Unbound Granular Base Research Articles

Can rubberized-asphalt comprising tire-derived aggregates produced through dry process be an alternative subsurface road material?

The major objective of this study was to investigate the suitability of utilizing tire-derived aggregates (TDA) at varying contents for the design of rubberized-asphalt base / subsurface layers through the dry process, along with (i) understanding the cracking potential and mechanical stress-strain response of the different materials under cyclic and confining stresses through triaxial resilient modulus (MR), dynamic modulus |E*|, and static semi-circular bend test, and (ii) assessing bonding strength of TDA with binder-aggregate matrix through moisture susceptibility test. The scope encompassed preparation of ten base course mixtures: one unbound granular base (UGB), three cement treated base (CTB), two asphalt treated base (ATB), and four rubberized-asphalt treated base (RATB) and obtaining mechanical performance at varying temperature-frequency combinations totaling 2636 data points. Triaxial MR tests indicated that CTB mix displayed highest modulus followed by ATB and RATB mixes, which was then followed by the UGB mix mainly ascribed to cement / asphalt treatment of the unmodified control subsurface material. Further, a finite element modeling study helped optimize the confinement levels to obtain realistic |E*| of ATB and RATB mixes. |E*| test results depicted that RATB mixtures would be rut-resistant at higher temperatures as they performed similar to the ATB mixes as well as crack-resistant at low to intermediate temperatures with significantly lower |E*| than ATB mixes, attributed to slower rate of change of viscosity with changing temperature in conjunction with enduring viscoelastic property (1.5–3 times higher phase angle than ATB) ascribed to high asphalt binder content and resilient nature of the rubber particles. Albeit the fracture toughness of ATB was twice higher than RATB, the latter had higher fracture energies, mainly due to the resiliency rendered by the rubber inclusions in concert with the extra viscous effect provided by the rubber-asphalt binder conglomerate. Based on the performance-based ranking, RATB mixes performed better than control mixes, and thus were adjudged as the most suitable alternative subsurface / base course materials in a pavement system. It is envisioned that this research will advance the current understanding of utilizing TDA in asphalt base / subbase courses using the dry process, and further assist in judging the viability of using rubberized-asphalt as potential sustainable alternatives to conventional systems to develop futuristic resilient pavement infrastructures with a strong emphasis on recycling of end-of-life tires, conservation of materials, and circular economy.

Parametric analysis and field validations of oxidative ageing in asphalt pavements using multiphysics modelling approaches

ABSTRACT Oxidative ageing in field asphalt pavements is a complex process with coupled multiple physics. This parametric study uses Multiphysics modelling approaches to evaluate the effects of material thermal properties, air voids content and distribution, mastic coating thickness, oxygen accessibility and binder oxidative kinetics on the spatial and temporal evolution of the oxidative ageing in the asphalt pavements. Results suggest that increasing the thermal conductivity of asphalt layers leads to a lower ageing gradient. The variations of base and subgrade layers’ thermal properties cause little to no effects on the oxidative ageing. A high activation energy of the asphalt binder (e.g. by adding anti-ageing additives) reduces the oxidative ageing significantly. Asphalt layers built on unbound granular base will experience greater overall ageing with a C-shaped ageing gradient compared to that built on treated base. Air voids content of <5% yields limited oxidative ageing. Five to nine percent air voids generate a gradually increased oxidative ageing with an obvious gradient across pavement depth. Air voids content beyond 9% leads to a consistently high oxidative ageing due to a full access to the oxygen. Finally, the findings were validated using available literature results and field data from 14 European road sections.

Pavement Quality Index Rating Strategy Using Fracture Energy Analysis for Implementing Smart Road Infrastructure.

Developing a responsive pavement-management infrastructure system is of paramount importance, accentuated by the quest for sustainability through adoption of the Road Traffic Management System. Technological advances have been witnessed in developed countries concerning the development of smart, sustainable transportation infrastructure. However, the same cannot be said of developing countries. In this study, the development of a pavement management system at network level was examined to contribute towards a framework for evaluating a Pavement Quality Index and service life capacity. Environmental surface response models in the form of temperature and moisture variations within the pavement were applied, using sensor devices connected to a data cloud system to carry out mathematical analysis using a distinctive mesh analysis deformation model. The results indicated variation in the Resilient Modulus of the pavement, with increasing moisture content. Increase in moisture propagation increased saturation of the unbound granular base which reduced the elastic modulus of the sub-base and base layer and reduced the strength of the pavement, resulting in bottom-up cracks and cracking failure. The horizontal deformation reduced, indicating that the material was experiencing work hardening and further stress would not result in significant damage. Increasing temperature gradient resulted in reduced stiffness of the asphalt layer. In tropical regions, this can result in rutting failure which, over time, results in top-down cracks and potholes, coupled with increasing moisture content.

