Tests on Stones
The
required properties of stones are ascertained by the following tests,
(1) Crushing
strength test
(2) Water
absorption test
(3) Abrasion
test
(4) Impact
test
(5) Acid
test
(1) Crushing strength test
To conduct this test, specimen of 40*40*40 mm is prepared
from parent stone. Place the stone in water for 3 days,
after the sides are finely dressed.
Plaster of Paris is provided on the top & bottom surfaces of the
saturated specimen to get even surfaces,
so that the load applied is distributed uniformly.
Also, instead of using P.O.P layer, uniform load distribution can
be obtained by providing a pair of 5 mm thick plywood.
14 N/ mm2 per minute load is placed on the specimen in the compression testing machine and crushing load is noted.
Crushing Strength =Crushing Load / Area over which load is applied
Take 3 specimens at least & take the average of them as the crushing strength.
(2) Water absorption test
Cube Specimen having weight about 50 grams are prepared for this test
& following steps are carried out
(a) Note the weight of dry specimen as W1.
(b) Place the specimen in water for 24 hours.
(c) Take out the specimen, wipe out the surface with a piece of cloth and
weigh the specimen. Let its weight be W2.
(d) Suspend the specimen freely in water and weight it. Let its weight be W3.
(e) Place the specimen in boiling water for 5 hours. Then take it out,
wipe the surface with cloth and weigh it. Let this weight be W4. Then,
Percentage absorption by volume = (W2- W1) x 100 / (W2-W3) -- b
Percentage porosity by volume = (W4- W1) x 100 / (W2-W3) --- c
Density = W1 / (W2-W1) --- d
Specific gravity = W1 / (W2-W3) --- e
Saturation coefficient
= Water absorption / Total porosity
= (W2- W1) / (W4-W1)
(3) Abrasion test
This test is done on stones which can be used as aggregates
for road construction. The test end result suggests
the suitability of stones against the grinding motion
under traffic. The following are the tests that may
be conducted to find out the suitability of aggregates.
(i) Los Angeles abrasion test
(ii) Deval abrasion test
(iii) Dorry’s abrasion test.
(i) Los Angeles abrasion test
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It consists of a hollow cylinder 0.7 m inside diameter and 0.5 m
long with both ends closed. It is set up on a frame so that it
could be rotated about the horizontal axis. IS code has standardized
the test method for different gradation of specimens. Along with
specific weight of specimen a specific quantity of cast iron balls
of 48 mm diameter are located inside the cylinder.
Then the cylinder is circled at a pace of 30 to 33 rpm for a
specific number of times (500 to 1000).
Then the aggregate is eliminated and sieved on
1.7 mm IS sieve. The weight of aggregate passing is found.
Then Los Angeles value is found as
= Weight of aggregate passing through sieve X 100 / Original weight
For road works, the following values are recommended
For bituminous mixes – 30%
For base course – 50%
(4) Impact test
The resistance of stones to impact is
found by conducting this test. It consists of a frame (with guides) in which a metal hammer weighing 13.5 to 15 kg
can freely fall from a height of 380 mm.
Aggregates of size 10 mm to 12.5 mm
are filled in cylinder in 3 equal layers; each layer being tamped 25 times. The
same is then transferred to the cup and again tamped 25 times. The hammer is
then allowed to fall freely on specimen 15 times. The specimen is then sieved
through 2.36 mm sieve.
Impact value = W2 / W1
Where W2 =
weight of fines
W1 =
original weight.
The recommended impact values for various works
are:
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(5) Acid test  |
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of calcium
carbonate, which weakens the climate resisting quality.
In this
test, a sample of stone weighing about 50 to 100 gm. is taken
and
stored in a solution of 1 per cent hydrochloric acid for seven days.
its sharp edges and continues its surface intact. If edges are broken
and powder is shaped at the surface, it shows the presence of calcium
carbonate. Such stones can have negative weather resistance.
REFERENCE BOOKS
1. BUILDING MATERIAL - RANGAWALA
2. BUILDING MATERIAL - SUSHIL KUMAR
3. BUILDING MATERIALS & CONSTRUCTION - B.P.BINDRA
4. BUILDING CONSTRUCTION - B.C.RANGWALA
5. BUILDING MATERIALS - A.KAMALA
6. BUILDING CONSTRUCTION & MATERIALS
-MR. SHRIKANT D. BOBADE
direct-link-445452,DirectLink_1,17084633,https://www.safestgatetocontent.com/girprigkfd?key=50bef049d46d5d216da32ccba87da5ee7. Basic Civil Engineering S.S. BHAVIKATTI
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