A new hypothesis for the development of blisters in asphalt pavements

Abstract

Asphalt layers used to provide smooth, compliant, surfaces on pavements often experience the growth of small uplift blisters. Conventional wisdom has it that these blisters are the result of a build-up of either volatile gases or water vapour beneath the asphalt that accompanies a significant increase in surface temperature. This paper argues that in many cases such a cause is unlikely. It suggests an alternative explanation based upon a gradual growth of upward thermal buckles, induced by the cyclical changes of membrane stresses that accompany the constrained in-plane expansion and contraction, resulting from fluctuations in surface temperature. With asphalt displaying reduced elastic-visco-plastic stiffness at high temperatures a proportion of the growth in an upward buckle, occurring at elevated temperatures, will not be recovered when temperatures again drop. Over time a form of thermo-mechanical ratchet process appears to be set in motion, resulting in the gradual upward growth of these blisters. Recognizing the correct physical causes of these blisters is suggested to be the important first step in evolving appropriate practical measures to prevent their increasingly prevalent and damaging future development.