Stiffness modulus of asphalts

Asphalts contain two materials with different mechanical behaviours bitumen, with viscoelastic behaviour under normal loading conditions, and aggregates, with almost elastic 

Considering the above, it is obvious that the asphalts cannot be characterised by the fundamental property of Young s modulus, or elastic modulus, used for linear elastic materials. 

Asphalts and viscoelastic materials are characterised by their stiffness modulus or, for simplicity, stiffness, designated as S or E. The designation E has been adopted by the CEN EN 12697-26 (2012) standard. 

Stiffness modulus was initially suggested by Van der Poel (1954). This most basic characteristic and fundamental property, in contrast to the elastic modulus where the deformation only depends on the applied load, depends on the temperature (T) and the loading rate (f). Hence, for a given asphalt, its stiffness modulus ( or S) is expressed as 

When the applied load is dynamic (short loading rate), the stiffness measured is called elastic or dynamic stiffness modulus or, for simplicity, stiffness. When the applied load is static (long loading time), the stiffness measured is called static stiffness (modulus), 

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Figure 7.14 Nomograph for evaluating the stiffness modulus of asphalts. (From Bonnaure F. et al., A new method of predicting the stiffness of asphalt paving mixtures. Proceedings of the Association of Asphalt Paving Technologists, Vol. 46, p. 66, 1977 Taken from Shell Bitumen, The Shell Bitumen Handbook, Chertsey, Surry, UK Shell Bitumen UK, 1990.)...

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