Concrete pad has micro-fractures - that bad?

[Tractor Seabee]

What I decided to do was put an impact sprinkler on it with a controller. The controller turns on the sprinkler every 6 hours and runs for 15 mins. I set the timing of the controller so it comes on during the hottest time of the day. Hopefully, that will help a bit.

The expansion cuts were made this afternoon, so about 24hrs after the pour.

Thanks for all the advice.

Waiting that long to do the expansion cuts (proper term is control joints); stand by, larger problems are looming ahead. Expansion cuts have to be made as soon as the saw can get on the slab even if it is midnight. Next day, too late, cracks have already startd where the concrete wants them to not where you want them.

I was a certified concrete inspector in my earlier construction career. There is way more inaccurate information on concrete outthere in the construction world than there is accurate information. A manual you can get on Amazon; "The Contractor's Guide to Quality Concrete Constructio" is a must read for anyone contemplating or doing concrete work.

The first step for slabs on grade is a good solid well and even compacted subgrade (95% density or more). W/O that you are beat before you start.

Ron

 

[Streetcar]

Set timer on sprinklers so that the concrete is always wet.

 

[Egon]

What's happened has happened. Keep the concrete wet may keep the micro cracks from expanding.

They may be surface cracks due to pouring & finishing methods a high temperatures.

The chances are all is fine but do put a proper sealer on thr concrete.

 

[Oldpath05]

("Structurally there is big difference between large crack and micro cracks")<<<<I didn't know that, thanks.

I would think that after one day adding water is to late, mine was poured at 6am finished at 9am by the concrete guy I hired, when he was done told me to keep the slab wet rest of the day with garden hose, couple days after that started building on it.

So I think after one day whats done is done and nothing more can be done except for tarring the slab up and doing it over again. Not sure of your cost but my 6x26x36 slab was just under 3k 5 years ago, not pocket change but I thought it was a fair price.

 

[dmccarty]

Our house is a slab which is not often done in my area of NC. We have a couple inches of insulation between the 67 gravel and the slab. We poured on the hottest day of the summer, , during a very hot season. :shocked: It was so hot, the builder who was up there in years, had to go home a bit early because the heat got to him. :shocked: I think we poured late morning or around lunch time so we were out there during the hottest part of the day. I had drawn up a decorative pattern for the concrete joints and the mason showed up the next morning to cut them. On the day of the pour, the builders son was supposed to show up with a part we needed to run the well, and he was not able to get the right part. :confused3: The neighbors let us fill up some garbage cans to transport water to the house to cool down the concrete and we got the right part the next day for the well. Not optimum but it seems things turned out ok.

No rebar in the slab.

We have a few places were the slab cracked. Interestingly, they are all at "inside" corners but one. The front port is L shaped and at a lower level than the house slab. This means there is an indentation in the house slab. A small crack formed on the inside corner of the indentation. The other "inside" corner cracks are in the master bath that has a walk in shower. The shower floor was to be poured by the tile guy so we blocked off the slab pour. This created stress in the slab at each corner and we have small cracks. What is interesting is that these cracks and the porch crack all have the same angle. The only other crack in the surface of the slab is where the cut in the concrete did not go deep enough. They pulled up on the saw a bit too early when getting near the edge of the slab. There ARE other cracks. Lots of them but they are all down in the cut concrete joints. :thumbsup: The cuts are decorative and did control cracking except as mentioned. The cracks have not moved or changed since they formed 13 years ago.

The cuts are roughly 3'x3' depending on what was requited to fit a room.

Later,
Dan

 

[Jstpssng]

("Structurally there is big difference between large crack and micro cracks")<<<<I didn't know that, thanks.

I would think that after one day adding water is to late, mine was poured at 6am finished at 9am by the concrete guy I hired, when he was done told me to keep the slab wet rest of the day with garden hose, couple days after that started building on it.

So I think after one day whats done is done and nothing more can be done except for tarring the slab up and doing it over again. Not sure of your cost but my 6x26x36 slab was just under 3k 5 years ago, not pocket change but I thought it was a fair price.

Up here the concrete alone would be at least $1800. Add on the rebar and labor, it seems like a good price

 

[Streetcar]

If you can, keep water on slab for a week. Concrete will have 90 percent of ultimate strength by then.
Sealing surface will help with the micro cracks.
Concrete will normally crack at 45 degree angle, due to weakness in tension

 

[EddieWalker]

What are micro cracks?

If I'm understanding this, do you have a lot of tiny, think cracks all over the place?

When too much water is added to the mix, you get large cracks when it cures because the volume taken up in the concrete evaporates and there is now less volume of concrete inside the poured area.

Lots of small cracks are something different. So far, I haven't read any comments on lots of small cracks, they are all talking about big cracks.

Was anything added to the mix? A chemical of some kind to deal with local temperatures? or something else that was supposed to improve the concrete in some manner that might have been done wrong?

Until I knew exactly what was causing the cracks, I would not build on that pad.

The first thing that I would do is hire an engineer who specializes in concrete.

I would also contact the plant where the concrete came from and speak to a manager there. Not the dispatcher. Not a driver.

Take pictures today from a spot that you can take the exact same picture again in 7 days. Put a ruler on the concrete when you take the picture for reference.

 

[ovrszd]

All. Concrete. Cracks. All. Concrete.

 

[Streetcar]

What are micro cracks?

If I'm understanding this, do you have a lot of tiny, think cracks all over the place?

When too much water is added to the mix, you get large cracks when it cures because the volume taken up in the concrete evaporates and there is now less volume of concrete inside the poured area.

Lots of small cracks are something different. So far, I haven't read any comments on lots of small cracks, they are all talking about big cracks.

Was anything added to the mix? A chemical of some kind to deal with local temperatures? or something else that was supposed to improve the concrete in some manner that might have been done wrong?

Until I knew exactly what was causing the cracks, I would not build on that pad.

The first thing that I would do is hire an engineer who specializes in concrete.

I would also contact the plant where the concrete came from and speak to a manager there. Not the dispatcher. Not a driver.

Take pictures today from a spot that you can take the exact same picture again in 7 days. Put a ruler on the concrete when you take the picture for reference.

I am assuming op is calling a series of small interconnected cracks as micro cracks .
Similar to spider web, cracks caused by excess water in surface during finishing