Evaluation of Bitumen-Aggregate Adhesion Bond Based on Surface Free Energy and Comparison with Moisture Sensitivity and Asphalt Performance Tests

The adhesion bond between aggregate particles and bitumen plays a crucial role in ensuring the durability of asphalt pavement, and it is influenced by factors such as bitumen-aggregate compatibility, moisture exposure, other environmental conditions, and traffic loads. Failure of the adhesion bond results in the detachment of bitumen from the aggregate surface and leads to stripping in the presence of moisture. This, in turn, leads to the development of macro cracks and disintegration within the asphalt pavement, ultimately reducing its lifespan. The existing laboratory tests for assessing bitumen-aggregate adhesion involve examining both loose and compacted asphalt mixtures, along with measuring the direct bond between the two materials. However, these methods often receive criticism due to their inability to accurately predict real pavement conditions. This issue is underscored by instances of asphalt pavement deterioration happening earlier than expected service life. Consequently, the development of novel techniques for evaluating the adhesion bond between bitumen and aggregate holds substantial importance in foreseeing pavement attributes related to moisture sensitivity, fatigue, and stiffness properties. This study utilized the concept of surface free energy to evaluate the adhesion bond between the aggregate and bitumen. The results were compared with other adhesion bond test results. The research involved three diverse sources of aggregates with varying mineralogy and three bitumen with different penetration grades and modifications. Additionally, two adhesive promoters, Wetfix BE and Hydrated lime, were used in the study. Different laboratory equipment was employed to examine the bitumen and aggregate separately as well as in combination.