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Slump test after adding Super P?

Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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.


RE: Slump test after adding Super P?

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?

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

Thank you for the replies.  

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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.


RE: Slump test after adding Super P?

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

RE: Slump test after adding Super P?

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?

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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.  

RE: Slump test after adding Super P?

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).

RE: Slump test after adding Super P?

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.


RE: Slump test after adding Super P?

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.


RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

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.

RE: Slump test after adding Super P?

Often the best super -P is water. I have seen many problems with concrete where w/c is kept very tight and and a tight tolarence on the slump. bumping the water at the site wil improve workability for a moderate sacrafice in strength. I have not seen loss of strength below design strength. I have seen very stiff concrete go into rebar congested forms and not be able to encapsulte the bars.
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?

DRC1...not sure where you practice, but I've seen many examples of adding water at the site compromise the design compressive strength.  More than I care to recall.

That practice should not be compromises the mix design which is the basis of f'c...the design.

RE: Slump test after adding Super P?

Every time I have seen issues with stiff concrete, it was because of a)trucks took too long to deliver b)improper equipment or procedures at the job site to handle the stiff mix or c)poor quality mix provided by readymix company. If super p is necessary, let the contractor request it ahead of time, let the engineer approve it ahead of time and don't rely on the truck driver who only gets paid by the hour to add in the proper amount of admixture and properly mix it in. I can almost guarantee that if that happens and there is a problem, the ready mix company will not warranty that concrete. Extra water should never be allowed. Maybe this is common procedure on residential work, but not anywhere else.

RE: Slump test after adding Super P?

Gents, I also agree that adding water to the mix at site is not really acceptable.

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?

dik...that was exactly my point.  I've dealt with this issue for many years and once someone other than the supplier adds water at the site, the supplier says "you bought it".


RE: Slump test after adding Super P?

Adding water not only reduces strength, it adversely affects durability, causes more shrinkage, and is generally not an acceptable practice.  If the concrete can't be placed and consolidated without additional water, something has gone wrong in the mixing or transport.  Time in truck and temperature of concrete are the most likely suspects.   

RE: Slump test after adding Super P?

you can tell by those that work directly by the book and those that actually do the work in the field. I agree with DRC, bump the slump up to a 4, you loose about 50psi in strength, and then add the super P you have something you can really work with.

RE: Slump test after adding Super P?

those of us who work by the book have very little to gain by doing otherwise. and there is no excuse for not being able to place per the specs.  

RE: Slump test after adding Super P?

AS Brownbag pointed out, it is easy to specify a particular slump, placing it can be more problematic. My point was that by keeping a low w/c you may end up with higher concrete strength, but a lower capacity of your reinforced concrete structure. There is a difference between producing a quality product and complying with a specification.

RE: Slump test after adding Super P?

With respect, DRC1 and brownbagg, you know not of what you speak.  May be best to leave the comments about placing concrete to those who have experience in building high quality reinforced concrete structures.  

RE: Slump test after adding Super P?

But with a four slump, most time you are still within the w/c ratio. Super P just does not like a dry slump of around 3. we are not talking 100"s of psi loss. Most mixes are design at a four, with a little safety built into them. A typical 4000 here poured a 4 slump with super p added is breaking 6200 so 50 psi is not a big loss. It still within spec.

RE: Slump test after adding Super P?

Well said hokie66.

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?

With respect, Hokie66 and Ron, you know not of what you speak. Have you read ASTM C 94, which allows one addition of water at the jobsite? Have you tried to pump or finish concrete with very little water added at the plant, but enough superplasticizer to still produce the specified slump? The concrete pump knows the difference between a water slump and an admixture slump. So do finishers. Your condescending comments about other posters and about contractors reveal an arrogance that should be removed from this web site. "May be best to leave the comments about placing concrete to those who have experience in building high quality reinforced concrete structures." In other words, anyone who disagrees with you has no experience with high quality concrete. I do have experience with high quality concrete. Your post, Hokie, should have been red flagged. And Ron's too. I'd guess that not many contractors even use this site because of the know-it-all arrogance of some regular posters. Many contractors know more about concrete technology and building with concrete than you seem to know based on your previous comments. For instance, when someone disagrees with Hokie—and supplies references--as with the discussion of clear cover for flexural reinforcement—you give a response that "There are more ideas about how to do it than Carter has little pills, and everybody thinks his way is best." Well you obviously think your way is best, Hokie, because you didn't have the data or references to dispute someone else's opinion that was backed by a reasoned and well thought out response. So sour grapes had to do.

RE: Slump test after adding Super P?

I was going to wade in, but decided not too... could be more fun to watch from the sidelines...


RE: Slump test after adding Super P?

My disagreement with DRC1 was his comment that "Often the best super -P is water."  I believe that is clearly incorrect.  The recommendation of Brownbagg's to "bump the slump up to 4 and then add Super P" is also inappropriate as a general statement in my opinion.  These decisions are best left to the individual project, where the material and climatic variables can be taken into account.

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?

Brownbagg's to "bump the slump up to 4 and then add Super P" is also inappropriate as a general statement in my opinion.

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?

First, thanks to Concretedoc for the support.
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?

Kinda late to jump in here.  It seems there is still a huge amount of misinformation regarding superplasticizers or high-range water reducers.

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?

On NYSDOT projects, central mix and transit mix concrete contains 90% of the design water when it arrives on site (at least it's supposed to). The remaining water is added to achieve the desired slump. If admixtures are used, the slump and air is measured after not before.

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?

The Slump Tests primary objective is to determine the  workability of the concrete for field use!

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?

Further to Ron's comments, slump is also a measure of the amount of shrinkage anticipated... I generally spec slump as 4" max. for general usage and 3" max. for slabwork and tell the testing agency that I expect this to be followed.


RE: Slump test after adding Super P?

What I tell my ACI Field Sampling & Testing Certification classes I teach is "the slump test is really only a measure of the slump of the concrete".  With today's admixture packages and supplementary cementitious materials added to the concrete, the slump test is primarily useful as tool to measure the load to load or batch to batch consistency of the concrete.  It cannot be used to measure the water added, w/c ratio, workability, strength, shrinkage, or any physical property other than slump. I've seen 6" slump concrete that is less workable than a 1" slump concrete.  I've had 8" slump mixes with 1/3 the shrinkage of a 4" slump concrete just due to proportioning and admixture packages.  Just by changing the aggregate proportions of a given cementitious content and water content, I've gone from a 2" slump up to a 7" slump and then back down to a 5" just by increasing the coarse aggregate content and reducing the fine aggregate.  

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.


RE: Slump test after adding Super P?

if the specifications mandate the Super-P slump to be between 7" to 9" (for example) and the pre-Super-P slump to be less than 3" (for example) than the contractor and concrete supplier have already agreed to meet this criteria and that it may/will be tested.

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