Stones
Tests of Stones
Stones
are main material used for wide range of civil engineering structures. For the
quality purposes few tests are important to carry out before use for a
particular structure. Here we study some important tests which we need to
perform before use of stones. From the tests we are able to understand about
their strength, characteristic and their behaviour under different conditions.
Most of the cases stones are liable to disintegrate due to weathering effects
on which we need to focus at the time of its application.
Today we will study about few tests for stones as listed below:
1.Acid test
2.Attrition test
3.Crushing test
4.Crystalline test
5.Freezing and Thawing test
6.Harness test
7.Impact test
8.Microscopic test
9.Smith's test
10.Water absorption test
1. Acid test
-This test is used for sandstone.
-Sample of stones weighing 50-100 grams is taken.
-Sample stones are placed in a solution of hydrochloric acid and kept it in for 7 days.
-Solution is agitated at regular intervals. If stone is able to maintain it's corner sharp and do not get powdered than it is a good building stone.
-If stone contains calcium carbonate is will disintegrate and powdered it can not be able to withstand weathering effects.
-So from this we can conclude that we can not use this test for limestone.
2. Attrition test
Attrition test is used to find wear on aggregate due to grinding effects of traffic on stone/aggregate in road construction.
Procedure:
- Sample of 60 mm size stones are selected.
- Sample of 5 kg weight put in both the cylinder of Deval's attrition testing machine. dimensions of the cylinder are 20 cm diameter and 34 cm length.
- Axis of cylinder makes an angle of 30° with horizontal.
- Cylinders are rotated at 30 R.P.M for 5 hours @ horizontal axis.
- After 5 hours of rotation cylinders are open and content taken out and sieve through 1.50 mm IS sieve.
- Quantity of material retained on sieve is weighted.
Devel's Attrition Machine
1.5 mm mesh/sieve
- Percentage wear on stone is worked out from following formula
Percentage Wear = (Loss on weight/Initial Weight)*100
3. Crushing strength test
Compressive strength of stone and aggregate both are different things, so don't confused between both of them.
- Stones of 40 mm size cubes are used for testing of crushing strength of stones.
- Cubes are finely dressed all side and finished well.
- Before testing cubes shall be placed in water at-least for 24 hours.
- Load can not applied directly so load bearing surface covered with plaster of paris or 5 mm plywood.
- Load is applied in compression testing machine at rate of 140 kg/cm2/minute.
- When cube failed result noted and crushing strength of stone can be found out.
4. Crystallisation test
- In this test same as crushing test cube of 40 mm size are used.
- Minimum four cubes are required to perform this test.
- Cubes are dried atleast for 3 days and then weighted before testing.
- Cubes are immersed into 14 % solution of Na2SO4 for 120 minutes, and then dried at 100° C. weight is noted after drying.
- Above process continue for five times each sample and every time loss of weight is noted with respect to initial weight. Loss of weight is expressed in percentage.
5. Freezing and Thawing test
- In this test stones are placed in water for atleats 24 hours.
- After that placed at a temperature of 12° C for a day in freezing mixture.
- It is then allowed to get thawed at atmospheric temperature. During this test stone is prevented to contact with wind, sun-rays, and rains etc.
- Above procedure is continued several times and behaviour of stone is studied at each and every time.
6. Hardness test
Hardness of the stone is found out by following procedure.
- A cylindrical specimen of 25 mm diameter and 25 mm height is cut out from the main stone sample, and weighted.
- Sample is then placed in Dorry's testing machine and applied a press with the pressure of 1.250 kg.
- Machine's annular rotating disc is then rotated at a speed of 28 revolutions per minute.
- During rotation of disc coarse sand of specified standards is spreads on the top of disc.
- Sample is taken out after 1000 revolutions.
- Coefficient of harness is then calculated from following equation.
Coefficient of Hardness = 20 - (Loss in weight in grams/3)
7. Impact test
To find impact strength of a stone testing is done in impact testing machine as follows:
- A cylindrical specimen of 25 mm diameter and 25 mm height is cut out from the main stone sample, and weighted.
- Sample is then placed on cast iron anvil of machine.
- A steel hammer of 2000 grams allowed to fall on the specimen in vertical direction.
- Fall of hammer is not constant, height of fall for each fall is added by 1 cm, for example first fall from 1 cm, second fall from 2 cm, third fall from 3 cm and so on.
- Fall for which sample of stone get cracked is considered as impact strength and fall value considered as toughness index.
- If sample fails at "n" th number of fall, "n" will be the toughness index.
8. Microscopic test
In this test stone is used to put in a microscope to analyze it at micro examination. Following properties are studied in this test
- Average particle size
- existence of pores, fissures, shakes and veins
- constituents of mineral
- characteristics of cementing material present in it
- Texture
- Amount of deleterious materials present in it etc.
9. Smith's test
Smith's test is carried out to study of soluble matter in the rocks/stones.
Procedure
- Broken pieces of stones or chips are taken and placed it in a glass tube.
- Then clear water is poured in this tube and make all pieces get submerged.
- After an hour shake the tube vigorously, and earthy matters present in it will convert clear water to dirty water.
- That means the rocks/stones contains presence of earthy minerals which reduce the strength and durability of rocks/stones.
- If water remains clear then it is free from earthy mineral and it is good stone for use.
10. Water absorption test
Procedure
- A cube of weight 50 grams prepared from given sample, and note down the weight.
- Cube is then immersed in water for 24 hours at least.
- After 24 hours cube is removed from water and surface wiped off with cloth.
- Weight again after wiped of with cloth.
- Cube is then suspended in a water and weighted.
- During suspension water is boiled and cube will remains in suspension up to 5 hours.
- After 5 hours cube is removed and wiped off with cloth and weighted again.
Results obtained from above observations:
W1= initial weight
W2= after 24 hours of immersion
W3= cube in suspension
W4= after 5 hours of immersion
Percentage absorption by weight after 24 hours =(W2 – W1)*100 / W1
Percentage absorption by volume after 24 hours = (W2 – W1)*100 / (W2 – W3)
Volume of displaced water = W2 – W3
Percentage porosity by volume = (W4 – W1)*100 / (W2 – W3)
Density =W1 / (W2 – W3) kg/m3
Specific Gravity = W1 / (W2 – W3)
Saturation Coefficient = (Water Absorption/Total Porosity) = (W2 – W1) / (W4 – W1)
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