or regular contractor work with these materials reliably? - Probably not. Is the material less expensive than a rebar mat? - Possibly. By the time one hires a company (an industrial contractor) with the design competence and skill to use/place these materials for a small backyard porch or residential slab; any material savings would surely be wiped out.

 

[matt_i]

I don't understand this 0.5%... how is this us to calculate the rebar spacing?

Let's roll thru an example....say the slab is 12ft wide and 4" thick. Have to visualize in your mind's eye the edge of the slab as if it were sawn completely thru, and one part removed so now we are looking at the fresh-sawn cross-section.

The total cross section of the slab is 144" x 4" = 576 in^2.

0.5% of cross sectional area = multiply by .005. (576 * 0.005) = 2.88 in^2. This is the total area of the steel reinforcement.

Each 1/2" dia (#4) rebar has an individual cross section of pi/4 (0.5)^2 = 0.1963 in^2.

So to find the number of rebars, (2.88 / 0.1963) = 14.67. The 0.67 rebar has not been invented yet so this rounds to 15 rebars within the 12 foot wide dimension.

Roughly 9-1/2" centers, maybe it would be easier to simply make it 9" centers.

 

[wssix99]

Roughly 9-1/2" centers, maybe it would be easier to simply make it 9" centers.

Correct. You'd also want to calculate for the average depth of the slab. For something like this, I'd add at least 0.5" (or whatever one is comfortable with) onto the 4" depth as a safety factor to account for variances in the placement. If you do that, the spacing should come down to around 8.5".

The formula above pastes well into a spreadsheet. You can replace the three variables with cell references and quickly test "what-if" scenarios for different combinations.

 

[Falcon67]

Pi is never a problem, unless it's coconut which is a real problem and a waste of a good Pi.

 

[Vintage Veloce]

Ok, I follow the math. As Matt shows, 9" centers is about right.
Cool information!

Now... has anyone done this and has pictures to post? It's important to note, this should result in more, smaller cracks... so I'd definitely want to see something first.

 

[ptgarcia]

Ok, I follow the math. As Matt shows, 9" centers is about right.
Cool information!

Now... has anyone done this and has pictures to post? It's important to note, this should result in more, smaller cracks... so I'd definitely want to see something first.

Like the commercials on TV say, "Your results may vary."

 

[Vintage Veloce]

We are digging for the forms now. It will be interesting to see what my wife decides.
I've been briefing her on the options.
(The deal was that I called the shots on the garage, the final say on the yard/patio decisions are all hers!)

 

[Vintage Veloce]

OK, here is the current plan.
The new patio is shown, between the two garages and the house. The very white walkway on the plans is already done: separate concrete pads with pebbles in between leading from the deck to the garages across the bottom of the drawing.
The "NEW PATIO" is about 20' x 18'. Note the top right corner has a 4" gravel "stream" that separates it from the rest of the pad. So that is a formed in separation.
My wife has declared one cross of control joints, as shown, as artistic, and necessary ;-). That leaves all the sections rather large, and the one on the bottom right very big, about 15' x 9'
Note the patio will be etched with Top-Cast #3 for a weathered/sandblast finish. We will use our normal selection of concrete, as that is what our finisher is used to working with, and we don't know what would happen with the Top-Cast and fiber... might end up furry! So no fiber, and regular rebar (16" centers).
It will be interesting to see what happens, crack wise!

This is the 5th pour on our property:
- The first garage floor, 16' x 16' was about 6" thick and had a cross tooled in the middle, so 8'x8' control joints. It has small cracks all over it now.
- The driveway was sawcut the day after the pour, in 2' squares. Looks great, no visible cracks. (That is how I would have done the patio, but it isn't my call. ;-) )
- The new garage is 21' x 25' and has 2 tooled joints across the short direction and one in the long direction (larger pads are 8.5' x 10'). It's a year old and no noticeable cracks.
- The back driveway is about 30' x 20' and has a bunch of tooled joints, but still cracked in an aisle between the buildings... a tough spot I have been told as the buildings constrain it. We probably should have put foam at the two foundations to allow expansion/contraction.

 

[LX-Markham]

Funny, we actually chose our landscape architect based on a previous project he did. We liked his intentional used of sawcuts.

