4" by 8" cylinders
4" by 8" cylinders
(OP)
Do you see many companies using the smaller cylinders ?
Does this met ASTM C-39 ?
Does this met ASTM C-39 ?
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RE: 4" by 8" cylinders
RE: 4" by 8" cylinders
The latest version of C 31 allows for use of 4 x 8 inch cylinders in lieu of 6 x 12 inch cylinders when job specs permit their use. However, since the version of ASTM C 31 recognized by the IBC does not permit for the use of 4 x 8 in cylinders as a standard specimen size, it is prudent to sell the idea to the building dept and EOR before using them.
There are several structural engineering associations currently evaluating the use of 4 x 8 in cylinders in lieu of standard 6 x 12 in cylinders. They will be relying on companion test results obtained from testing labs.
RE: 4" by 8" cylinders
RE: 4" by 8" cylinders
What I find interesting, is that the IBC accepts most of the editions of the ASTM standards listed in ACI 318, but when it comes to ASTM C 31, it references the 98 edition, while ACI 318 references the 03 edition.
The 98 edition of C31, stipulates 6 x 12 in as the standard compressive strength specimen size (for acceptance testing for specified strength) but the 03 edition of C 31 stipulates the 6 x 12 inches and allows the 4 x 8 inches when specified.
Was the listing of C31-98 as a referenced standard in the IBC an oversight or deliberate; deliberate because committee members did not feel there was not enough data out there to justify the use of 4 x 8 inches to verify compliance with the specified compressive strength?
RE: 4" by 8" cylinders
Even though concrete companies use the 4x8s, i don't think they would like 4x8s blanket approved for acceptance testing since the impact of a small flaw is magnified. Concrete companies have more lobbying power than CMTs too (read: all the power vs none).
off the subject,
i worked on a project where we were testing side by side with the concrete QC. The GC got test results from the concrete company and us separately. (Concrete QC doesn't usually distribute results until conflict) The EOR happened to see the results after a meeting in the trailer and compared with ours. The EOR asked the GC why the results would be consistently different, which they were. The GC passed this on to the concrete company that there was a consistent discrepency between the two. The QC at the concrete plant put together a letter to the owner & EOR trashing our technician's testing methods based on observations by the field QC for the concrete plant.
PUNCHLINE: Our breaks were consistently higher! Dumba$$
RE: 4" by 8" cylinders
I have been down that road before.
We like to use the 4 X 8 's but half the time we don't get the spec until the job is half over or there is a problem.
RE: 4" by 8" cylinders
1. Chapter 35 of the 2007 supplement to the 2006 IBC references C31-03a. As pointed out earlier, unlike earlier editions of C31, this edition of C 31 allows for 4 x 8 in cylinders when specified. http://www
2. Proposed Changes to 2005 ACI 318... will permit for either 6 x 12 in or 4 x 8 in cylindrical compressive strength specimens...and there'll be no language like "when specified" in the case of the 4 x 8 in specimens. The wording of the revised Sec 5.6.2.4 reads as follows " A strength test shall be the average of the strengths of at least two 6 by 12 in cylinders or at least three 4 by 8 in cylinders made from the same sample of concrete and tested at 28 days or at test age designated for determination of f'c".
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The 4 x 8 in cylinders will make life much easier for folks who do not like lifting 30 lb 6 x 12 in concrete specimens. And C 31-03 does permit internal vibration in lieu of rodding when consolidating specimens. How much easier can it get for concrete field technicians? They certainly need a break.
RE: 4" by 8" cylinders
RE: 4" by 8" cylinders
Maybe I'm the dumb-ass because I do not get, and frankly will never get, what the heck one set of test results being "higher" than a companion set of test results has to do with anything.
We still don't know if your test results were actually ACCURATE. It's entirely possible, and plausible, that both sets of tests were equally inaccurate!
RE: 4" by 8" cylinders
it's a lot more than one set of cylinders. it was a consistent common difference throughout the project. the story sounds fun, but it wasn't at the time. we internally investigated our own operations and found nothing. the only thing that makes sense is that the concrete company's break machine was off and low. The point of that story is to show how knee-jerk the "blame the ITL" reaction is at the concrete plant, even when there isn't a problem.
i don't believe you would have reacted the same as the concrete QC manager, so i don't accept your claim to potential dumb-assness.
RE: 4" by 8" cylinders
With that concrete QC discrepancy. I've never had a conflict like that with another agency and never want to, but I live in Seattle, and a big factor in our compressive strength is temperature of the cure. It gets so cold here in the wintertime that even our cure boxes don't insulate things properly, and this affects our breaks, especially on the high-early or PT.
It seems like to me there must have been other factors. Probably a dead issue by now, but that type of thing still sets me off. Find the problem and fix it, don't have blaming the other guy your first mode of action.
It could have been awhile before their load cell was calibrated, or your load cell was calibrated, pads were changed, ect. They could have forgone a cure box, or left it out in the sun (I'm pretty sure some of ours do). Results for the same concrete will differ even from cylinder to cylinder of the same mud, but to me methods of making them are pretty much foolproof, especially when there's someone watching over your shoulder. Water under the bridge, but that water's comin' from somewhere...
