The building stones are to be test for their different properties. Following are such tests for the building stones :

Acid test

In this test, a sample of stone weighing about 0.50 to 1 N is taken. It is place in a solution of hydrochloric acid having strength of one percent and it is keep there for seven days. The solution is agitate at intervals. A good building stones maintains its sharp edges and keeps its surface free from powder at the end of this period. If edges are broke and powder is form on the surface, it indicates the presence of calcium carbonate and such a building stones will have poor weathering quality. It is natural that this test cannot be apply to the limestones. This test is usually carry out on the sandstones.

Attrition test

This test is done to find out the rate of wear of stones which are use in road construction. The results of test indicate the resisting power of building stones against the grinding action under traffic. Following procedure is adopt :

• The sample of stone is broken into pieces of about 60 mm size.
• Such pieces, weighing 50 N, are put in both the cylinder of Deval’s attrition test machine. The diameter and length of cylinder are respectively 200 mm and 340 mm.
• The cylinders are close. Their axes make an angle of 30 degree with the horizontal.
• The cylinders are rotate about horizontal axis for 5 hours at the rate of 30 R.P.M.
• After this period, The contents are taken out from the cylinders and they are pass through a sieve of 1.50 mm mesh.
• The quantity of material which is retain on the sieve is weight.
• The percentage wear is work out as follows :

Crushing test

The compressive strength of stone is found out with the help of this test.

The sample of stone is cut into cubes of size 40 mm X 40 mm. The sides of cubes are finely dress and finish. The minimum number of specimens to be test is three. Such specimens should be place in water for about 72 hours prior to test and thereafter test in saturate condition.

The load-bearing surface is then cover with plaster of Paris or 5 mm thick plywood. The load is apply axially on the cube in a crushing test machine. The rate of loading is 13.72 N/mm2 per minute. The crushing strength of the stone per unit area is the maximum load at which its sample crushes or fails divide by the area of the bearing face of the specimen.

Crystallisation test

In this test, at least four cubes of stone with side as 40 mm are taken. They are dry for 72 hours and weight. Then immerse in 14 percent solution of Na2SO4 for 2 hours. They are dry at 100 degree celsius and weight. The difference in weight is note. This procedure of drying, weighing, immersing and reweighing is repeat at least five times. Each time, the change in weight is note and it is express as a percentage of original weight.

It is to be note that the crystallisation of CaSO4 in pores of stone causes the decay of stone due to weathering. But, as CaSO4 has low solubility in water, it is not adopt in this test.

Freezing and thawing test

The specimen of stone is keep immerse in water for 24 hours. It is then place in a freezing mixture at -12 degree celsius for 24 hours. It is then thaw or warm at atmospheric temperature. This should be do in shade to prevent any effect due to wind, sun rays, etc. Such a procedure is repeat several times and behavior of stone is carefully observe.

Hardness test

To determine the hardness of a stone, the test is carry out as follows :

• A cylinder of diameter 25 mm and height 25 mm is taken out from the sample of stone.
• It is weight.
• Then, it is place in Dorry’s testing machine and press with a pressure of 12.50 N.
• The annular steel disc of machine is then rotate at a speed of 28 R.P.M.
• During the rotation of disc, the coarse sand of standard specification is sprinkle on the top of disc.
• After 1000 revolutions, the specimen is taken out and weight.
• The coefficient of hardness is found out from the following equations :

Impact test

To determine toughness of a stone, the impact test is carry out in page impact machine as follow :

• A cylinder of diameter 25 mm and height 25 mm is taken out from the sample of stone.
• It is place on cast-iron anvil of machine.
• A steel hammer of weight 20 N is allow to fall axially in a vertical direction over the specimen.
• The height of first blow is 1 cm ; that of second blow is 2 cm; that of third blow is 3 cm; and so on.
• The blow at which specimen breaks is note. If it in nTh blow, n represents the toughness index of stone.

Microscopic test

In this test, the sample of stone is subject to the microscopic examination. The thin sections of stone are taken and place under the microscope to study various properties such as :

• Average grain size;
• Existence of pores, fissures, veins and shakes;
• Mineral constituents;
• Nature of cementing material;
• Presence of any harmful substance;
• Texture of stone; etc.

Smith’s test

This test is perform to find out the presence of soluble matter in a sample of stone. The few chips or pieces of stones are take and they are place in a glass tube. This tube is take fill with clear water. After about an hour, the tube is vigorously stir or shaken. The presence of earthy matter will convert the clear water into dirty water. If water remains clear, the stone will be durable and free from any soluble matter. On the other hand, if the water becomes dirty, it will indicate that the stone contains too much of soluble earthy and mineral matters.

Water absorption test

Following procedure is adopt for this test :

• From the given sample of stone, a cube weighing about 0.50 N is prepare. Its actual weight is record. Let it be W1 N.
• The cube is then immerse in distill water for a period of 24 hours.
• The cube is taken out of water and surface water is wipe off with a damp cloth.
• It is weight again. Let its weight be W2 N.
• The cube is suspend freely in water and its weight is record. Let it be W3 N.
• The water is boil and cube is keep in boiling water for five hours.
• It is then remove and surface water is wipe off with a damp cloth. Its weight is record. Let it be W4 N.