Asphalt mixture is mainly used for the construction of roads throughout the world. Large amounts of capital are spent for construction and maintenance of roads. Water is one of the major contributors towards the damage of the road structure. It is considered as the worst enemy of a pavement structure by directly causing a distress or indirectly magnifying a distress and hence damaging the road structure. Asphalt mixture loses its strength in the presence of water either through loss of cohesion within the bitumen or loss of adhesive bond between bitumen and aggregate. All the conventional techniques that are used for the determination of the moisture susceptibility of an asphalt mixture assess the material as a whole by using some mechanical testing technique without taking into account the individual physicochemical characteristics of both the bitumen and the aggregates. The surface energy properties of the materials, which are used to quantify their interfacial adhesion, play an important role in the final adhesive bond strength between these materials. The aim of this research is to produce detailed experimental techniques to measure the surface energy properties of bitumen and aggregate, and then combine them with a mechanical moisture sensitivity test procedure. This can greatly contribute towards the development of a powerful material screening protocol/tool for selection of bitumen-aggregate combinations that are less susceptible to moisture damage. This thesis describes the work that was carried out towards the development of a physico-chemical laboratory at the Nottingham Transportation Engineering Centre (NTEC). Four types of equipment were used, namely goniometer and dynamic contact angle analyser for determining the surface energy properties of the bitumen samples, and the dynamic vapour sorption and microcalorimeter systems for the surface energy properties of the aggregates. Large amount of material testing was carried out with these equipment and testing protocols were developed and improved over the course of experimental work. It was found that the dynamic contact angle technique and dynamic vapour sorption technique provides consistent results for bitumen and aggregates respectively as compared to the other two test equipment. The surface energy properties of the bitumen and the aggregates were then combined thermodynamically to determine the adhesive bond strength between the two materials, and the reduction in the adhesive properties if water is introduced into the system. The results showed that these thermodynamic properties generally correlate well with the moisture damage performance of these combinations from the laboratory testing. SATS mechanical test technique was used to determine the moisture susceptibility of different bitumen-aggregate combinations. The virgin material and the recovered material from the SATS tested cores were tested for the surface energy properties. It was found that the surface energy properties combined with SATS results can be used, with some exceptions, to identify compatible bitumen-aggregate combinations and hence improved moisture damage performance of the resulting asphalt mixture.

Research to improve the performance of asphalt mixtures through the addition of crumb rubber using the dry process has continued worldwide because of its potential as a recycling option for used tires. For decades, dry mixed rubberised asphalt mixtures have performed inconsistently in field trials and laboratory evaluations. However, current research has revealed that the performance of asphalt mixtures is highly dependent on the characteristics of its internal structure or phase constituents. A comprehensive methodology has been developed in this study to characterise the microstructural properties of dry mixed rubberised asphalt mixtures and correlate them with the mixtures' macroscopic response to compression and fatigue. The proposed methodology combines a non-destructive imaging technique; X-ray Computed Tomography (CT) and image processing and image analysis procedures to quantify the properties of air voids and cracks as well as the rubber distributions within the rubberised asphalt specimen. A gap graded mixture of Hot Rolled Asphalt (HRA60/20) containing different percentages and gradings of crumb rubber particles was compared to a conventional mixture (unmodified or control mix). The results showed that the addition of crumb rubber affects the formation and distribution of air voids in an asphalt mixture. Correlations between the internal structural damage parameters and the mechanical behaviour of the asphalt mixtures were unanimous in concurring that adding rubber improves a mixture resistance to fatigue failure. The modulus of the asphalt mixtures at peak stress under compression reduced when the rubber was introduced into the mixture although in contrast, the image analysis showed less fracture within the tested specimen in comparison to the control mix. The imaging procedures developed in this text are recommended as a guide to characterise the internal structure of rubberised asphalt mixtures.

Flexural fatigue is one of the main failure modes in asphalt mixtures. After reviewing and critiquing the current literature about fatigue in pavement engineering, this research project focused on dissipated energy approach because it takes into account the evolution of the material during a test. A comparison between the traditional method and several dissipated energy methods was made by using statistical analysis. Further research investigation involved the understanding of fatigue testing machines. Different categories of tests give different fatigue life values; so which one best represents the real world? This project focuses on pure fatigue tests and diametrical fatigue tests. The main innovative contribution of this thesis is the development of a new fatigue test: ITFT in strain controlled mode. It is a simple fatigue test widespread in UK often used by civil engineering firms to characterise stiffness and fatigue properties of asphalt materials mostly for construction and maintenance sites. Currently, the ITFT characterises the behaviour of asphalt material under repeated constant load; so no ITFT data obtained in strain control mode exist. To overcome this lack, ITFT in strain control mode was developed; this allows comparing results between simple flexural tests and diametrical tests. Results show that fatigue lives obtained by means of the ITFT are smaller than fatigue lives obtained by pure fatigue tests, this is due to the accumulation of permanent deformation during the ITFT; however ITFT results are reliable and statistically not different from 4PB results. It is true that pure fatigue does not really exist in real life; failure is a more complicated phenomenon. Thus, developing ITFT in strain control mode could reduce the gap between research in laboratory (where pure fatigue tests often are used) and in the fields (where experience showed that quick and simple tests are preferred by engineering consultancies).

