A modern road pavement is a highly complex structure. Paving materials can exhibit non-linear and time dependent material properties whilst subjected to complicated three-dimensional loading conditions that are functions of the specific construction of each pavement. Nevertheless, empirical or linear elastic techniques, which cannot fully describe such factors, are often used in road engineering to assess pavement deterioration. An alternative approach is the use of finite element techniques, incorporating more complex constitutive models, to describe the response of asphalts and other paving materials. This thesis is concerned with the experimental determination of the model parameters necessary for the characterisation of two UK asphalt mixtures, for use in a dynamic plasticity based constitutive model to simulate paving material response. The constitutive model is under development at Delft University of Technology in the Netherlands, where it will be implemented in a three-dimensional finite element code. The thesis describes the constitutive framework for the material response model. It also details the experimental work and numerical verification undertaken in the study to enable the determination of the basic model parameters required to describe a 10 mm dense bitumen macadam and 30/10 hot rolled asphalt mixture, for use in the constitutive model. The characterisation of the mixtures has been undertaken through a series of quasi-static uniaxial compression and tension tests, which due to the significant influence of strain rate and temperature on the response of the asphaltic materials, were undertaken over a range of displacement rates and temperatures. Through specification of key model parameters as functions of material strength, temperature and strain rate, and the development of relationships describing the hardening and softening characteristic of the mixtures, the constitutive model has been successfully utilised to simulate the temperature and rate dependent stress-strain response of the asphalt mixtures to compressive loads.

Current available methods for the design of unpaved roads, with and without geosynthetics, were used for sixteen full-scale test sections which were constructed at the Bothkennar Soft Clay Site, Airth, Scotland. The full-scale trials consisted of twelve pavements including geosynthetics and four control pavements incorporating two types of aggregate and two design life expectancies. The test pavements were instrumented to monitor the transient stress and strain distribution, permanent strain distribution, geosynthetic temperature and ground water level during the trafficking operation. Traffic loading was provided in two stages by a standard road-going vehicle. The vehicle used for Phase One applied an 80kN axle load and in Phase Two a 126kN axle load. Failure of the pavements was defined as a rut depth of 150mm. The passage of 2115 axles resulted in failure of three sections and significant deformations in many others. Back-calculation to compare predicted and measured performance was performed and hence the existing design methods were critically assessed. Where possible the measurements obtained from field trials were used to examine the assumptions made within the design methods. The existing design methods were found to be essentially static in approach and did not model transient stresses and strains or permanent strain development adequately. Pointers towards a new approach ensuring strain compatibility between the elements of the system are suggested. This should enhance the ability of the engineer to assess the value of differing products used in this application.

Alternative materials represent an important potential source of aggregates for road construction. At present, their use remains limited owing to the abundance and low cost of high quality natural aggregates, low costs of landfill disposal and generally restrictive specifications for pavement materials. Nevertheless, their influence in relation to the primary aggregates is likely to increase in the future with the enforcement of more strict environmental regulations at national and European levels. The objective of this research project was to investigate a wide range of alternative materials and provide a practical framework for their assessment enabling pavement engineers to deal with most applications in road construction. Initially secondary materials were assessed according to the present UK specifications and were found to fail the requirements in most cases. However, the current approach does not assess fundamental properties such as stiffness, resistance to permanent deformation, tensile strength, resistance to fatigue and the development of these with time, leading to an inadequate assessment of these materials. To advance towards the development of performance-based specifications repeated load triaxial and indirect tensile tests were used. For their performance the Nottingham 150x300 mm triaxial apparatus was used and an indirect tensile apparatus developed which evolved from the Nottingham Asphalt Tester used for bituminous materials. In triaxial testing, models used to study the resilient behaviour of granular materials were found to give good results for unbound but not for lightly-treated secondary materials. For these, a new resilient model was developed. Testing and specimen preparation techniques together with performance classification systems were developed for both tests and recommendations for an overall methodology for the evaluation of secondary materials are presented. An application of this methodology was made to the study of thirteen mixtures to be considered for full-scale trials. The application of secondary materials in pavements was evaluated using analytical methods of pavement design which demonstrated the potential of these at levels in the pavement as high as the roadbase and the overall thickness reduction that may result.

In order to achieve the goals of 'Sustainable Development', alternative (secondary) materials are being increasingly used as bulk-fill aggregate within pavement construction as substitutes for traditional aggregates. This finds an end-use for stockpiles of industrial by-products (and hence the allowing the land on which they stand to be reclaimed for other uses) and protects finite, natural resources which they replace from over-extraction. Previously, there has been very little research concerned with the leaching of contaminants from alternative materials in pavement construction and the subsequent risks to water bodies from pavement drainage. It is this topic which is addressed here. Two flow regimes within a pavement have been studied in order to predict contaminant movement: (1) vertical flow through the aggregate and pavement and then vertically through the natural subgrade to ground water below and (2) horizontal flow through the aggregate to be discharged through pavement sides drains. Using these analyses a generic user-friendly risk assessment guide by which contractors may assess an aggregate prior to use is presented. A case-study is provided to illustrate some of the issues of concern. Guidelines in the risk assessment guide recommend the suitability of different physical parameters of a potential aggregate at a proposed pavement construction site for both water flow directions. If the subgrade at the site does not allow sorption by the soil to enable any contaminants in vertical flow to be below Water Quality Standards (WQS), the use of a geotextile clay liner to further increase sorption is recommended. If the concentrations of contaminants in water discharged from side drains is not below WQS for horizontal flow, guidelines determine whether the site rainfall and surface runoff allow sufficient dilution. In most situations alternative materials appear to be acceptable for use if pavement construction is on clay subgrades, with an exception of sites where the subgrades are shallower than those recommended or where they are close to areas of higher sensitivity, such as those in close proximity to protected groundwater.

