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Modelling of Porous Materials

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Andrea Chiarelli
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The precise, quick and efficient simulation of asphalt concrete is an important step to select asphalt mixtures for a range of applications. A method to create virtual aggregates based on aggregates' topological properties and aggregate skeletons like those of asphalt concrete using a physics engine is proposed. It can produce hundreds of virtual aggregates with shape properties equivalent to these of real ones in a matter of seconds, pack them to a level of compaction like that of the Marshall compactor, and measure properties such as the expected air voids content and number of contacts between the aggregates. In the paper, only aggregates bigger than 2 mm have been considered due to computing efficiency. Besides, it was found that the main factors influencing asphalt compaction are the number of aggregates in the mixture and the amount of dust, or aggregates smaller than 2 mm, which correspond to the parts of the solid skeleton that have not been simulated.
Andrea Chiarelli
added a research item
This paper investigates the effects of air void topology on hydraulic conductivity in asphalt mixtures with porosity in the range 14%–31%. Virtual asphalt pore networks were generated using the Intersected Stacked Air voids (ISA) method, with its parameters being automatically adjusted by the means of a differential evolution optimisation algorithm, and then 3D printed using transparent resin. Permeability tests were conducted on the resin samples to understand the effects of pore topology on hydraulic conductivity. Moreover, the pore networks generated virtually were compared to real asphalt pore networks captured via X-ray Computed Tomography (CT) scans. The optimised ISA method was able to generate realistic 3D pore networks corresponding to those seen in asphalt mixtures in term of visual, topological, statistical and air void shape properties. It was found that, in the range of porous asphalt materials investigated in this research, the high dispersion in hydraulic conductivity at constant air void content is a function of the average air void diameter. Finally, the relationship between average void diameter and the maximum aggregate size and gradation in porous asphalt materials was investigated.
Andrea Chiarelli
added a research item
This paper investigates the effects of air void topology on hydraulic conductivity in asphalt mixtures with porosity in the range 14%-31%. Virtual asphalt pore networks were generated using the Intersected Stacked Air voids (ISA) method, with its parameters being automatically adjusted by the means of a differential evolution optimisation algorithm, and then 3D printed using transparent resin. Permeability tests were conducted on the resin samples to understand the effects of pore topology on hydraulic conductivity. Moreover, the pore networks generated virtually were compared to real asphalt pore networks captured via X-ray Computed Tomography (CT) scans. The optimised ISA method was able to generate realistic 3D pore networks corresponding to those seen in asphalt mixtures in term of visual, topological, statistical and air void shape properties. It was found that, in the range of porous asphalt materials investigated in this research, the high dispersion in hydraulic conductivity at constant air void content is a function of the average air void diameter. Finally, the relationship between average void diameter and the maximum aggregate size and gradation in porous asphalt materials was investigated.
Alvaro García
added a research item
Andrea Chiarelli
added 8 research items
This MATLAB algorithm allows you to pack n circles in a rectangular domain (see sample images).The void ratio (i.e., amount of empty space in the rectangle) is user-defined and met precisely.The domain has an arbitrary size that you can choose. Other parameters are also available for you to tweak.The position of all circles is randomised: this means that it is virtually impossible to obtain two packed domains that look the same.As an example, it is possible to pack >60,000 circles to a void ratio of 15% in 230 s (i7 4790k, DDR3 RAM 2400 Mhz).The algorithm works by seeding a starting population of tiny circles, which are grown until they touch another circle or a boundary of the domain. Once all circles have grown, a new generation of tiny circles are created and grown.This is repeated until the required void ratio is met.Results are displayed in a figure and saved in .mat format.The code is thoroughly commented to allow easy understanding of the process.Please remember that if you use this algorithm, you should cite it (e.g., articles, theses) and, in any case, leave the attribution text (MIT license). There is a link above that will show the citation information for this algorithm (DOI, authors, title).
This MATLAB algorithm (see https://dx.doi.org/10.6084/m9.figshare.3839532) allows you to pack n circles in a circular domain (see sample images at the DOI). The void ratio (i.e., amount of empty space in the circular domain) is user-defined and met precisely. The domain has an arbitrary diameter that you can choose. Other parameters are also available for you to tweak. The position of all circles is randomised: this means that it is virtually impossible to obtain two packed domains that look the same. As an example, it is possible to pack >142,000 circles to a void ratio of 15% in 870 s (i7 4790k, DDR3 RAM 2400 Mhz). The algorithm works by seeding a starting population of tiny circles, which are grown until they touch another circle or the boundary of the domain. Once all circles have grown, a new generation of tiny circles are created and grown. This is repeated until the required void ratio is met. Results are displayed in a figure and saved in .mat format. The code is thoroughly commented to allow easy understanding of the process. Please remember that if you use this algorithm, you should cite it (e.g., articles, theses) and, in any case, leave the attribution text (MIT license). If you follow the DOI link, you will find the citation information for this algorithm (DOI, authors, title).
In this paper, a proof of concept of a method is presented for the study of granular materials, such as asphalt, based on the use of a physics engine. To begin with, virtual aggregates are generated with randomized 3D shapes and a size distribution based on a chosen gradation curve. Then, the aggregates are placed in a constrained volume and subjected to a simulated vibration until satisfactory compaction is reached. Finally, the packed stone assembly obtained is saved as a 3D model, so that the virtual aggregates can be used for further studies such as the analysis of the void space in the material. All the steps in the method are described and discussed, along with the approximations made. Furthermore, an analysis of the void space is performed to determine if the method is able to generate air pores with realistic features. The analysis is performed by comparing the void space of a computationally packed aggregate assembly to that of a real asphalt core with the same aggregate gradation. The preliminary results obtained show that the modelling approach is able to represent effectively the air pores, thus, suggesting that further studies to advance this proof of concept should be conducted.