DELETERIOUS CONTENT OF AGGREGATES.
DELETERIOUS
CONTENT OF AGGREGATES.
( IS : 2386
– PART – 2 )
I.
DETERMINATION OF CLAY LUMPS:
Apparatus:
1) Balance – sensitive to 0.001 g, 2) Containers – size and shape that will permit the spreading
of the sample on the bottom in a thin layer, 3) Sieves – conforming to IS :
460-1962.
Sampling:
Samples shall be obtained by quartering or by the use of a sampler,
from a representative sample selected from the material to be tested. They
shall be handled in such a manner as to avoid breaking up clay lumps, which may
be present. Samples shall be dried to constant weight at a temperature not
exceeding 1100C.
Samples of fine aggregate shall consist of particles coarser than 1.18
mm IS sieve and shall weigh not less than 100 g.
Samples of coarse aggregate shall be separated into different sizes
using 4.75mm, 10mm, 20mm and 40mm IS sieves. The weight of the sample for
different sizes shall be not less than those indicated below:
In the case of mixtures of fine and coarse aggregates, the material
shall be separated into two sizes on 4.75mm IS sieve, and the samples of fine
and coarse aggregates shall be prepared as described above.
Procedure:
The sample shall be spread in a thin layer on the bottom of the
container and examined for clay lumps. Any particles, which can be broken into
finely divided particles with the fingers, shall be classified as clay lumps.
After all discernible clay lumps have been broken, the residue from the clay
lumps shall be removed by the use of sieves indicated below:
Calculations:
The percentage of clay lumps shall be calculated to the nearest 0.1
percent in accordance with the following formula:
(W – R)
L = ------------- X 100
W
Where, L =
percentage of clay lumps.
W = weight of sample.
R = weight of sample after removal of clay
lumps.
II.
DETERMINATION OF CLAY, FINE SILT AND FINE DUST.
Apparatus:
1) A watertight screw-topped glass jar of dimensions similar to a 1-kg
fruit-preserving jar, 2) A device for rotating the jar about its axis, with
this axis horizontal, at a speed of 80 +/- 20 rev/min, 3) A sedimentation
pipette of the Andreason type of approximately 25 ml capacity. This consists
mainly of a pipette fitted at the top with a two way tap and held rigidly in a
clamp which can be raised or lowered as required, and which is fitted with a
scale from which the changes in height of the pipette can be read, 4) A 1000 ml
measuring cylinder, 5) A scale or balance of capacity not less than 10 kg,
readable and accurate to one gram, 6) A scale or balance of capacity not less
than 250 g, readable and accurate to 0.001 g, 7) A well ventilated oven,
thermostatically controlled, to maintain a temperature of 100 to 1100C.
Chemicals:
A solution containing 8 g of sodium oxalate per litre of distilled
water shall be taken. For use, this stock solution is diluted with distilled
water to one tenth (that is 100 ml diluted with distilled water to one litre).
Test sample:
The sample for test shall be prepared from the main sample taking
particular care that the test sample contains a correct proportion of the finer
material. The amount of sample taken for test shall be in accordance with below
table.
All in aggregates shall be separated into fine and coarse fractions by
sieving on a 4.75 mm IS sieve and the two samples so obtained shall be tested
separately.
Procedure:
Method for fine aggregate: Approximately 300 g of the sample in the air dry
condition, passing the 4.75 mm IS sieve, shall be weighed and placed in the
screw topped glass jar, together with 300 ml of the diluted sodium oxalate
solution. The rubber washer and cap shall be fixed, care being taken to ensure
water tightness. The jar shall then be rotated about its long axis, with this
axis horizontal, at a speed of 80 +/- 20 rev/min for a period of 15 minutes. At
the end of 15 minutes, the suspension shall be poured into the 1000 ml
measuring cylinder and the residue washed by gentle swirling and decantation of
successive 150 ml portions of sodium oxalate solution, the washings being added
to the cylinder until the volume is made up to 1000 ml. The determination shall
be completed as described below.
Method for coarse aggregate: The weighed sample shall be placed in a suitable
container, covered with a measured volume of sodium oxalate solution (0.8 g per
litre), agitated vigorously to remove all adherent fine material and the liquid
suspension transferred to the 1000 ml measuring cylinder. This process shall be
repeated as necessary until all clayey material has been transferred to the
cylinder. The volume shall be made up to 1000 ml with sodium oxalate solution
and the determination completed as described below.
The suspension in the
measuring cylinder shall be thoroughly mixed by inversion and the tube and
contents immediately placed in position under the pipette. The pipette shall
then be gently lowered until the tip touches the surface of the liquid, and
then lowered a further 10 cm into the liquid. Three minutes after placing the
tube in position, the pipette and the bore of tap shall be filled by opening
and applying gentle suction. A small surplus may be drawn up into the bulb
between tap and tube, but this shall be allowed to run away and any solid
matter shall be washed out with distilled water from top end. The pipette shall
then be removed from the measuring cylinder and its contents run into a weighed
container, any adherent solids being washed into the container by distilled
water
from top end. The contents of the container shall be dried at 100 to
1100C to constant weight, cooled and weighed.
