ASTM D36 for softening point of bitumen (Ring-and-Ball apparatus)
ASTM D36 standard test method for softening point of bitumen (Ring-and-Ball apparatus)
9. Procedure
9.1 Select one of the following bath liquids and thermometers appropriate for the expected softening point:
9.1.1 Freshly boiled distilled water for softening points between 30 and 80°C (86 and 176°F); use Thermometer 15C or 15F. The starting bath temperature shall be 5 more or less 1°C (41 more or less 2°F).
9.1.2 USP glycerin for softening points above 80°C (176°F) and up to 157°C (315°F); use Thermometer 16C or 16F. The starting bath temperature shall be 30 more or less 1°C (86 more or less 2°F).
9.1.3 Ethylene glycol for softening points between 30 and 110°C (86 and 230°F); use Thermometer 16C or 16F. The starting bath temperature shall be 5 more or less 1°C (41 more or less 2°F).
9.1.4 For referee purposes, all softening points up to 80°C (176°F) shall be determined in a water bath and all softening points above 80°C (176°F) shall be determined in a glycerin bath.
9.2 Assemble the apparatus in the laboratory hood with the specimen rings, ball-centering guides, and thermometer in position, and fill the bath so that the liquid depth will be 105 more or less 3 mm (4 1/8 more or less 1/8 in.) with the apparatus in place. If using ethylene glycol, make sure the hood exhaust fan is turned on and operating properly to remove toxic vapors. Using forceps, place the two steel balls in the bottom of the bath so they will reach the same starting temperature as the rest of the assembly.
9.3 Place the bath in ice water, if necessary, or gently heat to establish and maintain the proper starting bath temperature for 15 min with the apparatus in place. Take care not to contaminate the bath liquid.
9.4 Again using forceps, place a ball from the bottom of the bath in each ball-centering guide.
9.5 Heat the bath from below so that the temperature indicated by the thermometer rises at a uniform rate of 5°C (9°F)/min (Note 7). Protect the bath from drafts, using shields if necessary. Do not average the rate of temperature rise over the test period. The maximum permissible variation for any 1-min period after the first 3 min shall be more or less 0.5°C (more or less1.0°F). Reject any test in which the rate of temperature rise does not fall within these limits.
NOTE 7 - Rigid adherence to the prescribed heating rate is essential to reproducibility of results. Either a gas burner or electric heater may be used, but the latter must be of the low-lag, variable output type to maintain the prescribed rate of heating.
9.6 Record for each ring and ball the temperature indicated by the thermometer at the instant the bitumen surrounding the ball touches the bottom plate. Make no correction for the emergent stem of the thermometer. If the difference between the two temperatures exceeds 1°C (2°F), repeat the test.
10. Calculation
10.1 For a given bitumen specimen, the softening point determined in a water bath will be lower than that determined in a glycerin bath. Since the softening point determination is necessarily arbitrary, this difference matters only for softening points slightly above 80°C (176°F).
10.2 The change from water to glycerin for softening points above 80°C creates a discontinuity. With rounding, the lowest possible asphalt softening point reported in glycerin is 84.5°C (184°F), and the lowest possible coal-tar pitch softening point reported in glycerin is 82.0°C (180°F). Softening points in glycerin lower than these translate to softening points in water of 80°C (176°F) or less, and shall be so reported.
10.2.1 The correction for asphalt is -4.2°C (-7.6°F), and for coal-tar pitch is -1.7°C (-3.0°F). For referee purposes, repeat the test in a water bath.
10.2.2 Under any circumstances, if the mean of the two temperatures determined in glycerin is 80.0°C (176.0°F) or lower for asphalt, or 77.5°C (171.5°F) or lower for coal-tar pitch, repeat the test in a water bath.
10.3 To convert softening points slightly above 80°C (176°F) determined in water to those determined in glycerin, the correction for asphalt is +4.2°C (+7.6°F) and for coal-tar pitch is +1.7°C (+3.0°F). For referee purposes, repeat the test in a glycerin bath.
10.3.1 Under any circumstances, if the mean of the two temperatures determined in water is 85.0°C (185.0°F) or higher, repeat the test in a glycerin bath.
10.4 Results obtained by using an ethylene glycol bath will vary from those using water and glycerin. The following formulas shall be used to calculate the differences:
Asphalt:
SP (glycerin) = 1.026583 x SP (ethylene glycol) - 1.334968°C
SP (water) = 0.974118 x SP (ethylene glycol) - 1.44459°C
Coal Tar:
SP (glycerin) = 1.044795 x SP (ethylene glycol) - 5.063574°C
†SP (water) = 1.061111 x SP (ethylene glycol) - 8.413488°C
† Editorially corrected.
