Softening point test Left

The consistency of the bitumen and the bituminous binders at elevated temperature is empirically determined with the softening point test, also known as a ring and ball (R B) test. Along with the penetration test, the softening point test is used for grading the oxidised bitumens. 

Bitumen, a viscoelastic material, does not have a defined melting point. It gradually becomes softer and less viscous as the temperature rises. 

Softening point is defined as the temperature at which material under standardised test conditions attains a specific consistency. The test is used to determine the softening point of bitumen and bituminous binders in the 28 C to 150°C range. 

Two horizontal brass rings (approximately 19.8 mm internal diameters) filled with bituminous binder are placed in a ring holder and heated at a controlled rate in a liquid bath while each supports a steel ball. The softening point is 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 mm. 

The average of the two measurements, rounded up to the nearest 0.2°C for bituminous binders with a softening point up to 80°C or up to the 0.5°C for bituminous binders with a softening point 80°C, is defined as the softening temperature or softening point ( r b)- 

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