Aggregate
crushing value is measured which relatively gives idea of his resistance to crushing
under the compressive load applied gradually. Lower the crushing value stronger
the aggregate again crushing. Therefore, good quality concrete, aggregate
having comparatively lower crushing value is to be preparable. Aggregate
crushing value should not be exceed 30 % for concrete used for wearing
surface such as road, runways and aggregate crushing value should not exceed 45
% for other than wearing surfaces and used for any
concrete work.
AIM:
To determine the aggregate
crushing value of coarse aggregate.
Apparatus:
- IS
sieves of sizes 12.5mm, 10mm and 2.36mm
- Steel
cylinder 15 cm diameter with plunger and base plate.
- Straight
metal tamping rod 16mm diameter and 45 to 60cm long rounded at one end.
- Compression
testing machine.
- Cylindrical
metal measure of sufficient rigidity to retain its from under rough usage
and of 11.5cm diameter and 18cm height.
- Balance
FIGURE:
Procedure:
1.
Sample of aggregate is prepared by sieve the
aggregate. The sample is passed through 12.5 mm sieve and retained at 10 mm
sieve.
2.
Sample is dryed in an oven at temperature
between 100 0c to 110 0c for four hours. Then along it to cooled.
3.
Put the cylinder in position on the base
plate and weigh it (W).
4.
Fill the cylindrical measure in three layers
each layer was tamped by tamping rod the top surface of the measure is levelled
off. The weight of the whole assembly was noted (W1).
5.
The cylindrical steel mould is fixed to base
plate and fill it with the aggregates removed from the cylindrical measure, in
a standard manner as filled in the cylindrical measure.
6.
The plunger is placed on the aggregate. The
whole assembly is placed between plates of compressive testing machine.
7.
The load is applied to the sample of
aggregate through the plunger at the rate of per minute up to 40 Tone.
8.
The load is released and sieve the material
the cylinder through 2.36 mm sieve weight the fraction passed through 2.36 mm
sieve (W2).
Calculation of Aggregate Crushing Value:
The ratio of
weight of fines formed to the weight of total sample in each test shall be
expressed as a percentage, the result being recorded to the first decimal
place.
Aggregate crushing value = (W2 x 100) / (W1-W)
W2 =Weight of
fraction passing through the appropriate sieve
W1-W =Weight of
surface dry sample.
The mean of two
result to nearest whole number is the aggregate crushing value.
PRECAUTION:
1.
The aggregate sample should be sieved and
weight correctly.
2.
Each time layer should be tamped 25 time with
the help of tamping rod.
3.
The cylinder at the test apparatus with
aggregate is carefully levelled and plunger inserted horizontally.
4.
The plunger should not touch cylinder.
5.
The load should applied uniformly into a
total load at 40 Tone in 10 min time.
RESULT:
The aggregate crushing value at the given sample
is _____________ %.You Might also like:
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