New driveway cracking like a potato chip 5

[ke6fx]

My new driveway began hairline cracking the day after pouring, and has continued for two weeks, looking like a 2500 sq ft jigsaw puzzle. Contractor used good base, half-inch rebar on 2’ centers, and poured under good conditions. He tried patching the first cracks with some cement/epoxy compound, and applied sealer over everything. The patches have not lightened and the cracks came through a day later. He suspects bad mud, and the cement rep is supposed to come out with his “expert” at repairing such problems.
I suspect that they’ll want to coat the entire surface with something to hide the cracks and make me go away. Does anything really exist that can be applied over this disaster and solve the problem, or am I facing a court battle?

 

[JAE]

That much cracking - sounds like "alligator" cracking which are cracks in every direction - would probably be caused by high water-cement ratio - probably a "poured" concrete driveway instead of a properly placed concrete.

You can determine the w/c ratio by taking core samples and sending them off to a testing lab. Also, could be they didn't use very large aggregate in the mix - the lab could verify this as well.

With all the cracks, the "patches" will probably not hold for long as you drive over the slab and wear down the aggregate interlock. Having the rebar in the slab helps...but only delays the inevitable I would think.

Suggest you contact a testing lab to look into it. Remeber - you purchased a good quality driveway - all concrete cracks, but not to the extent that you describe. I would insist on a new slab - otherwise you are buying essentially a gravel driveway with gray paint on it.

 

[jike]

If the cracking is a small random pattern of cracks resembling a crushed eggshell, this is commonly known as "crazing". It is similar to what you see when the surface of mud dries quickly...alot of shallow, random cracks on the surface. The same thing that causes mud to crack (rapid moisture loss at the surface) also can cause concrete to crack. Also, premature finishing (before bleed water is removed) can cause this type of problem.

I don't know if you can answer any of these questions, but they may be pertinet to the problem.

Was bleed water removed? How did the contractor protect the concrete surface from drying out? How was the slab cured? At what time did this protection or curing happen? What was the weather (temp., humidity, rate of change, etc.) during the day when it was poured and finished and the following night and day? How long has this contractor been in business?

I would be very reluctant to accept a fix, without knowing how it will perform over the long term.

 

[Ron]

ke6fx...both replies above are on target. The problem is in the type of mix used (probably high w/c ratio as JAE suggests) and the finishing technique. The crazing is a durability issue and will get worse with time as the concrete is weaker at its surface than below. This will cause premature wearing of the surface, and if severe enough, will cause dusting and erosion of the surface.

Don't let the contractor off the hook. Get it repaired now. Do not accept a thin surface treatment as this is a traffic slab with relatively high surface stresses and abrasion, to which thin toppings do not often respond well.

At a minimum, the repair should include scabbling to at least 3/4 of an inch below the existing surface, followed by placement of a polymer concrete topping designed for traffic. Otherwise, tear it out and start over.

 

[ke6fx]

Thanks all for your replies. The concrete rep and my contractor looked at my job today, and are supposed to get back to me tomorrow. (My new job prevents me from being home whenever they decide to show up.) The job was done in two pours the same day, about 8am and noon. Temp was about 75, humidity less than 50 % (Utah is usually very dry) but it did shower a bit two days later. Some sort of sealer was applied the afternoon of the pour, which causes water drops to bead up. The smeared-on repair patches applied days later remain dark grey over 2 weeks later, and sealer was applied over them while still wet, also.
The contractor first described the first appearance as normal shrinkage cracks, which chose not to conform with the control joints. But, there are just way too many of them. They are long, not straight, and go in random directions.

 

[Tryan]

ke6fx,I need to say it IS the contractors fault! The concrete mix is innocent! Everything that has been said is correct, however, if I could just put it into a bit more perspective.The cracking is shrinkage cracking [or alligator,although I haven't heard that term before, I'm from OZ] Yes, it is caused by a high water/cement ratio, but this alone doesn't CAUSE the problem! It is generally the contractor's lack of understanding of the process. Where I am from there is a saying amongst "concreters" that it is "grey and it goes hard"!To them it is that simple, so why make it any more complicated than it needs to be!BUT, what happens is, the concrete has more water added than the design mix calls for,[ high water cement ratio]the concrete is then layed on a base which is impervious to water ie. plastic or just the base wet down.The concrete is then screeded flat, and it's from here that the contractor needs to know what he is doing!It's from this point that the concrete needs to start the curing process, and this involves not letting the concrete "dry out" too quickly during the finishing stages! This is more pronounced on hot and/or windy days and the contractor needs to make the right decisions! Should this be the case, after screeding the contractor could spray on "aliphatic oil" to hold the moisture, or simply fog spray the slab between finishing procedures.But if something is not done, the concrete will dry out quicker on the top than on the bottom , because all the bleed water has to come out the top, and it will try to "curl" the slab, which, because the top is shrinking more than the bottom, it will try to lift the outside edges of the slab, and of course it can't do, so the "shrinkage" cracks are the result! The contractor would have already been told by his supplier's tech guys that it is his fault, but I doubt YOU will get to hear that! I don't believe there is a solution to your problem that isn't a compromise and the only outcomes are a free driveway, with cracks, or a new driveway, but whose to say he can get it right the second time anyway!Sorry for the long post!

 

[fuchsjr]

Excellent earlier responses! May also want to find out where the rebar was placed in the slab.

Sounds like the slab was not wet cured or protected from the drying elements.