Optimising the moisture durability SATS conditioning parameters for universal asphalt mixture application

Abstract

The saturation ageing tensile stiffness (SATS) procedure is the first laboratory asphalt mixture durability protocol to combine moisture damage and oxidative ageing during the conditioning of asphalt mixtures prior to mechanical testing. However, the application of the SATS procedure has tended to be predominantly targeted at base materials with relatively ‘hard’ binders and overall high stiffness modulus requirements and is considered potentially too severe for more standard asphalt mixtures. This research study focused on understanding the effect of changes to the SATS conditioning parameters on the relative moisture damage assessment performance of asphalt mixtures, particularly ‘softer’ binder, high binder content and, finally, low air void content mixtures. Using four different aggregate types, together with ‘hard’ 10/20 pen and ‘softer’ 40/60 pen bitumen, the parameters of pressure, temperature and duration were altered, either one at a time or in combination, to arrive at a suitable combination for testing more commonly used 40/60 pen material. The optimum combination of parameters to allow the SATS procedure to be used for a wide range of typically used asphalt mixtures was found to be 0.5 MPa pressure, 85°C temperature and 24 h duration. The revised SATS durability conditioning protocol was still able to successfully discriminate between ‘poor’ moisture susceptible aggregate and ‘good’ material.

Keywords:

• moisture damage
• ageing
• durability
• asphalt mixtures
• stiffness modulus
• saturation

Acknowledgements

The work described in this paper was carried out at the Nottingham Transportation Engineering Centre (NTEC) at the University of Nottingham. The authors are particularly grateful to Aggregate Industries, who supplied aggregate types A, B and C (aggregate type D was sourced from stock), and to Nynas bitumen, who supplied the 10/20 and 40/60 pen grade bitumen, since without their invaluable contribution none of this work would have been possible.