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The rehabilitation of rigid (concrete) pavements with the placement of an asphalt overlay is a common maintenance technique which results in a structure known as a flexible composite pavement. The most common form of distress in this type of pavement is reflection cracking which can be due to traffic and/or climatic loading and it is considered as a very complex deterioration mechanism. A simplified mechanics-based approach identified from the literature has been developed to model the progression of reflective cracking. To demonstrate the model, results have been compared with data from the Long-Term Pavement Performance (LTPP) database, which contains performance and traffic data from monitored in-service road sections in North America. Results reveal the development of reflective cracking at different periods after the placement of the asphalt overlay and with different rates of cracking depending on the structure and material properties of a section as well as the specific traffic axle loading of each pavement section. The results help in identifying those factors which have a greater influence on the progression of reflection cracking in flexible composite pavements.

X-ray computed tomography (CT) and laboratory permeability techniques were applied to study the internal properties of porous asphalt mixture. Specimens containing aggregate of different gradations and of different mineral compositions were prepared in the laboratory. The air voids of all the specimens were determined in the laboratory and the specimens were then scanned in X-ray CT. The same samples were then tested for laboratory permeability. The active air voids and contact points of aggregate with nearby aggregate particles were determined from X-ray CT images. The laboratory permeability test results were found in comparison with X-ray CT values of voids’ internal connectivity. A comparatively high permeability value was observed for porous asphalt with maximum aggregate size irrespective of its mineral composition. The size of air voids and volume of active (connected) air voids were also found high for mixtures made up of large aggregate size. The difference in mineral composition of aggregate was...

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. The superior performance of canonical variate analysis (CVA) for fault detection has been demonstrated by a number of researchers using simulated and real industrial data. However, applications of CVA to fault identification of industrial processes, especially for faults that evolve slowly, are not widely reported. In order to improve the performance of traditional CVA-based methods to slowly developing faults, a novel diagnostic approach is put forward to implement incipient fault diagnosis for dynamic process monitoring. Traditional CVA fault detection approach is extended to form a new monitoring index based on indices, Hotelling’s T2, Q and a canonical variate residuals (CVR)-based monitoring index Td. As an alternative to the traditional CVA-based contributions, a CVR-based contribution plot method is proposed based on Q and Td statistics. The proposed method is shown to facilitate fault detection by increasing the sensitivity to incipient faults, and aid fault identification by enhancing the contributions from fault- related variables and suppressing the contributions from fault-free variables. The CVR-based method has been demonstrated to outperform traditional CVA-based diagnostic methods for fault detection and identification when validated on slowly evolving faults in a continuous stirred tank reactor (CSTR) system and an industrial centrifugal pump.

The application of finite element modelling for assumed mesh elements is limited for asphalt mixtures because of the inclusion of air voids within the structure. A multiphase finite element (FE) model was applied to consider the effect of air voids on the properties of asphalt mixtures. The virtual microstructure of an asphalt mixture was incorporated into the FE model from the X-ray CT images of asphalt specimens. Considering the asphalt mixture as viscoelastic, the mechanical properties determined from laboratory tests were applied to the FE model. Analysis was performed on a representative volume element using the concept of continuum damage mechanics. It was found that X-ray CT images can be converted into a finite element mesh of the real geometry of the asphalt sample. It was also found from the analysis that the mesh generated from the actual geometry account of the stress concentrations due to air void distribution compared with the assumed simplified geometry. The FE model was also analysed using CAPA 3D to give a validation of the results.

Because of the difficulties associated with the generation of finite element meshes based on X-ray computed tomography scans and with the extraordinary computational demands in performing three-dimensional (3-D) finite element analyses, past modeling efforts have focused primarily on two-dimensional representations of asphalt mixtures and have placed no emphasis on the inclusion of the air voids network in the body of an asphalt concrete specimen. A 3-D micromechanical moisture damage model has been developed and implemented in the finite element system CAPA-3D capable of addressing individually the three main phases of asphalt concrete: aggregate, mastic, and air voids. The 3-D finite element meshes of different types of asphalt mixtures were generated on the basis of X-ray scans. By means of CAPA-3D, the significance of the air voids structure in the development of moisture damage in asphalt concrete specimens was demonstrated. Availability of the model enables evaluation and ranking of the contribution of the characteristics of the individual mixture components to the overall mixture moisture resistance.

This study investigated damage in asphalt due to moisture by using the modified saturation ageing tensile stiffness (SATS) test along with image analysis. Specimens made from both granite and limestone aggregate with a 40/60 penetration grade bitumen were tested in the modified SATS test. The samples were scanned within an X-ray CT facility before the SATS testing, after the initial saturation and at the completion of the SATS test. Bitumen was extracted from tested specimens and scanned separately in a high resolution Nanotom (high resolution X-ray CT). The extracted bitumen was tested in a DSR for shear rheological properties. The specimens made from granite (acidic) and limestone (basic) aggregate were found to have similar permeability and this was found to be high for specimens having high design air void content. Specimens made from basic aggregate had higher stiffness than the specimens made from acidic aggregate. The master curves of the aged binder are different from those of the virgin binder (bitumen). Also the microstructure of binder observed was different for aged and virgin binder.

