Gallium arsenide (GaAs), cadmium selenide (CdSe), and cadmium telluride (CdTe) are semiconductor materials with remarkable opto-electronic properties that make them suitable for a wide variety of applications including, light emitting diodes (LEDs), mobile phones, tablets, and solar panels. Due to the growing demand and the short lifespan of these electronic devices, a remarkable amount of electronic waste (e-waste) has been produced in the last decades. An important fate of e-waste is landfill disposal; therefore, there is an increasing concern about the release of toxic elements into the landfill environment and the potential risks for human health and the environment. Among the elements constituting GaAs, CdTe, and CdSe, tellurium (Te) has gained increasing attention in recent years. Tellurium is a scarce element on the earth’s crust, and a shortage in its supply might compromise the development of new advanced technology, particularly in the energy and defense fields. For these reasons, the US Department of Energy and the European Union regard Te as a critical element, and have urged the need to develop efficient and cost-effective processes to recover Te from waste streams. This thesis dissertation explored different aspects related to the fate and impact of the widely used semiconductor materials, GaAs, CdSe and CdTe in municipal mixed solid waste (MSW) landfills. Furthermore, it investigated the removal of the Te oxyanions, tellurite (Teᴵⱽ, TeO₃²⁻) and tellurate (Teⱽᴵ, TeO₄²⁻), from aqueous streams and the recovery of this strategic metalloid as biogenic, elemental tellurite (Te⁰) nanoparticles (NPs). In the first part this work, the dissolution of GaAs was evaluated under a range of redox conditions, pH levels, ionic strength, and the presence of organic constituents commonly found in landfills. Our results indicated that aerobic conditions and mildly alkaline pH conditions favor the dissolution and release of high levels of soluble arsenic (As) and gallium (Ga) to the synthetic leaching solutions. The rate of As and Ga dissolution in long-term exposure experiments was initially constant but later progressively decreased due to the formation of a passivating layer on the surface of GaAs. The leaching behavior of CdSe and CdTe was also investigated under different pH and redox conditions in solutions simulating landfill leachates. CdTe and CdSe were subjected to two different standardized leaching tests, the federal Toxicity Characteristic Leaching Procedure (TCLP) and the California Waste Extraction Test (WET). CdTe showed a very high leaching potential in both tests and the concentrations of Cd released were 1500- and 260-times higher than the regulatory limit (1 mg Cd L⁻¹), respectively. In contrast, CdSe was relatively stable and dissolved selenium (Se) in both leaching tests was below the regulatory threshold (1 mg Se L⁻¹). Tests performed under different pH and redox conditions confirmed a marked enhancement in CdTe and CdSe dissolution both under acidic pH and aerobic conditions, which is consistent with thermodynamic predictions. Due to the high leaching potential observed for CdTe in the previous batch experiments, leaching studies were designed to investigate the potential release of soluble Cd and Te from a commercially available CdTe thin-film solar panel under different chemical and biogeochemical conditions commonly found in landfills. The solar panel was subjected to two standardized batch leaching tests (i.e., TCLP and WET), and to a continuous column test designed to investigate the dissolution of CdTe under conditions simulating the acidic- and the methanogenic circumneutral phases of a MSW landfill. A negligible amount of Cd and Te was measured in the synthetic leachate of both batch tests. On the other hand, a significant amount of Cd and Te was released from the panel to the synthetic leachate of the column simulating an acid landfill after 30 days (73% and 21% of the total Cd and Te, respectively). In contrast, the amount of Cd or Te detected in the effluent of the column operated at circumneutral pH values was negligible. The marked difference in the leaching behavior of CdTe in both columns is related to the different aqueous pH and redox conditions promoted by the microbial communities in the columns. The microbial toxicity of the soluble species that can be released from CdTe and CdSe was also assessed as a part of this work. The toxicity of cadmium (Cdᴵᴵ), selenite (Seᴵⱽ), selenate (Seⱽᴵ), Teᴵⱽ, and Teⱽᴵ was evaluated in bioassays with different microbial targets, including acetoclastic and hydrogenotrophic methanogenic populations in a mixed microbial culture, similar to those involved in the stabilization of organic waste stabilization in a landfill, and the bioluminescent marine bacterium, 𝐴𝑙𝑖𝑖𝑣𝑖𝑏𝑟𝑖𝑜 𝑓𝑖𝑠𝑐ℎ𝑒𝑟𝑖 (Microtox® test). The acetoclastic methanogens were most sensitive to the presence of the various soluble species, with the toxicity decreasing in the following order: Cdᴵᴵ, Teᴵⱽ, Teⱽᴵ, Seᴵⱽ, while Seⱽᴵ was only toxic at non-environmentally relevant concentration. Hydrogenotrophic methanogens were highly inhibited by Cdᴵᴵ and Seᴵⱽ, but Teᴵⱽ and Teⱽᴵ only had a moderate toxic impact. The bacterium 𝐴. 