Characterisation of temperature and loading rate dependent bond strength on the Bitumen-aggregate interface using direct shear test

Abstract

The objective of this paper is to characterise the temperature and loading rate dependences of bond strength on the bitumen-aggregate interface. An aggregate-bitumen-aggregate sandwich sample was first employed to quantify its bond strength under four different temperatures (15, 25, 35, and 45 °C) and four levels of loading rate (5, 10, 15, and 20 mm/min) using a strain-controlled direct shear test. Then, a master curve of bond strength on the bitumen-aggregate interface was constructed via the time–temperature superposition principle traditionally used to determine the temperature-dependent complex modulus of polymer-based material (e.g., asphalt biner or mixture). After that, the impacts of temperature and loading rate on interfacial debonding were analysed based on SEM observation of the cracked bitumen-aggregate interface after the direct shear test. Lastly, percentages of cohesive and adhesive debonding at different temperatures were quantified. Results show that the time–temperature superposition principle applies to the quantification of bond strengths of bitumen under different temperatures and loading rates. Based on the comparative analysis of bond strength measured in the direct shear test, its master curve can well reflect the viscoelastic properties of the bitumen-aggregate interface over a wide range of temperatures and loading rates. At 15 °C and 25 °C, the interfacial crack mainly exhibits a combination of cohesive and adhesive debonding; however, at 35 °C and 45 °C, it is dominated by cohesive debonding. This observation is attributable to the fact that as the temperature rises, the chain network of bitumen molecules gets loosened and its kinematic activity enhances, which leads to the debonding between the bitumen molecules when subjected to shear loads and a higher percentage of cohesive failure.