A large, innovative torsional hollow cylinder apparatus has been designed and commissioned for research investigations on asphalt. It can apply the complex shear and normal stress paths experienced in a pavement under a moving wheel load. The resulting high-quality data on permanent shear and volumetric strains will assist with the development of theoretical methods for rut depth prediction and act as an accurate reference to assess the performance of simpler test equipment. A wide range of repeated load stress paths can be applied under constant temperature conditions. The 350 mm long test specimens have a wall thickness of 50 mm. They are produced by accurate coring from a roller compacted test slab of asphalt. A detailed description of the apparatus is presented along with some preliminary results.

In this paper mixing of reclaimed material with virgin asphalt material has been studied non-destructively. Specimens prepared with virgin asphalt mix and with asphalt mix containing reclaimed material were scanned in X-ray Computed tomography (CT). The obtained Images were analysed for particles and pores (air voids) distribution. All the specimens were also tested in compression test and X-ray scanned while testing. It was found that distribution of reclaimed is not uniform through the samples. There is no considerable effect of increasing the mixing time on particles’ distribution. Similar trend of increase in air voids (cracks) with the increase in load was found for both virgin mix and for asphalt mix containing reclaimed material. Only at failure the increase in voids was found higher for specimens containing reclaimed material.

Prediction of asphalt mixtures’ behavior during their service life is a challenge due to its complexity and sensitivity to environmental and loading conditions. It has been proved that, when subjected to loading conditions comparable with most pavement operating conditions, asphalt mixtures behave as linear visco-elastic (LVE) materials. Traditionally the LVE behavior of bituminous material is modeled via creep/recovery functions. In the past, several rheological models constituted by elastic and viscous elements arranged in series or in parallel (analogical models) have been proposed and specified for both bitumen and asphalt mixtures. The corresponding constitutive laws always involve first order derivatives of time with exponential type solutions but problems in setting parameters arise when both the creep and recovery behavior have to be modeled. In this paper it is shown that experimental creep data follow a power decay law, rather than an exponential one. As a consequence, a simple fractional model is here proposed for predicting creep/recovery behavior of asphalt mixtures with a small number of parameters and low computational efforts with respect to the classical analogical models. The proposed model is then calibrated by a best fitting procedure on experimental data from creep and creep/recovery tests carried out on asphalt mixtures under different load and temperature conditions.

This paper describes the development of a laboratory-based automatic torque bond test that is capable of quasi-static and repeated load interface testing. Results from quasi-static testing undertaken using either a controlled torque rate or a controlled rotation rate showed that the shear strengths and shear reaction moduli increased as the temperature decreased. Samples with interfaces treated with the cationic emulsion were found to display the highest shear strengths and those treated with no emulsion were found to display the lowest shear strengths. A reasonably good correlation was found between results from testing performed at 600 N m/min and testing performed at 180°/min. The nominal shear strength measured from a test performed at 180°/min was found to be approximately 1.9 times higher than the nominal shear strength measured from a test performed at 600 N m/min. The nominal shear reaction modulus from a test performed at 180°/min was found to be approximately 1.6 times higher than the nominal shear reaction modulus from the test performed at 600 N m/min. The effect of material compliance above and below the interface on the rotation of the interface and shear reaction modulus of the interface is likely to be relatively small unless the shear stiffness of these materials is very low and/or the thickness is large. Results from repeated load (fatigue) testing showed a higher fatigue life and greater sensitivity to shear stress level at the lower temperature.

X-ray Computer Tomography (CT) has been used to quantify the damage induced during constant strain rate and fatigue tests on asphalt. Using image analysis techniques grading of the aggregate was carried out from the X-ray images of compacted asphalt specimens. It was found that particles larger then 5mm can be seen in comparison to the mix design curve of the asphalt mixture. It was observed from X-ray scanning of the specimens tested in mechanical testing that the increase in the volume of void content is not uniform throughout the specimen. It was found from the constant strain rate tests that the damage (air voids) were found to increase with increasing strain as damage accumulates in the specimen. It was also found that there is a greater increase in damage (void content) for the specimens tested at the higher temperatures and lower strain rates. Similar behaviour was observed from the fatigue tests with the greatest increase in damage at the higher test temperature.

The field performance of dry process crumb rubber–modified (CRM) asphalt mixtures has been reported to be inconsistent with stripping and premature cracking on the surfacing. One of the concerns is that, because achieving field compaction of CRM material is difficult due to the inherent resilient nature of the rubber particle, nonuniform field compaction may lead to a deficient bond between rubber and bitumen. To assess the influence of compaction, a series of CRM and control mixtures was produced and compacted at two levels: 4% (low, optimum laboratory compaction) and 8% (high, field experience) air void content. The long-term durability, in regard to moisture susceptibility of the mixtures, was assessed by conducting repeated moisture conditioning cycles. Mechanical properties (stiffness, fatigue, and resistance to permanent deformation) were determined in the Nottingham Asphalt Tester. Results indicated that compared with conventional mixtures, the CRM mixtures, regardless of compaction effort, are more susceptible to moisture with the degree of susceptibility primarily depending on the amount of rubber in the mixture, rather than the difference in compaction. This behavior is different from that of conventional mixtures in which, as expected, poorly compacted mixtures were found to be more susceptible to moisture than were well-compacted mixtures.

