i. Preparation of test specimen

ii. Procedure of testing

iii. Interpretation of results

Preparation of test specimen:

i. Take three cubes of 15 cm sides and apply oil to its inner surface.

ii. Prepare the concrete mixture of required grade and fill it in each mould in 3 layers. Compact each layer 25 times with 16 mm dia. steel rod.

iii. Keep all the moulds at room temperature for 24 hrs for initial hardening and at relative humidity 90%.

iv. Remove cube moulds and keep concrete cubes under fresh water for curing for 7, 14, 21, 28 days.

Procedure of testing:

i. Remove cube from water after curing period and keep it under compression testing machine (CTM) for testing.

ii. Apply load at a rate of 35 N/mm2/min for 10 minutes or till failure load in N by cross sectional area of cube in mm2.

iii. Finally calculate compressive strength of cubes as failure load in N by cross sectional area of cube in mm2.

iv. The average of three test cubes can be calculated as average compressive strength in MPa

Interpretation of results:

i. If the calculated compressive strength is less than the grade of concrete used, then concrete can be rejected at site.

ii. When such strength is found more (say 23N/mm 2) than the specified grade M20, then that concrete is safe and good for construction.