 

[jives]

Our 1st floor house slab is about 1100 sq feet. No control cuts, no cracks. Rebar, no fiber mesh. 8 years old. Yes, the concrete is stained and is the finish floor.

 

[ard]

Our 1st floor house slab is about 1100 sq feet. No control cuts, no cracks. 8 years old. yes, the concrete is the stained and the finish floor.

So just 4 sack mix, no mesh, no fiber, no rebar?????

 

[wssix99]

The "NEW PATIO" is about 20' x 18'. Note the top right corner has a 4" gravel "stream" that separates it from the rest of the pad. So that is a formed in separation.

I'm not commenting on the design, but I often see this type of feature common in Putt-Putt courses. So you might want to make sure you fully consider that potential association or address it in the furnishings before committing to this design iteration.

If the stream was straight, you'd have no problems. However, as your curves become concave, they will start to resemble more like reentrant corners. In these instances, you may want to place some diagonal rebar to help ward off tendencies for cracks to form:

http://www.concreteconstruction.net...et-a-reentrant-corner-crack-ruin-your-image_o

My wife has declared one cross of control joints, as shown, as artistic, and necessary ;-). That leaves all the sections rather large, and the one on the bottom right very big, about 15' x 9'

That is big.

So no fiber, and regular rebar (16" centers).
It will be interesting to see what happens, crack wise!

16" probably won't be enough for a 15' section. What strength of concrete are you going to use and what thickness are you going with now? There are charts that will hint at how far you should reinforce for these situations.

- The back driveway is about 30' x 20' and has a bunch of tooled joints, but still cracked in an aisle between the buildings... a tough spot I have been told as the buildings constrain it. We probably should have put foam at the two foundations to allow expansion/contraction.

Do you have any drainage or anything in the middle? Generally, "constraining" shouldn't be an issue because the slab should shrink and give you a gap by all the fixed objects. Do you have a picture or diagram of this?

 

[Vintage Veloce]

I appreciate your comments wssix99!

I'm not commenting on the design, but I often see this type of feature common in Putt-Putt courses.

Haven't been to a put-put, but we think the rock stream is a cool feature anyhow.
Here is a picture of the walking path already in the back yard.
View media item 77010The new patio adjoins this to the left in this picture. And my wife is calling the control joints. I advise, but her stance is still that she would prefer cracks to control joints. Not sure where exactly the apex of the "re-entreant corner" is in the curve anyway.

What strength of concrete are you going to use and what thickness are you going with now? There are charts that will hint at how far you should reinforce for these situations.

3/8" 3000PSI, colored concrete Solomon Thyme, then we use Top-Cast #3 to etch

Do you have a picture or diagram of this?

View media item 77008You can't easily see the crack in this picture but it starts in the middle of the bottom control joint runs upward through this "aisle" between the two garages (garages are 7' apart) and continues to the next expansion joint. Hard to guess the actual cause...could be a number of things. but if I was doing it again, I might put a bit of foam along the foundation of the buildings. Actually, this picture illustrates my wife's opinion exactly: the control joints are easily visible and the crack is hard to see... so she prefers the crack.

 

[joes169]

So, do we all have to sit in suspense or do you have actual product information that you can share for these special fibers? It would be great if you could offer some specifics in what exact materials could be used to build this slab more economically.



/QUOTE]

It's called "Forta Ferro". You certainly won't find it mentioned in in the archaic libraries you like to Google, but engineers around the globe are converting to it to replace steel on a daily basis. ..........

 

[wssix99]

It's called "Forta Ferro". You certainly won't find it mentioned in in the archaic libraries you like to Google, but engineers around the globe are converting to it to replace steel on a daily basis. ..........

I don't know why you keep talking about Google. Everything I know comes from America Online.

Nothing about Forta Ferro is inherently special than any other fiber. Forta advertises the product as an enhancer and not as a replacement for primary crack control. I guess they don't know what they are talking about, either???

FORTA-FERRO® "Known as our most popular fiber on the market, FORTA-FERRO® is used to reduce plastic and hardened concrete shrinkage, improve impact strength, and increase fatigue resistance and concrete toughness. This extra heavy-duty fiber also offers maximum long-term durability, structural enhancements, and effective secondary/temperature crack control."