The hydro-mechanical interaction in novel polyurethane-bound pervious pavement by considering the saturation states in unbound granular base course

ABSTRACT The pore-water pressure generated by intermittent dynamic vehicle loading under various saturation states is recognized as a critical factor influencing the behaviour of permeable pavement structures, especially the behaviour of UGB layer. However, the underlying mechanisms of hydro-mechanical interaction in the UGB layer and the influence on the pavement structure are still unclear. This study aims to characterize the changes in dynamic response in permeable pavement structures under various saturation conditions by considering the hydro-mechanical interaction within the UGB layer. To achieve this objective, a full-scale test track with a PUPM wearing course was constructed. Pressures and water distribution were characterized by embedded sensors within different layers of the test track when subjected to the accelerating pavement test. Based on the coupled SAME model, the water distribution and the dynamic response of UGB in the rainfall events were both characterised and solved by FEM. The results predicted by the proposed SAME model correspond to the field measurements, and the influence of the water content on the resilient modulus distribution within the UGB layer was then estimated. Based on the predictions for the stress state of the UGB layer, the sensitivity analysis was also proposed.

Laboratory Investigation of Critical Factors Affecting Geogrid Reinforcement on Aggregate Base Using Loaded Wheel Tester

AbstractA modified loaded wheel tester, asphalt pavement analyzer (APA), was employed to evaluate the reinforcement effect of geogrids on unbound granular base course materials by applying simulate...

Cyclic load triaxial test procedures for soils in transportation engineering

Unbound granular base course is built in pavement structures between subgrade and bound base course. Its main function is bearing capacity - load transfer from upper layers to subgrade. For its successful design, one of the required parameters is resilient modulus. Resilient modulus describes behaviour of unbounded materials at various load conditions, and is defined as the ratio of the applied cyclic stress to the elastic strain. It can be determined with cyclic triaxial test that gives good simulation of stresses and strains which are result of traffic loads. In this paper resilient modulus testing procedure will be described with the emphasis on European Standard (EN 13286-7). Furthermore, it will be given comparison of European standard with other test procedures.

Quantifying the effects of geogrid reinforcement in unbound granular base

This study presents an effort to quantify the effects of geogrid reinforcement in the unbound granular base through laboratory testing. Two laboratory tests, the large-scale cyclic shear test and the repeated load triaxial test, were employed. The test protocol of the cyclic shear test was developed by modifying that for the triaxial test. The cyclic shear test was performed by applying a series of cyclic shear stresses to the geogrid-aggregate interface under different normal stresses. Two different types of geogrids were used as reinforcement in unbound granular material. Resilient modulus (MR) from the repeated load triaxial test and a term named resilient interface shear modulus (Gi) from the cyclic shear test was used to characterize the effects of geogrid reinforcement in unbound granular base, respectively. The results of triaxial tests showed that the inclusion of geogrid had a negligible effect on the resilient modulus, indicating that the triaxial resilient modulus test may not be effective in evaluating the geogrid reinforcement in unbound granular materials. Compared to the triaxial resilient modulus test, the cyclic shear test showed great potential in identifying the effects of geogrid reinforcement, with an obvious improvement in the degree of interlocking between geogrids and aggregates.

Modeling Stress-Dependent Anisotropic Elastoplastic Unbound Granular Base in Flexible Pavements

Unbound granular base (UGB) has a cross-anisotropic and nonlinear (stress-dependent) modulus with a plastic behavior. Existing UGB models address nonlinear cross-anisotropy and plasticity separately. It is unknown how the two characteristics are coupled into a finite element model (FEM) and how this will affect the pavement responses. This study presents a coupled nonlinear cross-anisotropic elastoplastic (NAEP) constitutive model for the UGB and implements it in a weak form equation-based FEM. No material subroutine is needed to address the circular dependence between the stress-dependent anisotropic modulus, structural stress responses, and elastoplastic deformation. The NAEP model was calibrated by triaxial resilient modulus and strength tests and validated using laboratory measurements in a large-scale soil-tank pavement structural test. It is found that the NAEP model is valid and effective in predicting the UGB responses in flexible pavements. The model predicted less horizontal tensile stresses at the base bottom and introduced compressive stresses in the middle and top of the base course. This is caused by an increasing confinement resulting from a horizontal plastic dilation in the base course, which cannot be modeled without considering plasticity. The stress-dependent modulus for the UGB material decreases with depth and the distance from loading centerline. Compared with a nonlinear anisotropic elastic model, the NAEP model predicted the same tensile strain at asphalt layer bottom, a higher base modulus, and a higher subgrade compressive strain. Thus, the nonlinear anisotropic elastic UGB model results in the same fatigue life as the NAEP model but may riskily under-predict rutting damage.

