A review of contact angle measurements for the characterization of pavement materials

Contact angle (CA) is an important material characteristic in the field of pavement materials. It has been instrumental to the development of new and evolving research areas such as the adhesion of pavement components, hydrophobic and superhydrophobic concretes, etc. Yet, there are several inconsistencies between studies when it comes to the CA characterization of various pavement materials. This is in part due to the lack of sufficient research and proper documentation of existing knowledge on the CA characterization of pavement materials. This current study has documented and analyzed the processes of measuring the CA of various pavement materials. This includes sample preparation, test conditions, and recommended practices. Studies on the refinement of existing methods for the estimation of CA were also reviewed. The relationships between CA and various pavement and material performances were also reviewed. The increased need for resilient pavements calls for the search for new and effective material characteristics parameters. CA measurements have the potential to change how the properties of fresh cementitious mixes are being assessed. The sessile drop method offers more flexibility for characterizing the CA of pavement materials. The potential application of CA for the improvement and development of new material performance characteristics was discussed. Insights on ways to advance the evaluation of hydrophobic characteristics of pavements were outlined. For example, the use of de-ionized or distilled water for the assessment of hydrophobic properties of concrete does not reflect the moisture condition in the field. CA measurements at different water PH levels should be carried out to replicate the true service condition of the concretes. • The CA of asphalt binder increases with aging, resulting in lower adhesion in AC. • Asphalt emulsions having lower CA possess improved surface binding ability. • Oil rejuvenators with lower CA hold better promise for the revitalization RAP. • PH value of water for assessing hydrophobic concrete should reflect field condition.