 

[Vintage Veloce]

Wish I could find some info on how these embedded fibers work with an etch like Top-Cast. I've heard the fibers can make things furry... I'd be concerned the etch would particularly expose them.

 

[wssix99]

Haven't been to a put-put, but we think the rock stream is a cool feature anyhow.
Here is a picture of the walking path already in the back yard.

That looks really cool! I wasn't thinking that the stream was level with the slab. The first thought that came to my mind was different levels. I was wondering about the trip hazard...

View media item 77010

Do you have to do anything to fix the stones, or does the edging hold them in?

The new patio adjoins this to the left in this picture. And my wife is calling the control joints.

There are repair mortars that you could also dye and fill in the control joints with to create an inlay effect. (Those materials don't shrink and can expand just a little bit to fill the voids tightly.)

Not sure where exactly the apex of the "re-entreant corner" is in the curve anyway.

If you curve the new slabs like your other ones, I wouldn't think you are deep enough to have a problem. They look pretty close to straight and the transitions are gradual.

3/8" 3000PSI, colored concrete Solomon Thyme, then we use Top-Cast #3 to etch

Here's a guide you can use for getting some assurance for your 15' joint spacing:

Since 6.5" would be the slab thickness you'd need for a 15' spacing on an unreinforced slab, I would think that you could cheat towards a thinner slab with added reinforcement. (It would be really nice if one of these was developed for steel area ratios, but I've never come across one.

View media item 77008You can't easily see the crack in this picture but it starts in the middle of the bottom control joint runs upward through this "aisle" between the two garages (garages are 7' apart) and continues to the next expansion joint. Hard to guess the actual cause...could be a number of things. but if I was doing it again, I might put a bit of foam along the foundation of the buildings. Actually, this picture illustrates my wife's opinion exactly: the control joints are easily visible and the crack is hard to see... so she prefers the crack.

You have a two potential reentrant corners there, off of your two main slabs. That middle piece connecting the two should be isolated. I can't tell from the picture, but it looks like you might have a tight cold joint or it might be continuous with one of the larger slabs. Either way, that could impart problematic stresses on that small square. (The safest bet for something like that would be to isolate it from the two larger slabs with a full expansion joint on either side where it meets each larger slab.)

 

[wssix99]

Wish I could find some info on how these embedded fibers work with an etch like Top-Cast. I've heard the fibers can make things furry... I'd be concerned the etch would particularly expose them.

Some fibers can be melted off, but you'd have to figure out what that would do to your finish.

 

[Vintage Veloce]

That looks really cool! ...
Do you have to do anything to fix the stones, or does the edging hold them in?
View media item 77010

Thank you! We are occasionally kicking some stones out, but it isn't a big deal. We probably have some of the stones a bit high. And the "streams" are spaced to be easy to step over.

It's actually a drainage strategy. For various reasons, those pads are pretty level, but the bottoms of the stone gutters slope down to the top right corner of the picture. We are hoping they work well for drainage.

The rock stream through the new patio continues the design. It makes a third "triangle with a wavy hypotenuse" in addition to the two in walkway picture above. My wife really is an artist, this is all her doing. And as I've said, she doesn't want control joints messing with her design. ;-)

 

[LX-Markham]

Really like the blue river stone, looks great.
Lucky you live in San Diego. Shoveling snow off that walkway might not be so fun.

 

[Vintage Veloce]

Ready for concrete Monday. We are going to do it like the rest and see what happens...
If you can see them in the picture, the cross of orange strings will be the only control joints, as decreed by "she who must be obeyed". ;-)
(My two garages are in the background of this shot.)
View media item 77028
View media item 77030

 

[wssix99]

Really like the blue river stone, looks great.

I really like this, too. I need to hide this from my wife, let it turn in to another project for me...

Lucky you live in San Diego. Shoveling snow off that walkway might not be so fun.

We could put in radiant melt systems...

 

[joes169]

I don't know why you keep talking about Google. Everything I know comes from America Online.

Nothing about Forta Ferro is inherently special than any other fiber. Forta advertises the product as an enhancer and not as a replacement for primary crack control. I guess they don't know what they are talking about, either???

FORTA-FERRO® "Known as our most popular fiber on the market, FORTA-FERRO® is used to reduce plastic and hardened concrete shrinkage, improve impact strength, and increase fatigue resistance and concrete toughness. This extra heavy-duty fiber also offers maximum long-term durability, structural enhancements, and effective secondary/temperature crack control."

