Abstract
In this paper, the topological properties of air voids in asphalt mixture: air void content, average void diameter, Euler number, genus, enclosed cavities, percolation number, aspect ratio, circularity and tortuosity were analysed using X-ray tomography scans and related to the hydraulic conductivity of a wide range of asphalt mixtures representative of those commonly used in practice. Moreover, a model for the hydraulic conductivity of asphalt mixture that is valid for the whole range of air void content was proposed. The model is based on statistical and physical considerations that lead to a system of functional equations. Finally, the model was related to experimental and literature data. It was observed that the range of asphalt mixtures studied hydraulic conductivity is related mostly to the air void content, while the topological parameters (e.g. tortuosity or aspect ratio) are not the primary factors affecting hydraulic conductivity. For this reason, the hydraulic conductivity of asphalt mixture commonly used in practice can be predicted using a simple hyperbolic equation with fixed, known, parameters.
Highlights
The hydraulic conductivity of asphalt mixture commonly used in practice can be predicted using a simple hyperbolic equation with fixed, known, parameters
Hydraulic conductivity of asphalt mixture has a substantial impact on the ability of roads to infiltrate the surface water to the sublayers
It can be seen that the average void diameter is directly related to the volume of the biggest air void in asphalt mixture (r = 0.90), and that the Euler number has a very high correlation to the number of air voids (r = 0.85) and percolation number (r = 0.84)
Summary
Hydraulic conductivity of asphalt mixture has a substantial impact on the ability of roads to infiltrate the surface water to the sublayers. An excess of water retained in asphalt may result in pavement distress through moisture damage, i.e. losing the bond between aggregates and the binder [2]. Moisture damage is associated with stripping, excessive permanent deformation and cracking [3, 4]. Predicting the hydraulic conductivity and understanding the factors influencing it will help to establish a balance between deterioration and drainage performance. Hydraulic conductivity of saturated asphalt mixture is defined as the rate of discharge flow of water through the cross unit area under laminar flow conditions [5]. Its value provides an indication of the drainage capacity of asphalt mixture pavements. Hydraulic conductivity is considered to be anisotropic; the hydraulic conductivity in the vertical and horizontal directions usually presents significative differences [6], the reason for this could be that the methods to measure vertical and horizontal hydraulic conductivities differ
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