Abstract
The application of the triaxial test for the determination of the mechanical properties of bitumenβaggregate mixtures is discussed, special stress being laid on the physical phenomena. An analysis of the resistance to plastic flow is given and the character of the physical magnitudes that describe this resistance is elucidated. The material is characterized as a viscous material showing a yield stress the value of which depends on the state of stress the material is subjected to. The influence of the presence of bitumen in the system is discussed and on the strength of test data a quantitative evaluation is given, taking into account not only changes in the properties of the bitumen, but also in the aggregate properties. This leads to a further analysis of the resistance of the material, with special emphasis on the function of the bitumen. A hypothesis is developed according to which the resistance of the material is partly due to the presence of bitumen adsorbed on the aggregate. As a consequence, the number of contact points between the aggregate particles greatly influences the properties of the material. The results of series of tests in which the composition of the mixtures is varied systematically make it possible to formulate the rules according to which the properties of the material are influenced by these variations. For comparison of the influence on the properties of the mix of bitumens showing variations in properties an arbitrary mix is chosen, the properties of which can be calculated from any other mix containing the same bitumen. Thus the influence of the bitumen on the properties of the mix can be described in a simple way. For the evaluation of the material for various applications a distinction is made between those applications in which the viscous properties of the material cannot be used to meet the external stresses and those in which such a contribution would lead to acceptable or even desirable deformations. Thus, for various applications, it is possible to design mixtures that meet certain mechanical demands. In this design use may be made of components of varying properties.