Analysis of the influence of design parameters of asphalt mixtures on their susceptibility to ageing phenomenon

Abstract

Bituminous mixtures are used as layers in a pavement structure to distribute stresses caused by loading, to protect the underlying unbound layers from the effects of water and to provide safe rolling surface for the users. To adequately perform these functions over the pavement design life, mixtures must be durable. One of the factors that affects the ability of bituminous mixtures to meet this requirement is ageing. This phenomenon has a significant impact on the performance and durability of asphalt mixtures, and it is vulnerable to a variety of factors that can be changed throughout both the design and manufacturing processes. The current thesis investigates the phenomenon of ageing in asphalt mixtures, taking into account both external and internal factors that influence ageing. The first section of the study used laboratory procedures to analyse the impact of temperature, time, and pressure on the ageing caused by bituminous mixtures. The ageing of two mixtures, manufactured with a high void content and two different modified binders (SBS polymer and crumb rubber), was examined as a function of several conditions (different temperatures, time and pressure conditionings) and compared with cores extracted from road sections that have used similar mixtures in the surface layer. For this purpose, stiffness and fatigue cracking tests were used. Based on the results obtained in the first part, the second part of thesis examined the impact of the main design factors (type and quantity of bitumen, filler dosage, and the impact of mineral skeleton) on asphalt mixture ageing rates. The results revealed that long ageing periods at a high temperature (at least 9 days and 135°C based on the results obtained in this research) were required to determine significant ageing influence while also allowing for the differentiation of ageing susceptibility of different materials. Moreover, the findings revealed that in spite of all factors had an impact on the range of changes in material stiffness, deformation susceptibility, and crack resistance due to the ageing process, the most relevant factors were the type of bitumen and filler content.