Vibratory Compaction of Base Course Aggregates

The focus of this paper is on laboratory compaction of unbound granular base course material for road pavement construction. The primary variables evaluated in this research were particle size distribution and dry density. This research addresses the applicability of current laboratory compaction techniques and outlines the changes needed to minimize the gap between laboratory and field compaction. The target density achieved in laboratory studies with the New Zealand standard test methodology, which is then used to target field compaction levels, is often too high to realistically achieve in the field. It was found that there is a ratio of maximum aggregate average least dimension (ALD) to specimen diameter and specimen height that must be adhered to when using laboratory testing as a means to evaluate, design, or construct pavement base course layers. In addition, the power input of laboratory vibratory hammers used for compaction must be controlled to minimize aggregate degradation, especially for test molds that do not satisfy the minimum diameter to ALD ratio. The ultimate goal of laboratory compaction should be to accurately simulate field compaction and provide realistic targets that can be achieved in the field. If unrealistic field compaction density targets are specified, then overcompaction can occur and cause aggregate breakdown. The research concluded that changes are required for test standards to better reflect field conditions, such as less lateral constraint, and better reflect achievable target field densities.

Geotechnical Aspects of Pavements: There’s More to Roads than Asphalt and Concrete!

When you jump on the highway to make that commute to work, do you think much about what's under the surface you ride on? Pavements are layered systems designed to provide a strong structure to support applied traffic loads (structural capacity), a smooth wearing surface (ride quality), and a skid-resistant wearing surface (safety). The system also must have sufficient durability so that it does not deteriorate prematurely due to environmental influences. Satisfactory pavement performance depends on the proper design and functioning of all components. The wearing surface provides sufficient smoothness, friction resistance, and sealing or drainage of surface water. The bound structural layers (i.e., asphalt or Portland cement concrete [PCC]) provide part of the load-carrying capacity, as well as barriers to water intrusion into the underlying unbound materials. The unbound granular base and subbase layers, complemented by features such as drainage systems, provide the remaining structural capacity.

Influence of Unbound Material Type and Input Level on Pavement Performance Using Mechanistic–Empirical Pavement Design Guide

For material characterization, the Mechanistic–Empirical Pavement Design Guide (MEPDG) has three input levels. Level 1 input values must be obtained through direct laboratory testing. Level 2 inputs are determined through correlations with other material properties. Level 3 inputs are simply typical default values. The level chosen for each design input parameter, however, may have a significant effect on project design, cost, performance, and reliability. The influence of the unbound granular base material type and material characterization input level on pavement performance, as predicted by MEPDG, was investigated for a typical flexible pavement section in climatic conditions in Egypt. Researchers analyzed seven types of virgin and recycled base materials at three weather stations representing climatic regions in Egypt: Alexandria, Cairo, and Aswan. For the typical pavement system, Level 1 data for the resilient modulus from measured laboratory values ( k1, k2, and k3 elastic response coefficients) were used for the first set of MEPDG simulation runs. The second set of computer simulation runs was conducted with Level 2 data—values of the California bearing ratio—for the investigated materials. The final set of runs used default resilient modulus values for the investigated materials on the basis of the AASHTO class (Level 3). MEPDG-predicted pavement distresses and roughness for the three input levels and seven base materials were compared, and the results showed significant variation in predicted performance as a result of the change in the input level and material type.

