Effect of short-term conditioning and long-term ageing on permanent deformation characteristics of asphalt mixtures

Abstract

Quantification of the effect of short-term conditioning and long-term ageing on the permanent deformation properties of asphalt mixtures is important for a reasonable estimation of rutting in the field. As the asphalt industry continues to develop more sophisticated mixtures, measuring the effect of short-term conditioning and long-term ageing on performance becomes even more critical. Significantly, more pavement are being built with reclaimed asphalt pavement, shingles, and warm mix asphalts, which may age very differently from mixtures with virgin asphalt. The use of warm mix asphalt in particular is rapidly increasing, which tend to soften the mixture in the early life of the pavement and impose a complex challenge for determining appropriate laboratory and field conditioning. For these reasons, it is critical that more precise determination of the effect of ageing on permanent deformation properties of asphalt mixtures to be made. This study proposes a new methodology that could be used in conjunction with the design of conventional asphalt mixtures and any new asphalt technology. Using incremental repeated load permanent deformation (iRLPD) test, which is the basis of the new methodology, the effect of short-term conditioning and long-term ageing on the permanent deformation properties of asphalt specimens can be evaluated. The minimum strain rate (MSR) property from the iRLPD test, measured before and after the ageing process, will show the rate of ageing and rate of change in the mixtures’ rutting performance. In this study, six mixtures were tested according to the iRLPD procedure and the ageing effect on permanent deformation properties of the mixtures was quantified. It is shown that different asphalt mixtures age in very different ways and this will significantly affect their short-term and long-term rutting performances. In addition, it was found that there exist a significant interdependence between short-term conditioning and long-term ageing of asphalt mixtures. Thus, adequate short-term conditioning is important for acceptable long-term rutting performance. The MSR master curve from the iRLPD test provided the necessary information for estimating rutting, considering the effect of temperature, tyre pressure, and ageing. In this respect, rut depths of the six mixtures were estimated using the hourly pavement temperatures for a 20-year period.

Keywords:

• asphalt mixtures
• rutting
• permanent deformation
• repeated load
• strain rate
• short-term conditioning
• long-term ageing

Acknowledgements

The authors would like to thank Steve Lenker, the Director of the Construction Materials Reference Laboratory, for his support throughout this study. The authors wish to acknowledge Frank Fee for coordinating the acquisition of the materials for this study. The efforts of State DOT and private agencies, which provided the materials and the corresponding mixture designs, are most appreciated. The agencies are Florida Department of Transportation, Gainesville; North Carolina Department of Transportation; Heritage Research Group, Indiana; MTE Construction, Wisconsin; and California Department of Transportation.