Concrete Mix Design Procedure. Data Required for Concrete Mix Design (i) Concrete Mix Design Provision ⦁ Characteristic Compressive Strength needed in the field at 28 days grade designation = M 25 ⦁ Maximum size of aggregate = 20 mm ⦁ Workability = 55-75 mm ( slump value ) ⦁ Degree of quality control = Good ( as per IS 456 )