Slump test after adding Super P? 7

[Mr168]

Please forgive my ignorance on the subject, as I am a welding guy trying to help a fellow QC guy find an answer.

Is it required or outlined in any code as to when slump tests should be performed when Super P plasticizer is used? The concrete had all tests run before adding the Super P, air tested ok, slump was routinely low. These results were documented, the Super P was added, and no additional testing was performed before it was poured.

This is foundation work for a fossil power plant.

We're going under the assumption that the addtion of the Super P would pretty much invalidate any slump test anyways, but we're looking for some evidence or section of code that confirms or refutes this process of running no further tests after the plasticizer is added (break tests were all coming back good).

This is pretty much a CYA scenario in case of a QA audit or something like that. Thanks for the help.

 

[concretemasonry]

The contractor was allowed to add a super plasticizer at the job site? - That can be much worse than adding water, which should not allowed either, unless you have a loose spec.

Do you have some strange weather conditions or a very, very remote site?

Superplasticized mixes are usually designed to provide the desired properties when the concrete is delivered. This is to provide the desired properties are acheived when delivered. Adding on site can be bad because adequate mixing time is required and it does not respond as fast as water.

Dick

 

[Mr168]

Yes, the plasticizer is being added on the site. We've been having consistent batch plant issues, and the plasticizer is being used in order to get suitable pumpability. It has been an ongoing issue, and they've fiddled with aggregate sizes, etc without success, but have had no issues to date when the plasticizer is used. The sites are remote, but not that remote to where there is some huge transit time between the site and the batch plant. I'm on the outside looking in here, so unfortunately I have very little actual detail.

Is there anything that states that slump tests must be performed after any admixtures, particularly Super P is added?

 

[emmgjld]

I have been on a number of jobs in the wilds of Western Colorado & Utah where Super Plasti. was added on site because of the very long travel time.
Just follow the rules for mixing time & speeds of drum rotation.

YES, the slump is taken BEFORE the addition, along with other plastic mix properties. Remember, the basic mix is without the Plasti.. This helps with the plant control.
Also, take plasticized property tests and cylinders after the addition, as this is the field control.

 

[Mr168]

Thank you for the replies.

 

[civilperson]

Slump is only a guideline for consistency of mix and should not be used as a criteria for acceptance or rejection of a mix. Super plasticizers were the chemical miracle that helped kill the usefulness of slump tests. After a mix design is approved with a given slump, additional water may be added up to the W/C ratio maximum to achieve the desired slump. 8"-10" slumps with F'c of 5500psi to 8600 psi are common using super P.

 

[DRC1]

With the new high end (as in expensive, not duration) Super P slump (and associated segergation) is not a problem. With more traditional Super-P slump can indicate the possibility of excess segragation if the slump is too high. Anything over six and I would start to check the mix to insure the stone is not settling out.
Most supplies have pumpable versions of common mixes. It generally involves smaller stone and higher cement content. Often times a yard or two of rich grout is mixed and pumped through the line prior to adding the concrete.

 

[Mr168]

Appreciate the replies. They were getting slumps right around 8" with the Super P.

 

[riccochet]

There is NO problem with adding Super P to the mix at the job site. On a general basis, Super P is only active in the mix for approx. 45 mins AFTER dosing. After that you will have a rapid set due to the w/c ratio. Job sites add Super P at the site to assist in prolonging the workability time frame. Usually in a pre-construction mtg, it will have been desiginated as a slump prior to and after the addition of Super P.

 

[irasamm]

Remember to rev the truck 30 rotations after the addition of on-site water or plasticizer. There is no problem with tuning in your load like this, as long as you get those revs and test after words.

 

[Ron]

civilperson...consistency in concrete is an important parameter and slump can be used to accept or reject a mix as delivered. Inability to maintain a design slump is a QC issue for the producer and should be dealt with, not modified at the site to accommodate their lack of QA/QC.

Trying to bring the concrete to its maximum W-C ratio at the site is impossible unless you know the moisture content of the aggregates at the time of mixing and how much water was added to the mix at the plant and the mix design is in hand. This should only be done by the producer and certainly not by those on the site without such mix design information.

 

[civilperson]

Ron...a mix as delivered is a load. A mix design is what I was refering to.

 

[cvg]

in over 23 years of experience, I have never seen slump, air or temperature measured before adding an admixture at the site - measurements have always been taken right before the concrete is placed in the forms. If Super-P is required, than the specs / engineer should allow the higher slump as long as W/C ratio and 28-day strength is OK. I agree with others that adding it at the last minute is risky especially for segregation and possibly reduction of the air content. How can the concrete supplier warranty the mix when the driver is simply dumping it in the truck at the site?

 

[civilmate09]

We also encountered same issue adding super plasticizer to the approved mix at site (Melbourne, Australia).

When slump test conducted there was an increase in slump thus, exceeding the permissible tolerance on slump on Australian Standard 1379.

Concrete strength results achieved the project requirements.

NCR was raised on slump issue. However, NCR closed out as designers noted that addition of super "P" will affect only the workability and not the strength of the concrete.

 

[hokie66]

Of course the super plasticizer increased the slump. That is its purpose. Sounds as if the contract documents did not cater for the methods adopted.

 

[BigH]

I have seen a weird spec and won't go into it - needless to say, we have argued to meet the "base slump" - before plasicizer is added; meet the spec (within the guidelines) and it is okay - then add the plasticizer - for increased workability on pumping and spraying (shotcrete).

 

[civilmate09]

Apologies for not detailing the situation on my previous information provided.

All project specs. captures all the requirements for all concreting work specifically concrete testing is concerned. Approved mix design slump is 110mm. +/- 15 mm tolerance.

During concrete pouring on the wall of a transformer building they found it hard for the concrete to settle in. Engineer in-charge contacted the designer and request approval over the phone to modify the approved mix design (additional plasticizer/decreased of water in the mix) to cater concrete workability at site. Designer verbally agreed in the condition to re-submit the modified mix design. Thus, they proceed batching and pouring concrete.

I, on the other hand who used to be the guy who checks all documents submitted to QC department conducted check and balance on the concrete test report provided. I found out that based on the approved mix design, the actual slump recorded (180 mm) on the report exceeded the base slump target.

Anyway, the real issue is engineer failed to provide the additional information to the agreed mix modification over the previously approved mix design.

Issue was resolved by engineer and submitted the modified concrete mix from concrete supplier and verification of verbal agreement by email correspondence notice from designer on the actual date of verbal agreement.

 

[dik]

I'm not sure what Ron was alluding to, but I think he briefly touched on the crux. The mix supplier is normally responsible for concrete delivered to the site. If it is modified by someone other than the supplier, then maybe no one is responsible for the mix.

My apologies to Ron if this is not what he was getting to.

Dik

 

[bb29510]

We use super P daily, It is a workablity agent, On a 3 1/2 to 4 slump the super going go 8-10 depending on cement content. The mixing time is five minute at high rpm before anything can be done. I have taken slump after the p been added but it is really an unuseable value. We record both slumps value on the paperwork but the slump before super P is the only one that has any importants.

 

[vollEngineer]

No problem adding super P? I have seen some serious segregation on a couple of sites. I would just be careful with that sort of statement. There. I feel better.