Fraass breaking point

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). 

The Fraass breaking point, according to CEN EN 12593 (2007), is the temperature at which the bituminous binder of a specified and uniform thickness will break under defined 

The test plates, made of tempered spring steel, have the following dimensions 41 mm long, 20 mm wide and 0.15 mm thick. The quantity of bituminous binder placed on the test plate is 0.40 x P25 (g), where P25 is the density of the binder at 25°C (in g/cm ), when the expected softening point of the binder is 100°C. 

The breaking point practically corresponds to an equi-stiffness temperature a temperature at which the bitumen reaches critical stiffness that fractures. It has been shown that upon fracture, the bitumen has a stiffness value of 2.1 x 10 which approaches the maximum stiffness value of bitumen, 2.7 x 10 Pa (Thenoux et al. 1985). 

The Fraass breaking point may be estimated by the penetration and the softening point using the Fleukelom chart. 

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When Severity 2 is selected, it shaii be associated with the requirement for Fraass breaking point or penetration index or both measured on the unaged binder (seeTable 3.3). 

As with common paving bitumens, the tests conducted on hard paving bitumens aim at determining their consistency at intermediate service temperatures (penetration test) and at elevated service temperatures (softening point and dynamic viscosity test) and their durability (resistance to hardening test). Kinematic viscosity, Fraass breaking point, flash point and solubility are also properties considered useful in the specification of hard paving bitumens. 

During the modification process of the bitumen, chemical and physico-chemical changes, depending on the type of modifier/additive used, occur. These changes affect the characteristic properties of the bitumen such as penetration, softening point, viscosity, cohesion, resistance to hardening, elastic recovery and Fraass breaking point. 

The addition of elastomer also lowers the Fraass breaking point. As a result, the modified bitumen is expected to crack at lower subzero temperatures compared to unmodified paving grade bitumen. 

Some of the characteristic properties of thermoplastic polymers are modified when they are added to bitumen. Penetration decreases and softening point increases in particular. These changes indicate that the bitumen becomes harder and less susceptible to temperature variations. Additionally, bitumen s binding ability increases. However, the Fraass breaking point and bitumen elasticity did not significantly improve (Brule and Lebourlot 1993). 

CEN EN 12593. 2007. Methods of test for petroleum and its products-bitumen and bituminous binders - Determination of the Fraass breaking point. Brussels CEN. 

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. 

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