Browsing by Subject "bitumen"
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Item Adhesion in bitumen-aggregate systems and quantification of the effect of water on the adhesive bond(Texas A&M University, 2005-02-17) Hefer, Arno WilhelmThis 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.Item Development of methods to quantify bitumen-aggregate adhesion and loss of adhesion due to water(Texas A&M University, 2007-09-17) Bhasin, AmitMoisture induced damage of hot mix asphalt pavements has a significant economic impact in terms of excessive maintenance and rehabilitation costs. The moisture sensitivity of an asphalt mix depends on the combined effects of material properties, mixture design parameters, loading conditions and environmental factors. Traditional methods to assess moisture sensitivity of asphalt mixes rely on mechanical tests that evaluate the mix as a whole. These methods do not measure material properties and their role in moisture sensitivity of the mix independently. This information is very important to select materials resistant to moisture induced damage, or to modify locally available materials to improve their resistance to moisture damage for economic reasons. The objective of this research is to develop experimental and analytical tools to characterize important material properties that influence the moisture sensitivity of asphalt mixes. Quality of adhesion between the aggregate and bitumen binder in wet and dry conditions plays an important role on the moisture sensitivity of the asphalt mix. A part of this research work was to develop the Wilhelmy plate method and the Universal Sorption Device to measure the surface free energy components of the bitumen and aggregate with adequate precision and accuracy, respectively. Surface energy of these materials was used to identify parameters based on thermodynamics that can quantify their interfacial adhesion and propensity to debond in the presence of water. The thermodynamic parameters were shown to correlate well with the moisture sensitivity of asphalt mixes determined from laboratory tests. Specific surface areas of the aggregates were also used to account for the influence of mechanical interlocking at the micro scale. In some mixes, chemical bonding also contributes to the adhesion between bitumen and aggregate. The use of a micro calorimeter was introduced in this research as a versatile and fast tool to quantify the combined effects of physical and chemical adhesion between these materials.