Compressive Strength of Cement
This test is carried out to determine the compressive strength of cement.
Test Procedure for compressive strength of cement:
(i) The mortar of cement and sand is prepared. The proportion is 1:3 which means that (X) gm of cement is mixed with 3(X) gm of sand.
(ii) The water is added to the mortar. The water cement ratio is kept as 0.4 which means that (X) gm of water is added to dry mortar.
(iii) The mortar is placed in moulds. The test specimens are in the form of cubes with side as 70.6 mm or 76 mm. The moulds are of metal and they are constructed in such a way that the specimens can be easily taken out without being damaged. For 70.6 mm and 76 mm cubes, the cement required is 185 gm and 235 gm respectively.
The mortar, after being placed in the moulds, is compacted in vibrating machine for 2 minutes.
(iv) The moulds are placed in a damp cabin for 24 hours.
(vi) The specimens are removed from the moulds and they are submerged in clean water for curing.
(vii) The cubes are then tested in compression testing machine at the end of 3 days and 7 days. The testing of cubes is carried out on their three sides without packing. Thus three cubes are tested each time to find out the compressive strength at the end of 3 days and 7 days. The average value is then worked out. During the test, the load is to be applied uniformly at the rate of 350 kg/cm2 or 35 N/mm2.
(viii) The compressive strength of cement at the end of 3 days should not be less than 115 kg/cm2 or 11.50 N/mm2 and that at the end of 7 days should no be less than 175 kg/cm2 or 17.50 N/mm2.
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