𝑓𝑖𝑠𝑐ℎ𝑒𝑟𝑖 was very sensitive to inhibition by Cdᴵᴵ and Seᴵⱽ, and Teᴵⱽ. In the last part of this work, the potential recovery of insoluble, elemental Te⁰ NPs from aqueous solutions containing soluble Teᴵⱽ or Teⱽᴵ was investigated in batch- and continuous flow bioreactors inoculated with a methanogenic granular mixed culture. In the batch experiments, the capacity of the culture to catalyze the reduction of the Te oxyanions and to produce Te⁰ NPs internally and externally to the cells was demonstrated. The granular sludge was found to contain enough endogenous substrates to provide the electron equivalents required to reduce both Te oxyanions and the reduction rates were only modestly increased by an exogenous electron-donor (e-donor) such as H₂. The effect of several redox mediators (RM), namely, anthraquinone-2,6-disulfonate (AQDS), hydroxocobalamin, riboflavin, and lawsone, was also tested. Riboflavin and lawsone caused a remarkable increase of the rate of Teᴵⱽ and Teⱽᴵ reduction, respectively, and also enhanced the fraction of Te recovered as extracellular Te⁰ NPs. The morphology and localization of the Te⁰ NPs were also impacted by the presence of a particular RM and e-donor in the system, suggesting that NP production can be tailored for a particular application. Finally, the feasibility of utilizing upflow anaerobic sludge bed (UASB) bioreactors to reduce Teᴵⱽ oxyanions to non-toxic Te⁰ NPs was also investigated. Two reactors were supplied with ethanol as the external e-donor source to promote the biological reduction of Teᴵⱽ. Riboflavin, a redox mediator, was supplied to one of the reactors to enhance Teᴵⱽ bioreduction. Continuous formation of Te⁰ NPs using an UASB was found to be feasible and remarkably improved by addition of riboflavin at the low Teᴵⱽ:riboflavin molar ratio of 4:1. This flavonoid enhanced the conversion rate of Teᴵⱽ and reduced the toxic impact of Teᴵⱽ towards the methanogenic consortium. Overall, the evidence found in this work indicates that recycling of decommissioned devices containing GaAs, CdTe, or CdSe is desirable to prevent the potential environmental release of toxic metals and metalloids in MSW landfills, but also to allow the recovery of critical resources. Microbial processes offer potential for the removal and recovery of soluble metals and metalloid ions leached from decommissioned semiconductor materials. In particular, this study demonstrated the feasibility of utilizing continuous UASB bioreactors for the removal of Teᴵⱽ from aqueous streams and the recovery of this valuable metalloid as biogenic Te⁰ NPs.

The cause and distribution of spatial variations in the mechanical properties of the continental lithosphere are fundamental questions for modern geology. In this study variations in long-term lithospheric rigidity have been investigated. These investigations used profile- and grid-based flexural models of the lithosphere’s response to geologically imposed topographic, or buried, loads. These models were constrained by topographic and gravity data allowing recovery of best fitting rigidity values. In Oman a Cretaceous ophiolite acts as a significant load on the continental crust. Flexural models along profiles orthogonal to the ophiolite strike show that the observed gravity data can be best modelled by an elastic beam with standard thickness (T_e) of 30 km. Along strike there is shown to be significant variation in the foreland shape and the observed gravity signal. This, it is proposed, relates to the complex tectonic processes which occurred as the ophiolite was obducted. The Himalayan foreland has been the focus of controversy over the recovered long-term rigidity of the continents, with recovered T_e values ranging from 40 to over 90 km. Both profile- and grid-based techniques show that T_e is high (>70 km) in the foreland region. Across the India-Eurasia collisional system as a whole T_e values are variable. Beneath the Tibetan plateau recovered values are generally low (<10 km), while the plateau margins are marked by regions of higher rigidity. Recovered T_e values across the Arabia-Eurasia collisional system range from over 60 km in the foreland region to close to zero beneath the high Zagros mountains. In the eastern part of the foreland, flexural models match the gravity data; however, they disagree with sediment thickness data for the material infilling the foreland. This discrepancy is interpreted in terms of de-coupling of the flexural lithosphere from the shallower crustal levels, caused by the presence of significant salt deposits in this region. Application of grid-based techniques to South America, North America and Europe recover a broad range of Te values from ∼0 to over 90 km. The low T_e values are explained in active orogenic belts in terms of current processes acting to weaken the lithosphere, and in the continental interiors as the relics of past orogenic events. High T_e values in the continental interiors correlate with ancient cratonic cores which have undergone little deformation since their formation in the Archean. This study shows that T_e variations have a critical influence on the development of large compressional orogenic belts. In the Himalayan and Andean orogens there is a correlation between the over-thrusting of the orogenic belt and high T_e foreland regions. Where lower T_e regions are seen, less over thrusting is apparent, and in the case of the India-Eurasia collisional system out-flow of lower crustal material may be occurring.

