Evolution of coefficient of friction between tire and pavement under wet conditions using surface free energy technique

Abstract

The interaction between tire rubber and pavement surface depends upon their surface characteristics and physical properties. Presence of water on the pavement surface aggravates the interaction and decreases the skid resistance drastically. Due to the interfacial water, the real contact area between pavement and tire decreases, which leads to decreased Coefficient of Friction (CoF). It is reported that CoF in this triphasic system (tire- water – pavement) can be derived from three components: hysterical, dry adhesion (tire-pavement) and wet adhesion (tire- water – pavement). The present study analyses a mechanistic-empirical model to evaluate the CoF between pavement and tire in wet conditions considering Surface Free Energy (SFE) characteristics of materials. The present study was conducted on five distinct types of rubber samples prevalent in Indian condition with basalt rock chosen as the surface mimicking pavement. Physical properties of the rubber samples (Hardness, material yield strength and tan delta values) were determined according to the ASTM standards. SFE parameters were calculated by measuring the contact angles using Sessile drop method. Surface roughness of basalt aggregate was measured using a Zeta Profilometer. Actual friction coefficient was measured using British pendulum (BP) tester under wet conditions. Further, theoretical CoF was calculated by inputting the experimental material properties into mathematical model. The results showed that the wet adhesive friction was the main contributor to the theoretical CoF, whereas dry adhesive friction was the least. Also, the correlation between actual CoF and the material properties was tried. The actual CoF showed fairly good correlation with the hardness of the rubber samples (R2 = 0.95). The study concludes that the SFE based model to determine friction coefficient between wet pavement and road shows potential to ascertain the frictional interactions taking place between the two surfaces.