B Flexural strength When both the following conditions are met the concrete complies with the specified flexural strength a The mean strength determine from any group of four consecutive test results exceed the specified characteristic strength by at least N/mm 2 b The strength determined from any test result is not less than specified characteristic strength less N/mm 2
4 ·According to Wikipedia Compressive Strength of concrete is defined as the Characteristic strength of 150mm size concrete cubes tested at 28 days Why do we test at 7 14 & 28 days Concrete is a macro content with Sand Cement & Coarse aggregate as its micro ingredient Mix Ratio and gains its 100% strength over time at the hardened state
Compressive strength of cement is determined by cube test on cement mortar cubes compacted by means of a standard vibration hydraulic machine Standard vibration for making cube is 12000 400 vibration per minute and it will vibrate for 2 minute 33N/mm2 53N/mm2 is Compressive strength of cement mortar after curing of 28 days
·Although there many studies [10] [11][12][13][14][15] have been conducted to predict and analyse the compressive strength of concrete or cement mortar on the 28th day or other days based on the
But the values of 3 days and 7 days test results are not used for acceptance purpose Concrete 28 Day Strength Test The 28 days concrete test results are accepted as standard compressive strength values The compressive strength acceptance is specified by of ACI 318 14 as
·Cubes cylinders and prisms were cast with each concrete mixture to measure strength at 7 14 28 and 90 days of curing Compressive strength under all curing conditions with and without PF
·Important Note As per IS 516 1959 Minimum three specimens should be tested at each selected age that means three specimens at 7 days three specimens 14 days & 28 days If strength of any specimen varies by more than 15% of average strength such specimen should be rejected Results of cube test Average Compressive strength at 7 days = N/mm²
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