Compressive Strength Test (IS: 1121 (Part I)) Samples of stone weighing at least 25 kg each of the unweathered spcimen should be obtained from quarry. To test stone for compressive strength, specimen pieces in the form of cubes or cylinders are made from samples of rock. The lateral dimension or diameter of test piece should not be less than 50 mm and the ratio of height to diameter or lateral dimension should be 1:1. A minimum of three specimen pieces are tested in each saturated and dry conditions. Separate tests should be made for the specimen when the load to parallel to the rift and perpendicular to the rift. In all twelve test pieces should be used.
The specimen pieces of diameter or lateral dimension 50 mm are immersed in water at 20 to 30 o C for 72 hours and are tested in saturated condition. The specimen pieces are also tested in dry condition by drying them in an oven at 105 ± 5 o C for 24 hours and then cooled in a desiccator to 20 -30 o C. These are tested in universal testing machine. The load is applied gently at a rate of 14 N/mm2 per minute until the resistance of the specimen piece to the increasing load breaks down and no greater load is sustained.
The compressive strength of the specimen piece is the maximum load in Newtons supported by it before failure occurs divided by the area of the bearing face of the specimen in mm2. The average of the three results in each condition separately should be taken for the purpose of reporting the compressive strength of the sample.
When the ratio of height to diameter or lateral dimension differs from unity by 25 per cent or more, the compressive strength is calculated by the following expression.
Cc=Cp / EbO 0.778 0.222 É Ù Ê h Ú
where Cc = compressive strength of standard specimen piece
Cp = compressive strength of the specimen having a height greater than the diameter or lateral dimension
b = diameter or lateral dimension h = height
The crushing strength of stones varies in the range of 15-100 N/mm2.