Robert Karlsson

Laboratory studies of diffusion in bitumen using markers

Performance of recycled asphalt pavements depends, among other things, on the degree of mixing of old and new binders. One of the factors contributing to the mixing is diffusion, which increases the homogeneity of recycled binders. In this study, FTIR-ATR (Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance) has been applied to investigate influence of temperature, viscosity of the diffusion medium, and diffusant size and polarity on diffusion characteristics. Several substances, referred to as markers, have been monitored when diffusing through different binders. By careful selection of markers, the importance of diffusant size and polarity on rate of diffusion has been demonstrated. Diffusion has been modelled using Stoke-Einsteins equation and compared with experimental data obtained by FTIR-ATR. The equation has shown useful in explaining the effects of temperature, viscosity and molecular size on diffusion.

BITUMEN REJUVENATOR DIFFUSION AS INFLUENCED BY AGEING

ABSTRACT This paper describes studies to illuminate the process of mixing old and new binder during asphalt recycling, or, more precisely, mixing by diffusion. FTIR-ATR (Fourier Transform Infrared Spectroscopy by Attenuated Total Reflectance) is used to study effects of the degree of ageing on the diffusion process. Generally, diffusion rates are influenced by temperature, size and shape of the diffusing molecules and the viscosity of the media in which the diffusion takes place. Since bitumen ageing normally leads to a considerable increase in viscosity, it was decided to investigate its influence on the diffusion process. The results presented in this study imply that it is the maltene phase viscosity that governs the diffusion rate rather than the viscosity of the bitumen as a whole. As the changes in maltene viscosity due to ageing are found to be small, it is postulated that ageing does not have a significant effect on the diffusion process.

Fatigue Modeling as Related to Flexible Pavement Design

ABSTRACT A literature study of rheological and fatigue modeling of asphalt mixtures is presented. Theoretical aspects on structural modeling, rheological behavior and the fatigue integration in design procedures are reviewed. In principle, pavement design methods can be categorized in three broad groups: empirical, semi-mechanistic and fully mechanistic methods. Pavement design is generally performed using semi-mechanistic methods comprising analytical or numerical structural response models and deterioration modeling based on transfer functions and shift factors. In the case of fatigue deterioration, several approaches have been elaborated e.g. classical models, fracture mechanics and damage mechanics. The approaches differ regarding theoretical foundation and evaluation methods used. Recognizing significant limitations concerning theoretical basis as well as lack of empirical support for current design methods, a shift in paradigm from semi-empirical methods towards more advanced fully mechanistic methods have been initiated. According to this approach, improved pavements are achieved by appropriate design methods which are capable of predicting fatigue resistance in the actual pavement environment, and thus taking into account complex stress conditions, influence of temperature and material characteristics, such as aging and healing.

Performance assessment of concrete roads in Sweden

ABSTRACT Results from follow-up studies of Swedish concrete roads are compiled and analysed regarding rutting, abrasion, friction, longitudinal evenness, noise and macro-texture. The four concrete roads included in the analysis have all been constructed in the 1990s and situated near Arlanda, Falkenberg, Fastarp and Eskilstuna. Differences between the roads are identified and examined and a discussion on long-term performance of the properties is also included. The paper aims at assessing the improved method practised when constructing the four concrete roads, which involved the use of dowelled joints, higher concrete strength, more wear resistant aggregate material, smaller maximum aggregate size and noise reducing surface treatments. The results show that the concrete roads constructed in Sweden after 1990 are performing well regarding the properties included in the study. The rut growth varies from non-significant up to 0.6 mm/year. The changes in longitudinal evenness are small with only one road showing a significant increase. The friction values for the four roads varied from 0.6-0.8.