Softening point (ring and ball) test is a method for the determination of the softening point of bitumen and bituminous binders, in the range 30 °C to 150 °C. Two horizontal discs of bituminous binder, cast in shouldered brass rings, are heated at a controlled rate in a liquid bath while each supports a steel ball. The softening point is reported as the
mean of the temperatures at which the two discs soften enough to allow each ball, enveloped in bituminous binder, to fall a distance of (25,0 ± 0,4) mm.
Equivalent standardized tests
The European Standard for R&B softening point test is EN 1427. Prior to 1999, most countries had their own versions of the test which were very similar to the harmonised test. The principal difference was that some standards, including ASTM D36-95, do not include stirring the liquid bath, as in EN 1427, without which the result will generally be 1.5 °C higher for unmodified bitumen; this difference may not apply to modified binders.
The precision quoted in EN 1427 is:
• Repeatability, r, of 1 °C and reproducibility, R, of 2 °C for unmodified bitumen in water.
• Repeatability, r, of 1.5 °C and reproducibility, R, of 3.5 °C for modified bitumen in water.
• Repeatability, r, of 1.5 °C and reproducibility, R, of 5.5 °C for oxidized bitumen in glycerol.
Relationship with other bitumen tests
It is generally considered that, for paving grade bitumens, the R&B softening point is equivalent to a penetration of 800 x 0.1 mm.
Although many test methods measure related properties and therefore there will be some relationship, no formal correlation has been found in the papers reviewed between the softening point test and other bitumen tests.
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