This research presents a methodology that accounts for variability of key pavement design input variables and variations due to lack-of-fit of the design models and assesses effects on pavement performance (fatigue and deformation life). Variability is described by statistical terms such as mean and standard deviation and by its probability density distribution. The subject of reliability in pavement design has pushed many highway organisations around the world to review their design methodologies to evaluate the effect of variations in materials on pavement performance. This research has reinforced this need for considering the variability of design parameters in the design procedure and to conceive a pavement system in a probabilistic way, similar to structural designs. This study has only considered flexible pavements. The sites considered for the analysis, all in the UK (including Northern Ireland), were mainly motorways or major trunk roads. Pavement survey data analysed were for Lane 1, the most heavily trafficked lane. Sections 1km long were considered wherever possible. Statistical characterisation of the variation of layer thickness, asphalt stiffness and subgrade stiffness input parameters is addressed. A model is then proposed which represents an improvement on the Method of Equivalent Thickness for the calculation of strains and life for flexible pavements. The output is a statistical assessment of the estimated pavement performance. The proposed model to calculate the fatigue and deformation life is very fast and simple, and is well suited to use in a pavement management system where stresses and strains must be calculated millions of times. The research shows that the parameters with the greatest influence on the variability of predicted fatigue performance are the asphalt stiffness modulus and thickness. The parameters with the greatest influence on the variability of predicted deformation performance are the granular subbase thickness, the asphalt thickness and the subgrade stiffness.

The permanent deformation of a pavement due to vehicle load is one of the important factors affecting the design life as well as the maintenance cost of a pavement. For the purpose of obtaining a cost-effective design, it is advisable to predict the traffic-loadinduced permanent pavement deformation. The permanent deformation in pavements (i.e. rutting) can be classified into three categories, including the wearing of the asphalt layers, compaction, and shear deformations. In the present study, discrete element analyses have been performed to predict the permanent deformation of a pavement when subjected to moving wheel loads. Note that the wearing of the asphalt layers has been disregarded. DEM biaxial test simulations have been carried out in terms of both unbonded and bonded granular materials. The typical stress-strain response, as well as the volumetric strain development, have been reproduced, in qualitative agreement with the experimental results. The factors affecting the mechanical behaviour of granular materials have been investigated, e.g. particle stiffness, sample compaction and parallel bond strength. In addition, the elastic properties, initial yield stress, strength parameters and so on have been analysed. These compression tests provided guidance for the selection of the particle parameters for the subsequent pavement simulation. The permanent deformation in unbonded pavements was represented under moving wheel loads, and proved to be qualitatively consistent with the laboratory tests. The initial self-weight stress had a significant effect on rutting. When the initial gravity stress was relatively high, both shakedown and surface ratchetting phenomena were observed for different loading levels. However, the accumulation of permanent deformation was continual for pavements with low gravity stress, even if the wheel pressure was small. Other factors affecting the rutting have been taken into consideration, e.g. specimen preparation, interparticle friction, etc. In the case of the single-layered pavement, permanent deformation ceased after the first wheel pass. Plastic deformation increased with the decrease in the self-weight stress. For the double layered pavement, the permanent deformation continually increased with wheel passes, probably owing to compaction of the bottom unbound layer. The pavement shakedown phenomenon was not observed prior to wheel pass 300. The permanent deformation increased augmentation of wheel pressure as well as decrease in the sample density and upper layer thickness. The residual stresses in both vertical and horizontal directions can be obtained using the measurement circle. For all the pavements in the current simulations, the vertical residual stress is nearly always zero, consistent with the equilibrium condition. In the case of the unbonded pavement, the large horizontal residual stress depends on the high initial gravity stress, instead of high wheel pressure or wheel pass number. For the single-layered pavement, the peak of the horizontal residual stress was observed near the pavement surface. The residual stress rises with the augmentation of the wheel pass number and the wheel pressure. In the double-layered pavement, the residual stresses are discontinuous at the interface between different pavement layers. The peak appears near the pavement surface and increases with the reduction in the upper layer thickness as well as the rise in wheel passes and wheel pressure. Nevertheless, residual stress is not apparent in the granular base. The probability density distribution was investigated in terms of the contact and bond forces. For the normal contact force, a peak generally appeared at small contact forces, followed by a drastic decrease and, after that, the probability density progressively approached zero. For the tangential contact force as well as the bond forces, in general, a peak of the probability distribution was observed at small contact forces, and then a sharp drop followed from the two flanks of the peak point. Finally, there was a gradual decrease until the probability density decayed to zero. The factors, e.g. pavement layer, wheel pass number and wheel pressure, mainly affect the probability distribution of the small contact or bond forces. For both single- and double-layered pavements, the absolute extrema of the bond forces in the top layer increased with the augmentation of the wheel pass number and the wheel pressure. For the unbonded pavement, the sliding contact ratio was studied and it was significantly affected by the pavement layer, initial gravity stress and sample compaction. The distribution of the pavement particle displacements were demonstrated. In the unbonded pavement, factors, such as wheel pressure and initial gravity, not only affect the distribution of the relatively large particle displacements but also increase the magnitude of the particle displacements. The directions of the large displacement vectors are diverse as the large gravity acceleration is assigned to the particles but are almost downward when the self-weight stress is small. In the single- or double layered pavement, factors, such as wheel pass number and wheel pressure, merely increase the values of the particle displacements. The distribution of the displacements is hardly affected. For the single-layered pavement, the large displacements were observed near the pavement surface and their directions are almost contrary to the movement direction of the wheel. In the double-layered pavement, relatively large particle displacements are widely distributed in the pavement. Their directions are in an almost vertical direction.

