Andrea Umiliaco

Evaluation of hydraulic permeability of open-graded asphalt mixes using a full numerical simulation

AbstractPermeability of open-graded asphalt mixes is defined as the ability to transmit fluids through the voids. The infiltration of water affects the durability and safety of pavement systems. Traditionally, an empirical approach, based on laboratory tests or on field measurements, is used to evaluate hydraulic permeability. In general, such an approach allows the ex post calculation of the drainage capability of the open-graded pavement. In order to evaluate the hydraulic permeability during the phase of mix design, in this paper a novel method is proposed, based on simulation of unsteady flow of water through open-graded mixture. In particular, a real sample of asphalt mix is simulated in the shape of a Marshall test sample. It is composed of a set of particles, selected according to the real grading, positioned in the space domain following the random sequence adsorption approach (RSA) and covered by a film of bitumen. The flow of water through the synthetical sample is simulated through the lattice ...

FDTD Simulation of the GPR Signal for Preventing the Risk of Accidents due to Pavement Damages

It is well known that road safety issues are closely dependent on both pavement structural damages and surface unevenness, whose occurrence is often related to ineffective pavement asset management. The evaluation of road pavement operability is traditionally carried out through distress identification manuals on the basis of standardized comprehensive indexes, as a result of visual inspections or measurements, wherein the failure causes can be partially detected. In this regard, ground-penetrating radar (GPR) has proven to be over the past decades an effective and efficient technique to enable better management of pavement assets and better diagnosis of the causes of pavement failures. In this study, one of the main causes (i.e. subgrade failures) of surface damage is analyzed through finite-difference time-domain (FDTD) simulation of the GPR signal. The GprMax 2D numerical simulator for GPR is used on three different types of flexible pavement to retrieve the numerical solution of Maxwells equations in the time domain. Results show the high potential of GPR in detecting the causes of such damage.

A simulation-based approach for railway applications using GPR

In this work a numerical model capable to predict the electromagnetic response of railway ballast aggregates under different physical conditions has been calibrated and validated by a simulation-based approach. The ballast model is based on the main physical and geometrical properties of its constituent material and it is generated by means of a random-sequential absorption (RSA) approach. A finite-difference time-domain (FDTD) simulator is then employed to calculate the ground-penetrating radar (GPR) signal response to the scenario. The calibration of the model has been performed by taking into account the main physical properties and the grain size characteristics of both the reference ballast material and a fine-grained pollutant material, namely, an A4 soil type material, according to the AASHTO soil classification. The synthetic GPR response has been generated by using the gprMax freeware simulator. Several scenarios have been considered, which in turn were reproduced in laboratory environment and used for the validation of the model. Promising results have demonstrated the high potential of such approach in characterizing the simulated response of complex coarse-grained heterogeneous materials.

AGGREGATE SIZE DISTRIBUTION AND HYDRAULIC PERMEABILITY OF HMA: A FULL SIMULATION STUDY

Water trapped within the Hot Mix Asphalt layers of a flexible pavement causes the loss of strength and durability of the material producing surface damages and deteriorations such as stripping and ravelling. Open graded pavements are considered potentially to be effective solutions to avoid these forms of infiltration-related distress. The main property that influences the performance of HMA is the hydraulic permeability. The permeability is a function of several properties of HMA which make the process of mix design very complex and uncertain. In this paper, starting from different grading curves, we evaluate the dependence of the permeability by the size distribution of aggregates using a full numerical model that has yet been validated through experimental tests and theoretical calculations. The correlation between the grain size distributions and the hydraulic permeability is very useful in order to simplify and optimize the design of open-graded pavements.