A time-dependent vapor flow model of asphalt concrete

ABSTRACT

It is straightforward to determine vapour flow for a non-absorbing medium using Darcy’s law. However, asphalt concrete (AC) sample absorbs moisture over time if it is exposed to a humid environment which causes swelling of the binder materials. This action reduces pore connectivity. As such, the flow properties of AC exposed to moisture can change with time due to clogging of capillary pores and reduced pore connectivity by swelling. To this end, this study develops a model by modifying Darcy’s law to quantify vapour permeability of an AC sample. The resulting model considers asphalt’s swelling using air voids and sample thickness (represents flow length) in addition to regular parameters of Darcy’s law. As a first step, the effects of air voids and thickness on vapour flow are evaluated. It is shown that vapour flow increases with an increase in air voids and with a decrease in thickness. Vapor flow shows a logarithmic correlation with time. As a second step, a permeability model is developed considering the time-dependent vapour flow rate in Darcy’s law. Next, the model is validated using laboratory tested data. The model is found to have good agreements with the tested data. The developed model is advantageous over simpler Darcy’s model for determining asphalt permeability considering binder swelling, pore connectivity and clogging.

Acknowledgements

The author would like to thank NMDOT for funding this study. Special thanks to Ph.D. Candidate Mr. Hasan Faisal for his help analyze the data.

Disclosure statement

No potential conflict of interest was reported by the authors.