MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
(OP)
WE ARE USING PLASTICIZER FOR WORKABILITY OF CONCRETE POURING BUT OUR DESIGN MIX SPECIFIED SLUMP NOT TO EXCEEDS 150mm FOR COLUMNS AND BEAMS. HOWEVER, SUCH SLUMP DOES NOT WORK PROPERLY RESULTING ONLY TO HONEYCOMB. CAN WE ADJUST THE SLUMP UP TO 200mm? Please any expert can give me advise on this.Thanks a lot.





RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
In my opinion, if you're using plasticizer with a 6 inch slump concrete, you're doing all you can from that end. I would try using a pea gravel mix or a superplasticizer rather than making the concrete too soupy.
Your article is in reference to tremie concrete. Is that the situation? It says that the use of Super-P is discouraged. However, it's from 1986 and I think that Super-P is more widely accepted now.
How congested are your columns?
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
First, please don't use all caps for posting. It is akin to "shouting".
Second, if the aggregate size is correct in your mix design for the actual rebar spacing, a 150mm slump should be fine, provided appropriate consolidation measures are being used in the field (vibration). If you are vibrating and still getting voids in the concrete, then it is likely you have the wrong coarse aggregate size for the rebar clearance and you should do as JedClampett noted...use a smaller coarse aggregate. If you get the slump too high for a vertical placement such as this, you will risk segregation of the aggregate.
Third...no one here can give you "permission" to go to a 200mm slump. That will have to come from the structural engineer of record or the architect. Perhaps the design did not appropriately consider constructability, so you might need to work with the design team to get this right. I would not recommend arbitrary nor capricious changes.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
Further clarifications: max size of c. aggregates is 19mm only, main rebars spacing is ok, but specified tie bars is three set. Pipe of pump crete can hardly reach to lower part of the column because of these tie bars, much less if using tremie. To me 150mm slump is quite ideal for columns and beams but for columns such as our case, honeycomb is a problem.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
The size of the bar is irrelevant to the CA size, so these rules of thumb apply to all bar sizes.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
Regards,
![[pipe] pipe](https://www.tipmaster.com/images/pipe.gif)
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
Dik
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
Ref ASTM C94 Standard Specification for Ready-Mixed Concrete - Tolerances in slump - When the project specification for slump are written as a "maximum" or "not to exceed requirement: If specified slump is more than 3"(75mm), then plus tolerance is 0" and minus tolerance is 2 1/2"(65 mm).
You may also refer to thread167-227472: Slump test after adding Super P? for discussion.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
ACI 318-05, section 3.3.2(c) lists nominal maximum size of coarse aggregate shall be not larger than 3/4 the minimum clear spacing between individual reinforcing bars, bundles of bars etc. The commentary even allows size limitations on aggregates to be waived if the workability and methods of consolidation of concrete are such that the concrete can be placed without honeycombs or voids.
The maximum size of coarse aggregate requirement in relation to clear spacing between bars is similar in ACI 301 and PCA Publication - Design and Control of Concrete Mixtures, 14th Edition.
Am I missing requirement given in some other code / standard?
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
By the way, Ron, where did that 60 mm come from? That's a lot more than the norm.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
For compressive stress across aggregate boundaries, 3 times the max. nominal CA size is mandated for testing.
Ideally this would be the case for in-place as well, but not practicable either. My 60mm reference was to that as a rule of thumb for cover...not interior rebar spacing.
For interior spacing, I would set max. CA size at 1/2 spacing gap.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
Cover for columns, in accordance with 7.7.1, should be 1.5" minimum, about 38 mm. My standard number is 40 mm. More cover is only used for severe exposure environments.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?
A lot of problems which show up on this site could be avoided by adequate consideration during design. Columns with congested reinforcement are not economical...higher concrete strength and/or larger columns are much better than adding reinforcement. Using "magic concrete" gets too much emphasis.
RE: MAX ACCEPTABLE SLUMP FOR CONGESTED COLUMN?