Compression Test

Cement. fine aggregate and coarse aggregate (up to 38 mm) to be used for making concrete are brought to room temperature (preferably 27:3°C) before commencing the test. The ingredients are weighed in the ratio to be used in the field and are mixed by hand mixing or by machine mixing. First, the cement and sand are mixed thoroughly till a uniform colour is achieved. The coarse aggregate are then added and mixed till these are distributed uniformly throughout the mix. The water is then added and the entire batch mixed untill the concrete appears to be homogeneous and has the desired consistency.

The test specimens recommended are 150 x 150 x 150 mm cubes or cylinders of 150 mm diameter and 300 mm height. The mixed concrete is filled into the moulds in layers of 50 mm to achieve full compaction. Each layer of mix so placed is tamped with bar. 16 mm in diameter and 600 mm long, 35 times or with a vibrator. The test specimens are stored at a temperature of 27: 3°C and at 90 per cent humidity for 24 hour from the time of addition of water to the dry ingredients. After this period the specimens are removed from the moulds and placed in water and kept there until taken out just prior to test. Normally, the recognized age of test of specimens is 7 and 28 days. At least three specimens, preferably from different batches, are tested at each selected age. The specimens should be tested immediately after taking out them from water with surface water wiped off.

The specimen is placed between the platens of the compression testing machine with the cate that the axis of specimen is aligned with the centre of thrust of the spherically seated platen. The compression testing machine should be able to apply gradual load of 14 N/mm²/ minute. Until the specimen is crushed.