![]() ![]() Are you a structural engineer, property developer or building contractor? It contains concrete, plaster, and mortar and varies in terms of grade and strength. The table shows the strength of concrete at different ages in comparison with the strength at 28 days after casting.Cement is an essential ingredient for building construction. The strength of concrete increases with age. ![]() N/mm 2 (at 28 days) Compressive Strength of Concrete at Various Ages N/ mm 2 (at 7 days)Īverage compressive strength of the concrete cube =. Appearance of fractured faces of concrete and the type of fracture if they are unusualĪverage compressive strength of the concrete cube =.Curing conditions, including date of manufacture of specimen.NĬompressive strength = (Load in N/ Area in mm 2)=.N/mm 2 Similar calculation should be done for 28 day compressive strength Calculations of Compressive StrengthĪrea of the specimen (calculated from the mean size of the specimen )=225 cm 2Ĭharacteristic compressive strength(f ck)at 7 days = The average of three specimens gives the crushing strength of concrete. If the strength of any specimen varies by more than 15 percent of average strength, the results of such specimens should be rejected. Minimum three specimens should be tested at each selected age. Record the maximum load and note any unusual features in the type of failure.Apply the load gradually without shock and continuously at the rate of 140 kg/cm 2/minute till the specimen fails.Rotate the movable portion gently by hand so that it touches the top surface of the specimen.Align the specimen centrally on the base plate of the machine.Place the specimen in the machine in such a manner that the load shall be applied to the opposite sides of the cube cast.Clean the bearing surface of the testing machine.Take the dimension of the specimen to the nearest 0.2m.Remove the specimen from the water after specified curing time and wipe out excess water from the surface.The water for curing should be tested every 7 days and the temperature of the water must be at 27+-2oC. The test specimens are stored in moist air for 24 hours and after this period the specimens are marked and removed from the molds and kept submerged in clear freshwater until taken out prior to the test. Level the top surface and smoothen it with a trowel.Compact each layer with not less than 35 strokes per layer using a tamping rod (steel bar 16mm diameter and 60cm long, bullet-pointed at lower end). ![]()
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