Sounds like they are of the opinion that the larger cylinders provide more confident results when compared to the smaller ones. I can't say I've ever seen 6x12 cylinders in practice, but I can vouch for the variability in results for the 4x8 cylinders. So much depends on the proper preparation of the cylinders, and the summer students performing the work.

A strength test is (2)6x12 or (3)4x8 so your first part they would need to test (6)6x12 or (9)4x8 to provide results for (3) consecutive strength tests.

I believe JAE has a faq written on this.

jayrod12, understood. To summarize my understanding:

At least (3) consecutive strength tests must have an average value that meets or exceeds f'c.
That average value is comprised of either the average of (2)6x12 or (3)4x8 specimens per strength test.

So by default, if you're not discarding any specimens and the concrete works just fine... you'd need to collect a MINIMUM (6)6x12 or (9)4x8 for each area of work.

Let's say the foundations are being poured in one single day and the testing company is collecting 4x8 specimens. By default, you'd expect them to collect at least 9 specimens.

Now, per 26.12.2.1 the number of samples that must be taken are as follows:


(1) at least once a day
So this means you need to collect (3)4x8 specimens to prepare for (1) strength-test? Since the entire pour happens in one day, the requirement yields (3) specimens.

(2) at least once for each 150 yd³ of concrete
Let's say the total volume being poured that day is 140 yd³.
Is this now in addition to the specimens collected in step #1? Are we now at a total of (6)4x8 specimens, or are we still at (3)4x8 specimens.

Now section 26.12.2.1.b goes on to say something that a little different than 26.12.3.1:


From my understanding, the frequency of testing shown above only allows for (2) strength tests, but we're required to have a minimum of (3). So we'd need to make sure we collect an additional (3) samples to get to a total of 9.

Since we have less than five strength tests due to frequency, we need to make sure that specimens are taken from 5 random batches. Since we have 140 yd³, we need to make sure that we select concrete from 5 random trucks out of the 14 total on site that day?