4" by 8" cylinders

[DIRTyEngineer]

Do you see many companies using the smaller cylinders ?
Does this met ASTM C-39 ?

 

[msucog]

astm and code allow 4x8 cylinders if approved by the structural engineer. the newest version of the astm says that you can use either 4x8 or 6x12 (no approval needed). however, ibc has not adopted the newest astm yet so technically, approval is still required. aci says that 3 4x8 cylinders will be required at 28 days to account for the added variability in the test results. currently, 2 6x12 cylinders are needed at 28 days to make up a set.

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.

 

[uwrockguy]

I agree with msucog. The smaller size samples are actually easier to protect and do not get "thrown" around. Also, it's interesting to note that the rationale behind the three 4x8s versus two 6x12s is not really based on any data. There are hunches and a lot of people have data on correlating the two sizes but no one has taken the time to write anything up and design the experiment so that it stands up to statistical standards. There will be a push in the near future to produce that document. It's part of a two step process. First, remove the "when specified" language in ASTM (it's only there because there wasn't a precision and basis statement for 4x8's). Second step, produce a 30 sample multi-region batch-to-batch statistical document showing that the batch-to-batch variables are identical whether using 4x8s or 6x12s. ACI just took a conservative approach for ACI 318-08 when choosing 3 cylinders instead of 2 for 4x8s. When in doubt, be conservative and error on the safe side. Unfortunately, the reduction to two 4x8s in ACI 318 probably will not occur until 2011. Until then, you can always get approval to reduce it to 2 cylinders from the structural engineer if they are willing.

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.

 

[nowata]

The only time I have ever seen all the required concrete testing methods performed was while I was working as QA during the construction of a nuclear power plant.

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