This paper presents a comparison of results from two wheel tracking devices. It is part of a larger on-going collaborative research project between the University of Nottingham in the UK, Delft University of Technology in The Netherlands and LCPC in France on the development and Finite Element (FE) implementation of a non-linear elasto-visco-plastic constitutive model for asphalt. Two devices, a large scale and small scale device, encompassed by the European Standard and the former British Standard were used. Rutting evaluation at the same temperature, on two different materials for pavement surface layers was tested under the same conditions allowing the evaluation of the rutting rate to be determined which was found to be very close from one test to another but sensitive to mixture type. In addition to rutting results, the contact dimensions and pressures from the two devices are evaluated in both the static case and during motion using a flat force transducer on the surface of the slab. The st...

This paper describes the linear viscoelastic (LVE) dynamic oscillatory properties of synthetic binders, as well as synthetic binder—bitumen blends, that have been synthesised from acrylic monomers by atom transfer radical polymerization (ATRP). The rheological properties of these binders have been determined using a dynamic shear rheometer (DSR) and frequency sweep tests. The results indicate that acrylic polymers, such as poly(ethyl acrylate) (PEA) and poly(methyl acrylate) (PMA), have rheological properties similar to that of 100/150 and 10/20 penetration grade bitumens, respectively. However, polyacrylates such as poly(butyl acrylate) (PBA) tend to be highly viscous at ambient temperatures and are therefore unsuitable as an asphalt mixture binder. The synthetic polymer binder—bitumen blends tended to be more compatible and stable when produced with a softer bitumen (70/100 pen or 100/150 pen) combined with a hard synthetic binder (PMA).

The spherical indentation response of a dense bitumen macadam asphalt mixture with two different volume fractions of bitumen binder is investigated both experimentally and via an analytical model. The model for the indentation of bitumen developed by Ossa et al. in 2005, was used to study the spherical indentation behavior of the mixtures with good agreement when compared to experimental results. An extensive experimental study of the monotonic and recovery spherical indentation behavior is reported for a range of temperatures. In line with the predictions of the model, the monotonic indentation response of the mixtures exhibits a power-law dependence on the indentation force. The model is also successful in capturing the indentation recovery behavior of the mixtures. A comparison of the material parameters obtained from uniaxial compression and indentation tests showed that indentation tests can be used in an easy and reliable way to obtain the fundamental asphalt parameters. Further, parameters found from indentation tests implicitly account for the confining conditions generated by the aggregate particles below the indenter.

This paper describes research undertaken to examine the option of replacing the upper portion of a rigid traditional brick access chamber with a flexible material, so that the system is more compatible with the surrounding flexible (asphalt) pavement construction, and is therefore less likely to exhibit premature failure. It focuses on one example of a suitable material, the influence of the confinement of this material within the surrounding pavement, and the importance of using a compatible backfill that acts as a bridge between the pavement and the ironwork. Full-scale experiments have been undertaken using a laboratory-based rolling-wheel test facility. Results show that flexibility incorporated into a road ironwork chamber can smooth out the step change in stiffness between a flexible pavement and a rigid chamber. Replacement of the upper portion of a chamber with a suitable flexible section results in the structure being more compatible with an asphalt pavement. It was also confirmed that the backfill around the chamber should be well compacted to provide good confinement, and the reinstatement material around the frame is a key element in the overall performance of a flexible chamber installation.

The use of discrete-element modelling (DEM) to simulate the behaviour of a highly idealized bituminous mixture under uniaxial and triaxial compressive creep tests is investigated in this paper. The idealized mixture comprises single-sized spherical particles (sand) mixed with bitumen and was chosen so that the packing characteristics are known and the behaviour of the mixture is dominated by the bitumen. The bitumen is represented as shear and normal (tensile and compressive) contact stiffnesses. Numerical sample preparation procedures for specimens containing spherical particles or clumps have been developed to ensure that the final specimen is isotropic and has the correct volumetric proportions. An elastic contact was used for the compressive normal contact stiffness and a viscoelastic contact was used for shear and tensile normal contact stiffness. Simulation results show that the idealized mixture is found to dilate when the ratio of compressive to tensile contact stiffness increases as a function of...

J.A. Moral-Munoz holds a FPU scholarship (AP2012-1789) from the Spanish Ministry of Education., Citation classics offer an outlook on those papers that have attracted great and historical interest by a research community and that could be also considered the basis of the research field. A new approach, which is called H-Classics, has been developed to identify such highly cited papers. It is based on the H-index and is sensitive to both the own characteristics of the corresponding research discipline and its evolution. The present study provides a useful insight into the development of the intelligent transport systems research field, revealing those scientific actors (authors, countries, and institutions) that have made the biggest research contribution to its development., Spanish Government AP2012-1789

