Hot Mix Asphalt Permeability: Tester Size Effects and Anisotropy

Abstract

Permeability of hot mix asphalt (HMA) is a property that is important to the pavement's durability. Measuring permeability along with density will give a better indication of a pavement's durability than density alone. The presence of water for extended periods of time in the pavement is directly linked to early deterioration.

The first goal of this research is to study the anisotropic nature of hot mix asphalt permeability within the lab, which required the development of a horizontal permeameter. This method is inexpensive and suitable for a lab technician to use and analyze. A series of samples with different air void contents were used to observe how the ratio of vertical to horizontal permeability changes with air void content.

The second goal was to develop a modified field permeameter to study the water-pavement contact area effect on field permeability. A reliable sealing system was created that is consistent and is not detrimental to the pavement surface. The results of the study show that larger contact areas yield increasing influence of vertical flow, which represents the one dimensional assumption of Darcy's Law falling head method.

The third goal was to validate the results by simulating the field permeability test with a finite element model. A number of simulations with different permeability values and anisotropic permeability ratios were conducted. The horizontal and vertical flows were observed within the test area to analyze the flow pattern and influence of the directional permeability. The results matched the trends found in the field permeability study.