The population and economy in the State of Qatar have been increasing significantly in the past 10 years. Accordingly, traffic loading has also increased rapidly, which merits consideration of the design and construction of long-lasting pavement structures that require minimal maintenance. This study started with an investigation of the feasibility and performance of the current asphalt pavement materials and structures being used in the country. This investigation utilised the analysis approach implemented in the Mechanistic-Empirical Pavement Design Guide (M-E PDG) software. The results evidenced how effective it is to replace the conventional unmodified 60-70 Pen bitumen with polymer-modified PG76-10 bitumen for pavements in Qatar and other countries in the region with similar climatic conditions. In addition, the results showed that the use of perpetual pavement structures is a viable option economically and that they are much more accommodating of increase in traffic loading, without causing excessive damage, than conventional pavement structures. The study also concentrated on the assessment of the long-term performance of different full-scale perpetual trial sections by conducting several field tests. The field performance evaluation results showed slightly low resistance to rutting, high IRI values, to some extent, and low stiffness during summertime when the temperature is high. These distresses and deteriorations are expected given the huge traffic loading and the big difference in temperature between seasons in Qatar. Then several field cores, field mixtures, and laboratory mixtures were tested and evaluated in order to assess the performance of different asphalt concrete mixtures against rutting, fracture, temperature susceptibility and fatigue damage. The conducted tests were useful to characterise and assess the performance of the mixtures against several major distresses. The results indicated that resistance of asphalt concrete mixtures to rutting was mainly affected by the bitumen grade, aggregate source and aggregate gradation. A well-designed mixture that uses polymer-modified bitumen (PMB) can achieve the high rut-resistance of asphalt mixtures either with Gabbro or limestone aggregates. The use of polymer-modified bitumen reduced the temperature and frequency susceptibility on the stiffness and rut-resistance. According to these results, it is obvious that rutting and cracking would not be major distresses for asphalt mixtures in Qatar if the mixtures were designed following a Superpave mix design with the appropriate content of polymer-modified bitumen. However, given the current mixture design system in Qatar, which utilises very low bitumen content, fatigue damage or cracking in general is a main distress, and its characterisation should be investigated in depth. The traditional methods to interpret fatigue tests data are not sufficient to characterise and evaluate mixtures against fatigue damage. Therefore, two advanced fatigue characterisation approaches were performed on the raw data obtained from the fatigue test of specimens prepared from different mixtures. The analysis of the fatigue tests focused on calculating the dissipated energy (DE) and obtaining damage characteristics curves following a comprehensive viscoelastic continuum damage (VECD) approach. The test results showed that the use of the VECD approach has major advantages over obtaining DE results only. However, the predicted fatigue life (Nf) for each asphalt mixture was affected by the uncertainty associated with fatigue tests as well as with model parameters. Therefore, it was important to develop a probabilistic analysis approach that accounts for the uncertainty and the variability associated with fatigue tests and analysis, respectively. To that end, a novel probabilistic analysis approach has been proposed in the last chapter of this study for predicting the performance of asphalt mixture against fatigue damage. The VECD characterisation approach was used in the development of this probabilistic analysis model. The random variables (RVs) of the fatigue life (VECD-Nf) model (|E*|LVE, a, b and α) were generated following normal distribution functions. However, it is suggested that more specimens should be tested in the future to specify the true distribution functions for the RVs. In conclusion, it is clear that the fatigue life results of the probabilistic analysis approach were much more consistent and reliable than those of the deterministic analysis approach. This probabilistic approach coupled with VECD results is very practical and useful for engineers and will be beneficial to predict fatigue cracking resistance of asphalt mixtures in the field.