RE: 4" by 8" cylinders
"but that type of thing still sets me off. Find the problem and fix it, don't have blaming the other guy your first mode of action."
--Would you be talking about the Concrete Company QC for writing the letter, the ITL who refers to them as dumbasses?
ironically, your point is same as the moral of the story i was telling, right.
as i've said before, it was investigated thoroughly on our side. People will just have to trust me on that. how else would i have been able meet this statement "the only thing that makes sense is that the concrete company's break machine was off and low."?
---------------
OK, now after you've accepted that there wasn't a consistent common error made by our lab/field testing method to give falsely high breaks.
The punchline to this story is that:
1. the letter issued by the concrete company observed ways our samples were incorrectly made.
2. our breaks were higher than theirs.
3. [speculation] the concrete company did not check to see what was going on before they wrote it, and probably thought the ITL breaks were lower (because that's how that letter read)
RE: 4" by 8" cylinders
RE: 4" by 8" cylinders
You are living in an idealistic land when it comes to testing concrete cylinders.
Cylinder testing is a low profit, variable volume testing process for local laboratories that helps them keep in contact with engineers, contractors and suppliers. Because of the variable volume, much of the actual preparation of samples and testing during the period of heavy construction activity is done by "grunts" with little real training. This even applies to certified laboratories because of the cyclical nature of construction.
ASTM standards represent the most responsible authority when it comes to standards and procedures. It is unfortunate that we have to deal with making the older standards and codes fit into the construction process while trying to retain a professional level of design and construction. This is in spite of the slow and tedious process of getting new findings, materials and procedures adopted by code authorities that really have little effect.
The idea of having parallel studies (size vs. aggregate) is not reponsible unless there is absolute long term uniformity of sample preparation, identical curing conditions, sample preparation by the same personnel, testing in the same facility with the same personnel and using the same testing equipment. This step has a major effect on the design and construction of all new structures.
Despite the the controls on the rate of loading (adjusted for sample size), larger testing machines with more rigid frames will provide higher and more consistant results.
In the past, independent laboratories provided the most accurate results compared to local suppliers results. With the advent of vertical integration of the concrete industry, supplier laboratories have surpassed many independent labs because of the international interest in research, quality control and local involvement. The days of "mom and pop" concrete plants are gone and the muscle of the the big four (or five) cement companies are concentrated on bringing the level of concrete oriented products up to the level of other advanced construction technologies.
RE: 4" by 8" cylinders
RE: 4" by 8" cylinders
anyway, since ibc currently recognizes c31-03a and aci318-05 does too, how are you guys getting around using 4x8 cylinders? are you asking the engineer if they can be used on each and every job or are 4x8 cylinders typically included as acceptable on the plans in your area?
i suspect ibc may pick up c31-06 on the next round of supplements (which would then allow either size cylinder). anyone know when that date might be since i can't seem to find it? also, when might the aci changes go in to effect (since you'd have to make 3 instead of 2 28-day cylinders for the smaller size)?
i'll keep looking and post if i find the answer to my own question...
RE: 4" by 8" cylinders
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i'm not sure when the change would actually be accepted as code though.
RE: 4" by 8" cylinders
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RE: 4" by 8" cylinders
How many times have cyls. been damaged due to an arguement with the contractor. As well as people using them for tables.When this comes into affect, plan to be doing alot of windsor probes as well as cores.
RE: 4" by 8" cylinders
i don't suggest windsor probe because it's hoaky for footings. it might be more applicable to slab areas but it's dependent on the finish...by the time you windsor probe the whole slab area, you could've just used cores. cores are ultimately required by all the engineers i've run across. i wouldn't trust windsor probe for evaluating in place strength.
i don't think the 4x8's are more prone to damage during fabrication...less chance of dropping the things since they weigh so much less.
just make sure to calculate the strength for the appropriate sized cylinder...been down that road where the supplier said we made the cylinders wrong because their companion cylinder broke much much higher than ours. as it turns out, they typically make 4x8 where they made 6x12 on this occassion since we were making 6x12. they forgot to adjust to the correct area of the specimen. they sat in a meeting basically called us incompetent. then they were forced to submit a letter to the owner stating that they'd screwed up and were wrong to make such accusations against the testing firm. turns out the whole thing was pretty funny looking back on it now. some of you may have read my thread about this incident before...
back to the subject of the thread...i expect ibc may adopt the newest astm in the next month or two. there again, it may be next year...who the heck knows. my guess is that it'll be adopted by summer time.
RE: 4" by 8" cylinders
And in regards to volume, we have implemented this and the space savings are tremendous, not to mention the greater ease in handling and processing.
RE: 4" by 8" cylinders
Supplier QC technicians and Independent Laboratory QC technicians are the SAME! Some are experienced and some are not.
Concrete tests in the field do NOT represent the area being placed. The tests represent the mix design.
All cylinder breaking machines must be calibrated yearly.
4x8 cylinders are just as accurate as 6x12's