P. Apostolidis

Rheological Behavior and Its Chemical Interpretation of Crumb Rubber Modified Asphalt Containing Warm-Mix Additives

The microstructure and chemical composition of asphalt binders have a significant effect on their rheological properties and, therefore, their performance as road paving binders. This study aims to investigate the effects of warm-mix asphalt (WMA) additives, organic type and chemical type, on the rheological properties and chemical internal structure of base asphalt and crumb rubber modified asphalt (CRMA). A set of dynamic shear rheometer (DSR) tests was conducted to obtain the rheological parameters (e.g., complex viscosity, complex modulus, phase angle) of asphalt binders. The flow activation energy was calculated from Arrhenius equation based on viscosity data to rank the thermal susceptibility. Black diagrams and master curves of complex modulus and phase angle were utilized to analyze the rheological properties. The molecular weight distributions of asphalt binders were inverted from the phase angle master curve to evaluate the molecular weight characteristics. It was found that the the addition of crumb rubber into base asphalt improves the rheological properties of enhanced modulus and elasticity. Organic and chemical types of WMA additives have different chemo-physical effects on both base asphalt and CRMA. Phase angle inversion method provides a powerful tool to monitor the molecular structure change and, therefore, the chemo-physical interactions of asphalt binders induced by modifications. Finally, there is a good correlation between flow activation energy and molecular weight.

Synthesis of Asphalt Binder Aging and the State of the Art of Antiaging Technologies

“Aging” is the accumulation process of diverse detrimental changes in molecular structures with advancing age. Resistance to aging is termed “durability.” Complex molecular systems such as asphalt binder (AB) need to be protected against aging. This paper provides a state-of-the-art review of antiaging technologies used to prohibit or to rejuvenate aged asphaltic materials. The kinetics of molecular structures during aging and the group of molecules that mainly are affected are discussed. The latest developments in antioxidation and rejuvenation technologies are presented, as well as evidence of the impact of antiaging technologies on AB.

Study of Asphalt Binder Fatigue with a New Dynamic Shear Rheometer Geometry

With the effort to precisely predict the lifetime of asphalt binders and subsequently optimize their utilization in a more economical way, the objective of this study was to introduce a new methodology to improve the fatigue characterization of asphalt binders through a new dynamic shear rheometer (DSR) sample testing geometry. Initially, numerical analyses were performed to study the geometry-related issues of a standard DSR sample on time sweep tests, and to assist in the effort to increase understanding of the DSR damage phenomena of asphalt samples. On the basis of these numerical analyses, a new testing geometry, the parallel hollow plate, was developed and its test results compared with the standard sample testing geometry. A single type of asphalt binder was assessed using amplitude sweep tests. The obtained results demonstrated a significant difference between the fatigue of the two sets of DSR sample geometries. On the basis of these, time sweep tests were conducted for the same sample geometries and the results demonstrated that the new testing geometry yields material response consistency under different loading conditions. The lifetime prediction of the standard parallel plates showed a significant difference with the newly developed DSR sample testing geometry by overestimating the total number of cycles until asphalt binder failure. The new testing geometry allowed the isolation of the damaged area of asphalt binder by localizing the shear stresses in the samples’ periphery.

Chemo-Rheological Study of Hardening of Epoxy Modified Bituminous Binders with the Finite Element Method

The chemical irreversible hardening of epoxy modified bitumen is affected by various physical factors and the successful application of this technology is directly linked with full understanding of chemo-rheological material characteristics. This study proposes a model to describe the material viscosity evolution during hardening of epoxy modified bitumen. The findings from numerical analyses performed to assess the mechanical response of epoxy modified bituminous binders are presented. Information of the chemical interaction of epoxy within a bituminous matrix was collected and all the influential factors have been determined. The proposed chemo-rheological model accounting for the polymerization of the epoxy in the bitumen was formulated and the sensitivity of material parameters, such as activation energy, reaction order and extent of hardening reaction until the gel point of epoxy modified binders, was demonstrated. Results of the analyses suggest that lower levels of activation energy increase the degree of hardening and the rate of viscosity development. By decreasing the hardening reaction until the gel point the achieved viscosity of epoxy modified bitumen was increased showing the importance of gel reaction extent on material viscosity evolution. The numerical studies have shown also that the polymerization rate in the epoxy modified bitumen is highly dependent on the temperature under various (non-) isothermal conditions. Also, the polymerization rate should be considered through all the material curing processes to avoid unwanted variations in the mechanical properties.

Toward the Design of an Induction Heating System for Asphalt Pavements with the Finite Element Method

Induction technology was introduced to the paving industry to assist pavement operations by heating asphalt layers efficiently from the surface. Many experimental studies have been conducted to investigate the impact of inductive particles on the heating efficiency of asphalt mixes. However, research is limited on the quantification of design, the operational factors, and the associated degree of heat generation of induction treatment. This study assessed the hypothesis that different systems of induction coils provoke different levels of heat generation within an inductive asphalt layer. First, a three-dimensional induction heating finite element model was developed to evaluate the design and effect of operational factors for a static single-turn induction coil system. The electrical conductivity values of the material in the inductive asphalt pavement were calibrated with a laboratory-scale induction device. Moving induction systems were analyzed with different operational conditions considered. The supplied power and the traveling speed of the induction system appeared to be the most influential operational factors for the development of a quick and highly efficient system. The developed model creates an opportunity to apply these analyses to asphalt pavements to optimize the technology in situ.