Stress–Strain Response of Unbound Granular Materials Under Static and Cyclic Loading

Resilient modulus is an important parameter in flexible pavement engineering design. The stress–strain behavior of unbound granular base materials under static and cyclic loading and the effects of the state of stress, moisture content and loading conditions have been analyzed in the present study. In this paper, the resilient behavior of unbound granular materials and the applicability of different constitutive models are examined in order to understand the behavior of granular material under static and cyclic loading. Since the aggregate material exhibits a complex stress–strain behavior, more than one model will be required to predict the stress–strain response of granular materials. Hence, different constitutive models have been considered in the present study which can adequately predict the stress–strain response of aggregate materials. Considering the constitutive models used in the present study, it could be said that the Lentz and Baladi model and the normalized degradation model suitably bring out a relation between static and cyclic tests. This is a useful input in pavement design and explains the variation of modulus with load repetitions.

The design model of unbound granular materials for flexible pavement

This study aims to introduce an alternative design model of unbound granular base course materials by utilising laboratory test results such as resilient modulus, permanent deformation and bearing capacity of base course materials. Current pavement designs mostly overlook all problematical behaviours of unbound granular base layers and consider only as a layer transferring traffic loads to underneath layers regardless on the unbound granular base course deteriorations. Based on the existing design protocols in Australia, there are only the design criteria of the horizontal tensile strains at the bottom of the asphalt layer and the vertical deformations occurring at the top of the subgrade. The actual performances of granular base course materials under traffic loads have been rarely accounted into the pavement design protocol. Currently, road activities are growing in terms of magnitude and frequency far beyond the past and causing the early road damages leading to major road maintenances. The study presents hypothetically the more rational approach of the stress and strain distribution in a flexible pavement using the finite element method with sophisticated laboratory results. In this study, the effects of a traffic load and material attributes which they were generated when vehicle travels, hence stress and strain contributing between tires and characteristics of unbound granular pavement materials were investigated. Moreover, the alternative design model for unbound granular layers was defined in order to draw up the guideline and recommendation on the current pavement analysis and design.

The design model of unbound granular materials for flexible pavement

This study aims to introduce an alternative design model of unbound granular base course materials by utilising laboratory test results such as resilient modulus, permanent deformation and bearing capacity of base course materials. Current pavement designs mostly overlook all problematical behaviours of unbound granular base layers and consider only as a layer transferring traffic loads to underneath layers regardless on the unbound granular base course deteriorations. Based on the existing design protocols in Australia, there are only the design criteria of the horizontal tensile strains at the bottom of the asphalt layer and the vertical deformations occurring at the top of the subgrade. The actual performances of granular base course materials under traffic loads have been rarely accounted into the pavement design protocol. Currently, road activities are growing in terms of magnitude and frequency far beyond the past and causing the early road damages leading to major road maintenances. The study presents hypothetically the more rational approach of the stress and strain distribution in a flexible pavement using the finite element method with sophisticated laboratory results. In this study, the effects of a traffic load and material attributes which they were generated when vehicle travels, hence stress and strain contributing between tires and characteristics of unbound granular pavement materials were investigated. Moreover, the alternative design model for unbound granular layers was defined in order to draw up the guideline and recommendation on the current pavement analysis and design.

Modelling of rutting of two flexible pavements with the shakedown theory and the finite element method

This paper presents a finite element program, for the modelling of rutting of flexible pavements. In its present version, the program incorporates a permanent deformation model for unbound granular materials based on the concept of the shakedown theory developed by Zarka for metallic structures under cyclic loadings and has been used to estimate the permanent deformations of unbound granular materials (UGM) subjected to traffic loading. The calculation is performed in two steps: the first step consists in modelling the resilient behaviour of the pavement in 3D, using non-linear elastic models, to determine the stress field in the pavement. Then stress paths are derived and used to calculate the permanent deformations and the displacements, using a Drucker–Prager yield surface. An application to the prediction of the permanent deformations of experimental pavements with an unbound granular base, tested on the LCPC pavement testing facility is presented.

Calibrating Mechanistic-Empirical Design Guide Permanent Deformation Models Based on Accelerated Pavement Testing

