Want to know the Strength of the Roof Slab

Dear Ravuri

             These are grade of cement concrete as M 15, M20, M25.
M15 denotes that the ratio of cement concrete is 1:2:4 means 1 part of cement, 2 parts of course sand and 4 parts of bazri ( stone ballast 12mm to 20 mm)

M20 denotes that the ratio of cement concrete is 1:1.5:3 means 1 part of cement, 1.5 parts of course sand and 3 parts of bazri ( stone ballast 12mm to 20 mm)

M25 denotes that the ratio of cement concrete is 1:1:2 means 1 part of cement, 1 parts of course sand and 2 parts of bazri ( stone ballast 12mm to 20 mm)