penetration (asphalt) - method for determining the consistency, of semi-solid bituminous (see bitumen) materials, in a penetrometer under conditions prescribed by test method ASTM D 5. The test sample is melted and cooled under controlled conditions, then a weighted standard needle is positioned at the surface of the sample and allowed to penetrate it, by means of gravity, for a specified time. The penetration is measured in tenths of a millimeter. See penetration grading (asphalt), viscosity (asphalt).