This paper investigates the use of discrete element modelling (DEM) to simulate the behaviour of a highly idealised bituminous mixture under uniaxial and triaxial compressive creep tests. The idealised mixture comprises single-sized spherical (sand-sized) particles mixed with bitumen and was chosen so that the packing characteristics are known (dense random packing) and the behaviour of the mixture will be dominated by the bitumen and complex aggregate interlock effects will be minimised. In this type of approach the effect of the bitumen is represented as shear and normal contact stiffnesses. A numerical sample preparation procedure has been developed to ensure that the final specimen is isotropic and has the correct volumetrics. Elastic contact properties have been used to investigate the effect of the shear and normal contact stiffnesses on bulk material properties. The bulk modulus was found to be linearly dependent on the normal contact stiffness and independent of the shear contact stiffness. Poisson’s ratio was found to be dependent on only the ratio of the shear contact stiffness to the normal contact stiffness. An elastic contact has been assumed for the compressive normal contact stiffness and a viscoelastic contact for shear and tensile normal contact stiffness to represent the contact behaviour in idealised mixture. The idealised mixture is found to dilate when the ratio of compressive to tensile contact stiffness increases as a function of loading time. Uniaxial and triaxial viscoelastic simulations have been performed to investigate the effect of stress ratio on the rate of dilation with shear strain for the sand asphalt. The numerical results have been validated with experimental data.

An extensive experimental study of the dilation behaviour of asphalt mixtures was performed. The effect of mixture composition (volume fraction, gradation, shape and size of aggregate) and test conditions (loading/unloading, temperature and confinement pressure) of idealized asphalt mixtures of various volume fractions of aggregate was performed. The volume fraction and angularity of aggregate was found to play an important role on the dilation behaviour whereas the experimental conditions were found to have no effect on the dilation behaviour of asphalt mixtures. A generic DBM mixture was fabricated with two different volume fractions of bitumen. It was found that an increase in bitumen content decreases the dilation gradient. An analytical model proposed by Goddard and Didwania (1998) was successfully used to predict the dilation gradient for mixtures with sub-spherical aggregate, but failed to predict the dilation behaviour of specimens with angular aggregate.

This paper summarizes a theoretical study undertaken to provide a deeper understanding of the consequences of poor bond on flexible pavement performance. Two different modeling approaches have been used. In the first, the pavement structure was analyzed using a layered linear elastic program taking into account different degrees of interface bond between pavement layers and a static horizontal load in addition to the standard vertical dual load. The results indicate that the condition of the bond between the binder course and the base can reduce the life of the pavement structure by up to 80%. For poor bond between the surface course and binder course, the pavement life was found to be particularly sensitive to any horizontal loading applied by the traffic. Static linear two-dimensional (2D) finite element (FE) modeling confirmed these results. Nonlinear 2D FE modeling was also performed to investigate the effect of more realistic bond conditions between pavement layers. The results cast additional light on the overall structural performance of pavement with different degrees of bond subjected to both horizontal and vertical forces.

This paper investigates the effects of surface cracks on the primary responses to wheel loading in a model of a flexible pavement structure. Details of the modelling procedure using finite-element analysis are presented and the effects of different material properties and crack lengths are reported. Results show that in an uncracked flexible pavement structure, the inclusion of horizontal tractions imposed by the wheel load results in narrow regions of horizontal tensile strain at the pavement surface and a high shear strain at the edge of the tyre which could lead to crack initiation. The presence of a surface crack results in a localised region of high horizontal tensile stress and strain at the edge of the tyre, making further crack propagation possible. The predicted horizontal tensile strains increase as the stiffness modulus of the asphalt layer is decreased. The presence of a surface crack results in a high value of shear strain at the crack tip, which increases as the stiffness modulus of the asphalt layer is decreased. The predicted horizontal tensile strain at the base of the asphalt layer is not sensitive to a surface crack until it reaches approximately 50 mm (25% of the layer thickness), after which it increases. The predicted shear strain at the crack tip increases linearly with increasing crack length.

A box test has been developed to simulate the effects of train loading and tamping on the performance of four different ballasts. The ballasts have each been loaded in the box by a simulated segment of sleeper for up to a million cycles of traffic loading, representing early life behaviour. Simulated tamping has also been performed on the ballasts causing rearrangement of grains. Results from the box tests have been found to be repeatable, and give realistic stiffness and settlement characteristics compared with full-scale tests on trackbeds in the UK. The performance of each of the four ballasts has been determined in terms of settlement characteristics, stiffness and degradation, and the results have been found to agree with results from Los Angeles abrasion tests and water absorption values, and also with petrographic analysis, thus demonstrating the usefulness of the box test for estimating the performance of ballast in the field.

The response of heel-toe runners to changes in cushioning of the impact interface was investigated. Ground reaction force and sagittal plane kinematic data were collected for six heel-toe runners performing barefoot running trials on a conventional asphalt surface and an asphalt surface with additional cushioning. Statistical analysis indicated that similar peak impact force values were maintained when running on the two surfaces (p 0.1). In addition, individual subjects demonstrated reductions in heel velocity and increases in knee flexion immediately prior to ground contact. The observed reduction in ankle dorsiflexion at impact, resulting in a flatter foot at ground contact, supports previous suggestions that this is a strategy to reduce local plantar pressure loads. The additional use of adjustments in heel velocity and initial knee flexion highlights the ability of some subjects to adopt compensatory measures to reduce peak impact loading. However, some subjects appear unable to make these adjustments, resulting in higher impact loading on the less cushioned surface for these subjects. This study provides experimental evidence to support the theoretical potential of heel impact velocity and initial knee flexion to influence impact loading in running.

