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Eco-friendliness, energy efficiency and cost effectiveness are major drivers responsible for cold recycled asphalt mixtures being considered as alternatives to hot mixtures. Although such mixtures are still regarded in some quarters as second class asphalt, results from field trials on such materials under temperate climates have been reported to be highly impressive and encouraging. Some developed countries with temperate climates have since developed guidelines for the production and use of cold mixtures in road building. However, evidence from the literature shows that little or nothing has been done to ascertain the performance and suitability of such sustainable materials in developing countries located in hot tropical climates. Ascertaining the performances of such will, among other things enable the formulation of guidelines required for producing and using these alternative sustainable materials and methods in developing countries with hot tropical climates, where available funds for road building are increasingly inadequate to meet demand. The work reported in this thesis attempts to simulate what should be expected in terms of the performance of flexible pavements containing cold mixes of bitumen emulsion stabilized RAP as road base in hot climates. Cold recycling in-plant was deemed appropriate for the obvious reason that it enables control of the quality of mixtures produced. The challenge of sourcing severely aged RAPs required for this study afforded the opportunity of developing a laboratory ageing protocol for producing RAPs with controlled properties, typical of those found in hot tropical belts (with residual binders of very low penetration). The result of the physico-chemical and rheological studies showed that ageing hot mix asphalt at 125⁰C does not degrade the binder when compared to that aged at 85⁰C, which is the conventional protocol (for temperate climates). A target mix design based on Overseas Road Notes (ORN) 19 and 31 for 20mm DBM, which the literature suggests is suitable for road base layers of road pavements, yielded an aggregate gradation containing RAP (with residual bitumen of 20dmm penetration), 5mm granite dust and granite mineral filler in the proportion 65:30:5 respectively. Further investigations patterned after Marshall and Hveem mix design methods, indicated that a cationic bitumen emulsion content of 6.5% and pre-wetting water content of 1.5% were suitable. Unlike hot mixtures, cold mixtures due to their peculiarity i.e. intermediate nature (close to unbound granular materials in early life and close to fully bound materials when fully cured), require curing before being assessed for mechanical properties such as stiffness, strength etc. Performances of the five cold bituminous emulsions mixtures (CBEMs), one with 100% virgin aggregate, the others including RAP with binder penetrations 5, 10, 15 and 20dmm, manufactured at 20⁰C and 32⁰C (to reflect average minimum and maximum temperatures in hot tropical climates) showed that: • Properties of CBEM are dependent on the state of curing or maturation attained i.e. early life, intermediate life and fully cured or stable condition; • High air void content in CBEMs appears to be inevitable; • Mixing and compaction temperature is very important for achieving relatively low air void contents in CBEMs. For example, mixing and compacting CBEMs at 32⁰C gave better results than at 20⁰C; • Indirect Tensile Stiffness Modulus is useful for quickly ranking the CBEMs; • The RAP CBEMs performed better than the virgin aggregate CBEM in terms of water susceptibility; • An increase in stiffness modulus up the range from 10dmmCBEM to 15dmmCBEM and to 20dmmCBEM, with higher values than the virgin aggregate CBEM as observed in this work gives the impression that the residual binder in the studied RAPs is active as a result of possible softening or rejuvenation. Alternatively, the stiffness enhancements could possibly have been caused by the alteration of the volumetrics of such RAP CBEMs which consequently enhanced their compactability; • Overall, RAP CBEMs are better than virgin aggregate CBEM in mechanical performance and durability; • Fatigue lives of the CBEMs are generally lower than those for hot mix asphalt (HMA); • The CBEMs are stress-dependent as they all fitted the k-Θ model. The results of the analytical pavement design showed the importance of using tools such as KENLAYER which account for the non linearity of CBEMs. Although the structural design was a hypothetical case, the results confirmed that the virgin aggregate CBEM was inferior in terms of axle loads to failure compared to the RAP CBEMs, and the RAP CBEMs were inferior to HMA. The findings of this limited investigation suggest that the studied RAP CBEMs are suitable for low volume traffic roads, an indication of the great potential of these sustainable materials when properly harnessed. In the light of this, a short and concise set of guidelines for mix design of RAP CBEMs and structural design of pavements containing such non linear materials was proposed in the thesis.

