Hefer, Arno Wilhelm (2004-12). Adhesion in bitumen-aggregate systems and quantification of the effect of water on the adhesive bond. Doctoral Dissertation.
Thesis
This research is intended to contribute toward the understanding, development, and implementation of a more fundamental design process for bituminous pavement materials, utilizing thermodynamic properties of the materials involved. The theory developed by van Oss, Chaudhury and Good forms the basis of this research. Optimization of techniques to characterize surface energy, as well as consideration and evaluation of additional factors that influence adhesion in the presence of water, are pursued. A synthesis of theories and mechanisms of bitumen-aggregate adhesion is presented, and existing and potential techniques for surface energy characterization are reviewed to establish firm background knowledge on this subject. The Wilhelmy plate technique was scrutinized and improved methodologies and analysis procedures are proposed. Inverse gas chromatography (IGC) is introduced as an alternative technique. A reasonable comparison of total surface energy values form these techniques with mechanical surface tension values were found. Results suggest that bitumen surface energies do not vary substantially. Inability of these techniques to detect the effect of a liquid additive is rationalized by the ?potential? surface energy concept. Suggestions for a more realistic characterization of bitumen polar surface energy components are presented. A static gravimetric sorption technique was employed to characterize aggregate surface energies. Dynamic vapor sorption was identified as a candidate alternative technique for aggregate surface energy characterization. A study on the effect of pH on surface energy components of water revealed that this effect is practically negligible. Calculation of the free energy of electrostatic interaction (DGEL) indicated that this term contributes less than 1% to the total free energy of adhesion. Despite this finding, it is shown that DGEL alone is able to distinguish moisture sensitive mixtures. The significance of electrical phenomena at the interface is elucidated through another mechanism following the work of M.E. Labib. The relationship between pH and electron donor-acceptor properties of aggregate surfaces is presented. The Labib approach potentially offers the solution to quantify the effect of pH on adhesion. In addition, it should be possible to resolve issues with the acid-base scale proposed by the founders of the current theory, by replacing it with a more absolute donor-acceptor scale.
This research is intended to contribute toward the understanding, development, and
implementation of a more fundamental design process for bituminous pavement
materials, utilizing thermodynamic properties of the materials involved. The theory
developed by van Oss, Chaudhury and Good forms the basis of this research.
Optimization of techniques to characterize surface energy, as well as consideration and
evaluation of additional factors that influence adhesion in the presence of water, are
pursued. A synthesis of theories and mechanisms of bitumen-aggregate adhesion is
presented, and existing and potential techniques for surface energy characterization are
reviewed to establish firm background knowledge on this subject.
The Wilhelmy plate technique was scrutinized and improved methodologies and
analysis procedures are proposed. Inverse gas chromatography (IGC) is introduced as an
alternative technique. A reasonable comparison of total surface energy values form
these techniques with mechanical surface tension values were found. Results suggest
that bitumen surface energies do not vary substantially. Inability of these techniques to
detect the effect of a liquid additive is rationalized by the ?potential? surface energy
concept. Suggestions for a more realistic characterization of bitumen polar surface
energy components are presented.
A static gravimetric sorption technique was employed to characterize aggregate
surface energies. Dynamic vapor sorption was identified as a candidate alternative
technique for aggregate surface energy characterization.
A study on the effect of pH on surface energy components of water revealed that this
effect is practically negligible. Calculation of the free energy of electrostatic interaction
(DGEL) indicated that this term contributes less than 1% to the total free energy of
adhesion. Despite this finding, it is shown that DGEL alone is able to distinguish
moisture sensitive mixtures. The significance of electrical phenomena at the interface is
elucidated through another mechanism following the work of M.E. Labib. The
relationship between pH and electron donor-acceptor properties of aggregate surfaces is
presented. The Labib approach potentially offers the solution to quantify the effect of
pH on adhesion. In addition, it should be possible to resolve issues with the acid-base
scale proposed by the founders of the current theory, by replacing it with a more