Mostrou-se que notas atribuídas por motoristas e passageiros podem ser usadas como dados para avaliação de comportamento da superfície de pavimentos durante o tráfego de veículos. Também, através de estudo sobre a história de avaliação docomportamento da superfície de pavimentos, recorda-se que o conhecimento sobre essas variáveis pode contribuir para identificar relações entre o grau de satisfação de quem usa rodovias e características da estrutura e manutenção de pavimentos,os defeitos da superfície de vias. Relatam-se conclusões de análises estatísticas efetuadas para comparar médias de notas atribuídas, por avaliadores treinados, a segmentos de ruas de São Carlos-SP e índices padronizados para mesma escala de medida, obtidos a partir de características da superfície de pavimentos, visando sustentar conclusões para indicar que processos de avaliação a partir de notas atribuídas por avaliadores poderão fornecer resultados de classificação de estado de pavimento compatíveis com a cultura sobre conforto e segurança durante o tráfego de veículos daqueles que usam as vias. / It was showed that the scores from drivers and passengers should be useful as input to evaluate the behavior of pavement surface during traffic of vehicles. Also, studying the history of the pavement surface evaluation it was recalled that the knowledge of such variables should contribute to identify relationships among the road user satisfaction and the distress of the pavement surface. And it was reported some conclusion obtained from statistical analysis to compare scores media attributed by evaluators to street segments of the city of Sao Carlos SP with standardized index trying to support conclusions to indicate that the evaluation processes done from evaluator\'s scores should conduct to pavement condition indexes closed to the culture on comfort and security of traffic from the users of the roadway.

The increase of road infrastructure around the world involving the traditional hot mix asphalt (HMA) technology and its effects on the environment and health means that serious attention needs to be paid to building more sustainable flexible pavements. Cold bitumen emulsion mixture (CBEM) as an increasingly attractive cold asphalt mixture is therefore becoming an important subject area for study. Despite the efforts applied during the last few decades to enhance and develop CBEM application, certain issues still exist that make it inferior to HMA, resulting in limiting or minimizing its use. However, the enhancement of CBEM for flexible pavements construction, rehabilitation and maintenance is increasingly gaining interest in both pavement engineering industrial and research sectors. Therefore, the main aim of this study is to gain a deep insight and understanding into the impact response of using natural and synthetic fibres as reinforcing materials, on the mechanical properties and water susceptibility of CBEM including indirect tensile stiffness and resistance to rutting, cracking and moisture damage. Four different types of fibres were used: glass as a synthetic fibre, and hemp, jute and coir as natural fibres. Various samples of CBEM, with and without fibres, were fabricated and tested. Traditional hot mix asphalt mixture was also used for comparison. By achieving this aim it is expected that the use of CBEM would increase, allowing such mixtures to be used as structural pavement materials with some confidence. In spite of the quality of an asphalt mix being one of the most important and significant factors that affect the performance of both hot and cold mix flexible pavements, and the high quality mixes are often cost effective as these mixes require less maintenance and increase the service life of the pavements, it is also cost efficient to replace the semi-experimental flexible pavement design methods with fast and powerful software that includes finite element analysis. Several finite element models (FEM) have been developed to simulate the behaviour of hot mix asphalt, but none exists for cold mix asphalt reinforced by natural and synthetic fibres. This study also describes the development of a three-dimensional (3-D), finite element model of flexible pavements made with CBEMs, which has itself been reinforced with natural and synthetic fibres. The 3-D finite element model was employed to predict the viscoelastic and viscoplastic responses of flexible pavements based on CBEM when subjected to different multiple axle loads, bituminous material properties, tyre speeds and temperatures. The pavements were subject to moving and static loading conditions to test for permanent deformation (rutting). The results indicate a significant improvement in the indirect tensile stiffness modulus, for all fibre-reinforced CBEMs, over different curing times. The improved tensile behaviour represents a substantial contribution towards slowing crack propagation in bituminous mixtures, while scanning electron microscopy analysis confirmed the fibre shape and surface roughness characteristics. The improved performance of the reinforced mixtures with both natural and synthetic fibres facilitated a substantially lower permanent deformation than traditional hot and cold mixtures at two different temperatures (45 °C and 60 °C). When using glass and hemp fibres as reinforcing materials, there was a significant improvement in CBEM in terms of water sensitivity. These reinforcing materials can extend the service life of flexible pavements. Finally, the results show that the finite element model can successfully predict rutting of flexible pavements under different temperatures and wheel loading conditions.

