Strength of concrete IS 516
Compressive strength
Maximum breaking load is given on the cube speciment untill it breaks and no further load can applied. So, compressive strength can be defined as the load which causes failure of specimen per unit cross sectional area in uniaxial compression machine. Strength of specimen is expressed in N/mm2. Generally in 1 min the load reading should be 315 kN
Rate of loading in compressive testing machine should be 14N/mm2/min.By hand the concrete cube should be filled by 3 layers 35 tampings on each layer by rod 16 mm dia. There should not variation of +- 15 % from the average of the three cubes to each individual readings/ strength
Core/cylinder strength
Its 0.8 x concrete cube strength, The dia of concrete cylinder should be 150 and height will be 300. The height / diameter ratio will be 2.
Fluxural strength
Its checked in case of road n runways, the flexural strength is checked of a beam casted 150 x 150 mm x 700 mm size. On tensile side if crack occurs greater than 20 cm from nearest support measured from centre line then fb= p x l/b x d2 and if the distance of crack is less than 20 cm then fb = 3p x a/b x d2
where a = crack distance in cm, b = 15 cm, p = breaking load, and l = span between two supports. rate of loading of 40 N/min for the 15.0 cm specimens
Split tensile strength
In split tensile method 150 mm dia and 300 mm length concrete specimen is rested in cube machine laterally position. 3 mm ply is provided at upper and at bottom side. It is checked on 7 and 28 days. Tsp = 2P/∏ DL
where Tsp = split tensile strength, P = max load, D = diameter , L = length of specimen. Rate of loading will be 0.7 to 1.4 N/min
Age strength of concrete
ft = t/a+bt x f28
t= strength on day,f28 = chracterstic strength of concrete, a = 4.7 and b = 0.833
Maximum breaking load is given on the cube speciment untill it breaks and no further load can applied. So, compressive strength can be defined as the load which causes failure of specimen per unit cross sectional area in uniaxial compression machine. Strength of specimen is expressed in N/mm2. Generally in 1 min the load reading should be 315 kN
Rate of loading in compressive testing machine should be 14N/mm2/min.By hand the concrete cube should be filled by 3 layers 35 tampings on each layer by rod 16 mm dia. There should not variation of +- 15 % from the average of the three cubes to each individual readings/ strength
Core/cylinder strength
Its 0.8 x concrete cube strength, The dia of concrete cylinder should be 150 and height will be 300. The height / diameter ratio will be 2.
Fluxural strength
Its checked in case of road n runways, the flexural strength is checked of a beam casted 150 x 150 mm x 700 mm size. On tensile side if crack occurs greater than 20 cm from nearest support measured from centre line then fb= p x l/b x d2 and if the distance of crack is less than 20 cm then fb = 3p x a/b x d2
where a = crack distance in cm, b = 15 cm, p = breaking load, and l = span between two supports. rate of loading of 40 N/min for the 15.0 cm specimens
Split tensile strength
In split tensile method 150 mm dia and 300 mm length concrete specimen is rested in cube machine laterally position. 3 mm ply is provided at upper and at bottom side. It is checked on 7 and 28 days. Tsp = 2P/∏ DL
where Tsp = split tensile strength, P = max load, D = diameter , L = length of specimen. Rate of loading will be 0.7 to 1.4 N/min
Age strength of concrete
ft = t/a+bt x f28
t= strength on day,f28 = chracterstic strength of concrete, a = 4.7 and b = 0.833
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