To certain the
required properties of stones, the following tests can be conducted:
(i) crushing strength test
(ii) water absorption test
(iii) abrasion test
(iv) impact test
(v) acid test.
(i) Crushing Strength Test:
For conducting this test, specimen
of size 40 × 40 × 40 mm are prepared from parent stone. Then the sides are
finely dressed and placed in water for 3 days. The saturated specimen is provided
with a layer of plaster of paris on its top
and bottom surfaces to get even surface so that load applied is distributed
uniformly. Uniform load distribution can be obtained satisfactorily by
providing a pair of 5 mm thick playwood instead
of using plaster of parislayer also.
The specimen so
placed in the compression testing machine is loaded at the rate of 14 N/mm2 perminute. The crushing load is noted. Then crushing
strength is equal to the crushing load divided by the area over which the load
is applied. At least three specimen should be tested and the average should be
taken as crushing strength.
(ii) Water Absorption Test:
For this test cube
specimen weighing about 50 grams are prepared and the test is carried out in
the steps given below:
(a) Note the weight of dry speciment 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 weight =(W2- W1)/(W1)x100 ---------(1)
Percentage absorption
by volume =W2-W1/W2-W3X100--------(2)
Percentage porosity
by volume =W4-W1/W2-W3X100-----------(3)
Density =W1/W2-W1----------------------------------------------------(4)
Specific gravity=W1/W2-W3-------------------------------------------(5)
∴ Saturation coefficient =Water
absorption / Total porosity =W2-W1/W4-W1
(iii) Abrasion
Test:
This test is carried
out on stones which are used as aggregates for road construction. The test
result indicate the suitability of stones against the grinding action under
traffic. Any one of the following test may be conducted to find out the suitability
of aggregates:
(i)
Los Angeles abrasion test
(ii) Deval abrasion
test
(iii) Dorry’s abrasion test.
However Los Angeles
abrasion test is preferred since these test results are having good correlation
with the performance of the pavements.
The Los Angeles apparatus consists of a hollow cylinder 0.7
m inside diameter and
0.5 m long with both
ends closed.
It is mounted on a
frame so that it can be rotated about horizontal axis. IS code has standardised
the test procedure for different gradation of specimen. Along with specified
weight of specimen a specified number of cast iron balls of 48 mm diameter are
placed in the cylinder.Then the cylinder is
rotated at a speed of 30 to 33 rpm for specified number of times (500 to 1000).
Then the aggregate is removed 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/
Original weight × 100.
The following
values are recommended for road works:
For bituminous mixes
– 30%
For base course – 50%
(iv)
Impact Test:
The resistance of
stones to impact is found by conducting tests in impacting
testing machine 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 the specimen 15 times. The
specimen is then sieved through 2.36 mm
(v) Acid Test:
This test is normally
carried out on sand stones to check the presence of calcium
carbonate, which weakens the weather
resisting quality. In this test, a sample of stone weighing about 50 to 100 gm
is taken and kept in a solution of one per cent hydrochloric acid for seven
days. The solution is agitated at intervals. A good building stone maintains
its sharp edges and keeps its surface intact. If edges are broken and powder is
formed on the surface, it indicates the presence of calcium
carbonate. Such stones will have poor
weather resistance.