Pavement performance is a broad term that tries to describe how changing usage and varying conditions effect changes in pavement conditions. Measures of performance such as the Pavement Serviceability Index (PSI), the Pavement Condition Index (PCI) or Pavement Quality Index are available for use. Modeling pavement management is an essential activity of a pavement management system. Currently, models are used in the pavement planning and budget development process, as well as in helping to determine pavement life cycle management (George, Rajagopal, and Lim 1989). This process provides a means to plan for both routine maintenance and full rehabilitation of current roads. Maintaining these roads in good order is essential to providing a safe and rapid means of ground transportation in order to support both the current and future economic needs of our communities. System Dynamics is a simulation modeling process that was developed by Jay Forrester while at MIT. The modeling process allows the modeler to capture both the structure of the system under study and the decision rules used by members of the system that affect the behavior of the system. The modeling process is based on the concept that real world systems are non-linear in nature and the results of actions taken feedback and effect the system necessitating new actions. The objective of this study will be to use the System Dynamics modeling process to: Determine if and how current pavement management practices contribute to problems that pavement managers deal with on a day to day basis. Develop a set of recommendations to improve those practices that are found to contribute to or create the problem. Provide a tool that pavement managers can use to test their own proposed changes to their management practices in the form of a simulated environment.

Pavement performance is a broad term that tries to describe how changing usage and varying conditions effect changes in pavement conditions. Measures of performance such as the Pavement Serviceability Index (PSI), the Pavement Condition Index (PCI) or Pavement Quality Index are available for use. Modeling pavement management is an essential activity of a pavement management system. Currently, models are used in the pavement planning and budget development process, as well as in helping to determine pavement life cycle management (George, Rajagopal, and Lim 1989). This process provides a means to plan for both routine maintenance and full rehabilitation of current roads. Maintaining these roads in good order is essential to providing a safe and rapid means of ground transportation in order to support both the current and future economic needs of our communities. System Dynamics is a simulation modeling process that was developed by Jay Forrester while at MIT. The modeling process allows the modeler to capture both the structure of the system under study and the decision rules used by members of the system that affect the behavior of the system. The modeling process is based on the concept that real world systems are non-linear in nature and the results of actions taken feedback and effect the system necessitating new actions. The objective of this study will be to use the System Dynamics modeling process to: Determine if and how current pavement management practices contribute to problems that pavement managers deal with on a day to day basis. Develop a set of recommendations to improve those practices that are found to contribute to or create the problem. Provide a tool that pavement managers can use to test their own proposed changes to their management practices in the form of a simulated environment.

This research developed a new methodology and new models for assessing the potential of motorcycle crashes and selecting countermeasures to improve motorcyclist safety in a motorcycle-dominated traffic environment of urban roads. The crash risk models were developed based on discrete choice models and traffic conflict techniques. The innovative features of this research are that the non-lane-based movements of motorcycles were captured to evaluate their contributions to crash risk and a new concept - that of the Conflict Modification Factor (CoMF) - was proposed to use as a surrogate measure to assess the relative contribution of risk factors to crashes. In addition, a methodology was also developed to enhance the existing International Road Assessment Programme (iRAP) star rating system for motorcyclists. The developed models were fitted and validated using data collected from urban roads in the city of Danang in Vietnam. The operating speed, speed difference, traffic density, front distance, longitudinal gap, lateral clearance and road surface condition were found to significantly contribute to motorcycle crash risk and several countermeasures have been consequently identified to improve motorcyclist safety including: installing changeable speed limit signs, installing changeable gap warning signs, installing changeable road surface condition warning signs and providing segregated motorcycle lanes.