Most of the current seal designs are based on the volumetric properties of materials and voids. In order to improve seal design, the possibility of introducing mechanistic principles into the seal design was investigated. Introducing mechanistic concepts into the seal design meant that principles such as elasticity and viscoelasticity could be used in terms of stress-strain to explain phenomena such as damage in the seal structure. Viscoelastic parameters of bituminous materials such as complex modulus (G?) and phase angle (?) are key elements in the understanding of performance, damage and failure of seal bituminous materials. Two main failure parameters of seal are cohesion failure (fatigue cracking due to ageing of binder and loss of elasticity) and adhesion failure or stripping (occurring between stone to bitumen or bitumen to base).
The aim of this study was to model the response of a seal?s binder and the cohesion and adhesion damage of seals materials This Research also investigates the testing procedure of Cohesion Fatigue Damage (CFD) and Adhesion Fatigue Damage (AFD) of bituminous seal material using the Dynamic Shear Rheometer (DSR). The research was based on the Lifetime Optimisation Tool (LOT) research programme from Delft University of Technology.
The response model was performed by means of the DSR parallel plate and modelled using the linear viscoelastic rheological master curves. In addition to the binder models an ageing model was developed base on the G* master curve using the recovered field-aged bitumens and the fresh binder from the plant.
The modelling of CFD and AFD of the seal was based on investigated DRS test protocols results and was established on the ?stiffness reduction? principle of materials under the action of cyclic stress.
From the ageing model it appeared that PAV ageing does not necessary simulate the long term ageing of bitumen. An investigation into ageing of non-modified and modified binder is suggested (e.g. by comparing PAV ageing with Q-sun ageing). The recovery of bitumen method needs to be revisited using technique such centrifugal force.
The CFD and AFD models offer a practical advantage consisting of the possibility to be adapted and incorporated in the recursive simulation models as developed in the South African Road Design System (SARDS). It was observed that the generalised model for CFD depends more on stress, while the generalised model for AFD appears to depend more on temperature. This observation seems to agree with the fact that adhesion damage is more sensitive to temperature change, whereas cohesion damage is more prone to be influenced by applied fatigue stress. The CFD and AFD models provide an indication of non-linear development of the fatigue damage during-life period within bitumen and between bitumen and stone in the case of seal. This is represented by the modelling of the change of G?, as suggested in this investigation.