Actually, Forta Ferro is quite a bit different than anything else on the market, do a little more Googling. If you look at their site a little deeper, you'll see you can consult with their own engineers to convert your project from steel to Forta Ferro. I see that happening A LOT around here in the last year or two. You'll also see a number of completed project examples that were converted away from steel entirely. Many are to extend joint control joint spacing, which I thought the premise of this whole thread was supposed to be about?


To the OP, I like the existing sidewalk, very nice design & execution!

Your patio looks fine as well, and you "shouldn't" have any issues with errant cracking with the joints you have laid out with string line. My biggest concern is that the grade looks anything but flat, a lot of "up's and down'", which is not ideal when trying to combat errant cracking. Not sure there's much you can do about it as this point with the rebar in place. Best of luck.

 

[yeldogt]

I have done many 16 and 18 squares - that's the size you need for a square table. never have I had one crack ... we use 4000psi.

I use bricks set in fines for the same reason you have the stones -- drainage. I don't like seeing the drains

 

[wssix99]

Actually, Forta Ferro is quite a bit different than anything else on the market, do a little more Googling. If you look at their site a little deeper, you'll see you can consult with their own engineers to convert your project from steel to Forta Ferro.

It seems that your advice is for members of this community to gamble their money on an exotic material (not yet independently tested for this purpose) to replace tried-and-true reinforcing steel to control cracking in concrete. Even though the manufacturers warn in print that this material isn't to be used for this purpose, you are certain that they can consult the manufacturer for an off-label certification.

Given that the material is not available off the shelf, requires the use of water reducers and/or other exotic admixtures, (this raises the cost of the concrete in addition to the fiber cost) and requires specialty labor familiar with the material; we seem to be lacking an economical justification for this advice.

I see that happening A LOT around here in the last year or two. You'll also see a number of completed project examples that were converted away from steel entirely. Many are to extend joint control joint spacing, which I thought the premise of this whole thread was supposed to be about?

None of us can see these examples. Why can't you show us any or back this stuff up?

 

[Vintage Veloce]

Lets not get in an argument in this thread please.

Actually, I did find some stuff that promotes using "Forta-Ferro" as a rebar replacement. However, it is not something I'd try without local references and old examples (poured more than a year ago), and evidence it wouldn't be furry after the Top-Cast #3 etch.
Interestingly, the few pictures I found of Forta-Ferro reinforced concrete with distant control joints were during the pour/finishing. I'd want to see pictures a couple years later!

Generally, residential contractors aren't good references for stuff like this, cause they never visit the jobs again after they are done. You have to check old work.

Heck, I even had a good friend claim his garage floor had no cracks, and then when I visited I looked down and said, what this? He said, gee I've never noticed that.
(I'd also dare someone who claims there floor is perfectly flat to get an 8 foot straight edge and try it on 20 places around their floor.)

One of the more interesting Forta Ferro sites I found:
http://rizizco.com/media/files/Forta-Ferro Presentation-com.pdf

 

[joes169]

It seems that your advice is for members of this community to gamble their money on an exotic material (not yet independently tested for this purpose) to replace tried-and-true reinforcing steel to control cracking in concrete.

You're assuming it hasn't been tested for extended joints yet,
I'm fairly confident it has been. Perhaps their website isn't updated on this yet, but being the international concrete icon that you are, I'm sure you can simply give them a call, let them know who you are, and they will gladly share all of their accreditations and certifications with you. Can you personally guarantee that the rebar you're prescribing for extended control joints will work?

Even though the manufacturers warn in print that this material isn't to be used for this purpose, you are certain that they can consult the manufacturer for an off-label certification.

Again, maybe you should give them a call. I have a supplier/representative 3 miles down the road from me who is the regional supplier for Forta, as well as 3 other fiber manufacturer's. I can call his cell phone to get answers I need.