Submitted by PPG Filosofia (filosofia-pg@pucrs.br) on 2017-11-24T12:51:18Z No. of bitstreams: 1 DIS_IURI COELHO OLIVEIRA_COMPLETO.pdf: 1662744 bytes, checksum: 675c0cc2e152bbef478b5b960d034479 (MD5) / Approved for entry into archive by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-12-01T13:12:02Z (GMT) No. of bitstreams: 1 DIS_IURI COELHO OLIVEIRA_COMPLETO.pdf: 1662744 bytes, checksum: 675c0cc2e152bbef478b5b960d034479 (MD5) / Made available in DSpace on 2017-12-01T13:17:04Z (GMT). No. of bitstreams: 1 DIS_IURI COELHO OLIVEIRA_COMPLETO.pdf: 1662744 bytes, checksum: 675c0cc2e152bbef478b5b960d034479 (MD5) Previous issue date: 2017-08-31 / Conselho Nacional de Pesquisa e Desenvolvimento Cient?fico e Tecnol?gico - CNPq / This study aims to develop two key concepts for the theistic argument of John Duns Scotus, namely that of essentially ordered causes (ceo) and that of accidentally ordered causes (cao). These concepts appear in both the different versions of his argument (Lect., Ord., Rep. I-A e TPP) as well as in a passage from his commentary on Aristotle?s Metaphysics. Thus, first of all, it is necessary to treat in a general sense the characteristics of these texts and to say where, in themselves, those concepts are found, besides indicating how the frame of the theistic argument of Scotus leads him to causality. Secondly, it is important to devote a little attention to the doctrinal sources on which Scotus based himself to formulate his own concepts, namely on Aristotle and Avicenna. In this chapter it is also shown in which the Scotistic notions approach and depart from those of his sources. In addition, the differences indicated by Scotus between the ceo and cao, on the one hand, and per se and per accidens causes, on the other, are clarified. Finally, it deals exclusively with ceo and cao, initially, presenting the characteristics of the members of each causal series in their respective processes of action; then, it is studied how these causes are structured as series, where the treatment of the bond of both with the First Cause is initiated through three propositions in which the fineness of the ceo is proved, the possible infinity of the cao and how the First Cause acts in relation to these two causal series. This chapter is finished discussing the exclusive characteristics of the Causa Prima in its relation to the others (ceo and cao), and saying how these two series contribute to a causal theory in theistic argument of Duns Scotus. / Este estudo tem em vista desenvolver dois conceitos-chave para o argumento te?sta de Jo?o Duns Scotus, a saber, o de causas essencialmente ordenadas (ceo) e o de causas acidentalmente ordenadas (cao). Estes conceitos aparecem tanto nas diferentes vers?es de seu argumento (Lect., Ord., Rep. I-A e TPP) quanto em uma passagem de seu coment?rio ? Metaf?sica de Arist?teles. Assim, em primeiro lugar, ? preciso tratar em sentido geral das carater?sticas destes textos e onde, nos mesmos, aqueles conceitos aparecem, al?m de indicar como a estrutura do argumento te?sta de Scotus leva-o ? causalidade. Em segundo, ? importante dedicar um pouco de aten??o ?s fontes doutrinais em que Scotus se baseou para formul?-los, a saber, Arist?teles e Avicena, mostrando em que as no??es scotistas se aproximam e em que se afastam das de suas fontes, al?m de esclarecer as diferen?as indicadas por Scotus entre as ceo e as cao, de um lado, e as causas per se e per accidens, de outro. Por fim, trata-se exclusivamente das ceo e das cao, inicialmente, apresentando as caracter?sticas dos membros de cada s?rie causal em seus respectivos processos de atua??o; a seguir, estuda - se como estas causas se estruturam enquanto s?ries, onde se inicia o tratamento do v?nculo de ambas com a Causa Primeira atrav?s de tr?s proposi??es em que se prova a finidade das ceo, a poss?vel infinidade das cao e como a Causa Primeira atua em rela??o a estas duas s?ries causais. Conclui-se ent?o o cap?tulo tratando das caracter?sticas exclusivas da Causa Prima em sua rela??o com as outras (ceo e cao), e de como estas duas s?ries contribuem para uma teoria causal no argumento te?sta de Duns Scotus.

