4x 8 concrete cylinders vs. 6x12

huangyhg

4"x 8" concrete cylinders vs. 6"x12"
a local material and inspection company has sent out a letter to the local engineers informing them that they will now be using 4" diameter x 8" tall concrete test cylinders as their standard concrete test cylinder, instead of the more traditional (at least around here) 6" x 12" cylinder.
the firm indicates this is now allowed by the most recent edition of astm c31.
the testing firm goes on to say that they realize their is some adjustment factor between the two cylinders, as the 4" x 8" cylinder will typically give a higher break strength, but that there is no nationally accepted value for this adjustment factor. however, they did some testing on their own, and are proposing to use a 5% adjustment.
have other encountered this idea in your area? what are your thoughts on this? how do your local testing firms adjust between the two sizes of cylinders? or do they adjust the results? does it seem right to base the adjustment factor off of a relatively few (less than 50 ) locally performed tests that are not sanctioned by a major code or industry standard?
just looking for thoughts on the issue. thank you for any and all repsonses.
we've been using 4x8 cylinders in canada for several years and you shouldn't have any concerns.  test results (stress) are indistinguishable from 6x12.  they have an advantage of being smaller, lighter, easier to handle, less disruption in moving, smaller storage space and require smaller testing machines.  they also require less concrete and provide less aggregate/landfill... no downside.  only thing is that with the 6x12 and 4x8 cylinders, the maximum aggregate size is dia/3 so the mix size is limited... cannot use 1-1/2 aggregate, but for 3/4" or 20mm ok.
dik
there are numerous studies on the effect of msa and specimen size on uniaxial compressive strength. we had discussed this a while back
henri2:
are you saying that it's only referenced in c31-06 and they can only be used for codes referencing that document?
dik
dik, for building departments that use the ibc, that should be the case, unless the enforcing agency grants pemission or does not enforce the code.
i am sure that in time, 4 x 8 cylinders will be used extensively out here.
thanks henri2... the only thing i noticed when the 4x8 cylinders were used, was that there was no reduction in the cost of doing them... a sneaky way not to implement an extra to contract...
dik
dik, it's high time labs started making some easy money...lol.
our company, location nh, still uses the 6x12.  the reason being, we only have a psi machine for the 6x12, and would have to cap both ends of a 4x8, if we were to test it.  a machine does exist, and a chart also exists, for testing the 4x8, and calculating the total lbs, and total psi.
it is true that the code being enforced will refer to a specific version of a referenced standard (chapter 35 of the ibc).  the codes being on a different cycle than standards, typically lag the standards.
however, the building official can accept, as provided in chapter 1 of the ibc, as an accepted alternative, new revised standards like the newer referenced standards.  a conservative building official may require you to adjudicate a varience but should not oppose it.
don phillips
all:
thanks.