URGENT, PLEASE COMMENT

[AdM22]

i've just poured a waffle roof slab(flat) of a single family home. The beams are 6"x6" spaced 24" in both directions with 4-#3rebars and its slab is 3".
Now here comes my problem. The structural engineer specified the concrete resistance at 200kg/cm2 and they used 150kg/cm2. The structural engineer is not in town so I came here....

How critical is it?

*Attached is a JPEG
The area in red is my concern since it spans +/-14'
Everything is in centimeters.

 

[engineertipsman]

I wouldnt worry about it today, they are not going to remove the forms today correct? Long term might be an issue, but for the next couple days till the engineer returns, it will be curing and not achieve the 200kg anyway.

 

[AdM22]

attachment...

 

[BAretired]

Could not find your attachment.

The concrete strength specified is 2840 psi. The concrete strength used is 2130 psi.

When you say the beams are 6"x6", do you mean the overall depth is 9" including slab? Or is it only 6"?

The low strength will affect deflection. It should not significantly affect strength in bending, but it will affect shear strength.

Best plan is to wait for the engineer to return and give you his opinion.

BA

 

[PEinc]

I agree. Wait for the engineer and also the cylinder breaks for the concrete samples. Maybe the 200kg/cm2 will be there when tested. Maybe the design still works with 150 kg/cm2.

http://www.PeirceEngineering.com

 

[AdM22]

Thanks for your response.
No, they just pour it today but it has accelerator. Why will it be an issue in the long term? What can be done about it now? I don't want to waste 407ft3 of concrete....

 

[SlideRuleEra]

Waiting for the Engineer to return is reasonable. To answer you second question:
"What can be done about it now?"
Regardless of what the specification requires for curing - start a "traditional" wet cure NOW. Keep the concrete CONSTANTLY wet with sprinklers, soaker hose, burlap, Burlene, etc. At least this step will make the the 150 kg/cm2 concrete be its best.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[AdM22]

Answering BAretired:

Correct, the overall depth is 9". I've attached the file separately.

Let me clarify, it has already been poured, by the time he comes back it will be cured since is has accelerator...
If it's a major issue I rather remove the concrete NOW while I can.

 

[engineertipsman]

I dont see how you even know what the strengh is. Certainly they are not going to remove it based on your word, and not wait for the engineer. Long term, it might be that the design doesnt work, i.e. after 28 days, etc. For now, let it cure, cure it correctly and see what you get in 28 days. Also, by then, the engineer might say its ok with 150.

 

[SlideRuleEra]

Since your say that you are willing to remove the concrete, that is the best option. Much easier now and the long term technical and possible financial problems go away. Even if the Engineer can and is willing to accept the concrete, the Owner may deduct partial payment from you as fair compensation for accepting substandard material. As a former Owner's representative, I would.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[BAretired]

AdM22,

Follow SlidRuleEra's advice and wait for the engineer.

BA

 

[BAretired]

Oops, SlideRuleEra came up with some more advice. I was referring to his earlier thread where he advised you to wet cure it. That would be my advice.

BA

 

[AdM22]

Answering to engineertipsman:

1-I know because I order it myself.
2-yes, they will remove it based on my word.

I already got hold of the engineer, I am waiting for his response.

 

[BAretired]

AdM22,

It never pays to rush into things until you have had an opportunity to review all aspects. There may well be a method of strengthening the most critical area (shaded red) after the concrete sets.

BA

 

[AdM22]

I agree BAretired, that's why I am waiting until he calls me back this afternoon.

Going back to your question regarding the slab, sorry, it's 6.5" overall.

Thanks to you all. I will keep you posted.

 

[Ron]

AdM22...an accelerating admixture does not shorten the curing time...it only shortens the initial hydration time and initial set time. Keep the curing process the same.

 

[DRC1]

I would advise you not to remove shoring until the matter is resolved. This will prevent any excessive deflection. If strength or deflection is an issue, an intermediate support may be required to resolve the situation. Did want to commend you for standing up and being forthright about the problem.

 

[dik]

Wet curing is good and leaving the shoring in as long as possible is good... best to wait until the engineer has reviewed it.

SRE... you may have to be careful about holding back some of the funds... in many jurisdictions, this has to be in agreement with the Contractor. In some jurisdictions, the only manner in which funds can be withheld is for the engineer to reject that portion of the Work outright.

Dik

 

[AdM22]

Answering to DRC1:

Absolutely, if there´s an issue, I leave finger pointing aside and focus on resolving the matter. We all make mistakes, the problem is the cost associated with it. This is a great forum and I am very fortunate.

Answering to Dik:

Yes, wet curing is currently in the works and yes, shoring is not going anywhere.

Regarding your second comment, it´s not a concern first because I am in Mexico and second because I am the one in charge of construction. Nevertheless, thanks for your advise.

 

[SlideRuleEra]

dik - I know what you mean. I have spent a career negotiating this type settlement with Contractors. The Contractor always is given the option of removing and replacing the substandard material.

Usually it takes the stark choice between material replacement or negotiations to convince the Contractor that he can not disregard the specification, intentionally or accidentally, without (financial) consequences. Am happy to say that no contract that I've helped settle has resulted in legal action or arbitration. Also, the vast majority of the time, the Contractor would bid on and be awarded future projects - he must have been treated fairly during negotiations or we would not have heard from them again.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net