Estudamos a adsorção de Te em superfícies de GaAs(001) e InAs(001) com periodicidades 1x1, 1x2, 2x1 e 2x2, para as concentrações de telúrio Tc= 0, 1/4, 1/2, 3/4 e 1. Realizamos cálculos dentro do formalismo do funcional da densidade empregando pseudopotenciais de norma conservada. Para a relaxação das estruturas empregamos a dinâmica molecular de Car e Parrinello. Nossos resultados apontam para uma redução na estabilidade das superfícies na proporçã em que aumenta a concentração de Te na uperfície. A cobertura de As (Tc = 0) é energeticamente mais favorável que as recobertas com qualquer concentração de Te, tanto na superfície de GaAs(001) quanto na de InAs(001). Observouse ainda nas superfícies com Tc = 0 Tc = 1, que a dimerização dos átomos de As e da ordem de 30% mais intensa que dos átomos e Te. Comparando as dimerizações do Te nas superfícies com concentrações Tc 1/2, observamos que elas são maiores sobre o InAs(001) (célula terminada em In) que sobre o GaAs(001) terminada em Ga). Outra tendência verificada e a \"flutuação\" do Te sobre as superfícies. Para uma mesma concentração verificamos a \"preferência de adsorção\" em sítios fora da cadeia de dímeros indicando uma adsorção monoatômica. Para concentração Tc = 1 na superfície GaAs(001):Te2x2 observamos duas geometrias possíveis: uma com cadeias de dímeros seguindo o modelo \"dimerrowmissing\" e outra com dois tipos de dímeros em posições alternadas ao longo da dir~ao (110). Analisando as energias de adsorção nas duas superfícies verificamos que a adsorção sobre o InAs é mais favorável que sobre o GAs. Analisamos ainda a estrutura eletrônica das superfícies em todas as reconstruções e concentrações consideradas e verificamos anda o caráter semicondutor das superfícies com concentração Tc = 1/2. / We have carried out ab initio density functional calculations to investigate the adsorption of Te on GaAs(001) and lnAs(001) surfaces as a function of Te surface coverage: Tc = 0, 1/4, 1/2, 3/4, 1. In order to determine the equilibrium atomic positions, the geometry was relaxed according he calculated total energy and forces following the Car Parrinello approach for molecular dynamics. Our calculations indicate that a full monolayer of As (Tc = 0) is energetically more favourable than any of the studied coverage of Te (Tc = 1/4, 1/2, 3/4, 1), where the stability is educed with increasing Te coverage. The dimerization of surface As atoms is about 30% more intense than surface Te atoms. Comparing the Te dimerization on InAs(001), In terminated, and aAs(OOI), Ga terminated, we observed that the Te atoms dimerize more over lnAs than GaAs surface. Another observation is the tendency of the Te atoms to \'l1oat\" from the surface with increasing coverage. For the same concentrations of Te the atoms \"prefer\" to be adsorbed on the offchain sites indicating a monoatomic adsorption. The adsorption energy of Te on InAs(001) is more favorable than GaAs(001). We also determined the surface band structure for all reconstructions and Te concentrations, veryfying the semiconductor nature for Tc = 1/2.

After natural/man-made disasters, a major challenge faced by governments is to ensure a speedy recovery of roads and transportation networks. In order to achieve this, a new road recovery priority (RRP) model has been developed to identify key issues and their inter-relationships giving a better understanding of factors that govern prioritisation across the affected regions. Interviews are conducted with experts in road reconstruction and maintenance organisations to investigate respondents’ evaluation and understanding of the RRP model in terms of its ease of use, usefulness, comprehensiveness, applicability, feasibility and structure. A questionnaire survey is conducted to investigate the impact of the important proposed affecting factors that can be critical for successful implementation and application of the RRP model in the road rehabilitation sector. A field survey is carried out to collect data which are essential to determine parameters in the model’s application. Four case studies are carried out to investigate the RRP model’s application in a variety of road conditions. The application of this model may solve the problem of decision making in road recovery priority determination in a hierarchical manner so that the recovery process can be accomplished from an urgent repair need to a lower recovery priority.

