W/c ratio for 3000 psi mix design
W/c ratio for 3000 psi mix design
(OP)
Hi All
I recently started reviewing concrete mix designs and I have noticed the w/c ratio is higher than the typical 0.45 recommended amount. The main complaint I am getting is that 0.45 is typical of 4000 psi and not 3000 psi. I am concerned about durability and cracking. Also, I noticed the air content is really low. I don't want to change the design specs but if 0.45 is not appropriate for lower strength concrete then I would like to know.
Thanks
I recently started reviewing concrete mix designs and I have noticed the w/c ratio is higher than the typical 0.45 recommended amount. The main complaint I am getting is that 0.45 is typical of 4000 psi and not 3000 psi. I am concerned about durability and cracking. Also, I noticed the air content is really low. I don't want to change the design specs but if 0.45 is not appropriate for lower strength concrete then I would like to know.
Thanks






RE: W/c ratio for 3000 psi mix design
I have always disagreed with putting too many prescriptive parameters in specifications. If you want 3,000 psi concrete, ask for it, but don't tell the concrete supplier what water/cement ratio to use--let him do his job.
If you want a 0.45 water:cement ratio, ask for it, but don't tell the concrete supplier the concrete will be 3,000 psi.
Now, I will admit all of the cementitious additives we use these days (fly ash, slag, silica fume) make it difficult to know what w/c ratio goes with what strength.
DaveAtkins
RE: W/c ratio for 3000 psi mix design
RE: W/c ratio for 3000 psi mix design
RE: W/c ratio for 3000 psi mix design
RE: W/c ratio for 3000 psi mix design
CSA has a couple of alternatives for concrete supply. Alternative A is the most common that I've encountered. It does not require a design, it is prescriptive. The mix design can be treated as s proprietary mix. The supplier has to only provide a history of use. I usually stipulate that the concrete must be supplied in accordance with A23.1, except as noted herein (Project Notes).
I spec a minimum concrete strength and a max W/C ratio, usually. For a W/C ratio less than approx. 0.5, you will likely get a strength of 3000 psi min. With all the admixtures, W/C seems to be less significant, but I spec it anyway, for durability, or whatever.
Dik
RE: W/c ratio for 3000 psi mix design
I`m under the impression that too much water can exacerbate each of these problems, even if the concrete meets the strength that you specify.
Does the concrete supplier accept that responsibility?
Couldn't they just as easily blame the control joint spacing, reinforcing, etc that you specified - thus making the cracking from the wet concrete your problem?
The client doesn't come after you for issues associated with these cracks?
RE: W/c ratio for 3000 psi mix design
BUGGAR,
Really, 2500 psi - what application? Round here, never see anything less than 4,000 psi specified, and more often 5,000 psi min.
RE: W/c ratio for 3000 psi mix design
If you want a specific w/c ratio, then understand why you want that w/c ratio. Most often, a limitation on w/c ratio has to do with durability, although the compressive strength of concrete is clearly and directly related to the w/c ratio. The lower the w/c ratio, the higher the strength (Abrams Law).
The lower the w/c ratio, generally, the higher the durability of the concrete for most applications.
For 3000 psi concrete, the w/c ratio can be as high as about 0.60. For 4000 psi concrete, the w/c ratio can be in the range of 0.50 to 0.52, depending on other aspects of the mix design.
Review ACI and PCA requirements for mix designs.
RE: W/c ratio for 3000 psi mix design
Mike McCann, PE, SE (WA)
RE: W/c ratio for 3000 psi mix design
That's a bald-faced and blatant bit of flattery, but you deserve it. Merry Christmas.
RE: W/c ratio for 3000 psi mix design
RE: W/c ratio for 3000 psi mix design