ACI Density Test: ASTM C138 Density (Unit Weight) 2019
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- Опубликовано: 23 май 2019
- Density (Unit Weight)
ACI Technician Workbook CP-1
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* Density *
To figure out the density, you are filling up a container with concrete. This container must have a known volume (4), minimum .20 cubic feet. First weigh the empty container (1) and record that value to the nearest tenth (.1) of a pound. After performing the proper procedures for filling the container (i.e. filling it in three lifts, mallet blows, rodding, striking off with strike-off plate), follow these steps:
* Density Calculation Steps *
Weigh the container with the concrete (2) - record value to nearest tenth of a pound
Subtract the empty container weight from the full container weight (2) - (1) = weight of concrete (3)
Divide the weight of concrete by the known volume (3) / (4) = density, or fresh unit weight
There’s a few unique procedures listed in the ASTM C138 to remember:
* Slump *
If less than 1": Must use vibrator capable of at least 9,000 vibrations per minute
If between 1" and 3": use vibrator or tamping rod
If greater than 3" = Can’t use vibrator, only use tamping rod
If using vibrator, fill and vibrate measure in two equal layers, not three
Insert vibrator at three different points for each layer approx. 3 inches into the underlying layer
Mallet mass must be 1.25 +- .5 lb for containers .5 cu.ft. or smaller
Mallet mass 2.25 +- .5 lb for containers larger than .5 cu.ft.
Use strike-off plate, not bar
Metal strike-off plate dimensions - 1/4" thick
Glass or acrylic plate dimensions - 1/2" thick
* Yield *
Yield is used to determine if the concrete supplier has delivered the amount of concrete ordered.
For example, if the contractor orders 7 yards and the concrete pour comes short of filling the structure, a yield test can be performed to determine if 7 yards were actually delivered. To calculate yield, follow these simple steps. Note that you must calculate density prior to calculating yield.
You will take the total mass of all materials batched (aggregate, water, cement-this figure will be given to you on the test) to begin. The total mass of the materials is the total weight.
a. The yield per batch cu.ft.Total weight / fresh unit weight = yield per batch in feet
b. The yield per batch in cu.yds.Total weight / (fresh unit weight x 27) = yield per batch in yards
c. The yield in cu.m.Yield per batch in cu.yards x .764 = yield in cu.meters (1 cu. yd. = .764 cu. meters. This will not be on the test.)
d. The yield per cubic yard in cu.ft./cu.yd.Yield per batch [result from (a)] / cu.yds delivered = yield per cu.yd. in cu.ft./cu.yd.
RELATIVE YIELD is the ratio of the actual volume of concrete obtained to the volume as designed for the batch. It is understood as a 1:1 ratio. If the relative yield calculates out to 1.00 or greater, then the yards delivered is equal to or greater than what was ordered. If it calculates to less than 1.00, then the yards delivered is less than what was ordered.
RELATIVE YIELD = yield per batch in yards (b) / cu. yds. delivered
* Air Content Calculation *
Air content can be calculated in the event that your air meter does not work properly. In order to calculate this, you must have the theoretical density. This information can be obtained from the concrete supplier, who has this information on the mix design for the mix you are working with. Again, you will need your results from the fresh unit weight.
THEORETICAL DENSITY = actual density (fresh unit weight) / theoretical x 100 = calculated air content
Since the theoretical density from the lab has no air, you are comparing that laboratory weight to the fresh weight which contains air. The air in the fresh weight sample makes it lighter than the theoretical.
The formula above allows you to subtract the fresh from the theoretical and come up with a calculated percentage of air content without performing an actual test. For the ACI test, all that is necessary is to be able to recognize the order of the formula written above.
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I’m ACI certified for field tech grade 1 but I still come back to these videos because they’re so well made. Good work
dear which test include grade1?
What is aci....
@@ZiaKhan-cf9xi American Concrete Institute
sweet, thanks
Thanks for sharing.
NICE SKECHERS
「あなたの動画はとても良いですし、メッセージがた
32.865÷0.2504=131.25
no gloves?
We do that so different in Australia.
Because you’re all criminals
Is the required frequency of this test daily or weekly per mix design?
kromekicks depends on the job and what engineers want you to do
Some projects it's daily, fdot it's a must..some commercial projects also
How did you get the mold volume
All meters come machined to a precise size from the manufacturer, 0.25 cuft
By measuring the weight of water of the container considering volumetric correction factor depending on water temperature.
(Weight of concrete + Weight of empty measure) - weight of measure / volume
(32.865 - 7.79) lb / .25 FT CUBE
100.3 LB/FT CUBE IS THE DENSITY
32.865 lbs is the weight of the concrete without the weight of the container/mold. So you're subtracting 7.79 lb that was Already Subtracted. That's where the error is.
Safety issue! No gloves, concrete is caustic to the skin.
Some of us don't have an issue with it
Hes using fly ash, but yes you can get some pretty bad concrete burns from this
is the math correct?
I think it’s wrong I got a different result! I got D=100.3
Sir, you don't zero the scale AFTER you get the tare weight. Pointless to get a tare weight if you zero it out. Therefore your math is now wrong.
Hey Jimmy, you record the weight prior to the tare. You can see this graphic representation on the screen as we do it. As long as you note this, you can account for it in the end. There’s more than just a single way to do this.
Well with most if not all calibrated scales once you get the weight of the pot and get the tare the scale resets to 0 then once the pot is removed it would show into the negative. Example. If the pot is 8lbs and you get a tare down to 0 once the pot is removed the scale will read -8lbs if I’m not mistaken.
@@tanumie2657 To prevent concrete from sticking, making it easier to clean. Keep your tools happy, and your tools keep you happy.