Concrete Slab Cracks - Should I Worry?

[DougWil]

Think so? The slab cracked before any weight was put on it.

Well see if you can spot the issues.


Ill prepared soil and base.
Watery, high slump, low strength concrete. <<< Good chance, we need to know more.
Lack of primary reinforcement,,,, talked into fibermesh.
Not sawing the joints soon enough or not sawing any joints. <<< Maybe.
Not curing the concrete properly. <<< Bullseye.
Poor surface finishing from weather or workmanship.

 

[lakeroadster]

Well see if you can spot the issues.

Ill prepared soil and base. If the sub grade wasn't tested after compaction, nobody knows.
Watery, high slump, low strength concrete. Low strength (3,000 psi), yes. That doesn't mean that is why it cracked in this case. Watery, High Slump..nobody knows unless they were there during the pour or they have access to the mix sheets now and know how much water was added.
Lack of primary reinforcement,,,, talked into fiber mesh.
Steel reinforcement wouldn't have changed the cracking.. the slab has had no weight on it at this point.
Not sawing the joints soon enough or not sawing any joints. Again, unless you were there, you don't know.
Not curing the concrete properly. That looks to be the case here.
Poor surface finishing from weather or workmanship. That doesn't appear to be the issue from the photo's.

Sure, see above in Green, as applicable to the OP's query.

 

[walrus]

So, if he wants to put a 2-post lift where one of those cracks is located, is OP SOL?

For best practice, should you always put rebar where you want to place a lift? Seems like you could end up drilling holes and hitting steel and then WTF do you do?

It's called a rebar cutter, goes into a hammer drill with hammer off and cuts right thru rebar

An excellent summation!

I just wonder if anyone looks at these forums before starting construction. With something as basic and permanent as a slab, there should be a high degree of interest in getting it right the first time.

 

[DougWil]

Sure, see above in Green, as applicable to the OP's query.

You really don't get it or don't want to get it.
Now that the slab is extensively cracked, there is no primary reinforcement to keep it together.

So no, not having rebar isn't what caused the slab to crack into several distinct pieces, along with sawcuts.
But now that it has, NOT having rebar is going to significantly shorten the life of that slab.

 

[lakeroadster]

So no, not having rebar isn't what caused the slab to crack into several distinct pieces.

Exactly...

 

[pmiranda]

Yup, but now there's nothing to keep the pieces from moving, right?

 

[lakeroadster]

....Reinforcing is nice, but it is not a "normal" thing and it isn't required. (It would have kept the cracks thinner, though.)

There is no evidence of and the OP has not mentioned vertical displacement. With a proper base, this will NEVER happen.

Shrinkage cracks like this do develop that quickly, which is why it's so important to do the saw cut joints so quickly. More could develop over time, but they will be small in comparison to what has already happened.

Everyone has these cracks - they just usually form inside the control joint troughs and stay out of site when those cuts fill up with dirt and crud. Contraction cracks alone are no cause for alarm.

.....