This paper investigates the use of distinct element modelling to simulate the behavior of a highly idealized bituminous mixture in an uniaxial compressive creep test. The effect of bitumen is represented as shear and normal contact stiffnesses. Elastic contact properties have been used to investigate the effect of sample size and the effect of the values of the shear and normal contact stiffnesses on bulk material properties. It was found that a sample containing at least 4,500 particles is required for Young's modulus and Poisson's ratio to be within 2% of the values calculated using a much larger number of particles. The bulk modulus was found to be linearly dependent on the normal contact stiffness and independent of the shear contact stiffness. Poisson's ratio was found to be dependent on only the ratio of the shear contact stiffness to the normal contact stiffness. A simple elasto-visco-plastic Burger's model was introduced to give time dependent shear and normal contact stiffnesses.

This paper describes laboratory work undertaken to measure the resistance to crack propagation of bituminous materials comprising a range of binder grades from different sources. The compact tension (CT) test has been adapted for use with bituminous materials, and an image analysis technique, based on digital photographs of the specimen taken during testing, has been used to quantify crack length. Linear elastic fracture mechanics (LEFM) principles have been used to calculate the mode I stress intensity factor (SIF), and the Paris law has been used to quantify crack growth. Results show that the general trend is for the Paris law exponent n to decrease and for the multiplier A to increase with increasing temperature for each of the materials, indicating that, the harder the bitumen, the greater is the sensitivity to overloading. A good correlation was found between the values of A and n, and also between the values of A in the Paris law and the stiffness modulus of the asphaltic mixture. It was found that mixtures containing the nominal 15 penetration grade binders were least sensitive to variations in stiffness of the mixture, and mixtures containing the nominal 35 and 50 penetration grade binders were most sensitive to variations in stiffness of the mixture. The number of standard wheel loads required to cause a crack to propagate through the asphalt layer of a typical minor and major flexible pavement structure have been estimated using data from the CT testing. Results show that there is a good correlation between the stiffness modulus of the asphalt mixture and the predicted number of load applications to failure. The predicted number of load applications to failure increases as the stiffness modulus of the asphalt increases.

Interest in the rheological and fracture characteristics of low penetration grade bitumens has increased in recent times due to greater use of progressively stiffer base materials and the growing concern over the durability of these extremely hard, high stiffness modulus materials. This paper investigates the high and low temperature rheological characteristics, tensile fracture modes and cohesive properties of a series of semi-blown, polymer modified and straight-run (direct distillation) low (15) penetration grade bitumens using a Brookfield (rotational) viscometer, Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), Direct Tension Tester (DTT) and Vialit Pendulum Cohesion apparatus. The binders have been tested in their virgin (unaged) condition and after short-term, Rolling Thin Film Oven Test (RTFOT) and long-term, High Pressure Ageing Test (HiPAT) ageing. The results show considerable differences in the high and low temperature rheological and fracture properties of the 15 penetrat...

This paper describes an evaluation of the absorption of different sources and grades of bitumen into particles of crumb rubber using a basket drainage method. The effect of the rubber–bitumen interaction has been investigated in terms of the absorption of the light fractions of the bitumen into the rubber and the chemical composition and rheological properties of the residual binder. Eight bitumens from two crude oil sources and four penetration grades ranging from 200 to 35 pen have been mixed with 2–8 mm sized granulated crumb rubber at three rubber to binder ratios of 1:4, 1:6 and 1:8 by mass. The increased mass of the crumb rubber was used to determine the loss of volatiles and light fractions absorbed from the different bitumens. The residual binders were then subjected to asphaltene content tests, high temperature viscosity and dynamic mechanical analysis using a dynamic shear rheometer to determine the chemical composition and rheological properties of the binders following their interaction with c...

This paper investigates errors associated with weigh-in-motion (WIM) measurements using data from 15 Department of the Environment, Transport and the Regions (DETR) WIM systems operated on motorways and trunk roads in England. Three sources of error have been identified: calibration errors, random sensor error and dynamic load effect. The 5-95 percentile range and the standard deviation of the calibration errors were found to be 30 and 11 per cent respectively. The average value of the random sensor error plus dynamic load effect was found to be 11 per cent. The effects of these errors on pavement design traffic and subsequent pavement thickness design have been investigated. It is found that, using a fourth power law, the effect of sensor/dynamic and calibration errors is likely to overpredict the traffic by typically between 15 and 20 per cent, which would result in a 5-15 mm overdesign of pavement thickness for typical flexible pavement structures.

This paper describes the use of the Dynamic Shear Rheometer (DSR) to characterise the steady-state shear deformation properties of two grades of bitumen over a wide range of stresses and strain rates. The steady-state shear strain rate has been used to characterise the quasi-static deformation behaviour of the bitumen. Results indicate that at low levels of shear stress the behaviour of the bitumen is linear whereas at higher levels of shear stress the behaviour is non-linear. A simple model has been developed to compare results from the DSR test to results that would be obtained from a test with uniform shear stress and shear strain rate conditions. The model assumes linear behaviour at low stress levels ( 100 kPa). Between these two stress levels there is a transition region where the behaviour changes from linear to power law creep. A power law creep exponent of n =2.4 was used for both bitumens. Results from the model show reasonably good a...

