B.5.1 Step 1: Sampling
Determine the mass of the necessary sample by applying Equation (B.10):
bulk est. 95 3
= 150 ( ) 1 kg
m ρ D W (B.10)
where
m is the mass of the sample used for determining D95, in grams (g);
ρbulk is the bulk density of the material, in grams per cubic centimetre (g/cm3);
Dest. 95 is the estimated maximum particle size, in centimetres (cm).
Take a sample of this mass from the stockpile.
The purpose of a specific sampling programme should be kept in mind. As the purpose is only to obtain an estimation of D95, the sample can be taken based on the knowledge of the sampler. This means that the sampler can take a sample for which he can assume that all particle sizes are present.
B.5.2 Step 2: Weighing the sample
Weigh the sample (m0).
For the accuracy of the weighing, Table B.1 is used:
Table B.1 — Accuracy of weighing Size of the sample
kg
Accuracy of the weighing g
1 to 5 0,1
5 to 10 1
10 to 50 10
> 50 100
B.5.3 Step 3: Sieving the sample
Transfer the entire sample on a sieve with a sieve aperture equal to the estimated D95. If there is no sieve aperture equal to the estimated D95, two sieves shall be used. The sieve with the largest aperture has an aperture adjacent to but larger than D95, while the sieve with the smallest aperture has an aperture adjacent to but smaller than D95.
Sieve the sample either manually or mechanically. Check if the material that remains on the sieve(s) consists of individual particles. If so, proceed to Step 4.
When macro-aggregates are present, the macro-aggregates are pushed through the sieve. However, this may only be done when the method of sampling is capable of taking a part of a sample. When macro-aggregates are to be seen as individual particles during sampling, the macro-aggregates are left on the sieve.
B.5.4 Step 4: Weighing the sample part(s)
Weigh the part of the sample that remains on the sieve (m1) or weigh the parts that remain on both sieves (m1 and m2). The accuracy of the weighing should fulfil the conditions given in the table in Step 2.
B.5.5 Step 5: Determination of the maximum particle size
B.5.5.1 Step 5.1: Calculation for one sieve
If only one sieve is used, the maximum particle size is calculated according to Equation (B.11):
sample 1
0
100 m %
w = m (B.11)
where
wsample is the mass fraction of the sample that remains on the sieve, in percent (%);
m1 is the mass of the part of the sample that remains on the sieve, in grams (g);
m0 is the total mass of the sample, in grams (g).
If
⎯ wsample < 5 % the used sieve aperture was too big. The aperture size is used as an assumption for D95, or the sieved part of the sample is sieved again with a sieve with smaller aperture. In the latter situation, go back to Step 3 and the calculation of the D95 is then carried out in accordance with Step 5.2.
⎯ wsample = 5 % the used aperture was exactly right and is used as an estimation of D95.
⎯ wsample > 5 % the used aperture is too small. Go back to Step 3 and use the fraction m1 for a second sieving. D95 is calculated according to Step 5.2.
B.5.5.2 Step 5.2: Calculation when applying two sieves
If two sieves were applied, D95 is calculated according to Equation (B.12):
sample,1 1
0 sample,2 2
0
= 100 %
= 100 %
w m
m w m
m
(B.12)
where
wsample,1 is the mass fraction of the sample that remains on the sieve with the largest aperture, in percent (%);
wsample,2 is the mass fraction of the sample that remains on the sieve with the smallest aperture, in percent (%);
m1 is the mass of the part of the sample that remains on the sieve with the largest aperture, in grams (g);
m2 is the mass of the part of the sample that remains on the sieve with the smallest aperture, in grams (g);
m0 is the total mass of the sample, in grams (g).
If
⎯ wsample,1 = 5 % the aperture of sieve 1 is exactly right. This aperture size is used as an estimate for the D95.
⎯ wsample,1 > 5 % the used aperture of the sieves is too small. Go back to Step 3 and use fraction m1 for a second sieve step. The D95 is determined according to Step 5.2 using the newly produced sieve fractions.
⎯ wsample,1 + 2 < 5 % both applied sieves are too big. Assume that D95 is equal to the aperture of sieve 2 or go back to Step 3 and sieve the total sample again on a set of smaller sieves. D95 is then estimated according to Step 5.2 using the newly produced sieve fractions.
⎯ All other situations: estimate D95 by interpolation between the two sieve aperture sizes. Linear regression can be used for this interpolation.