Showing papers in "Road Materials and Pavement Design in 2013"

The mechanisms of hydrated lime modification of asphalt mixtures: a state-of-the-art review

Abstract: Although already known for a long time, hydrated lime (HL) attracted a strong interest as an asphalt additive during the 1970s in the USA, when moisture damage and frost became some of the most pressing pavement failure modes of the time. Given its extensive use in the past 40 years, HL is known to be more than a moisture damage additive: it is an “active filler” that also reduces the chemical ageing of the bitumen and stiffens the mastic more than a normal mineral filler above room temperature. These properties impact durability, and HL is now seen as an additive that increases asphalt mixture durability. This article is a literature review on the fundamentals of the effect of HL on asphalt mixtures. The reasons for it being so effective lie in the strong interactions between both the aggregate and the bitumen and a combination of four mechanisms, two on the aggregate and two on the bitumen. HL modifies the surface properties of the aggregate, allowing for the development of surface composition and rough...

Evaluating the effect of rejuvenators on the degree of blending and performance of high RAP, RAS, and RAP/RAS mixtures

Abstract: The objective of this study was to examine if asphalt rejuvenators can offset the stiffness attributed by the hardened binder from reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in mixtures that incorporate high RAP and RAS content without adverse impact on the performance of the mixtures. Also, to assess, if rejuvenators can help the hardened binder from the RAP/RAS comingle with the virgin binder. Overall, the results showed that asphalt rejuvenators can mitigate the stiffness of the resultant binder. The cracking characteristics of the mixture improved by the addition of the rejuvenators, however, the rutting and moisture susceptibility were adversely impacted at the dosage and the testing conditions used. Also, the tests results at 4°C generally showed that there was blending of the rejuvenated and virgin binder, however, no conclusion could be made at the higher temperatures.

Micromechanical investigation of phase separation in bitumen by combining atomic force microscopy with differential scanning calorimetry results

Abstract: The thermo-rheological behaviour of bitumen depends largely on its chemical structure and intermolecular microstructures. Bitumen is a complex mixture of organic molecules of different sizes and polarities for which the micro-structural knowledge is still rather incomplete. Knowledge at that level can have great implications for behaviour at a larger scale and will help to optimise the bitumen in its production stage. The present study is focused on understanding the fundamental mechanisms behind the micro-structural phase appearance and the speed or mobility at which they change. To do so, atomic force microscopy was utilised at different temperatures to investigate the phase separation behaviour for four different types of bitumen and co-relate it with the differential scanning calorimetry measurements. Based on the experimental evidences, it was found that the observed phase separation is mainly due to the wax/paraffin fraction presence in bitumen and that the investigated bitumen behaves quite differe...

Development of a failure criterion for asphalt mixtures under fatigue loading

Abstract: The failure criterion defines the applicable region associated with the continuum damage model and is important in characterising the service life of asphalt mixtures. A proper failure criterion should consistently predict the failure of the material that reaches macro-fracture. A previously developed criterion that uses the viscoelastic continuum damage (VECD) model exhibits high variability and is considered to be inefficient because it requires calibration tests at different temperatures. In this paper, a new concept that involves released pseudo strain energy is introduced. This released pseudo strain energy concept focuses on the dissipated energy that is related to stiffness reduction only and is fully compatible and predictable using the VECD model. A characteristic relationship is found between the stable rate of pseudo energy release during testing and the final fatigue life of the same mixture, independent of strain amplitude and temperature. Based on these observations, a new failure criterion ...

Understanding mechanisms leading to asphalt binder fatigue in the dynamic shear rheometer

Abstract: Asphalt binder fatigue resistance is important in determining overall pavement fatigue performance. One procedure commonly used to characterise asphalt binder fatigue resistance is the time sweep test, which consists of repeated cyclic loading in the dynamic shear rheometer (DSR). Generally, apparent changes in complex modulus and phase angle with respect to number of loading cycles are used to define fatigue performance. Although results from DSR testing have been shown to correlate well with asphalt mixture fatigue performance, the mechanisms responsible for changes in binder properties in the DSR were previously not well understood. Results in this study demonstrate that fracture can explain the changes in loading resistance during fatigue testing in the DSR. Under cyclic torsional loading of cylindrical specimens, fracture manifests as a circumferential crack that starts at the periphery of a sample and propagates inward, reducing the effective sample radius. Digital visualisation of binder specimens ...