Compaction forms an integral part in the formation of the aggregate orientation and structure of an asphalt mixture and therefore has a profound influence on its final volumetric and mechanical performance. This article describes the influence of various forms of laboratory (gyratory, vibratory and slab-roller) and field compaction on the internal structure of asphalt specimens and subsequently on their mechanical properties, particularly stiffness and permanent deformation. A 2D image capturing and image analysis system has been used together with alternative specimen sizes and orientations to quantify the internal aggregate structure (orientation and segregation) for a range of typically used continuously graded asphalt mixtures. The results show that in terms of aggregate orientation, slab-compacted specimens tend to mimic field compaction better than gyratory and vibratory compaction. The mechanical properties of slab-compacted specimens also tend to be closer to that of field cores. However, the results also show that through careful selection of specimen size, specimen orientation and compaction variables, even mould-based compaction methods can be utilised with particular asphalt mixtures to represent field-compacted asphalt mixtures.

In this paper, we highlight the conceptual structure of the intelligent transportation systems (ITS) research field in the period 1992-2011. To do that, an automatic approach for detecting and visualizing hidden themes and their evolution across a consecutive span of years is applied. This automatic approach, which is based on co-word analysis, combines performance analysis and science mapping. To show the conceptual evolution of ITS, three consecutive periods have been defined, i.e., 1992-2001, 2002-2006, and 2007-2011. We have identified that the ITS research has been focused on six main thematic areas, i.e., VEHICLE-AND-ROAD-TRACKING, DRIVER-BEHAVIOR-AND-SAFETY, SCENARIOS-SIMULATION, TRAFFIC-FLOW-AND-TRAFFIC-MANAGEMENT, VEHICLE-CONTROL, and VEHICLE-NAVIGATION.

This paper presents a study on the production of asphalt test specimens in the laboratory containing reclaimed asphalt. The mixtures considered were stone mastic asphalt concrete mixtures containing up to 30% of reclaimed asphalt. Specimens were compacted to the reference density obtained from the Marshall mix design. Gyration compaction method was used for preparing specimens for the experimental programme, while coring and cutting methods and X-ray computed tomography (CT) were used to investigate the change in properties within the specimens and to validate the selected methodology. The study concluded that gyratory compaction is suitable to produce homogeneous test specimens also for mixtures containing high amount of reclaimed asphalt. Nevertheless, preliminary trials for each material are mandatory, as well as final coring and trimming of the specimens due to side effects.

This paper investigates the use of weigh-in-motion (WIM) data in the context of UK pavement design procedures. The effects of different power laws on the production of vehicle wear factors (VWFs), design traffic and subsequent pavement thickness design are investigated using two sources of WIM data. With the exception of one site, the average VWFs obtained are lower than those currently used in UK pavement design procedures, although the variability is quite high. Typically, the minimum pavement design traffic prediction was obtained using a fourth power law. Using current UK pavement design procedures for a range of materials, the effect of different exponents can make a difference of up to 50 mm to the pavement design, depending on the expected traffic level. The various errors associated with WIM measurements and the effects of these errors on the production of VWFs and subsequent pavement thickness design are investigated. Three effects have been identified, these being those due to calibration error, random sensor error and dynamic loading. It is found that, using a fourth power law, the effect of sensor/dynamic and calibration errors is to overpredict the traffic by typically 15–20% which is likely to result in a 5–15 mm overdesign of pavement thickness for typical flexible pavement structures.

This paper investigates the quasi-static permanent deformation (rutting) behaviour of two idealised bituminous mixtures (sand asphalts). The permanent deformation behaviour is assessed using simplified quasi-static uni-axial and tri-axial laboratory tests performed over a range of temperatures, stress levels and strain rates. The results are compared to results from a standard repeated load laboratory test and a more simulative laboratory scale wheel tracking test performed at different temperatures and load levels. Results from the quasi-static uni-axial testing show that the deformation behaviour of the idealised mixtures follows the same pattern as the deformation behaviour of the bitumen used in the idealised mixtures (previously measured). At high stress levels the response is non-linear with a power law creep exponent of approximately 2.4. At lower stress levels the effective power law exponent decreases and the behaviour becomes more linear. The effect of the aggregate is to reduce the str...

This paper describes tests undertaken to characterize the deformation behaviour of idealized bituminous mixtures and the development of a model to describe the permanent deformation exhibited by these mixtures in a wheel-tracking test. Steady state uniaxial and triaxial tests are used to characterize the deformation behaviour of the idealized mixtures over a range of stress levels, strain rates and temperatures. Results show that at low stress levels the deformation mechanism is linear viscous flow whereas at high stress levels the deformation mechanism is non-linear viscous flow with a power-law creep exponent of approximately 2.4. Wheel tracking tests have been performed over a range of applied stress levels and temperatures. Results indicate that the accumulation of permanent deformation in these idealized mixtures is non-linear. The measured uniaxial and triaxial properties have been used in a viscous model to predict the permanent deformation measured from wheel tracking tests. A method is presented for incorporating the observed non-linear behaviour of these materials in a linearized viscous approach. The results indicate good agreement between predictions and measurements, indicating the applicability of this type of model.

