Development of methods to quantify bitumen-aggregate adhesion and loss of adhesion due to water

Abstract

Moisture induced damage of hot mix asphalt pavements has a significant\neconomic impact in terms of excessive maintenance and rehabilitation costs. The\nmoisture sensitivity of an asphalt mix depends on the combined effects of material\nproperties, mixture design parameters, loading conditions and environmental factors.\nTraditional methods to assess moisture sensitivity of asphalt mixes rely on mechanical\ntests that evaluate the mix as a whole. These methods do not measure material properties\nand their role in moisture sensitivity of the mix independently. This information is very\nimportant to select materials resistant to moisture induced damage, or to modify locally\navailable materials to improve their resistance to moisture damage for economic reasons.\nThe objective of this research is to develop experimental and analytical tools to\ncharacterize important material properties that influence the moisture sensitivity of\nasphalt mixes.\nQuality of adhesion between the aggregate and bitumen binder in wet and dry\nconditions plays an important role on the moisture sensitivity of the asphalt mix. A part\nof this research work was to develop the Wilhelmy plate method and the Universal\nSorption Device to measure the surface free energy components of the bitumen and\naggregate with adequate precision and accuracy, respectively. Surface energy of these\nmaterials was used to identify parameters based on thermodynamics that can quantify\ntheir interfacial adhesion and propensity to debond in the presence of water. The\nthermodynamic parameters were shown to correlate well with the moisture sensitivity of\nasphalt mixes determined from laboratory tests. Specific surface areas of the aggregates\nwere also used to account for the influence of mechanical interlocking at the micro scale.\nIn 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\nand fast tool to quantify the combined effects of physical and chemical adhesion between\nthese materials.