Calculations: The proportion of fine silt and clay or fine dust
shall then be calculated from the following formula:
100 1000W2
Percentage of clay and fine silt or fine dust = -----
( ---------- - 0.8 )
W1 V
Where, W1= weight in g of
the original sample, W2= weight in g of the dried residue, V= volume in ml of
the pipette & 0.8 = weight in g of sodium oxalate in one litre of the
diluted solution.
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III.DETERMINATION
OF LIGHT-WEIGHT PIECES.
Apparatus:
1) Balances – for weighing fine aggregates, a balance having a capacity
of not less than 500 g, sensitive to at least 0.1 g; for weighing coarse
aggregates, a balance having a capacity of not less than 5000 g, sensitive to
at least 1 g.
2) Containers – containers suitable for drying the aggregate sample,
and containers suitable for holding the heavy liquid during the sink-float
separation.
3) Skimmer – a piece of 300-micron sieve cloth of suitable size and
shape for separating the floating pieces from the heavy liquid.
4) Hot-plate or oven.
Heavy liquid: The heavy liquid shall consist of a mixture of
carbon tetrachloride, and 1, 1, 2, 2-tetrabromoethane, bromoform, and
monobromobenzene, or bromoform and benzene, in such proportions that the
desired specific gravity will be obtained. Bromotrichloromethane may be used as
a heavy liquid having a specific gravity of 2.00. The specific gravity shall be
maintained within +/- 0.01 of the specified value at all times during the test.
The approximate volumes of materials to be combined to produce a
mixture of the desired specific gravity may be computed from the following
specific gravities of the different liquids:
For determining coal and lignite, the heavy liquid used shall have a
specific gravity of 2.00 +/- 0.01.
Test Sample: The minimum size of test sample shall be as
follows:
Procedure:
1) Fine aggregate: Allow the dried sample of fine aggregate to cool to
room temperature and then sieve over a 300-micron IS sieve until less than one
percent of the retained material passes the sieve in one minute of continuous
sieving. Weigh the material coarser than the 300-micron IS sieve to the nearest
0.1 g; then introduce it into the heavy liquid in a suitable container, the
volume of liquid being at least three times the absolute volume of the
aggregate. Pour the liquid off into a second container; passing it through the
skimmer and taking care that only the floating pieces are poured off with the
liquid and that none of the sand is decanted onto the skimmer. Return to the
first container the liquid that has been collected in the second container and,
after further agitation of the sample by stirring, repeat the decanting process
just described until the sample is free of floating pieces. Wash the decanted
pieces contained on the skimmer in carbon tetrachloride, until the heavy liquid
is removed, and then dry. The pieces will dry very quickly, but may be placed
in an oven at 1050C for a few minutes if desired. Brush the dry
decanted pieces from the skimmer onto the balance pan and determine the weight
to the nearest 0.1 g.
2) Coarse aggregate: Allow the dried sample of coarse aggregate to
cool to room temperature and sieve over a 4.75 mm IS sieve. Weigh the material
coarser than the 4.75 mm IS sieve to the nearest 1 g; then introduce it into
the heavy liquid in a suitable container, the volume of the liquid being at
least three times the absolute volume of the aggregate. Using the skimmer,
remove the pieces that rise to the surface, and save them. Repeatedly agitate
the remaining pieces and remove the floating pieces until no additional pieces
rise to the surface. Wash the decanted pieces in carbon tetrachloride until all
of the heavy liquid is removed, and allow to dry. Determine the weight of the
decanted pieces to the nearest 1-gram.
Calculations: Calculate the percentage of lightweight pieces as
follows:
For fine aggregate: L = (W1/W2)x100
For coarse aggregate: L = (W1/W3)x100
Where, L = percentage of lightweight pieces, W1 = dry weight in g, of
decanted pieces, W2 = dry weight in g,
of portion of sample coarser than 300-micron IS sieve & W3 = dry weight in
g, of portion of sample coarser than 4.75 mm IS sieve.
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DETERMINATION
OF SOFT PARTICLES.
Apparatus: The apparatus shall consist of a brass rod, having a Rockwell hardness of 65 RHB to 75
RHB. A brass rod of about 1.6mm diameter and of proper hardness inserted into
the wood shaft of an ordinary lead pencil is a convient tool for field or
laboratory use.
Test Sample: Aggregates for the test shall consist of material
from which the sizes finer than the 10mm IS sieve have been removed. The sample
tested shall be of such size that it will yield not less than the following
amount of the different sizes, which shall be available in amounts of 10
percent or more:
Procedure:
Each particle of aggregate under test shall be scratched with the brass
rod with a small amount of pressure (about 1 kg). Particles are considered to
be soft if during the scratching process, a groove is made in them without
deposition of metal from the brass rod or if separate particles are detached
from the rock mass.
Calculations: The report shall include the following information.
a) Weight and number of particles of each size of each sample tested
with the brass rod.
b) Weight and number of particles of each size of each sample
classified as soft in the test.
c) Percentage of test sample classified as soft by weight and by number
of particles.
d) Weighed average percentage of soft particles calculated from
percentage in item (c) and based on the grading of sample of aggregate received
for testing.
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