Modern high-speed rail lines are being built increasingly on marginal land, to reach city centers while avoiding housing areas. Often this land is composed of soft alluvial soils, which exhibit a low resilient modulus. The measurement, prediction, modeling, and implications of resilient modulus values for such subgrades are discussed. Measurement considers the use of repeated-load triaxial testing, resonant column, and in situ methods, illustrating these with sample data. Prediction draws on both analytical and finite-element techniques to illustrate the critical speed (the bow-wave effect) and how it is influenced by resilient modulus. Modeling reveals the available relationships—and their limitations—for deriving subgrade stiffness in this dynamic situation. Implication then uses these to define the relevant effects of resilient modulus values on design problems.

This paper examines the effects of ‘road friendly’ heavy goods vehicle suspensions on long-term flexible pavement performance. A deterministic ‘whole-life pavement performance model’ (WLPPM) is used to calculate pavement damage due to realistic traffic and environmental loading. The traffic is modelled first as a fleet of steel-sprung heavy goods vehicles and second as a fleet of ‘road friendly’ air-suspended vehicles. The pavement life predictions are compared for the two cases and with results from a simple road damage analysis based on the ‘fourth power law’. It is concluded that changing to a fleet of ‘road friendly’ vehicles would not significantly affect the life or maintenance costs of thicker asphalt pavements (motorways and trunk roads) where the mode of failure is permanent deformation (rutting). However, the life of thinner pavements (minor roads) that fail by fatigue damage and pot-holing would be increased significantly if the vehicle fleet changed to road friendly suspensions. Predictions from the simplified fourth power law approach tend to significantly overestimate the benefits of road friendly suspensions for major road conditions compared to the WLPPM predictions. It is concluded that the potential economic benefits in England and Wales of converting to air suspensions may be only 30 per cent of those predicted by the authors of the EC ‘road friendly suspensions’ regulations.

This study highlights the importance of defining appropriate specimen manufacturing procedures when assessing the fundamental properties of reclaimed asphalt (RA) mixes for further modelling purposes. Two gyratory compactor procedures were used: the first leading to specimens with a non-uniform air voids distribution and the second tailored to obtain homogeneous specimens. The study was performed by using three stone mastic asphalts incorporating up to 30% of RA but designed to have identical properties. A detailed characterisation of the loose mixes and binders, an X-ray computer tomography micro-structural study of the manufactured specimens and a further mechanical characterisation showed that testing non-homogeneous gyratory specimens leads to a significant overestimation of the mechanical properties of asphalt mixes. This study has been developed within the FP7 project ReRoad.

Imaging techniques have been used to characterise laboratory fatigue testing on asphalt mixtures. Specimens were tested in tension-compression cyclic testing at different temperatures. Testing was stopped at predefined stages, and specimens were scanned in X-ray computed tomography. A three-dimensional image of the original specimens was developed for analysis. It was found from the image analysis that the damage (air voids) were found to be increasing with an increase in strain as damage accumulated in the specimens. An energy-based damage mechanics model was used to calculate the increase in damage. Dissipated pseudo-strain energy and adhesion between binder and aggregate were used in the model. Pseudo-strain energy was calculated from laboratory testing, and the adhesion parameter was determined from surface energies of aggregate and bitumen (binder). Values obtained from a numerical model were found to have a similar trend as that of the data from X-ray computed tomography and image analysis.

This study examines the performance of stress-absorbing membrane interlayer (SAMI) under traffic loading. Accelerated pavement test facility at the University of Nottingham was used for the study. It involves construction and trafficking of a pavement with sections having SAMI and without SAMI. The study indicates that the SAMI is able to delay reflective cracking. It shows that the performance of the SAMI depends on the thickness of the SAMI and the interface bonding between the overlay and the SAMI. Also, it reveals that when SAMI is used between an existing cracked pavement and an overlay, the interface shear stiffness of the overlay and SAMI plays a role in isolating the overlay from the relative deflection of the cracked underlying layer due to traffic loading.

This study has investigated the crack resistance potential of selected SAMIs subjected to wheel loading. Tests were carried out in a wheel tracking facility and temperature-controlled environment to simulate field stress and strain conditions. The results indicate that the potential of SAMIs to retard crack growth depends on factors such as the SAMI stiffness and thickness, the overlay thickness, the load level and temperature. It was found that the relative benefit of SAMIs was higher when lower SAMI and overlay thicknesses were used. The study also showed the SAMIs to be effective at 20 °C and 30 °C but relatively ineffective at 10 °C.

