Bitumen brittle point

Bitumen can only be used industrially in a limited range of temperatures. The upper limit is marked by the softening point R B (DIN 52 Oil, ASTM D 2398-68) and the lower hmit by the breaking point according to FraaB (DIN 52 013, IP 80 153). This range, also called the plasticity span, is limited towards lower temperatures by increasing brittleness and towards higher temperatures by plastic deformation under load. To extend this plasticity span, mixtures have been tested, with nearly every polymer, but only a few of these became commercial products. 

Paving grade bitumens are characterised by their consistency at intermediate (determined by penetration test), consistency at elevated service temperatures (determined by softening point or viscosity test) and durability (determined by resistance to hardening test). Their brittleness at low service temperature (determined by the Fraass breaking test) and temperature dependence of consistency (determined by the penetration index) may also need to be determined to meet regional requirements for specific conditions such as extreme cold or wide ambient temperature variations. Flash point is also determined as well as, optionally, the density. 

The properties specified for all polymer-modified bitumens ensure (a) consistency at intermediate service temperatures (with reference to penetration at 25°C), (b) consistency at elevated service temperatures (with reference to softening point), (c) cohesion (with respect to force ductility, tensile test or Vialit pendulum), (d) resistance to hardening, (e) brittleness at low service temperature (with respect to Eraass breaking point) and (f) stain recovery (with respect to elastic recovery). 

The Eraass breaking point provides a measure of brittleness of bitumen and bituminous binders at low (subzero) temperatures. The Eraass breaking point test was developed in 1937 (Eraass 1937) and began to be broadly used upon the advent of modified bitumens, since, by executing this test, the effect of the chemical additive on the behaviour of the modified bitumen could be determined. Nowadays, it has been adopted by many organisations and has been incorporated in European standards for specification requirements of paving grade bitumens (CEN EN 12591 2009) and of modified bitumens (CEN EN 14023 2010). 

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