The main aim of this research was to improve laboratory test methods for describing pavement foundation materials so that analytical design based on appropriate mechanical parameters of materials could be performed in practice. The study started by assessing the relevance of currently available methods to describe materials in pavement foundations and reviewing factors influencing the responses of these materials to repeated loading. Two simplified repeated load triaxial apparatuses of different sizes have been developed and their capabilities in characterizing materials in sub-base and sub grade layers have been examined. The large one is for specimens of size 280 mm diameter and 560 mm high and is suitable for full scale Department of Transport Type 1 sub-base granular materials. The small one is for cohesive soil specimens, either recompacted or undisturbed, with a diameter of 103 mm and height of 206 mm. Both apparatuses are equipped with simple loading mechanisms, user-friendly computer data acquisition systems and high precision on-sample, but easy to fix, instrumentation to monitor axial and radial displacements. A complete testing method necessitated the provision of the associated testing techniques. The whole test, including aggregate and soil preparation and testing, was designed to be conducted by one person. Development of the test procedures is detailed. Evaluation of the simplified repeated load apparatuses and the testing techniques involved testing 13 aggregate specimens and more than 26 soil specimens. Furthermore, comprehensive preliminary tests have been performed on the tested materials to provide background information which enabled results from the simplified repeated load triaxial apparatuses to be assessed in detail. For unbound granular materials, the tests included a series of particle examinations and shear box testing. For soils, besides classification tests, the soil suctions and the permanent deformation development under wheel loading were examined. To check the reliability of the two simplified facilities, tests were also carried out on pre-existing sophisticated repeated load triaxial apparatuses. Comparison of aggregate test results has enabled further understanding of the effects on resilient strain, permanent deformation and compressive strength of grading, density, shape, surface profile, surface friction and material type to be gained. Effects from waveform and frequency of load pulses were also discussed. For-soils, sufficient test results not only allowed different materials to be compared but also permitted models to describe resilient strain behaviour and permanent deformation development to be developed.

The maintenance of road pavements in England has become a costly necessity, due largely to the large volume of commercial vehicles using the roads which cause pavements to deteriorate quickly, and makes their repair more difficult to carry out. These roadworks incur not only direct works costs, but also indirect costs from factors such as congestion, motor accidents and pollution. There is obviously a need for cost-effective maintenance that minimises the occurrence and duration of these disruptions. To strengthen pavements bituminous overlays are often used, but may crack prematurely when placed over a layer with discontinuities such as cracks or joints, or deform excessively under wheel loading. The problem of 'reflective cracking' is widespread and reduces the life of maintenance treatments considerably. To increase the time before cracking appears on the surface of a pavement, a (more expensive) thicker overlay may be used, but this can lead to problems with property thresholds and bridge clearance. One possible option of reducing the thickness of overlays by making them more resistant against cracking and deformation, is to place a layer-of reinforcement within or at the bottom of the overlay. Although this approach has been used occasionally to reinforce overlays, over 40 years or so, it is not favoured with many road authorities, as the results of these treatments are difficult to anticipate, and may not be cost effective. This thesis describes an investigation into the effect of reinforcing thin bituminous overlays to identify key factors that significantly influence their performance. By identifying these factors, optimum use of reinforced asphalt should be possible, and thus maintenance of the road network made more cost effective. The investigation was principally carried out in the laboratory using beam tests, shear box tests, tensile tests on reinforcement and large-scale wheel tracking tests. 2-D Finite Element Analysis was used in the analysis of test results. Results show that properly constructed reinforced overlays can be between two or three times more resistant to cracking, and have less than half the permanent deformation of unreinforced materials.