A series of tests was conducted on a British trunk road in which the dynamic tyre forces generated by approximately 1500 heavy goods vehicles (HGVs) were measured using a load measuring mat containing 144 capacitive strip sensors. The data were used to investigate the relative road-damaging potential of the various classes of vehicles. Air suspensions were found to be more effective at static load equalization than steel suspensions. Two criteria were used to rank axle groups in terms of road damage: the average dynamic load coefficient and the 95th percentile aggregate fourth-power force. These criteria were found to rank axle groups in different orders, due to spatial correlation between tyre forces. On average, air suspended vehicles were found to generate smaller dynamic loads and hence less road damage than steel suspended vehicles. However, some air suspensions with inadequate suspension damping were found to generate very high dynamic loads and consequently very high levels of road damage.

A new asphalt layer modulus degradation model for use with flexible-pavement analysis procedures is described. The model is capable of determining the reduction in stiffness of the asphaltic material in a flexible pavement due to cumulative fatigue damage. Measured surface deflection bowls from a number of test pavements are used with a pavement parameter back-calculation procedure, to determine the reduction in stiffness of the asphaltic material throughout the life of the pavement. Results show an exponential relationship between the reduction in asphalt layer stiffness and cumulative fatigue damage. This type of relationship does not agree with an earlier theoretical continuum damage mechanics model, where the relationship between the reduction in asphalt layer stiffness and cumulative fatigue damage was predicted to be linear.

A new ‘whole-life’ pavement performance model (WLPPM), which is capable of making deterministic pavement damage predictions due to realistic traffic and environmental loading, has been developed. A vehicle simulation is used to generate dynamic tyre forces that are a function of distance along the road. These dynamic tyre forces are then combined with the appropriate pavement primary response influence functions (stress, strain and displacement) to give primary response histories at regularly spaced points along the pavement. The primary response histories are then transformed into pavement damage (fatigue and permanent deformation) using an appropriate damage model. The result is an increment of damage at each point along the pavement due to a single vehicle pass. The pavement surface profile is then updated to reflect permanent deformation damage and the layer material parameters are changed to reflect fatigue damage. The procedure is then repeated for the next vehicle pass. Particular attention is given to modelling strength variations in the pavement and dynamic tyre forces. The model is used to investigate the relationship between ‘hot spots’ (due to peak dynamic loads), ‘weak spots’ (due to initial pavement stiffness variations) and long-term pavement damage.

A new whole–life pavement–performance model (WLPPM) that is capable of making deterministic pavement–damage predictions due to realistic traffic and environmental loading has been developed. A vehicle simulation is used to generate dynamic tire forces that are a function of distance along the pavement. These dynamic tire forces are then combined with the appropriate pavement primary–response influence functions to give primary–response histories at regularly spaced points along the pavement. The primary–response histories are then transformed into an increment of damage at each point along the pavement due to a single vehicle pass, and the surface–roughness profile is updated. This procedure is then repeated until pavement failure occurs. Using the WLPPM, the performance of two classes of pavement are examined operating under climatic conditions typical of the United Kingdom. It is concluded that both dynamic vehicle loads and asphalt–layer stiffness variations can significantly influence long–term flexible–pavement performance.

A portable mat for measuring the dynamic tyre forces of commercial vehicles is described. The mat is 56 m long, 13 mm thick, and has 141 capacitative strip sensors, spaced at 0.4 m intervals. The accuracy of the mat for measuring dynamic tyre forces generated by heavy commercial vehicles is assessed using an instrumented vehicle. The measured dynamic wheel loads generated by 14 articulated vehicle configurations (three tractors with five trailers) are assessed in terms of a variety of road damage criteria. The results are used to investigate the effects of vehicle configuration, vehicle dynamics, speed, road strength, and road damage criteria on the relative theoretical road damage caused by the vehicles. Conclusions are drawn about tests for measuring and assessing the road-damaging potential of heavy lorries.

Although the use of Stress Absorbing Membrane Interlayers (SAMIs) to control reflective cracking has been proven to be effective under certain circumstances, the mechanisms involved are not agreed and design is therefore difficult for engineers to implement with confidence. This paper describes simulative laboratory tests utilizing two different SAMI systems, part of a broader project designed to throw light on the subject. The simulation was conducted to investigate the effectiveness of SAMIs under trafficking. Trafficking was carried out in the Nottingham Pavement Test Facility on a pavement consisting of a thin overlay to a cracked asphalt substrate, and this demonstrated a measurable benefit from the two SAMI systems trialed. Data analysis was then carried out and deductions made regarding those properties of SAMIs that appeared to contribute most to reflective crack resistance.

Flexural fatigue is a process of cumulative damage. It is also one of the main failure modes in asphalt mixtures and flexible pavement structures. This means good prediction of a pavement’s fatigue life will help to develop and improve pavement design procedures.

This paper proposes a mechanistic-empirical pavement damage model to predict changes in 3D road profiles due to dynamic axle loads. The traffic is represented by a fleet of quarter cars which allows for statistical variability in model parameters such as velocity, suspension stiffness, suspension damping, sprung mass, unsprung mass and tyre stiffness. The fleet model generates statistical distributions of dynamic force at each point which are used to predict pavement damage. As the pavement deteriorates, the distributions of dynamic axle force are changed by the changing road profile. This paper introduces a 3D approach – the transverse position of the wheel is represented by a Laplace probability distribution. This influences the extent to which the force patterns are spatially repeatable. Differences in the range of 10–30% are found between 2D and 3D predictions of pavement life.