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This study assesses the contribution of some selected stress absorbing membrane interlayers (SAMIs) on overlaid pavement performance in delaying the offset of reflective cracking using laboratory and full scale testing. Materials characterization were carried to have knowledge of the properties of the SAMIs and overlay and some of the properties were required as input for the finite element modelling. The characterization tests include the particle size distribution, penetration and softening point tests, dynamic mechanical analysis, indirect tensile stiffness modulus test (ITSM), indirect tensile fatigue test (ITFT) and repeated load axial test (RLAT). The interface bond was investigated using the Leutner shear test and pull off test. The assessment of the contribution of selected SAMIs on overlaid pavement performance in delaying offset of reflective cracking was carried out using a wheel tracking test supported by finite element modelling, a large scale pavement test facility test and a thermal cycling test. The Leutner shear test and pull-off test were used to examine the strength and stiffness of the overlay-SAMI interface. The interface strength/stiffness was determined because it is one of the factors that influence the crack resistance of SAMIs. The wheel tracking test was carried out to evaluate the effects of the thickness and stiffness of SAMI, thickness of overlay, SAMI composition, interface stiffness, load level and temperature on the performance of SAMIs under traffic loading. To study the performance of SAMIs under conditions close to the field, a large pavement test facility test was carried out. The finite element analysis of the wheel tracking test was carried out to evaluate the deflection, stress and strain distribution in a cracked pavement with and without SAMIs. The performance of SAMIs under thermal loading (temperature variation) was investigated using the thermal cycling test. The study shows that SAMI composition, SAMI thickness and stiffness, overlay thickness, interface stiffness, temperature and load levels influence the performance of SAMIs under traffic loading. It also demonstrates that the main factor that influences the performance of SAMIs under thermal loading is the interface stiffness. Design guidelines for the successful use of SAMIs against reflective cracking were prepared and the OLCRACK software was used to demonstrate the benefits of SAMIs in an overlay over a cracked pavement.

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 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.