Slump test after adding Super P?
Slump test after adding Super P?
(OP)
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.
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.





RE: Slump test after adding Super P?
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
RE: Slump test after adding Super P?
Is there anything that states that slump tests must be performed after any admixtures, particularly Super P is added?
RE: Slump test after adding Super P?
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.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
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.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
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.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
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.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
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.
RE: Slump test after adding Super P?
My apologies to Ron if this is not what he was getting to.
Dik
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
Many applications especially flat work (except decks)concrete strength is not a major factor. Increase the slump with water instead of super P will give a much better finsh, especially in hot weather.
My one point is that, with in reason, and with consideration, raising the w/c at the job is not a cardnial sin.
My other comment is although good documentation is important, it is increasingly difficult to deal with field conditions in the field.
RE: Slump test after adding Super P?
That practice should not be allowed....it compromises the mix design which is the basis of f'c...the design.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
However, Is it possible between concrete supplier and the QC personell in charge to the mix to have an arrangement for some allowances to put extra water or plasticer to site due site condition and or type of structures to be poured without compromising the mix design itself?
I think this case is acceptable to some degree.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
Concrete can be properly designed for numerous applications and construction techniques. It's not that difficult to match the two and they don't have to be incompatible. The problem comes when you have contractors and subcontractors who know NOTHING about concrete technology indiscriminately adulterating a mix for their purposes. That causes concrete failures..both strength and durability for the sake of placement ease.
Compressive strength is only one parameter of quality concrete, and by far the easiest to meet. Placeability and durability can be achieved consistent with strength.
Don't screw it up in the field. Don't bring a residential concrete mentality to a structural concrete necessity.
RE: Slump test after adding Super P?
RE: Slump test after adding Super P?
Dik
RE: Slump test after adding Super P?
Concretedoc, I admit my comment on rereading does sound arrogant. I apologise. Feel free to red flag any of my comments which you consider inappropriate. That is what the red flag function is for.
I agree that many contractors know a lot about concrete, but there are also a lot who don't, and only want to know what benefits them.
As to the other quote of a comment made by me, it does sound a bit flippant, but I don't think it was sour grapes. I will try to find the discussion and see what it was about.
RE: Slump test after adding Super P?
How would it be inappropiate, according to aci I am allow one inch tolerant at 3 inch slump. so basically I,m legal within the slump range.i just remark that super p does not like dry slumps. The slump mostly is base on concrete before the super p added.
RE: Slump test after adding Super P?
I have been building bridges and foundations for too many years now. I have been sworn at by too many inspectors becuase I have taken 3 inch slump to 6 inch slump. Everbody thinks that the spec is what needs to be followed when a.) the engineer never considered the congestion of the rebar in the design of the mix (Often I do not think the engineer has any clue as to how congested the rebar designs have become) B. Uses a spec that has been used on 100 prevoius jobs with out any thought that pouring in April is any different than pouring in July. C. The concrete now has so much chemistry in it, the suppliers will tell you "Sure we can produce it for a steep surcharge, but we have no idea if it will do what you want it to do". D. The engineer assumes anything that water can do super P can do which is not always the case. For example, mix designs assume the concrete is consistent through out the load, which it is not. As you move through the load, the consistancy of the mix will change. Sometinmes, especially on a dry load, a little water can improve the last few yards. E. All concrete does not need the same perfomance criteria. A four foot high retaining wall does not need to meet the same requirements as a 50 ft long cast in place self supproting deck. Yet with today's Q/C proceedures, documentation is required to show that all the parameters were met. All this ends up costing the owner considerable money yet does not result in a better structure.
Quality of Design and Quality of construction needs to be better enforced for the industry as a whole to improve.
RE: Slump test after adding Super P?
I'll start with the original question. So far as I know, there is no code guidance regarding testing the properties of the concrete before or after adding the super. Best practices would dictate that one should verify the initial slump before super to assure the mix is properly proportioned as delivered. Then the concrete should again be tested after the super for plastic properties and compressive strength.
I typically recommend not exceeding an 8" slump unless the concrete is designed to meet self-consolidating stability requirements or there may be risk of segregation.
Testing the properties of the concrete after the super is an absolute must as some super's add entrained air while others will cause the air content to drop. In most cases, the super will provide additional strength due to better cement particle dispersion. I've seen increases as high as 1500 psi.
So far as adding at the site or the plant, it all depends on the haul time plus unload time. In most cases I see it added at the site to provide the longest possible working time. Someone at the site, either QA or QC should be assigned the task of monitoring the final mix time.
What the slump should be before the super depends on the mix requirements. In most cases it is easier to control all the properties if the initial slump is 3-4", but I have designed mixes with basically no-slump prior to the super in order to meet project requirements.
Superplasticizer technology has come a long long way in my 20-years of seeing it develop. We are to the point where we will choose between multiple super's based on the performance requirements of the plastic or hardened concrete.
RE: Slump test after adding Super P?
NYSDOT uses a somewhat idiot proof system. The specs provide the contractor with the mix design and there are enough safeguards to ensure that 3000psi is consistently achieved. What is required of the contractor is to meet the air and slump requirements for the specified mix. Of course, from my days as an inspector, there were some concrete truck drivers who could turn a 4" slump into 12" slump.
RE: Slump test after adding Super P?
I would have the slump taken at batch plant, and on site after all additional mixtures are added, remember to keep the concrete trucks drum rolling at the correct rotation.
It is essential to take your cylinder samples to prove that the concrete is still at designed strength after the additives are mixed in with the concrete.
Maybe run a 3 day compressive break as well as a 7 day and a 28 day break. This should cover you from a QA/QC point of view. (If I am not mistaken)
RE: Slump test after adding Super P?
Dik
RE: Slump test after adding Super P?
The slump test will alert you to something being different in the load such as water content, air content, aggregate proportions, admixture dosage, admixture compatibility, time since batching, temperature, foreign matter contamination, or some other cause I'm not able to come up with right now. A significant change in the slump should send up the yellow or red flag that something in this load of concrete is different and a decision must be made as to if the deviance is acceptable after investigating the likely causes.
Some rules of thumb that will remain true given all else being equal:
1 gallon of water per yard is equal to 1" change in the slump,
1% variance in air is equivalent to 3/4" of slump
10 degrees F is equivalent to 1" of slump.
These get a little tricky with air entrained mixes, because the air usually goes up when water is added.
Greg
RE: Slump test after adding Super P?
Check http://www.todaysconcretetechnology.com
RE: Slump test after adding Super P?