When I was working in a concrete batching plant before, I was the one who is managing all the tests as per plant quality control procedures like checking the moisture content of aggregates, flakiness index and elongation index, pH value of water and many more.
The most important test is the sieve analysis of aggregate, whether it is 20mm, 10mm, 5mm and 1mm sizes. The crucial thing is I have to do it every delivery of aggregate and as per the frequency of sieve analysis, which is written in this article frequency of tests.
As a quality engineer in the concrete batching plant, you have to see to it that the sieve analysis is done regularly, as per plant standards and quality procedures. There are certain purposes why you need to do this test, first, is you need to know if the delivered aggregate in your plant is a true size what I mean is “Is this really a 20mm size?” I will show how you will say that it is satisfactory or unsatisfactory and then how you will conclude that the aggregate you received is acceptable.
Second, is you have to determine the gradation or the distribution of aggregate particles by size, within a given sample in order to determine the concrete production requirements and the design of concrete mix.
You have to determine also the proportion of all-in aggregates within a sample to be used on concrete because if you will not get the appropriate proportion it may affect to the strength of your concrete, so it is really necessary to “do sieve analysis continually.”
Moreover, this sieve analysis procedure can be used by people who are working in the laboratory like government laboratory, private independent laboratory or even schools so this would help students make their “sieve analysis” done.
First here are the apparatus of the sieve analysis.
|1||Sieves||Use to get the wt. of sample retained on each sieves and to determine the particle size distribution|
|2||Balance or Weighing Scale||Use to weigh the sample from dry and wet condition and the wt. of sample retained on each sieves|
|3||Mechanical Sieve Shaker||Use to shake the sample once it is inside the sieves|
|4||Oven or Hot plate||Use to dry the sample and maintain the temp. of 110 +/- deg. Celsius|
|5||Steel brush & Paint Brush||For removing entrapped material from sieve holes & cleaning|
|6||Sample Splitter||Use to reduce the sample to "mass test portion"|
|7||Spoons||Use to take sample from pan and for seggregating material|
|8||Pans||For handling samples|
Here is the full procedure on “How to do the Sieve Analysis of aggregate.”
1. Taking the representative sample. Take the samples with a minimum of 25kg. in the aggregates stockyard or storage bin by scattered basis, take from bottom, middle and top of the dumped aggregate, do not take from just one area. Place the sample in clean container. You can see in this video.
2. Reduce the sample to “Minimum Mass of Test Portion.” There are minimum masses that you would need to take corresponding to each size of aggregate that you are going to do sieve analysis. This time we’re going to use 20mm aggregate, so we will reduce the sample to 2 kilograms (minimum weight) but you can make it more than 2kgs as long as you will follow the process. There are two ways how to reduce the weight of the sample, one is by using the riffle box which you can see it on this video which I almost can’t speak.. haha lol! “How to reduce sample using riffle box” and the other by manual splitting called “Quartering Method” which is also a very simple way. See photo below of a sample quartering.
3. Washing the sample. Once the sample has been reduced to 2 kilograms or to a “minimum mass” then wash it with a clean water or faucet water, make sure it is thoroughly cleaned before oven drying. Weigh the sample, mark as mass at wet condition Mass 1 (M1).
4. Oven dry the sample. Oven dry it for 24 hours before you will conduct sieve analysis, but make sure weigh the sample and record before you put the sample inside the oven, mark as sample at moist condition as per Item 3. Put the oven to a temperature of 110 degree Celsius. Once the sample is oven dried, weigh the sample, mark as Mass at Dry condition, or M2.
5. Sieving the sample. The sieves number that you will use in the 20 size aggregate samples are 37.5 mm, 20.0 mm, 14.0 mm, 10.0 mm & 0.075 mm. Place the bigger size of sieve on top of smaller and in order from from top to bottom. And then put the dried sample on topmost sieve (37.5 mm) be careful on placing the sample to avoid throwing out of some pieces of aggregate that would create error on the calculations. Put the sieve on the sieve shaker or you can make sieve shaking manually for 10 minutes long.
6. Weight the retained material on sieves. You can weigh now the material retained on each sieve. But make sure you remove the trapped material from the holes of the sieve, remove by steel brush or paint brush accordingly. You can then weight now and include the material to the mass retained and record it.
7. Calculations. Once you have finished recording the mass retained samples. You can easily calculate the percentage retained and cumulative percentage retained. See below calculations.
So in the above calculations the result of cumulative percent passing is within the limits, in the first place we can initially conclude that the 20mm size aggregate sample as a representative of the delivery is acceptable.
And the final conclusion can be obtained from the result of “material finer than a 75µm in percent.” The standard say’s “the course aggregate shall have not less than 5 percent of material passing 75µm sieve.” So therefore, the 20mm size aggregate delivered in this instance is satisfactory.
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