allowable slump for concrete with superplasticizer
allowable slump for concrete with superplasticizer
(OP)
hi guys,
what is the acceptable range for concrete slump (during a slump test) for a ready mixed concrete with superplasticizer ?
the poured element is a reinfoced concrete element. Is 21 cm ok ?
THank you.
what is the acceptable range for concrete slump (during a slump test) for a ready mixed concrete with superplasticizer ?
the poured element is a reinfoced concrete element. Is 21 cm ok ?
THank you.






RE: allowable slump for concrete with superplasticizer
If the slump is too high they can just let it sit in the truck longer. If too low then they may add water to make it pass.
All I specify is that the contractor must specify his desired slump ahead of time to ensure workability and as long as the concrete meets the w/cm ratio and the other specs I've asked for then I don't care.
RE: allowable slump for concrete with superplasticizer
To me, measuring slump for any concrete mix serves as a sanity check more than anything. If you have 20 trucks with the same slump range, and the 21st truck is way off, could be indicative of a problem with that concrete before it is placed.
RE: allowable slump for concrete with superplasticizer
In my occasionally humble opinion, waiting to determine the performance of concrete is not a good way to assess its potential quality. This must be done at the time of batching/placing/finishing.
The mix design for superplasticized concrete should be cognizant of both the pre-dosing slump and the post-dosing slump; whether the dosing takes place at the plant (most commonly done) or at the site (less common these days). Only the slump of the pre-dosing condition has any relevance to the historically predictable properties of concrete, with the obvious exception of workability.
RE: allowable slump for concrete with superplasticizer
I don't particularly care what that slump is or how they get the slump to what they want (plasticized or not). As I said previously, it needs to provide the performance I'm asking for. I'm not a mix designer, nor am I a concrete placer. I leave things like that up to the professionals.
For what it's worth. I've seen plasticized concrete that had immeasurable slump because it was basically soup. But all the specs came back as designed and the concrete still looks fantastic.
RE: allowable slump for concrete with superplasticizer
That's the problem....they are likely not professionals in the subject either. The contractor probably knows less about the properties of concrete than you. The ready mix supplier should know more than all on the team; however, they only supply what they are asked. You are letting a contractor with little or no training in the properties of construction materials make an engineering decision for you. The chances of that biting you in the a$$ might actually be small; however, when it does happen it can happen big.
The contractor will make a decision based solely on cost and expedience. You would be making a decision based on an engineering need. There's a big difference.
Sorry, but I disagree with you on this one.
RE: allowable slump for concrete with superplasticizer
another question: during the inspection, i saw electrical cables passing inside the concrete slab. personally, i dont have an objection since the cable diameter is small (less than 5cm) And spacing between the cables is ok (>1 or 2 meters). It becomes fichy when the cables converge to a single point. So the spacing will decrease and u will have congestion of many cables in one particular area which will reduce considerably the concrete section strength.
obviously, a bad coordination between the designs engineers (electrical and strucural).
What do u do in such case ? Is there any limitation regarding the spacing or location of electrical cables ?
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
1) Min spacing at least 2x aggregate.
2) Min spacing at least 3x largest of adjacent conduits.
3) Conduits must exist within middle 1/3 of slab depth.
4) No more than two layers of crossing conduit anywhere.
5) Extra rebar where conduit is excessively dense.
6) Conduit tied in groups where density is excessive.
And still, where all of the conduit meets up in an electrical room, you're probably going to have to visit site and apply some additional judgement. I've taken to trying to build shaft walls around electrical rooms so that the structural demand on the slabs inside is minimal.
I'm with Jayrod on the slump business. Maybe it's a Canadian thing. I ask for stamped mix designs and a stamped quality control plan. Those stamps invariably belong to professionals more qualified than I when it comes to mix design and quality control. And, while I won't spec a slump value, that does not preclude slump measurement from being used as a monitored parameter of the QC program.
The closest that I ever came to legal problems regarding concrete specification was on a super flat industrial SOG. I was too heavy handed in the specification of the concrete and had to have the finishers school me on what really needed to be done to achieve our goals. Complex projects can't be realized unless the white collars place some trust/faith in our blue collared brethren.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: allowable slump for concrete with superplasticizer
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: allowable slump for concrete with superplasticizer
Regarding the conduits, if we are dealing with 1 layer of conduit pipes, its location within the slab is not a big deal since it wont reduce the section strength. Things become scary when a big amount of conduits are there. I think the best solution in order not to jeopardize the structure is an architectural one and is to provide a shaft.
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
In the end, my concrete specification basically got whittled down to "awesome concrete, I want frickin' awesome concrete". And all objective indicators point to my having got it. Once I adapted to it, the arrangement was kind of liberating. I really do just want frickin' awesome concrete.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: allowable slump for concrete with superplasticizer
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: allowable slump for concrete with superplasticizer
We have had success requiring the plumbers and electricians to submit sleeve layout drawings so we can get the bigger opening handled before we get on site, but the conduits are always a problem. They need to be there, so sometimes cleaning them up as in KootK's pic is the best you can do (still a terrible jumbled mess bottom center but better than it started).
I am just barely old enough to get my curmudgeon on, so I still spec slumps but since I am a modern man I will allow deviations at the contractor's request if in my judgement the overall mix still looks good. I see no point in having a stamped mix design or QA program by the supplier.
RE: allowable slump for concrete with superplasticizer
I would still advocate that slump be tested for each batch so we have some idea of consistency between batches of the same mix design as noted above. But that's more of a comparative test. I want each slump to come out to about the same number because that indicates that the batches are relatively consistent and I can expect my final results to be somewhat consistent. I don't necessarily care what that number is, so long as it's consistent.
Call it lazy engineering, I guess. I'd call it giving the contractor the flexibility to build as he/she sees fit as long as the final product provides what we need.
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
RE: allowable slump for concrete with superplasticizer
You would also want to check the crack control parameter Z as increasing the depth has an impact on that as well.
if they were off 20mm in a 200mm deep slab then it's more cause for concern.
RE: allowable slump for concrete with superplasticizer
Doing slump post-modifier is really useless for checking concrete quality. Flow tests are valuable as a way make sure concrete will consolidate and aggregates will stay in suspension.