Evaluation of high RAP-WMA asphalt rubber mixtures

Abstract: This study focused on evaluating the stiffness, fatigue cracking, reflective cracking, rutting, moisture damage, and workability of asphalt rubber (AR) surface mixtures with reclaimed asphalt pavements (RAP) contents up to 40% with and without a warm mix asphalt (WMA) technology. RAP increased the stiffness of the mixtures; however, WMA mitigated that increase. The addition of RAP had an adverse effect on the resistance to fatigue and reflective cracking of the mixtures. This effect was magnified with the use of WMA regardless if RAP was incorporated in the mixture. Therefore, it was recommended to further investigate the proper drop in temperatures for AR mixtures that incorporate WMA. All mixtures passed the rutting and moisture damage test. The WMA technology improved the workability of the mixtures.

Performance evaluation of a cold-recycled mixture containing high percentage of reclaimed asphalt

Abstract: Cold recycling of asphalt pavements proved to be an effective maintenance and rehabilitation technology for both environmental and economic reasons. Nevertheless, the use of cold-recycled (CR) asphalt mixtures requires a careful assessment of their mechanical properties, especially when they are designed to replace traditional hot-mix asphalt concrete (AC) mixtures. In this study, the potential use of a CR asphalt mixture as base course of an Italian motorway was evaluated. The studied mixture was produced in a central plant employing high-reclaimed asphalt (RA) content and used to construct two experimental sections along an in-service Italian motorway. In particular, a special mixing procedure, involving the use of water vapour and bituminous emulsion, was tested. A third experimental section was constructed with the same layer thickness using the AC mixture currently used in rehabilitation projects, incorporating 30% of RA. Volumetric properties, stiffness, resistance to permanent deformation and fatig...

Tyre rubber-modified bitumens development: the effect of varying processing conditions

Abstract: Tyre rubber-modified binders (TR-MBs), produced through McDonald's wet process and used worldwide (e.g. asphalt rubber), have been demonstrated to provide various benefits to pavements and, moreover, they represent a good opportunity for recycling tyre rubber (TR). However, this technology is still struggling to be fully adopted in Europe, mainly because of their poor stability during high temperatures storage, which leads to high initial costs in modifying existing asphalt plants. Storage stable TR-MBs are proving to be a great option and their development could be the key to spread the recycling of TR within paving applications in Europe. This paper aims to enrich this field of research by presenting the results of a study focused on the optimisation of laboratory procedures to better understand the effect of varying processing conditions on the rheology of TR-MBs. The experimental programme has been carried out by a preliminary selection of materials, followed by the production of the TR-MBs, via pract...

Influence of reclaimed asphalt pavement content on complex modulus of asphalt binder blends and corresponding mixes: experimental results and modelling

Abstract: The objective of the presented study is to determine linear viscoelastic (LVE) properties of corresponding binders and mixes and to check how they change with reclaimed asphalt pavement (RAP) content. The investigation is part of a wider on-going research project, in the framework of a PhD thesis, in collaboration between Universite de Lyon/Ecole Nationale Travaux Publics de l'Etat (ENTPE), EIFFAGE Travaux Publics and Beyond Petroleum. Dynamic shear rheometer and tension/compression (using a Metravib device) complex modulus tests were performed on nine different bitumens, produced as blends of two different base bitumens and RAP-extracted bitumen in various proportions. LVE properties of six asphalt mixes, produced with the same materials and proportions of certain bitumen blends among the nine tested ones, were measured in tension/compression mode. 2 Springs, 2 Parabolic Elements, 1 Dashpot model was used to fit experimental data both for binders and mixes. Shift-Homothety-Shift in time-Shift transformation (developed at ENTPE) was applied to verify the correspondence of LVE behaviours of related binders and mixes.