This thesis is concerned with producing a simple method to design low volume roads (LVR) by means of a rationale which accounts for permanent deformation development in granular layers. Rutting is regarded as the main distress mode in unsealed and thinly sealed pavements. Hence, it is desirable that it be analytically approached rather than empirically, as in most design methods. The overall aim of this PhD thesis was to look into the behaviour of in-service roads and from a newly developed process, to advance, in a systematic manner, the elements required to produce a simple mechanistic design procedure. The study took as its basis an assessment of the proximity of the stress distribution in the pavement to the material’s failure envelope. After a literature review on unbound granular materials mechanical behaviour and on low volume roads pavement design methods, Chapters 4 and 5 discuss full scale trials carried out in Scotland on typical forest roads. The overall goal of the trials carried out within the Roads Under Timber Transport project was to establish the effect of weather and seasonal effects on the rutting of forest roads and to improve their performance while enabling the roads to be economically constructed and maintained. It appears that most of the rutting occurring in the sites surveyed came shortly after their construction/resurfacing, leading to the assumption that workmanship may be a highly important variable. Lack of compaction of the layer could be one of the likely reasons for the high initial rutting rates. Establishing the effect of weather on rutting further to the existing knowledge was, however, difficult to achieve; this was mainly due to the difficulties faced in monitoring traffic conditions. A newly developed method was needed to quantify permanent deformation development due to wandering traffic on a non-level pavement; this was achieved by the use of wheel path areas, and seemed to be a way forward in the analysis of rutting in unsealed roads. Accelerated pavement trials are reported that aimed to evaluate the performance of aggregate under soaked conditions and the relative pavement deformation caused by different timber haulage vehicles. A road segment simulating a standard forest road section was constructed in a purpose-built facility located at the Ringour Quarry facility. Ten different trials were carried out combining three different aggregate materials and five types of vehicles. Tyre fitment, axle configuration and tyre pressure were assessed and demonstrated to play an important role on the study of rutting development. Conclusions drawn from the results suggest that management of the tyre inflation pressure and axle overload may be one of the most economic means of managing pavement deterioration in the forest road network. A mechanistic analysis of a variety of unsealed pavements was carried out in Chapter 6; and the newly proposed methodology is described in Chapter 7. With changing loading conditions – e.g. as a consequence of the introduction of Tyre Pressure Control Systems and super single tyres – more detailed analyses are required, so that their effect can be analytically assessed. Then an analytical method is introduced for evaluating the stress-strain condition in thinly surfaced or unsurfaced pavements as typically used in LVR structures. It aims to improve the understanding of the effect of tyre pressure and contact area in regard to permanent deformation. To achieve this, several scenarios were modelled using Kenlayer software varying aggregate material, thickness, stiffness, tyre pressure & arrangement. The results usually show a fairly well defined locus of maximum stresses. By comparing this stress envelope with failure envelope, conclusions could be established about the more damaging effect of super singles over twin tyres and, likewise, the greater damage inflicted by high tyre pressures compared to that incurred by lower tyre pressures. Finally, the framework of the proposed method contributes to LVR pavement design procedures mainly due to its simplicity. It still treats the pavement analytically, permitting a more fundamental description of the behaviour of granular layers than in simple linear elastic analysis, but by simplifying the elasto-plastic analysis for routine use it thereby reduces demands of material characterization and computational skills, thus increasing its utility in practical application.

A significant growth has been shown in recycling of the old asphalt pavement as a technically and environmentally preferred way of rehabilitating the existing pavements during the three decades. However, savings acquired by using this technology may be lost through excessive maintenance processes if the recycled pavement exhibits too much deterioration. The current design methods for recycled HMA hypothesize a state of complete blending between the recycling agent and RAP binder. In practice, the complete blending does not occur as the recycling agent does not penetrate the whole layer of the aged binder around RAP particles (Carpenter and Wolosick, 1980). As a result of this, the resultant binder within the recycled mix differs from the desired binder, leading to dissimilarity in properties of the recycled and virgin mixes. Consequently, if the recycled mix was subjected to ageing and recycling for second time, the respond of its resultant binder will not the same as if it was the desire binder. This in turn may make the performance of recycled mix of second cycle differs from that of first cycle. Therefore studying the effect of repeated recycling on performance of the recycled HMA was the aim of this research. First, three types of RAP (reclaimed asphalt pavement) were manufactured in the laboratory and were utilized to produce three types of recycled HMA. After testing the recycled mixes, they were aged again to the same ageing time and temperature, then were crushed to be used as RAP for next generation of recycling. This process was repeated three times. Bitumen 40/60 pen and 70/100 pen were used for the virgin and recycled mixes respectively. All virgin and recycled mixes were designed to have identical aggregate grading, bitumen content, air voids, and binder viscosity. Stiffness and fatigue characteristics were measured after each cycle by the Indirect Tensile Stiffness Modulus test (ITSM) and Indirect Tensile Fatigue Test (ITFT). The results showed that, in spite of, presence deterioration in stiffness or fatigue resistance after the first cycle, the repeated recycling had no further significant effect on deterioration of these properties. Because there was considerable degradation in performance of recycled mixes after the first cycle, certain factors that were believed to improve the efficiency of mixing of these types of mixtures were investigated. These factors included size of RAP agglomeration, mixing temperature, dry mixing time between superheated aggregate and RAP, warming of RAP, and mixing mechanism. The results showed the importance of all factors in improving the mechanical properties of recycled mixes. However, the most influential factors were mixing temperature and warming of RAP. Durability of recycled mixes to resist moisture damage was assessed by the water sensitivity test. The results demonstrated that the recycled mixes were not susceptible to moisture damage and can resist the harmful action of water better than the virgin mix. An interesting element in this research was the possibility of using the Hirsch model to estimate the rheological properties of effective binder within recycled mixes without applying recovery process.

