Influence of specimen dimension and test speed on the shear strength of bituminous interfaces

Abstract

In view of the fact that pavements are multilayer systems, achieving high bonding between layers is a key element to increase service life. Interface debonding is mainly responsible for the slipping failure of pavements that leads to high rehabilitation and maintenance costs. The bonding between asphalt layers is usually evaluated by testing the interlayer shear strength and is affected by several parameters such as test speed, test temperature, normal stress applied and specimen diameter. This paper focuses on the effect of test speed and specimen diameter on the shear strength evaluated through the Leutner equipment, for a typical dense graded asphalt mixture. Leutner tests were carried out on double-layered specimens with a diameter of 100 and 150 mm and with interlayer deformation rates corresponding to nominal test speeds of 1, 2.5, 5, 10, 25 mm/min. The effective interlayer deformation rate was calculated by measuring the deformation through an external transducer in order to perform a reliable data analysis. Results showed a steady increase in the shear strength with the increase in the interlayer deformation rate. Moreover, a clear scale effect was observed at any test speed resulting in higher values for shear strength measured on specimens with diameter of 100 mm.