Impact of loading rate and temperature on tensile strength of asphalt mixtures at low temperatures

Abstract

Low temperature cracking of an asphalt mix with specific design is primarily influenced by the loading rate and the temperature. For laboratory testing of hot mix asphalt (HMA), several test methods have been developed and standardised in the last decades to assess the resistance to low-temperature cracking. In order to characterise a mixture efficiently and economically, the test has to be kept within acceptable timeframes. Therefore, low temperature test methods apply fixed parameters, as Uniaxial Tensile Strength Test (UTST) and Relaxation Test (RT) according to EN 12697-46. To study impact of time and temperature on the low temperature behaviour, loading rate at UTST and initial stresses at RT are systematically varied at four temperatures (-20 | -10 | 0 | +10 °C). UTST are carried out at 3 strain rates (1.6 × 10-4-1.6 × 10-2 mm/s). The tensile strength βt and failure strain εfailure are determined and evaluated. Furthermore, RTs are performed at 3 different initial stresses, depending on the strength determined by UTST (0.75 | 0.5 | 0.35* βt). This will reveal how the level of initial stress influences the relaxation time and ratio. The results of this study can be used for modelling and simulation of pavement structures employed on bridges for expansions joints with low deformation rates and high absolute deformations.