Abstract One of the challenges to the implementation of the mechanistic-empirical pavement design guide (MEPDG) comes from calibrating the transfer functions. This paper focuses on calibration of one of the major distress models in flexible pavement: permanent deformation or rutting. Two key aspects are critical to a successful rutting model calibration: data and method. Regarding the data, existing in-field information only provides total rut depth, which could not meet the requirement of permanent deformation in each structural layer by the MEPDG. Concerning the method, existing work either fails to address calibration factors from a holistic perspective by only focusing on individual sections separately or ignores variability inherent in those factors. In this study, layer-wise permanent deformation from instrumented pavement under accelerated pavement testing serves to accommodate the models calibration. A systematic calibration procedure is established, which globally optimizes all available information across all test sections. Through simulation and numerical optimization, optimal calibration shift factors for three typical flexible pavement materials, asphalt mixture, unbound granular base, and finegrain soil are obtained as 0.60, 0.49, and 0.84, respectively. This implies that the uncalibrated MEPDG is biased toward overprediction of rut depth. It is further suggested that a more rational result for each calibrated factor is to introduce an appropriate distribution to characterize its uncaptured variability. In addition, a case study involving using calibrated MEPDG to predict pavement performance or life indicates that (1) model calibration has a significant impact on the prediction and (2) the “fourth power law” is supported by the MEPDG.

Prediction of Permanent Deformation of Pavement’s Unbounded Layers Based on Cyclic Triaxial Tests

This research presents an analytical model for determining permanent deformation of pavement's sub-grade and unbound granular base and sub-base material due to cyclic traffic loading. The model is given for interpreting results of repeated load triaxial tests. It considers long term elastoplastic behavior and resilient behavior of sub-grade and unbound granular material. Permanent deformations are expressed as a function of the number of loading cycles and the spherical component and the deviatoric component of the repeated loading. The permanent axial deformation is given as a function of the resilient modulus and the secant modulus for different states of spherical and distortional stresses, and number of loading cycles. By analytical derivation it is presented that the normalized permanent axial strain can be expressed with the modulus values and the parameter D. The moduli are expressed as the functions of the spherical stress component and the distortional stress component. The magnitude of normalized permanent axial strain depends on the limit value of the resilient modulus and ratios between resilient and secant modulus. The parameter D gives the shape of the change of the normalized permanent axial strain with the number of cycles, and is a function of the change of modules with the number of cycles. The applicability of the presented model is demonstrated on the practical example of a repeated load triaxial test of sub-base granular material.

Three-Dimensional Nonlinear Finite Element Model for Simulating Pavement Response: Study at Canterbury Accelerated Pavement Testing Indoor Facility, New Zealand

A three-dimensional nonlinear finite element model (3D-FEM) was developed as part of a study of the effect of increasing axle load and tire pressure on pavement deterioration. The measured strains, interface stresses, and deflections were collected from the instrumented Canterbury Accelerated Pavement Testing Indoor Facility in New Zealand. In addition, two multilayer elastic models were used to compare the values from the finite element simulation and the actual measurements. The first elastic multilayer model was developed with ELSYM5 software, and the second model was developed with CIRCLY software. CIRCLY differs from ELSYM5 in the ability to account for material anisotropy; ELSYM5 considers the pavement materials to be isotropic. The actual strains and deformations were measured by Emu strain gauges embedded at different depths in the base and subgrade materials. Both the unbound granular base and the subgrade materials were modeled in 3D-FEM as elastic plastic materials. The results showed that for the unbound base layer, the strains calculated from the two elastic models were in reasonable agreement with the values measured in the instrumented test track, while the 3D-FEM model tended to overestimate the strains at the bottom of the base. While none of the models provided a perfect fit to the measured strains in the subgrade layer because the subgrade is less homogenous than assumed, 3D-FEM provided the closest fit. Also, CIRCLY provided better results than ELSYM5, which underestimated the displacement values compared with values obtained with CIRCLY and 3D-FEM.

PAVEMENT DETERIORATION OF AREAS ENDURING HIGH SHEAR STRESSES - SUGGESTED REVISIONS TO ROAD NOTE 31.

Keywords PNG TECHNOLOGY UNIVERSITY, PAPUA NEW GUINEA TECHNOLOGY UNIVERSITY PAVEMENTS, DETERIORATION, AREAS, HIGH, SHEAR, STRESS, ROAD NOTES, ROADS, COUNTRIES, DEVELOPING, TROPICAL, TROPICS, UNBOUND, GRANULAR, BASES, THIN, SEALING, COATS, SURFACES, FAILURES, LOADING, HORIZONTAL, LOADS, ACCELERATION, DECELERATION, FORCES, WHEELS, VERTICAL, STRAIN, ELASTIC, CROSS ANISOTROPIC, HALF SPACE, RATIOS, ESTIMATING, LIFE, BUS STOPS, INTERSECTIONS, JUNCTIONS, BENDS, MAINTENANCE, ROADBASE, DESIGN, APPLICATIONS, ROUNDABOUTS LAE CITY PAPUA, NEW GUINEA... Show All