ASTM D243 standard test method for residue of specified penetration
7. Procedure
7.1 Weigh a 100.00 +/- 0.1-g sample of the material to be tested into a tared container; then place the container in the air bath in position to be heated. Support the thermometer in the sample equidistant from the sides of the container and with the bottom of the bulb neither more than 6 mm above nor touching the bottom of the container. The bulb shall be completely immersed in the sample throughout the heating. An assembly of the apparatus is shown in Fig. 2.
7.2 Heat the sample as rapidly as possible without foaming to a temperature of 249°C (480°F) and during the evaporation, maintain the temperature between 249°C (480°F) and 260°C (500°F). Stir the sample with the thermometer from time to time to prevent local overheating and, to maintain a homogeneous sample, flux into the sample all cakes of hardened bitumen that form at the sides of the container.
NOTE 2 - Precaution: Certain types of road oil will readily form rings of hard asphalt at the side of the container. Take great care that this material is completely fluxed into the sample before the penetration of the residue is determined.
7.3 An experienced operator can judge approximately what percentage of residue should be obtained to secure the desired penetration. When it is supposed that the residue will show the required penetration, return to the container the bitumen on the thermometer that may be readily scraped off; then remove the container from the air bath and cool and weigh it. Determine the penetration of the residue in accordance with Test Method D5, except use the container in which evaporation was conducted, as specified in this test method, instead of using the smaller container specified in Test Method D5.
7.4 It frequently is necessary to make several trials before a residue of the required penetration is obtained. If it is determined to be greater than that required, remove all water from the container and the surface of the sample, and repeat the heating and determination of penetration as before. Ordinarily, a residue shall be considered as satisfactorily obtained when its penetration is within 15 dmm of that desired, and its percentage by weight of the original sample shall be calculated. When it is necessary to determine more precisely the percentage of residue having the specified penetration, such a percentage shall be calculated by interpolation between percentages of two residues, one having a penetration greater and one having a penetration lower than that specified.
