Mechanical properties of bitumen

Unlike many traditional construction materials such as iron, cement and so on, whose mechanical behaviour is almost independent of temperature and duration of loading, the behaviour of bitumen is not and it changes from elastic to viscous. When the load (stress) is applied for a very short time and at the same time the temperature is very low, the bitumen behaves as a purely elastic material. Conversely, when stress is applied for a very long time and the temperature is high, the behaviour of the bitumen is viscous. 

Between the abovementioned two extreme conditions, bitumen behaves as a viscoelastic material and such conditions are those that exist on project sites. Therefore, in service, the bitumen behaves as a viscoelastic material and its mechanical properties depend on both temperature (T) and stress (a) loading time (t). 

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Apart from the normative tests, many laboratories perform additional tests for the determination of fundamental mechanical properties of bitumen such as stiffness modulus, tensile strength and resistance to fatigue. These properties are of key importance for predicting the mechanical behaviour of bitumen and thus of the bituminous mixture. 

Bitumen is a viscous material unlike other construction materials such as steel or concrete, which are elastic materials. In 1954, Van der Poel introduced the concept of stiffness modulus as the fundamental parameter to describe the mechanical properties of bitumens by analogy to the elastic modulus of solids (Van der Poel 1954). 

Synthetic binders are special formulations with a clear appearance that imitate, or even improve, the mechanical properties of bitumen [18]. Typical formulations consist of blending a tackifying resin, a dispersing oil [19] and a polymer [16,20,21]. This formulation enables the manufacture of organic binders from renewable raw materials of vegetal origin [18]. 

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