Factors affecting hydraulic conductivity of asphalt mixture

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

Novel and Compact Reconfigurable Antennas for Future Wireless Applications

PhDThe development of reconfigurable antennas is considered to be very promising in modern and future communication systems. Reconfigurable antennas have made use of many reconfiguration techniques that are centred upon switching mechanisms such as p-i-n diodes or MEMS. Other techniques such as optical switches, mechanical structure changing or the ability to change the permeability or permittivity of smart substrate materials have also been used. Reconfigurable antennas have created new horizons for many types of applications especially in Cognitive Radio, Multiple Input Multiple Output Systems, personal communication systems, satellites and many other applications. Cognitive Radio is one of the potential wireless applications that may place severe demands on RF systems designers and particularly antenna designers, when it comes to providing exible radio front-ends capable of achieving the set objectives of the technology. The aim of this work is to investigate possible roles that different categories of reconfigurable antenna can play in cognitive and smart radio. Hence, the research described in this thesis focuses on investigating some novel methods to frequency-reconfigure compact ultra-wideband antennas to work in different bands; this will offer additional filtering to the radio front-end. In the ultra-wideband mode, the antenna senses the spectrum for available bands with less congestion and interference and hence decides on the most suitable part to be reconfigured to, allowing reliable and efficient communication links between the radio devices. Ultra-wideband antenna with reconfigurable integrated notch capability is also demonstrated to provide further enhancement to interference rejection and improve the overall communication link. Furthermore, the design of novel pattern and polarisation reconfigurable antennas will be also investigated to assist Cognitive Radio through spatial rather than frequency means. An ultimate target for this research is to combine different degrees of reconfiguration into one compact, state of the art antenna design that meets the growing demand of cognitive and smart radio devices for more intelligent and multi-functional wireless devices within the personal area network domains and beyond

Virtual porous materials to predict the air void topology and hydraulic conductivity of asphalt roads

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

Dynamics of water evaporation from porous asphalt

The dynamics of water evaporation from porous asphalt mixture, with porosity ranging from 15% to 12 29%, have been investigated in this article. In order to test the same samples under different conditions, the pore structure of asphalt was quantified using X-ray Computed Tomography (CT) scans and 3D printed in transparent resin blocks. 3D printed transparent resin samples were tested under controlled laboratory conditions to understand the effect of pore space topology on the water retention and drying dynamics. The macroporosity, pore size distribution, air void tortuosity, water conductivity, and water retention curves of the 3D printed porous asphalt samples were quantified by means of image analysis. Moreover, a model was developed and tested experimentally to estimate the evaporation rates from porous asphalt materials under a wide range of porosities. Within the range of asphalt mixtures studied in the present work, the evaporation rate is related predominantly to the porosity, pore size distribution and tortuosity. It was found that the period over which water evaporation occurs at the surface is relatively short during drying of porous asphalt materials due to their relatively large pores weakening the capillary forces. This results in significantly shortening the so-called stage-1 evaporation (when the drying rate is controlled by liquid vaporisation at the surface) and early onset of the transition period (when both surface water evaporation and vapour diffusion inside porous asphalt play a comparable role in supplying the 26 evaporative demand). The transition period is followed by the stage-2 evaporation when the process is limited by the vapour diffusion inside the porous asphalt. Our results illustrate that the beginning of the stage-2 evaporation depends on the porosity and tortuosity of the porous asphalt material among other parameters. Our results and analysis provide new insights into the dynamics of water evaporation from asphalt materials

Effect of air voids content on thermal properties of asphalt mixtures

Air voids content is considered as one of the factors that may affect heat transfer through asphalt mixture, although their specific role on the asphalt mixture temperature is still unclear. The objective of this research is to have a deep insight of the effect of air voids content on the temperature evolution, transport and storage of heat in asphalt mixture under dry conditions. With this objective, asphalt mixture slabs with different air voids content have been built and their thermal conductivity, specific heat capacity, light absorptivity and thermal diffusivity related to their temperature evolution have been measured when they are exposed to infrared light and during the cooling process. It was observed that asphalt mixture with high air voids content exhibited slightly higher steady state temperatures than denser asphalt mixture and that the heating and cooling rates are higher in porous asphalt mixture than in denser materials. The reason for the faster increase and decrease in temperature of porous mixture and for the higher temperature reached by porous asphalt is its lower specific heat capacity and thermal conductivity. Finally, it could be observed that the connectivity of air voids in asphalt mixture did not play an important role on the temperature reached by asphalt mixture

Reconfigured and Notched Tapered Slot UWB Antenna for Cognitive Radio Applications

A compact reconfigurable and notched ultra-wideband (UWB) tapered slot antenna (TSA) is presented. The antenna reconfiguration operation principle relies on 2 mechanisms: in the first mechanism a resonator parasitic microstrip line electrically coupled to the TSA is used to notch the TSA at a specific frequency and the second mechanism relies on changing the input impedance matching of the antenna by means of changing the length of a stub line extended from an additional tiny partial ground on the back side of the antenna. The reflection coefficient, radiation patterns, and gain simulations and measurements for the proposed antenna are presented to verify the design concepts featuring a very satisfactory performance. Total efficiency simulations and measurements are also presented to highlight the filtering performance of the reconfigured antenna. When the antenna was reconfigured from the UWB to work into multiple frequency bands, the radiation patterns were still the same and the total peak gain has slightly improved compared to the UWB case. In addition, when the antenna operated in the notched mode, the gain has significantly dropped at the notch frequency. The simplicity and flexibility of the proposed multimode antenna make it a good candidate for future cognitive radio front ends

Frequency and Pattern Reconfigured Planar UWB Antenna Array for Future Cognitive Radio Portable Devices

No abstract available