ACI ASTM C231 - Air Content: Pressure Method (Newer Version Available, Click Top Right Corner)
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- Опубликовано: 3 дек 2011
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• ACI ASTM C231 - Air Co...
Air Content: Pressure Method
ACI Technician Workbook CP-1 (13)
@ Danny - this is a great Q Danny, and a bit of a complex one. See Section 6 in C231 for an explanation of the test procedures. You can't do this in the field; you need access to the raw materials. Most concrete providers have this factor to give you because they can easily run the test in plant. What's happening is there is a small percentage of air entrapped in aggregate - like .1 to .7 percent, barring unusual circumstances. This is air your meter can't detect - must add back in to final air.
He did not mention the subtraction of the aggregate correction factor from the air reading.
@Paul - Paul, thanks. You may have too much concrete build specifically around or within the opening where water can be inserted. This can happen over time even with diligent cleaning. A good tap and die set could ream it back out. That or your close/open valve isn't working properly - when you think you've opened it, it's actually still shut. Or you accidentally had it closed during the test. Your air was probably close anyways, but still not valid if you were not able to add water to capacity.
Thank you for your reply. I will check the meter tomorrow.
@ Lori - better late than never, right? The aggregate correction factor would actually be added to the final reading, not subtracted. This is because the air entrapped in the aggregate is not detectable by the air meter, but should be accounted for and ultimately added in at the end for a final, accurate air content reading.
@emadnadi He depresses the air valve with his left hand just prior to striking the air pot. First depress valve to release the air, then strike the air meter bowl on its sides to assist in stabilizing your reading.
Great lesson. During one of my air tests I could not get water to come out of the other petcock. All the other steps were as specified. I was puzzled and finally continued on with the next steps. My air was 4.5% for a 4000-3/4 mix. What does this mean?
Since this entrapped amount is typically very low, it's not even a consideration on the majority of job sites. But it certainly can make a difference if your air tests are on the upper ranges of your tolerance. And this entrapped air in the aggregate does play the role that the detectable air plays in freeze/thaw cycles in the life of the concrete. So by all means, why not account for it. I'd start by asking the concrete producer to provide this number for the mix. It's their responsibility.
Add the aggregate correction factor??? Review C231 section 9.1. The aggregate correction factor is subtracted from the reading on the gauge to get the air content of the concrete. We are interested in the amount of entrained air and entrapped air of the concrete. And if the air in the aggregate is not detected by the air meter, as you say, then why do you use the air meter to determine the aggregate correction factor? The standard requires the subtraction of the agg correction factor, so always should be done.
Does anyone know how to do an aggregate correction factor?
Don't ever force your water through the petcock as he does in the video it will create a void on the top surface of the concrete and will give you a false reading. Pretty much don't stick anything into the petcock the gap on the lid will allow water to flow without having to do that.
@ exloaded - Yes, you don't want to force the water through the petcock. But either method is correct, provided that if you insert the syringe into the opening, you use a little finesse and gently introduce the water. If you held a full syringe or nozzled-hose a few inches away from the opening and pushed the water stream through with enough force, you would essentially create the same problem you are proposing to avoid. The water pressure is more critical than the water source distance.
aggregate correction factor to find out
I think you missed a step...or your video skipped a step at min 1:49 where you release the air to the sample