Input (grade 9): Concrete can be made to have high compressive strength, e.g. many concrete structures have compressive strengths in excess of 50 MPa, whereas a material such as soft sandstone may have a compressive strength as low as 5 or 10 MPa.
Output (grade 4): Concrete can be made to have high compressive strength e.g. many concrete floors have compressive strength of 3000 p.s.i..