deciphering mix placement requirements
deciphering mix placement requirements
(OP)
OK, got a shearwall 1' thick and and 28' long capped on each end by 24"x32" symmetrically placed columns. The shearwall requires 5K concrete and the columns require 10K concrete. There is a note stating that the columns and walls must be placed monolithic.
I asked the EOR (out of sheer curiosity, no pun intended) how this could be accomplished. He said that was means/methods which, of course, means it's up to the contractor to figure out.
This requirement would appear to be further complicated by a pesky line in the project manual forbidding fresh SP mixes to come in contact with fresh non-SP mixes.
The contractor evades the requirement by placing the whole thing with 10K. But what if they wanted to place 5k and 10K, could it be done with that mesh form?
I asked the EOR (out of sheer curiosity, no pun intended) how this could be accomplished. He said that was means/methods which, of course, means it's up to the contractor to figure out.
This requirement would appear to be further complicated by a pesky line in the project manual forbidding fresh SP mixes to come in contact with fresh non-SP mixes.
The contractor evades the requirement by placing the whole thing with 10K. But what if they wanted to place 5k and 10K, could it be done with that mesh form?






RE: deciphering mix placement requirements
Is there a real need for the concrete to be monolithic? or for the columns to be 10ksi at the ends of the wall.
I guess it's possible to cast the 10ksi concrete for the columns and letting the concrete flow into the wall form and supplement this with 5ksi stuff... tricky and I think your contactor using 10k for all has chosen the best solution... still think it's a bad detail.
RE: deciphering mix placement requirements
In Russia, prior to 1995, precast concrete was the only concrete used in construction. Even after that, much of the technology was used despite a shift away from precast toward cast in place and masonry.
I have seen structural walls panels made from normal weight concrete (6000-8000 psi) and lightweight concrete (4000-5000 psi) using vertical dividers/bulkheads that were stripped upward immediately after the concurent concrete placement and vibration. Granted, this is a factory process, but moving bulkheads could be used the same way on site.
They even routinely carried the same process on to several types of concrete sandwich panels (normal concrete, polystyrene, lightweight concrete and normal concrete, lightweight aggregate, lighweight concrete) and even to precasting individual housing modules.
The tesing of the actual complete fabricated panels and modules was impressive and done in detail.
It was an impressive process, but the practical applications were something to be desired - Want to buy several hundred 20+ story apartment buildings that are in the process of failing without a viable method of repair?
Dick
RE: deciphering mix placement requirements
But, to your question...yes it can be done. Place the 10 ksi in the columns with the wall form/column form separated by a slice gate and simultaneously fill the wall forms with 5 ksi. Fill at same rate and raise the slice gate a little behind the concrete placement so that the two concrete bond and slightly mix at the interface. Putting a vibrator on the slice gate as it is raised (yeah, I know you should vibrate the forms!) will enhance the mixing.
....more trouble than it's worth.
RE: deciphering mix placement requirements
These 24"x32" columns are heavy with 20 #10 verts and #4 ties @ 5". The SW is just #4 @ 12" EW.
RE: deciphering mix placement requirements
Thanks, Ron... was aware of the problems with high concrete strengths and never thought to include this be... 10ksi can be a little tricky and there is likely quite a difference in colour... so hope there are no architectural issues...
Dik
RE: deciphering mix placement requirements
RE: deciphering mix placement requirements
RE: deciphering mix placement requirements
RE: deciphering mix placement requirements
RE: deciphering mix placement requirements
concrete, monolithic—concrete cast with no joints other
than construction joints.
monolith—a body of plain or reinforced concrete cast or
erected as a single integral mass or structure.
The exact spec reads:
"Place scheduled columns monolithic with shearwall."
I thought that the intent of the spec was to require a "seamless" piece: no construction joints between columns and shearwall. Now I'm thinking it must mean that the reinforcing (the horizontals) is continuous through the members.
column/shearwall/column O----O
The ACI-116 term "Monolith" appears to imply seamlessness. The ACI-116 term "Monolithic Concrete" obviously allows construction joints which appear to me to be seams!
If he had wanted it seamless maybe he should have written:
"Place scheduled columns and shearwall as a monolith."
RE: deciphering mix placement requirements
Dik
RE: deciphering mix placement requirements