Any Concrete Experts here?

[Julian]

So our subdivision had bricks removed from around the pool and had it replaced with concrete. The work is done and there are a number of thin cracks in the concrete. The contractor says that is normal....to me it doesn't look right? Expert opinions?

 

[redthumper9]

Hairline cracks are normal........it sucks, but they are. Before going strictly into the turf grass business, we were my dad and I were general contractors (still are really). Cracks like that are nearly impossible to avoid around here. The soil types here are just too inconsistent. If the contractor did all the necessary preparation (soil tamping, reinforcing fiber in the concrete mix, and possibly even wire mesh installed during the pour) then he truly did everything he could. We even used to run sprinklers on driveways after they hardened a bit to slow down the drying process. Seems like they were more likely to happen when it dried in the faster. Some concrete guys put an accelerator in the mix to speed of the drying. We never allowed our guys to do this after learning of it. I would of course note them and if they start to separate further or if you see one side of the crack settle more and create a hazard, then bring it to his attention.

 

[Julian]

Thanks @redthumper9 for the quick reply! I'm not sure what they put in for reinforcement (if anything), but it is around a pool that has been there for 30 years...so there was no subsurface prep needed really....just pull the bricks out and replace with concrete.

 

[Bruce]

There is concrete that has cracked and concrete that will crack is the typical statement about concerte cracks here. Those are hairline cracks and are probably just part of the curing process.

 

[Murf'n'surf]

@Speedling is our local concrete man

 

[Bruce]

@Speedling is our local concrete man

I believe his expertise is stacking things with concrete between them. He is a great source of advice.

 

[Speedling]

I believe his expertise is stacking things with concrete between them. He is a great source of advice.

Yup. Not a concrete expert.
But i do know that concrete does two things.
1. Get hard
2. Crack

 

[Gym]

I am also NOT a concrete expert but I had the same treatment done to my pool about 9 years ago and only have 2 hairline cracks that showed up about 3-4 years after the work was done. I did keep the concrete wet and shaded with burlap for a week after the pour which I believe helped to reduce the cracking. The concrete was also reinforced with fibers. I also noticed you have some cracking right next to an expansion joint. I question if they 1) added any reinforcing, 2) performed a slump test to determine the concrete's workability. I found this out the hard way when a foundation I was having poured was a "hot pour" due to the concrete truck breaking down on the way to my job causing the concrete to start to set up. The driver just added some water so it would flow down the chute which made the mix weaker.

 

[Julian]

This comes with a 1 year warranty. .. so I guess we'll just have to see if they get bigger....?

 

[Zarrella]

I had a new driveway poured 2 weeks ago. The contractor said the same as @Bruce .
There are only 2 kinds of concrete.....concrete that has cracked and concrete that hasn't cracked yet!

 

[Eurocat]

Although I am not a contractor, I have subbed enough to observe a thing or 2. Hairline cracks are almost impossible to avoid over most surfaces, however, if you notice correctly, some of them happened inches away from the stress cuts. those cuts, or gaps are there so the concrete can expand and have some movement without cracking. By the looks of it, there are too many, and being that some are so close to the stress points, might be an indicator that something is not up to par. Maybe the curing process was forced, or simply not slowed down enough, or, the incorrect psi was used, or, not enough solids in the mix. from the way you took picks I also cannot see the thickness of it. Too many variables...
One thing is for sure, if you are in an area that has freeze/thaw cycles it will become a big problem in just one or 2 seasons.
My 2 cents are to get an opinion from another contractor or even a couple of different ones. Look for guys that handle specific concrete work, or consult with Pool builders that work with concrete. They might ask for a consulting fee and in this case it is preferable, but don't promise any work so it does not bias the opinions. (remember I am far from an expert)

 

[Speedling]

How thick is the concrete?

 

[Bruce]

It replaced bricks so I am guessing it to be pretty thin.

 

[Speedling]

Thicker concrete is less prone to crack.
Slabs are 4" minimum and footings 8" min.

 

[clint6760]

Most concrete guys around here will guarantee concrete for fire and theft. Haha. And all concrete will crack some and those small ones are inevitable.