Transportation is a central component to most political, economic, social and environmental issues throughout most inhabited societies. The concerns of transport have become widely acknowledged. It is broadly accepted that promoting alternative forms of transport such as walking, cycling and public transport use is one solution to tackle environmental concerns. Although, delivering, implementing and developing transport strategies to reduce car usage is still highly debated. Transport stakeholders (e.g. planners and policymakers) have long strived to reduce car usage. Many studies have attempted to develop strategies or understand triggers that might encourage and promote a reduction in car use. Despite this, the car usage has typically intensified and alternative forms of transport have become marginalised or discouraged when compared to the car. This research investigates travel attitudes and behaviours of individuals along a specific urban travel corridor within an area of Birmingham, UK. It explores socio-demographic factors using a mixed methods approach that incorporated questionnaires, travel diaries and interviews. This work identified a series of transport measures conceived upon different urban demographic characteristics in order to meet different individuals’ transport need. A significant finding from this work indicated there was an appetite amongst the sampled participants to be willing to reduce their car use if the right transport strategies were introduced. Initially the results from the questionnaire suggested age influenced car use the most, however, other demographic characteristics (e.g. gender and deprivation) were found to be an influential factor.

The research was aimed at the development of an optimal road fund allocation model for road maintenance to three road agencies in Ghana. The objective was to compare a novel model by multicriteria analysis (MCA) with deterministic outcome and a model based on preferential analysis to determine optimality. The deterministic model was efficiency based with quantitative analysis from a decision maker’s perspective whilst the approach by preferential analysis was equity based with qualitative analysis from stakeholder perspective. The input parameters of the deterministic model were based on the value function method (VFM) and the concept of efficiency frontier. It determined a scaler index for the proportionate allocation of road fund by road type. It was based on a set of attributes including road length, traffic, pavement roughness and percentage of work achievement. The concept of efficiency frontier was used to sub divide the proportion of funds allocated by road type into economic efficiency and equity components based on the Net Present Value/Capital, Vehicle Operation Cost (VOC) and income. The values of the selected attributes were generated from the outputs of HDM-4 analysis. The model based on the preferential analysis was set on the Analytical Hierarchy Process (AHP). It involved pairwise comparison of defined criteria and sub criteria by stakeholder priority at national, district and community levels. Priority vectors were estimated for road fund allocation into efficiency and equity proportions by road type. A comparison of the outputs of the two models on the basis of the impact on pavement roughness performance indicated the stated preference based model yielded better impacts than the model with deterministic approach. It was concluded that road fund allocation based on a well logically determined value judgement with mathematical analysis yields better results.

This thesis reports an investigation into the relationships between the tyre strain feature and tyre operating conditions based on finite element analysis and experiments for the development of a strain-based intelligent tyre system, which could estimate the tyre operating characteristics for optimising vehicle dynamics control and improving vehicle safety. A 175/505R13 tyre is adopted as the subject of this study. An efficient and effective material property determination procedure is developed for investigating the rubber and reinforcement material properties by experiment. Considering the possibility of the absence of tyre composite profile due to proprietary protection by tyre manufacturer, a novel imagebased method is developed to capture the tyre geometry feature from the tyre product cut cross-section. Both the 2D and 3D finite element tyre models are created in the commercial finite element code ABAQUS. The generated finite element tyre models are validated with experimental data and then adopted to construct the comprehensive relationship between tyre strain feature and tyre operating characteristics. Experimental validation of these estimation models are implemented based on a custom designed test system. Finally, some recommendations are presented for improving the capability of the finite element tyre model and the strain-based intelligent tyre test system.

A study of the factors affecting the packing and porosity of particles has been made and a general theory for the combining of aggregates of varying shapes and sizes in order to achieve minimum porosity is proposed. Arising out of this theory experiments have been carried out from the results of which graphs have been prepared to enable the determination of the optimum percentage of fine material for maximum density in two component systems. A method for extending the application of these results into the province of the design of multicomponent systems of both the continuous grading and intermittent grading types has been devised, and in the latter type the inherent gaps in the grading have been related to measured void characteristics. From another graph the value of porosity appropriate to any such mixture can be estimated. The theory and relevant graphs are believed to be of general application in the fields of mixtures comprising aggregates of any shape or combination of shapes whether these be dry aggregates, wet aggregates, bitumen or tar coated aggregates or concrete aggregates, and to cover all possible environmental conditions of the particulate mass such as the applied compactive effort and boundary effects.