Given that the material is not available off the shelf,

I can have it added when I solidify my "will call"in to the ready-mix plant, generally about an hour before I expect the truck to be on-site. I completely understand that it's not used, or stocked, throughout the entire country, yet. I stated that was one of the downsides early on in this thread.

requires the use of water reducers and/or other exotic admixtures,

I've never used any additional water reducers with it,
perhaps your first-hand experience with it is different? I do realize that it tends to "stick together" more in the plastic state due to the interweave of the fibers, but if you can get past that striking off the concrete, the rest of the process is similar to non-fibered concrete.

(this raises the cost of the concrete in addition to the fiber cost)

I can easily make the case that water-reducers can save money by replacing Portland cement.

and requires specialty labor familiar with the material; we seem to be lacking an economical justification for this advice.

After using it, I'd have to disagree with your assumption that it requires any special labor. I've used it a number of times with my crew,
and not having to deal with cribbed steel, I think everyone of us would prefer pouring with Forta Ferro. Also, as I stated earlier, the fiber at a 5#
per yard dosage costs between $25-30 per yard, which is much cheaper than I can have #4 rebar tied on 8, 12, or 16" centers.

None of us can see these examples. Why can't you show us any or back this stuff up?

They have 100+ project examples on their website. Here's five examples, let me know if you need more:


http://www.forta-ferro.com/blog/projects/mcmaster-carr/

http://www.forta-ferro.com/blog/projects/rigbys-family-entertainment-complex/

http://www.forta-ferro.com/blog/projects/atlanta-botanical-gardens-walkway/

http://www.forta-ferro.com/blog/projects/attaway-waste-services/

http://www.forta-ferro.com/blog/projects/cover-all-structures-inc/

 

[wssix99]

Generally, residential contractors aren't good references for stuff like this, cause they never visit the jobs again after they are done. You have to check old work.

You've notices that, too? lol In partial defense of contractors, I've seen many instances where the user/owner is so oblivious to quality issues and/or problems that come up and their implications, (even ones that would trigger a warranty claim) that they never call. (For example, if an outdoor concrete slab cracks, how many homeowners would understand the importance of filling the crack to prevent more damage from freezing, etc.?)

Interestingly, the few pictures I found of Forta-Ferro reinforced concrete with distant control joints were during the pour/finishing. I'd want to see pictures a couple years later!

I'd also want to see a design or spec for what's under the surface. The manufacturer advertises being able to provide secondary reinforcement and extend the capabilities of rebar, so it would be interesting/important to know how much rebar is actually there and how it's employed. The admixtures are important also, as are the techniques for mixing the product and placing it. (pump, conveyor, etc.)

Heck, I even had a good friend claim his garage floor had no cracks, and then when I visited I looked down and said, what this? He said, gee I've never noticed that.

Cracking is also a game of probabilities. A good design helps weigh the numbers in the designer's favor. Even with a good design, cracks can happen. Even with a poor design, the owner can get lucky and end up with a fine slab.

 

[joes169]

Lets not get in an argument in this thread please.

Actually, I did find some stuff that promotes using "Forta-Ferro" as a rebar replacement. However, it is not something I'd try without local references and old examples (poured more than a year ago), and evidence it wouldn't be furry after the Top-Cast #3 etch.
Interestingly, the few pictures I found of Forta-Ferro reinforced concrete with distant control joints were during the pour/finishing. I'd want to see pictures a couple years later!

Generally, residential contractors aren't good references for stuff like this, cause they never visit the jobs again after they are done. You have to check old work.

Heck, I even had a good friend claim his garage floor had no cracks, and then when I visited I looked down and said, what this? He said, gee I've never noticed that.
(I'd also dare someone who claims there floor is perfectly flat to get an 8 foot straight edge and try it on 20 places around their floor.)

One of the more interesting Forta Ferro sites I found:
http://rizizco.com/media/files/Forta-Ferro Presentation-com.pdf

My apologies, I was typing, and then interrupted by my kiddos, while you posted. I just like to offer an "on the ground, first hand experience" when I read what I consider to be bovine excrement on the interwebs. SImply ignoring it tends to lead to more ignorance IMPO.

That said, I will not respond to Mr. "wssix99" anymore in thread, I promise!

 

[Vintage Veloce]

Mission accomplished!
View media item 77449
(no unplanned cracks yet.)

 

[spudley]

That looks pretty snappy! Good job.

 

[flan]

25x40 no control joints 8 reentrant corners no cracks. Base prep, no direct wind and sunlight plus rebar layout help a lot.