Sieve Analysis
Gradation of aggregates is determined from sieve analysis, in which a representative
sample of aggregate is passed through a series of sieves and the weight retained in each
sieve – expressed as a percentage of the sample weight – is compared with the grading
limits specified.
A sieve is an apparatus – round or square in shape – with square openings, identified
either by the size (clear) of the opening or by a number. The higher the number, the
smaller the opening. The standard sieves for coarse aggregate are No.4, 3/8 in., ½ in., ¾
in., 1 in., 1 1/2 in., 2 in., and 2 1/2 in. The standard sieves for fine aggregate are nos. 100,
50, 30, 16, 8 and 4. The sizes of openings for these sieves are shown in the table. It can
be seen that most of the sieves are arranged so that each has an opening size that is onehalf that of the upper or twice that of the lower sieve. For example, the No. 50 sieve has
an opening of 0.3-mm, which is twice the size of the opening of the No. 100 sieve (equal
to 0.15-mm), and half that of the No. 30 sieve (equal to 0.6-mm). These sieves are called
full sieves. Sieves that do not fall into this arrangement, such as 1 in and ½ in, are called
half sieves.
Sieve Designation
Normal opening
in.
mm
in.
mm
Type
2
50
2
50
H
1½
37.5
1.5
37.5
F
1
25
1
25
H
¾
19
0.75
19
F
½
12.5
0.5
12.5
H
3/8
9.5
0.375
9.5
F
No. 4
4.75
0.187
4.75
F
No. 8
2.36
0.0937
2.36
F
No. 16
1.18
0.0469
1.18
F
No. 30
0.0234
0.60
F
600 m
No. 50
0.0117
0.30
F
300 m
No. 100
0.0059
0.15
F
150 m
No. 200
0.0030
0.075
F
75 m
Sieve (or mechanical) analysis consists of determining the proportionate amounts of
particles retained on or passing through each of a set of sieves arranged in decreasing
sizes. Using the percentages of weights retained in each sieve, a graph, called a particle
size distribution curve, shown below, is drawn by plotting the log of the opening size on
the x-axis and the percentage of particles, by weight, coarser than or finer than the
particular sieve on the y axis. A uniform shape, like an escalator, shows uniform
gradation. A horizontal or near-horizontal shift, like a landing, shows that some
intermediate particle sizes, corresponding to the top of the landing, are missing. When a
large part of the aggregate is made up of particles of one size, it is reflected in the graph
as a near vertical drop. A gradation chart that remains closer to the origin has a large
percentage of finer particles – a finer gradation – and similarly, when it shifts away from
the origin, a large percentage of coarser particles – a coarser gradation.
The sieve analysis of fine aggregate is commonly carried out in a mechanical shaker that
is designed for 8 in. diameter round sieves; that of course aggregate may be carried out in
the same shaker designed for 8 in. round sieves, or by using larger rectangular sieves
mounted in frames designed to accommodate them. The mechanical shaker imparts
lateral (or lateral and vertical) motion to the set of sieves, causing the particles thereon to
bounce and turn so as to present different orientations to the sieving surface. This aspect
is important, for the sieve openings are square whereas the particles are neither square
nor round.
The test sample is placed on the top sieve, the lid is put on, and the set of sieves is
agitated in the mechanical shaker. By measuring the weights of particles retained in each
sieve – after the agitation – the percentage of weight passing through (finer than) or
retained (coarser than) in each sieve is calculated. These values are plotted in a chart, as
previously described, and then compared with the specified or standard limits to establish
the suitability of the aggregates.
TEST
Purpose: to determine particle-size distribution and fineness modulus of coarse
aggregate (CA) by sieving.
Related Standard: ASTM C136
Definition: the fineness modulus is the sum of the total percentages of material in the
sample that is coarser than (cumulative percentages retained) each of the following sieves
and divided by 100: No. 8, No. 4, 3/8 in., ¾ in., 1 ½ in., and larger, increasing in the ratio
2:1.
Equipment: Balance, sieves, mechanical shaker, oven.
Sample: Dry coarse aggregate of weight equal to the following:
Weight of
sample [lb (kg)]
33 (15)
22 (10)
11 (5)
Maximum size of
CA [in. (mm)]
1 ½ (37.5)
1 (25)
¾ (19)
Use the same weight (same as that for ¾ in.) when the maximum size is less than ¾ in. +
Two different course aggregate and one fine aggregate samples will be used in the
sieve analysis.
Procedure
1.
Weigh the dry sample accurately. Course aggregate samples should be at least 11
lbs.
2.
Weigh each empty sieve and the pan.
3.
Nest the suitable sieves in order of decreasing size of opening from top to bottom.
Place the pan at the bottom of the set.
4.
Place the sample on the top sieve.
5.
Place the lid, and agitate the sieves in the mechanical shaker for about 5 minutes,
or long enough to distribute all the aggregate. .
6.
Weigh the sieves with the material retained.
7.
Determine the weight retained in each sieve. The total weight of the material after
sieving should check closely with the original weight of the sample.
8.
Calculate the percentage coarser than and the percentage passing.
9.
Draw the particle-distribution curves for all aggregates, and calculate the fineness
modulus for the fine aggregate.
10.
Place all sieved materials into separate 5-gallon buckets. Separate approximately
10 lbs of both of the coarse aggregates for the specific gravity experiment. The
smallest course aggregate should be larger than the No. 4 sieve (i.e., not pass
through the No. 4 sieve.)
Report:
1. Make a table that includes: the pan used and its weight, the initial weight of the
sample, the weight of the material retained in each pan, the % retained, the %
coarser than.
2. Plot the particle-size distribution for each of the samples tested.
3. Using the particle-size distribution charts, characterize each of the sample
batches. For example, is it well graded, are there any missing sizes, etc.
4. Using the table below, determine the blend required to make a well graded
sample for ¾ in. coarse aggregate.
5. Report the fineness modulus and average sample size.
6. Using the chart below, determine if the size distribution for fine aggregate is
well graded for making concrete. If not, explain how to adjust the mixture so that
it is well graded.
7. Discuss the significance of size distribution on aggregate packing.
Following the above steps:
8. Make a blend of coarse and fine aggregate that satisfies steps 4 and 6.
9. Accurately weigh out two samples (nominally 10-lb) of the blended coarse
and fine aggregate.
10. Place the samples from step 8 in the oven, at 110oC and dry for not less than
24 hours.