- Maximum construction site have the cube testing machine of capacity 100 ton/ 1000 KN. We calculate the compressive strength as Load / Area i.e. N/mm².
- If we increase the loading area, the load for crushing or the load at which it fails also increases.
- If you are checking M30 grade concrete and you require minimum compressive strength of 33 N/mm² and the size of cube is 150 mm, then the load required to get this much strength is 742.5 KN.
⇒ Compressive Strength = Load / Area
⇒ Load = 33 x ( 150 x 150 ) = 742.5 KN
- If you use cube of size 300 mm, the load required becomes 2970 KN which is practically not possible because to crush the respective cube we require 3000 KN/ 300 ton capacity machine.
- When the applied load is much more, the additional safety factor needs to be increased because when the cube fails under such loads, it may hit anything in room with bullet speed.
- Also, casting of this size cube and handling is not easy.
- For feasibility, safety and ease of work therefore we prefer the 150mm size cubes.
- If you have a machine with less capacity and load to crush the cube is more than the capacity of machine; you can further reduce the size of cube to 100 mm preferably.