Moisture 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.
Moisture 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.