The aim of this thesis is to provide a framework for a decision making system to operate a highway network, to evaluate the impacts of maintenance activities, and to allocate limited budgets and resources in the highway network. This integrated model is composed of a network level traffic flow model (NTFM), a pavement deterioration model, and an optimisation framework. NTFM is applicable for both motorway and urban road networks. It forecasts the traffic flow rates during the day, queue propagation at junctions, and travel delays throughout the network. It uses sub-models associated with different road and junction types which typically comprise the highway. To cope with the two-way traffic flow in the network, an iterative algorithm is utilised to generate the evolution of dependent traffic flows and queues. By introducing a reduced flow rate on links of the network, the effects of strategies employed to carry out roadworks can be mimicked. In addition, a traffic rerouting strategy is proposed to model the driver behaviour, i.e. adjusting original journey plans to reduce journey time when traffic congestion occurs in the road network. A pavement age gain model was chosen as the pavement deterioration model, which is used to evaluate the current pavement condition and predict the rate of pavement deterioration during the planning period. It deploys pavement age gain as the pavement improvement indicator which is simple and easy to apply. Moreover, the deterministic pavement age gain model can be transformed to a probabilistic one, using the normal distribution to describe the stochastic nature of pavement deterioration. A multi-objective and multi-constraint optimisation model was constructed to achieve the best pavement maintenance and rehabilitation (M&R) strategy at the network level. The improved non-dominated sorting genetic algorithm (NSGA-II) is applied to perform system optimisation. Furthermore, the traffic operations on worksites, i.e. lane closure options, start time of the maintenance, and traffic controls, are investigated so as to prevent, or at least to reduce, the congestion that resulted from maintenance and reconstruction works. The case studies indicated that NTFM is capable of identifying the relationship between traffic flows in the network and capturing traffic phenomenon such as queue dynamics. The maintenance cost is reduced significantly using the developed optimisation framework. Also, the cost to the road users is minimised by varying the worksite arrangements. Consequently, the integrated decision making system provides highways agencies with the capability to better manage traffic and pavements in a highway network.

Renewable energy combined with energy efficiency can offer a viable and influential solution to minimise the harmful consequences of both fossil fuel depletion and increases in the cost of power generation. However, in most cases renewable energy technologies require high initial investments that may deter potential users. Pavement Energy Systems (PES) potentially offer a low-cost solution to sustainable and clean energy generation by utilising the thermo-physical properties and design features of new/existing pavement infrastructure. Within the PES, fluid-filled pipes are buried in the pavement at varying depths and transfer heat to and from the surrounding material, for application as a solar energy collector and/or thermal storage media. The fluid in the pipes can absorb/reject heat to the pavement and deliver useful energy to nearby buildings as well as benefiting the pavement structure and pavement users (in terms of reduced rutting, winter road maintenance, etc.). A significant advantage of such systems is that the pipes can be installed within pavements that are already needed for structural reasons and need not to be installed as single-function elements, as do conventional thermal utilisation systems. In this project, the effect of pavement materials and layer design optimisations on the performance of PES was investigated both theoretically and experimentally. The thermo-physical properties and load-bearing performance of concrete and asphalt pavements, consisting of conventional and unconventional components, were determined. In addition, pseudo 3D transient explicit finite-difference software was developed for modelling and performance analysis of the PES under various operating conditions and configurations. This software is capable of predicting the outlet fluid temperature and temperature distributions within the pavement structure. Furthermore, large-scale physical models of the PES were designed and constructed to compare the performance of the thermally modified pavement structures with those of conventional ones and also to validate the model. The physical model consisted of copper pipes embedded in pavements which were irradiated (causing surface heating) using halogen lamps. The results of thermo-physical optimisation of pavement materials, coupled with mechanical testing, showed that it was possible to achieve a wide range of thermally-modified pavements that can also meet the rigorous functional requirements of an airfield pavement. The experimental comparison between the thermally modified and unmodified concrete pavements revealed that there was potential to enhance both the heat collection and storage capability of concrete pavement structures. In addition, the model’s predicted temperatures in concrete pavements were in good agreement with the experimental ones with a mean error of less than 1°C. A similar comparison on asphalt pavements showed that although the surface temperature was lowered by asphalt modification, there were significant discrepancies between the measured and predicted surface temperatures for both modified and unmodified pavements. Further study was conducted on the pipe/pavement interface using X-Ray Computed Tomography (XRCT). The X-ray images revealed improper bonding between the pavement’s matrix and the pipe that was evidenced by the presence of air voids accumulation around the pipe perimeter, and could explain the significant discrepancy in the modelled temperatures. Furthermore, the validated model was used, for genuine temperature patterns, to simulate the relative influence of both the thermo-physical properties of pavement materials and the pavement layer sequences on the performance of the PES and to determine the implications for pavement design. It was concluded that the enhancements could allow pipes tobe installed deeper within the pavement without having any negative effect on their thermal performances. Pipe installation deeper in the pavement is expected to reduce ‘reflective cracking' under traffic loading as well as enabling future resurfacing of the pavement without damaging the pipe network.

