delay in concrete trucks 6

[joncle10]

Hello,

While casting a retaining wall and because of the heavy traffic, a delay of 2.5 hours between the concrete trucks was noticed.
When the concrete arrived at the site, the slump was taken and found to be 16 cm (a super plasticizer was used - no water has been added to the mix during the travel since one of our workers was next to the driver). Therefore, the engineer agreed to cast the concrete.
Regarding the concrete which has already been casted and located in the formwork, should I worry about any cold joint formation ? the concrete initial setting time is set to 2 to 3 hours.
I have verified the wall reinforcement and found that it was enough to cater for the shear friction through the entire area of the retaining wall.
Any remarks regarding the above or things should I do in case this situation happens again ?
thank you

 

[BUGGAR]

What is your responsibility? Engineer of Record, Inspector? This could define your contractual duty.

 

[joncle10]

Inspector

 

[EngineeringEric]

What is the allowable batch to placement time? typically we have 90 mins and if exceeded the truck is rejected. I don't think you gain more time by adding a plasticizer not really sure how that would work (haven't thought about it honestly nor ran into in person...)

 

[joncle10]

Yes it is 90 minutes. But here is the situation. if you will reject the truck, the next truck u will ask for will also be in a delay so most probably, u will face the same situation.
For this reason, the slump was taken. If the slump was too low, it would have meant that the concrete has began to harden. Therefore, it will be rejected. Otherwise, if the slump is still ok, the concrete could be used.

 

[BUGGAR]

Check your contract. When I worked on BART and CALTRANS as an inspector, our specific responsibilities were to "Observe and Report" as defined in the Construction Contract, no more. Practicality will dictate when you need to expand this and maybe it's time to ask boss how far he wants your responsibility to go.

I had your situation many times and finally carried a copy of the specs describing contract concrete requirements and inspection requirements which I gave to the Contractor when this issue arose. As an inspector, I never had authority to direct construction except in an emergency situation. But the concrete superintendent would turn them away when he saw me recording the times on the tickets.

 

[allgoodnamestaken]

Did you take concrete temp readings when you measured the slump? How hot was the concrete?

 

[joncle10]

Less than 30 degrees..another parameter that showed me that the cement hydration have not started yet

 

[allgoodnamestaken]

Did you take samples/cylinders?

 

[joncle10]

Sure this is part of the quality control

 

[Ron]

The slump, when using a plasticizer, can be misleading. If the plasticizer was a set retarding admixture, then the placed concrete might be OK; however, you still have the cold joint issue. You probably can't get around that one,so evaluate carefully.

 

[JStephen]

Several years back, we had some concrete breaks come in low- the design still worked, but strength was lower than specified. That was resolved by adjusting the contract price- and that might be one option here.

 

[MacGruber22]

As Ron said, if the producer designed the mix with a retarding admixture then it may be just fine. You can design set retarded concrete for much longer than 2.5 hours and not affect the design strength. The concrete submittal should have had the cut sheet for the set retarder - Euclid Chemical and Grace tend to be the manufacturers I see the most. Someone from the concrete producer needs to confirm the products and the dosages used, and the EOR should be requesting to receive a letter saying that the mix design has a history of performing properly in that amount of time, along with the backup data to show it. Grace, Euclid, or whoever made the admixture may be able to provide some guidance if it is clear there is no issue.

Always take an extra set of cylinders in those situations when it is not clear whether the contract requirements have been violated. The special inspectors can't stop a contractor from working, you can only inform them that their material or workmanship violates the contract documents. In fact it is very risky telling them to stop, because if they do and you are wrong, they will come after your company. As others can surely relate to, I have told contractors hundreds of times that their work is not meeting the contract - they continue anyways. Document, document, document!!! and get in touch with the EOR ASAP.

"It is imperative Cunth doesn't get his hands on those codes."

 

[joncle10]

Ok thank you guys for your valuable input.
In case of a cold joint formation and as a I have indicated in my first post, the existing reinforcement is verifying the shear friction through the entire area. Should I have any other worries ?
6 cubes were taken from each delayed concrete truck. therefore, I can and will assess if any decrease in the specified strength of the concrete is noted and will act correspondingly.

 

[Ron]

MacGruber22.....good advice!

 

[MacGruber22]

Should I have any other worries ?

Water intrusion? Maybe not depending on what this wall is doing.

6 cubes? Why cubes? of just the cement matrix?

"It is imperative Cunth doesn't get his hands on those codes."

 

[MacGruber22]

Thanks, Ron. It is always nice to know that some of my advice isn't a big steamy turd in disguise.

"It is imperative Cunth doesn't get his hands on those codes."

 

[Ingenuity]

6 cubes? Why cubes? of just the cement matrix?

The OP is in the country "AO" (Angola?) and they probably use cubes not cylinders for compression testing, likely to British standards.

 

[TehMightyEngineer]

Cubes are more standard in Europe than cylinders, from my understanding.

Professional and Structural Engineer (ME, NH, MA)
American Concrete Industries

http://www.americanconcrete.com

 

[joncle10]

Right I am in Angola. We take cubes rather than cylinders for strength testing.
Thank you all for your input.