SAPEM Chapter 2 - Sanral

South African Pavement Engineering Manual
Chapter 2: Pavement Composition and Behaviour
10. MATERIAL SCIENCE
To be able to model material and pavement behaviour in any detail, fundamental response models can be used.
There are three fundamental types of theoretical material responses used to model material behaviour applicable to
pavement engineering:
Elasticity
Plasticity
Viscosity
There are very few road building materials that follow one discrete mode
of response. The response models often need to be combined to model
material behaviour more accurately, as shown in the examples below:
Elastic material behaviour: cement or concrete
Elasto-plastic material behaviour: granular materials
Visco-elastic material behaviour: bituminous materials
Visco-elasto-plastic material behaviour: asphalt
The basics of these response models are described below. Thereafter, their application to granular, cemented and
bituminous materials is explained.
10.1 Elasticity
Elasticity Symbol
Elasticity is represented by a spring.
When a load is applied to a material it deforms. Elastic behaviour occurs when the load is removed and the materials
completely recover the deformation back to the original geometry of the material, as shown in Figure 25.
Load
Time
Displacement
Time
Figure 25. Elastic Response to a Load, Sustain, Unload Cycle
Linear elastic behaviour implies that the relationship between stress and strain is linear. According to Hooke's Law, a
simple relationship exists between stress and strain for linear elastic behaviour. This law states that the slope of the
stress-strain relationship reflects the material stiffness or Elastic Modulus, also known as Young’s Modulus, see Figure
26, and Equation (4).
Section 10: Material Science
Page 28