What is the acceptable maximum slump for column considering congested rebars and workability?

[foxview11]

I have columns with congested rebars and tie bars. I'm planning to order a ready mix concrete with slump of 125 +/- 25mm. Our mix design is 35 MPa with max aggregate nominal size of 19mm with water-cement ratio of 0.42. What is the acceptable max slump for column? Please any expert on concrete to give your suggestions. Thank you

 

[Ron]

There really is no maximum allowable unless you have a code mandate in your location. In any case, you have to look at the spacing between rebars, spacing between the rebar and forms, height of placement, method of placement, whether you can get internal vibration or not, etc.

Assuming you have a clear spacing between all that is about 60mm or more, then your slump range and aggregate size are reasonable, assuming you can get internal vibration (vibrating the form itself or the rebar causes problems, so don't do that. If your spacing is less, then reduce your aggregate size accordingly (but not below 12mm) and increase your slump to 150mm +/- 25mm.

Remember, when you reduce your aggregate size you will need to increase the cement content and the water content to maintain the same w/c ratio.

Use a high quality plasticizer to increase the slump without increasing the mix water.

 

[KootK]

Self consolidating concrete is sometimes used for columns in my area: Link. Slump is so high that contractors have to watch that it doesn't leak out the bottom of the forms.

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.

 

[JedClampett]

Don't let a contractor talk you into excessive slump to get into congested cages. Smaller aggregate, yes, but high slump, no. Five inches should be plenty. I'd allow super P (which is just a crutch), but most important is proper vibration. Make sure the stingers can get to the bottom of the pour. Give the vibrator a cash bonus for no rock pockets.
We use a lot of bar (#10's @ 6" are not unusual in walls) and hold our slumps to 4 to 6 inches.

 

[foxview11]

Thank you sirs for your great idea