Full depth concrete cracks (water leaks) 2

[concretebaby]

Dear All,
We have noticed the leakage from casted concrete slabs for a tower building when it rained heavily recently. The cracks seems not be be visible by naked eye since the day of pouring. The issue of leakage is almost in all slabs casted since last 6-8 months! nobody noticed big cracks by naked eyes except minor cracks here and there...which were repaired by cementitious grout. Nothing seemed to be serious until it rained heavily recently and all slab bottoms were observed to be leaking
- all slabs poured were 250-400 m3 and average time taken to cast each slab is around 5-10 hours. The pouring rate is governed by contractor as he is the one who dictates it. RMC supplies concrete as per order, truck-by-truck
- avg ambient temperature= 38-42 Deg C (during day), Fresh concrete temp checked for every truck is not above 27 Deg C.
- Avg humidity 35%
- Wind speed varies from 13-15 KMPH
- If it wouldn't have rained heavily nobody would have witnessed the leaks, means the cracks are negligible in width to get caught by naked eyes

Please your expert advice(s)on the possible root cause(s) on the given situation. And what is the way forward?
Thanks in advance

 

[Ingenuity]

Please your expert advice(s)on the possible root cause(s) on the given situation

Tensile forces exceeded the tensile strength of the concrete! You need to give a lot more info!

And what is the way forward?

Hire an engineer! Give him/her copy of the original structural drawings and other relevant information. Have him/her conduct a site review.

 

[hokie66]

What are the plan dimensions of the floors? From your description, I take it that the building is incomplete, with floors exposed to the weather.

These sound like drying shrinkage cracks. Atmospheric conditions during construction have probably contributed. Those are severe hot weather concreting conditions. What curing practices were used?

 

[concretebaby]

The tower is still under construction and exposed to external climate. Curing compound was applied after final finishing of concrete surface. We suspect plastic shrinkage cracks due to evaporation rate exceeding bleeding rate of concrete as the mix contains high amounts of supplementary cementitious additives (silica fume and flyash) and weather was hot during concrete placement. The cracks weren't visible during or post concreting operations (few cracks here and there were treated by cementitious grout repair) but after rains the slabs show leaks at many random locations. Attached picture in initial post will show typical crack patterns. Another point of concern is slow pouring rate of (40-50 m3/hour) requested by contractor which may have caused cold joints at some locations. There are lot of photos to share but unfortunately I am unable to attach multiple photos here.

 

[hokie66]

If the cracks weren't visible soon after casting, they are not plastic shrinkage cracks, which as the name implies, occur during the plastic stage of concrete, before hardening. Lack of curing is probably a contributor, as most 'curing compounds' don't help very much.

 

[Smoulder]

Will there be water inside when finished building? Water leaks not a problem if closed in. Any sign of strength problems?

 

[LittleInch]

concretebaby,

Ig f you use the image function you can load a few photos, but no more than 3 or 4 please.

Or paste them into a word file, pdf it and post that.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[DTS419]

If the cracks weren't visible soon after casting, they are not plastic shrinkage cracks, which as the name implies, occur during the plastic stage of concrete, before hardening. Lack of curing is probably a contributor, as most 'curing compounds' don't help very much.

I'll add to this that shrinkage cracks can occur long after the pour because the concrete continues to shrink over time. They can also occur while the concrete is plastic but go unnoticed. Please avoid describing cracks as "big" or "small". That is purely a matter of perspective and means nothing to anybody else. Important information about cracks is width, length, and specific location. As we all learned in Reinforced Concrete 101: all reinforced concrete cracks. Most cracks are undetectable and not a structural concern; making a CIP concrete surface 100% waterproof can be extremely challenging. Your best course of action is likely to consider a waterproof coating or a crystalline sealer. But, it's hard to give specific advice here without any other information.

 

[cliff234]

Is there sufficient reinforcing steel in both directions? Is there any excessive restraint inhibiting shrinkage? (For example, are there opposing shear walls at each end of the floor preventing the slab from shrinking?) Was the mix design configured to minimize shrinkage? (i.e., low w/c ratio, well-graded aggregate, Are cracks occurring randomly, or is there a consistent pattern from floor to floor? How wide are the cracks? (Hairline cracks might let water through, but might otherwise not be an issue.) Assuming there will be a roofing membrane on the roof, hairline cracks may be ok if they are static and are not structural. Are the cracks structural? (Are they in the bottom at mid-span or top at the end of the spans? Are they near the columns? (punching shear?). Are the cracks consistently through the slab? You did not describe the structural system other than to say it’s a concrete slab.

You did not provide enough information to assess the cause and propose remedial measures to fix the cracks, and even if you did, it is difficult to render a good opinion without looking at the slab in-person. I suggest hiring a knowledgeable and experienced local engineer (one experienced in troubleshooting concrete construction) to look at the cracks in person. (I say “knowledgeable” because not every engineer will be able to identify the cause of the cracks and provide solutions.) Ingenuity said the same thing - much more concisely!

 

[TLHS]

That's not even necessarily a deficiency. Unless this was designed as a water retaining structure it's expected that a bunch of ponded water will result in seepage. Under normal bending stresses you're going to see cracks large enough for water seepage. You have to actively keep the bending stresses very low with additional reinforcing if you expect something to hold water, in addition to paying close attention to your mix and other things. When that isn't done, you'd normally give a slab a waterproofing membrane if you expected it to hold back water.