Many of the proposed rational design methods for flexible pavements are concerned with the stresses and strains which occur in the various layers of the structure. The purpose of the work reported is to investigate, in the laboratory, the complete stress and strain distributions set up in the different layers under dynamic loads. Two systems have been investigated, a single layer of clay and a two layer system consisting of a granular base on a clay subgrade. The loading in each case consisted of a single pulse having a duration of loading between 0.1 and 2 sec. The load was uniformly distributed over a circular area and of varying magnitude. In-situ measurements of stress and strain were made using pressure and strain cells, -, at various orientations. Surface deflection was measured with a rectilinear potentiometer. Stress and strain distributions were determined by moving the load relative to the buried transducers. By superimposing results, values of principal stresses and strains and maximum shear were derived. By combining stress and strain measurements, values of in-situ elastic modulus and Poisson's ratio were calculated. Results were compared with elastic theory, both Boussinesq and layered system, the latter being computed using a recently developed program. Stresses showed good agreement with theory in both systems, but strains, being dependent on modulus, were less easy to predict theoretically. In-situ values of modulus were stress dependent for both materials. For the clay, at low stress levels, the modulus increased sharply with decreasing stress, while for the granular material modulus increased with stress level. In the two layer system results compared less favourably with theory, but the important values of tensile horizontal stress above the interface and vertical strain below the interface appear to be predicted adequately. The values of modular ratio were near to unity and hence Boussinesq theory was equally as adequate as the layered system approach for most effects. Strains were predicted with fair accuracy when local values of modulus were used i.e., those in the neighbourhood of the points concerned. The assumption of perfect roughness at the interface, used in most theoretical solutions, was shown to be valid. The stress dependence of modulus is thought to be one of the main problems at present in the application of layered system theory and, for the calculation of strains, in the use of the Boussinesq approach also.

Skid resistance, the road surface’s contribution to friction, is a crucial property of a road surface course required to maintain a safe and serviceable road network. Measurement of skid resistance is restricted by the need to measure the forces acting on a rubber wheel or slider while it is dragged across the surface. If the skid resistance of the road could be determined without the need for contact then measurement could be cheaper and more thorough. One route to achieving this goal is by measurement of the texture of the road that generates the friction experienced by a sliding tyre. However, the form and scale of the texture required is not well defined. The work presented in this thesis attempts to establish a robust methodology for measurement of texture on the surfaces of aggregate particles (the main constituent of the road surface course) so that it can be compared with friction. The stages of development are described in detail and the methodology is employed to examine the changing texture on two types of aggregate. The mechanisms by which these aggregates polish, methods for characterising their surface texture, and the consequences for the friction they are able to generate are explored.

Pavements represent an important infrastructure to all countries. In Saudi Arabia, huge investments have been made in constructing a large network. This network requires great care through conducting periodic evaluation and timely maintenance to keep the network operating under acceptable level of service. Pavement distress prediction and pavement condition prediction models can greatly enhance the capabilities of a pavement management system. These models allow pavement authorities to predict the deterioration of the pavements and consequently determine the maintenance needs and activities, predicting the timing of maintenance or rehabilitation, and estimating the long range funding requirements for preserving the performance of the network. In this study, historical data of pavement distress and pavement condition on the main and secondary road network of Riyadh, Saudi Arabia were collected. These data were categorized, processed, and analyzed. These data have been employed to generate prediction of pavement distress and condition models for the Saudi Arabia Urban Road Network (SAURN). Throughout the study, the most common types of pavement distress on SAURN have been identified. The behavior of these distress types has been investigated. A sigmoid function was found to be an excellent representation of the data. Seven for urban main pavement distress models (UMPDM) have been developed. In addition, six urban secondary pavement distress models (USPDM) have been developed. Moreover, two pavement condition models have also been developed, one for urban main pavement condition (UMPCM), and the other for urban secondary pavement condition (USPCM). The developed models provide a reasonable prediction of pavement condition. The models were assessed by standard error and residual analysis. A suitable procedure for the implementation of the models has also been proposed.