Behavior of Stone Mastic Asphalt at Low Temperatures

Abstract This paper presents a detailed analysis of the influence of bitumen on low-temperature cracking of MAS 16 asphalt mixtures (stone mastic asphalt) used as wearing course on heavily trafficked roads. The study combines conventional bitumen tests (penetration, softening point, Fraass breaking point, ductility, Brookfield viscosity) with fundamental performance-related tests according to the SHRP methodology (Bending Beam Rheometer – BBR, Dynamic Shear Rheometer – DSR), as well as the Thermal Stress Restrained Specimen Test (TSRST) performed on asphalt mixtures. Five bitumens, both unmodified and polymer-modified, from two different sources were analyzed. The results show that polymer-modified binders exhibit a more balanced behaviour under extreme temperatures, with larger plasticity ranges, lower stiffness at low temperatures and improved thermal stability at high temperatures. TSRST fracture temperatures of mixtures containing modified binders are significantly lower (−35…−37 °C), whereas the corresponding cryogenic fracture stresses are higher, compared to mixtures based on unmodified binders. A good agreement was found between the stiffness limit temperature obtained from BBR tests and the fracture temperature determined by TSRST, confirming the relevance of fundamental binder testing for predicting mixture performance at low temperatures. Short-term ageing of bitumen (RTFOT) led to an increase of TSRST fracture temperature by 2–3 °C and to a performance decrease of up to 12 %, which highlights the need to define low-temperature performance requirements based on aged binder.