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Advanced rheological performance evaluation and 3d discrete element modelling of bituminous mastics and mixtures

Keywords: Asphalt pavement, Rheology, Asphalt Concrete, Asphalt mastic, DEM
Fig. 1. DEM approach for asphalt concrete simulation (Author: Valeria Vignali).
Fig. 2. 3D DEM simulation of a Dynamic Shear Rheometer test on a bitumen sample (Author: Valeria Vignali).
Fig. 3. 3D DEM simulation of a Dynamic Shear Rheometer test on a mastic sample (Author: Valeria Vignali).
Fig. 4. 3D DEM simulation of a flexible pavement - contact forces inside the layers produced by road traffic (Author: Valeria Vignali).

Road pavement performances are still under in-tensive research because it has been necessary to simplify their constituent materials behavior, modeling them as a continuum. In reality, how-ever, they exhibit discontinuous performances, which do not always fit to the advanced continuum models.

Numerous research works, in fact, show that for these types of mixtures it is very important to take into consideration their micromechanical behavior, at the scale of an aggregate particle, because it is an essential factor in terms of overall system performance.

To overcome this limitation, the Distinct Particle Elements Method (DEM), which schematizes a granular material by means of particles that dis-place independently from one another and interact only at contact points, becomes a good answer. In this way, in fact, is possible to analyze the discrete character of mixes through a microscopic approach (Figure 1).

The aim of the research is the microscale DEM analysis of the interaction between aggregates, bitumen and filler and the evaluation of its in-fluence on the macroscale performances of the asphalt mixture. Thus, starting from a multiscale approach based on the interaction study between the asphalt mixture components, models have been implemented to simulate the load conditions under which the bitumen and the bituminous mastic (bitumen + fillers) are subjected as a results of the vehicular traffic action. In particular, from the 3D particle model it is possible to obtain the rheological parameters simulating the shear stress conditions imposed in the laboratory by the Dynamic Shear Rheometer (Figures 2 and 3).

The results from previous research works allowed to evaluate that DEM approach, developing a very reliable description of real phenomena. This represents a valid evolution of the traditional meth-ods in the simulation of the visco-elastic behavior of asphalt mixtures both for small samples during laboratory tests, and for larger portions of flexible pavements.

Moreover, using the DEM method, a "virtual laboratory" could be created to study the features of asphalt mixtures that cannot be measured in conventional laboratory tests. With the advancement in computer speed and storage ca-pacity, this approach could be an inexpensive tool to provide a precise control of every variable being studied. Once the model is calibrated, it could be used to run as many simulations as required. In time, therefore, these models could provide a crucial missing link for the development of true performance-related specifications for asphalt pavements (Figure 4).

Main publications

Dondi G, Vignali V, Pettinari M, Mazzotta F, Simone A, Sangiorgi C. (2014). Modeling the DSR complex shear modulus of asphalt binder using 3D discrete element approach. Construction and Building Materials, 54, 236-246.

Vignali V, Mazzotta F, Sangiorgi C, Simone A, Lantieri C, Dondi G. (2014). Rheological and 3D DEM characterization of potential rutting of cold bituminous mastics. Construction & Building Materials, 73, 339-349.

Dondi G., Simone A., Vignali V. and Manganelli G. (2012). Numerical and experimental study of granular mixes for asphalts. Powder Technology 232, 31–40.

Dondi G., Simone A., Vignali V. and Manganelli G. (2012). Discrete element modelling of influ-ences of grain shape and angularity on perfor-mance of granular mixes for asphalts, Procedia - Social & Behavioral Sciences. 53, 399-409.

Dondi G., Simone A., Vignali V. and Manganelli G. (2012). Discrete particle element analysis of aggregate interaction in granular mixes for asphalt: combined DEM and experimental study, Proceedings of 7th RILEM International Confer-ence on Cracking in Pavements, Delft, The Neth-erlands, ISBN 978-94-007-4565-0.

Dondi G., Simone A. and Vignali V. (2010). Mi-cromechanical modelling of aggregate–aggregate interactions with distinct particle element method for virtual laboratory simulation. Proceedings of the 11th International Conference on Asphalt Pavement. Nagoya.

Dondi G., Bragaglia M. and Vignali V. (2008). Evoluzione dei criteri di calcolo delle pavimenta-zioni flessibili: i modelli particellari. Atti del XVII Convegno Nazionale SIIV "Le reti di trasporto urbano. Progettazione, costruzione, gestione". Enna (CT). Edizioni Caracol (ITALY). ISBN 978-88-89440-40-7.

Dondi G., Bragaglia M. and Vignali V. (2007). Flexible pavement simulation with Distinct Particle Element Method, Proceedings of the IV Inter-national Congress SIIV, Palermo, Italy, ISBN 978-88-8207-260-5.

Dondi G. and Bragaglia M. (2006). Modellazione ad elementi distinti particellari della prova ITSM. Atti del XVI Convegno Nazionale SIIV. Arcava-cata di Rende (CS). Centro Editoriale e Librario (ITALY). ISBN: 88-7458-050-9.

Dondi G., Vignali V. and Bragaglia M. (2006). Modellazione mediante elementi distinti particellari delle prove sui materiali granulari. Atti del XVI Convegno Italiano di Meccanica Computazionale. Bologna. ISBN 88-371-1621.

Dondi G., Bragaglia M. and Vignali V. (2005). Bituminous mixtures simulation with Distinct Par-ticle Elements Method. Proceedings of the 3rd International SIIV Congress. Bari, Italy.

Research projects

PRIN 2007. Advanced Numerical Techniques for Perpetual Pavement Modelling. Chief researcher: Prof. Ing. E. Santagata, Politecnico di Torino. Operative Units: Università di Bologna (Ref: Prof. Ing. A. Simone), Università Politecnica delle Marche, Università di Parma, Università di Pisa.