Cracks in concrete slab

Regarding the concrete slab... Owner of the new store has asked an enginer (structural) to come and evaluate. Here in Mississippi- there's no telling what we'll get for that. In response to a request or mention of a core sample, the contractor said that would only tell us that "One- it is conrete; and two- it has a 3000 mix". The contractor also said that if the floor was to be carpeted, she wouldn't know the difference. He said that this floor holds no weight (steel beams were installed prior to the conrete being poured) and should not make a difference. As far as moisture- he said a vapor barrier was installed to handle that. One structural engineer said that my friend should expect additional cracks and those she already has would probably worsen. My problem is that everyone seems to be downplaying the issue of whether or not this concrete is actually "good"- "they" seem to feel that it won't make a difference. Can someone tell me what I can tell my friend- that she might be able to understand- as to why the condition of the concrete should concern her? like what problems she might run into if the concrete is bad and is ignored? We should have something (God knows what) from our structural engineer soon. (I know this guy and have my doubts, but I can only voice an opinion as I don't really have a dog in this fight.) I do know the contractor is aggravated to say the least- doesn't seem concerned that the concrete is so porous etc. but I expect that from him. He has in turn passed the buck to the guy that poured the concrete- who tried to pass it on to me as I scored the concrete in another section AFTER the crack appeared. One has offered to remove and cut out the cracked area and pour in a patch or to resin fill the crack- no mention of the crumbling etc. Also- these guys said that wxpansion joints or saw cuts weren't necessary- "you don't do those on a foundation for a house and they're fine". Any good arguments out there that I can throw at them? I certainly appreciate this and so does my friend.
Jane

 

[austim]

Hi again, Jane.

In all honesty, I am not particularly well qualified to give you detailed advice. For one thing I have never worked in the USA, and I had never heard of slabs being ¡¥scored and stained¡¦ until I read your earlier message. So in that regard, you are the expert here.

However, I believe that any half-way experienced structural engineer reading your description of events would have concluded (as I did) that there were some significant problems with the slab. The extent of very early cracking, porosity, the weakness demonstrated by your scoring causing small chunks to be removed from the sides of the cut. All those point quite clearly to a pretty low quality slab. As you said yourself, concrete of normal quality does not behave like that, (whether it is in Mississippi or Australia).

I get the impression that ¡¥these guys¡¦ are trying all of the age-old arguments. Yes, concrete cracks, but not usually so soon after placing and so significantly that it becomes a talking point among the other workers on the site. And good concrete is not porous, good concrete does not crumble when a concrete saw is used. The matter of whether/not to use control joints in a floor slab is much more involved than the simple view expressed by the builder. (Is it possible that the building designer specified joints that were omitted on site, and builder is trying to cover his tracks?)

The suggestion that the slab ¡§doesn¡¦t have to carry any weight¡¨ sounds to me like total rubbish (somewhat like the concrete ?). If the slab is supported by steel sub-beams, then the usual situation would be that the slab has to bridge between the beams, rather than simply spread loads directly into the underlying ground.

In those circumstances, the slab should incorporate properly designed steel reinforcement (not just fibres mixed into the bulk concrete) , and the duty required of the concrete would be considerably more severe than for a simple slab-on-ground. It would need adequate compressive strength (which appears questionable, regardless of the statement that it was supplied as a 3000 psi mix), and it requires to be non-porous and generally free from obvious cracking. Otherwise, the reinforcement will not be properly protected against long-term corrosion, with the risk of local damage to the floor at some time in the future (but probably well beyond the life of any warranty to which the builder could be held). With under-strength concrete there could be a risk of excessive deflections resulting in a wavy floor surface.

There is a wide range of possible causes for the slab as constructed behaving badly. The concrete supplied may not have been to specification when it left the concrete supplier; it may have been ¡¥adulterated¡¦ before/during placing, by the addition of surplus water or unapproved additives to make it easier to place; there may have been no attempt at curing the concrete after placement; it may not have been properly compacted (vibrated) during placing, there may have been an excessive delay between mixing and placement. Ask around your concrete trade contacts ¡V I am sure they will be able to extend my short list.

I hope that your doubts about the structural engineer are unfounded. (I like to think that all structural engineers are wise and ethical, and bring nothing but light and happiness wherever we go ļ). It would be nice to think that the ultimate owner who, after all, is the one paying for the builder to get things done properly, will be astute enough to assess the value of the advice he receives, and seek a second opinion if necessary. (perhaps a word in his ear from you could help?).

