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

摘要

Moisture induced damage of hot mix asphalt pavements has a significanteconomic impact in terms of excessive maintenance and rehabilitation costs. Themoisture sensitivity of an asphalt mix depends on the combined effects of materialproperties, mixture design parameters, loading conditions and environmental factors.Traditional methods to assess moisture sensitivity of asphalt mixes rely on mechanicaltests that evaluate the mix as a whole. These methods do not measure material propertiesand their role in moisture sensitivity of the mix independently. This information is veryimportant to select materials resistant to moisture induced damage, or to modify locallyavailable materials to improve their resistance to moisture damage for economic reasons.The objective of this research is to develop experimental and analytical tools tocharacterize important material properties that influence the moisture sensitivity ofasphalt mixes.Quality of adhesion between the aggregate and bitumen binder in wet and dryconditions plays an important role on the moisture sensitivity of the asphalt mix. A partof this research work was to develop the Wilhelmy plate method and the UniversalSorption Device to measure the surface free energy components of the bitumen andaggregate with adequate precision and accuracy, respectively. Surface energy of thesematerials was used to identify parameters based on thermodynamics that can quantifytheir interfacial adhesion and propensity to debond in the presence of water. Thethermodynamic parameters were shown to correlate well with the moisture sensitivity ofasphalt mixes determined from laboratory tests. Specific surface areas of the aggregateswere 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 versatileand fast tool to quantify the combined effects of physical and chemical adhesion betweenthese materials.