At the present time (1978) new roads in the United Kingdom are designed empirically. However, over approximately the last twenty years pavement technologists throughout the world have been advocating fundamentally based procedures. Such procedures, when applied to flexible pavements, require a detailed knowledge of the two main modes of failure, fatigue of the bituminous bound layers and excessive permanent deformation of the pavement as a whole. The research described herein was aimed at improving knowledge of the permanent deformation behaviour of flexible pavements, and at developing a technique for predicting this deformation which could be incorporated in a fundamental design procedure. Three laboratory experimental pavements were trafficked with a rolling wheel facility under conditions of constant temperature, load and speed, and the resulting deformations were monitored. These deformations were compared with predictions using models developed from the results of repeated load characterisation tests on the pavement materials and utilising a digital computer. A review of previous work is presented ill two parts, the first considering the resilient and permanent deformation response of pavement materials, the second considering proposals for the prediction of permanent deformation in pavements. The development of the wheel loading facility, and the construction, instrumentation and measurements from the pavements are described briefly. More attention is given to the theoretical approach, materials characterisation testing and the prediction of resilient and permanent deformation response of the pavements. The prediction techniques and their accuracy are assessed, the problems involved in the development of such procedures are discussed, and the conclusions which can be drawn from the work are presented. A number of suggestions regarding further work in this field are made. Finally, an Appendix considers an alternative to the method of modelling permanent deformation presented in the main part of the text.

Bitumen emulsion mixtures, or cold mix, offers certain advantages over hot bituminous road mixtures in terms of potential cost savings, environmental factors, energy savings and easing of logistical difficulties inherent with hot mix. For these reasons, they are currently used in a number of regions including the United States of America, Continental Europe, Scandinavia, Southern Africa and Australia. However, cold mix has not been seriously evaluated or utilized in the UK until comparatively recently. This is due to the slow rate at which it builds strength or cures and its susceptibility to rainfall, particularly during this curing period. The overall aim of this research was, therefore, to study the behaviour of cold mix in terms of mechanical properties and the mechanisms involved in emulsion breaking and mixture curing to gain an insight into how performance may be improved. Mechanical properties were shown to be affected by a number of parameters, including binder grade, void content, curing time and additives such as cement. Fatigue tests showed that without cement, the performance in-situ of cold mix would be very poor. Pavement design calculations revealed that, with cement, emulsion mixtures could be expected to perform similarly to equivalent hot mix. Field trials have indicated that cold mix can be manufactured using conventional hot mix plant and laid using similar techniques. However, problems are still to be overcome in terms of the control of mixture composition and laying in adverse weather conditions. Fundamental tests have shown that emulsion droplet coalescence (which is an essential part of the curing process) was affected by pressure, bitumen type, emulsifier level, cement and temperature and that cement can cause emulsion charges to become more positive (or less negative) but other parameters had no effect on charge. It was also proved that cement can cause bitumen emulsion to set completely and that the residual binder has an increased viscosity compared with unmodified binder. This was shown to be due to the formation of a composite bitumen cement binder.

The shakedown concept has been widely applied in structural and mechanical engineering numerical models. The concept is related to the response of a structure to load repetitions in a resilient manner without further permanent deformation. More than 40 wheel tracking tests were conducted with various wheel load levels for each test to check the validity of the shakedown concept in the pavement foundation. Six different types of soils with different characteristics were used in the wheel tracking tests. These were a silt (from gravel pit washings), a silty-clay (Mercia Mudstone, referred to here by its earlier name of Keuper Marl), two sands (Portaway and Langford Fill), and two crushed rocks (Carboniferous Limestone and Granite). Three different sized wheel-tracking facilities were used; a small wheel tracker (SW), a larger Slab Testing Facility (STF) and the half-scale Nottingham Pavement Testing Facility (PTF). These allowed various wheel specifications and test specimen sizes to be investigated. The test programme embraced one, two and three layered systems. The permanent vertical deformation of each system was measured after a certain number of passes. The soil is said to be under shakedown if after a certain number of passes, there is no further permanent deformation. The experimental result was compared with the theoretical shakedown prediction. A series of static triaxial tests for each soil, with the test conditions close to the wheel tracking tests, was carried out to identify the shear strength to be used as input parameters for the theoretical shakedown prediction. The theoretical shakedown limits of the various soil combinations show a good agreement with the wheel tracking test results.

This dissertation is concerned with the fatigue cracking of bituminous paving mixtures. It considers both the life to crack initiation and the life for crack propagation, including the development of a method for calculating the number of wheel load applications to either critical or failure condition. The development and subsequent validation of the Indirect Tensile Fatigue Test (ITFT) are described. Both the repeatability and reproducibility of the method are examined as well as its correlation with two other fatigue test methods. The test is shown to be a suitable method for measuring the life to crack initiation of bituminous paving mixtures as well as being an economically viable test. Poisson's ratio for bituminous paving mixtures is examined showing that, provided at least 500 conditioning pulses are used in order to achieve steady state conditions, 0.35 is an appropriate value. Prior to these early load applications Poisson's ratio is shown to be variable and often in excess of 0.50, an explanation of which is given in detail. Crack propagation was experimentally simulated using beams of material with a crack initiated on the underside. The work shows that the rate of crack propagation can be described by a power relationship between the stiffness of the mixture and the number of cycles to failure, which is mixture and binder dependent. A general equation is developed which allows the critical and failure lives of bituminous pavements to be calculated and these are compared to two traditional pavement design methods, giving equivalent results for unmodified mixtures but, giving more realistic results for polymer modified mixtures. Image analysis of the cracks demonstrates that they propagate around coarse aggregate trying to separate it from the matrix and that they travel in the straightest line possible between the point of crack initiation and the point of applied load.