Meantime, I strongly support the suggestion that you keep your attorney husband working on the documentation that you may need to keep you out of court.

This has been a rather long ramble. In view of the disappearance of your first post, I recommend that you save the whole page (as a web page), just in case you wish to refer to it again.

Good luck.

 

[Qshake]

I agree with AUSTIM. There are a lot of aurguments being made that simply don't hold water when evaluated against a consumer buying a new product. In fact, forget engineering for minute - we (those in the business) all agree that the concrete slab is bad and that it is very likely poor quality and possible questionable workmanship. Moving on to what a business owner, homeowner or consumer in general can expect with respect to new products is a well constructed, safe, sustainable (for a relatively long life) product that is free of defects which would immediately cost the owner-consumer to mitigate. For example - the Lemon law for vehicles - Why pay a nice sum of money for something that you'll replace the engine just after you round the first block!

The best argument that I have used in my early years as a construction inspector is to ask the contractor - workers if that is what they want in their house? And in this case I think a note to the BBB is also a good threat to the contractor. As I've stated, after all the engineering is sorted out, it comes down to whether or not the product is what it should be based on the expectations of the consumer tempered with the expectations of the industry as a whole.

By the way, a lot more can be determined from a core sample than what you've stated the contractor said.

Good Luck.

 

Thanks for the advice- once again. We'll see what the engineer has to say and perhaps he'll surprise me. The last time I tangled with him was after his community sewage station flooded my house with neighborhood sewage! He wanted to send carpet cleaners in to clean my padding and carpet and I threatened to bring the EPA in to test the carpet after they were finished. He was flabbergasted that I would think of such, but who wants a floor and padding staurated with e-coli? He later saw my husband and said that he would much rather deal with him in the future than me!!!! I don't think he knows yet that I will be doing the acid staining work, etc. Should be comical when he does.
As far as not knowing about staining concrete, etc- go to a web site for The Stamp Store in Oklahoma City (stamp being concrete stamping techniques and supplies). Should find that interesting. After being stained, the concrete resembles marble as the stain reacts with the aggregates and has many depths and dimensions. This technique seems to be the hottest thing now in residential construction. High quality sealers are placed on top of the stain after it is neutralized and the durability much exceeds that of linoleum, etc and is much more cost effective. Also beneficial to those who suffer allergy problems.
Much appreciate the insight and opinions- its nice to know there are "smart people" out there who don't mind helping others out. THANKS! Jane

 

[Imagineer]

Jane,
Is this a consultant engineer or the local city/county engineer? Imagineer

 

This fellow is affiliated with a local engineering firm and happens to be the city's engineer. I hear that he has a degree in structural engineering. Late today. I was told that he was to do the inspection- but something has changed his mind and he now says he cannot. Whatever this is worth-this engineer had to come and inspect in order for the addition to be made on the structure or the pouring of this slab and building, etc. The owner is now seeking a testing lab (local) that supposedly can evaluate the concrete and an engineer (structural) to view the slab. We'll see what this brings. Meanwhile- contractor is pushing to continue and appears nervous- wonder why. Keeps ranting that we are concerned with cosmetics. Have not determined is control joints were on blueprints or not. Thanks guys! Jane

 

[Ron]

Hi Again Jane...
Info above is right on target as usual for these guys. My addition is that even if the control joint pattern is not shown on the plans, there are plenty of data pointing you to accepted industry practice (for which the contractor is responsible to know). Check ACI 302 (Concrete Slabs)and you will get the appropriate guidance for control joints, finish and tolerances, including thickness (by reference to ACI 117, Tolerances).

Of all the concrete failure investigations I do, by far the most common has to do with exactly the problems you have described...workmanship (or obvious lack thereof). You can have concrete that meets the minimum compressive strength requirement, yet still performs horribly. It is necessary to achieve durability as well as strength, a concept that eludes many contractors, since they are usually the reason for durability issues.

Remember...good concrete comes from good aggregate, good cement, and good water....bad concrete can come from the same stuff!

 

[RDK]

If there is a problem with the competence and or qualifications of someone calling himself an engineer, then this is an issue for the local professional association. They should be able to recommend someone who can take a look at the building in question and quickly determine if it is necessary to take action.

In Mississippi the association’s web site is

http://www.pepls.state.ms.us/

follow the links there and you can find the right contacts and procedure to follow in reporting unprofessional conduct. If unprofessional conduct can be proven then you are in good shape for any suit for damages.

It sounds like you have a good case to prove unprofessional practice.

Let us know what turns out. There are some of us here who believe in our profession and want to help.
Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com