Review of glass fibre grid use for pavement reinforcement and APT experiments at IFSTTAR

Abstract: Reinforcement using an interlayer system has been demonstrated for more than four decades as a multi-purpose solution to improve performance, to extend service life and thus to reduce maintenance costs of road pavements. Among a large number of existing interlayer systems, glass fibre grids have shown effective use in pavement reinforcement with a hot mix asphalt overlay. Recently they have received increasing attention from the pavement community. However, as for other types of interlayer systems, the mechanisms underlying the effectiveness and proper installation of this type of reinforcement system are still not fully understood, and the choice of the most appropriate grid (e.g. mesh size, tensile strength) and its optimal location in the pavement system are mainly based on experience. This article presents firstly a literature review on the use of glass fibre grids in pavement reinforcement. Then some results of recent full-scale tests on the accelerated pavement testing facility of the IFSTTAR are pr...

An improved image processing technique for asphalt concrete X-ray CT images

Abstract: This paper presents a comparative evaluation of two image segmentation techniques for processing asphalt concrete microstructure images obtained with X-ray computed tomography (CT). These are the adaptive enhancement-based thresholding algorithm (AETA) and the watershed segmentation embedded into the volumetric-based thresholding algorithm (VTA). Both these methods were used to process the X-ray CT images of nine asphalt concretes. These consisted of three mix types, each prepared with three aggregate types. The mix designs included a coarse matrix high-binder Type C mix, a gap-graded porous friction course mix, and a fine-graded Superpave Type C (Superpave) mix. The three aggregate types included hard limestone, granite, and soft limestone. All mixtures were prepared with a PG 76-22 modified binder. The comparison of the two methods was carried out both visually and quantitatively. The later was accomplished by comparing the gradation estimated from the images using purpose-designed software to the grada...

Laboratory evaluation of the mechanical properties of plant-produced warm-mix asphalt mixtures

Abstract: This paper presents a laboratory evaluation of plant-produced asphalt mixtures containing the control hot-mix asphalt (HMA) and four warm-mix asphalt (WMA) technologies: an organic additive (Sasobit®) and three foaming processes (Advera®, low-emission asphalt, and Gencor). These asphalt mixtures were produced using a single binder performance grade (PG 64-22) and 9.5-mm nominal maximum aggregate size Superpave mix design compacted to 75 design gyrations. Dynamic modulus (E*), flow number, and Hamburg wheel–track tests were utilised to evaluate the mechanical properties of the asphalt mixtures. The PG of the asphalt binders containing the WMA technologies was also verified. In addition, their rheological properties were evaluated using shear modulus master curves and multiple stress creep recovery tests. It was found that the asphalt binder containing Sasobit® technology increased the continuous high-temperature binder grade by 6°C and measured higher elastic properties. In general, the asphalt mixture pre...

Investigation of a pavement structural behaviour during spring thaw using falling weight deflectometer

Abstract: The response of an instrumented flexible pavement structure in southern Sweden, subjected to seasonal freeze–thaw cycles, was investigated during the spring thaw and the recovery periods in 2010 The pavement environmental condition was continuously monitored by measuring subsurface temperature and moisture contents The mechanical behaviour of the pavement structure was investigated by conducting frequent falling weight deflectometer (FWD) measurements throughout the study period Considerable decrease in the pavement-bearing capacity was observed as thaw penetrated the pavement structure and consequently moisture content increased in all pavement unbound layers Highest annual moisture content in the subgrade upper section was registered as thaw penetrated the subgrade and pavement exhibited its weakest structural condition The analyses of the deflection basin indices and back-calculated unbound layer stiffness from the FWD measurements exhibited a clear correlation with the measured subsurface moisture content Furthermore, the dissipated energy measured from the FWD time–history data was calculated, exhibiting its highest annual value during the thawing period Using the back-calculated layer stiffness and moisture measurements in unbound layers, a degree of saturation-based moisture-stiffness model was developed for the granular layer and the subgrade This model fell on a unique curve showing promising agreement with the laboratory-based model proposed by Mechanistic-Empirical Pavement Design Guide that analytically predicts changes in modulus due to changes in moisture

The multiple stress creep-recovery test: a detailed analysis of repeatability and reproducibility

Abstract: The multiple stress creep-recovery (MSCR) test was recently introduced to evaluate bituminous binders at high service temperatures, in particular to evaluate the stress or loading resistance. This test allows classifying binders at the high-performance graded temperature, according to the traffic loading, starting from standard, to heavy, very heavy and extreme traffic loading. It is the intention that this test includes nonlinear binder properties. In this study, five laboratories have participated in a round robin test to evaluate the repeatability and reproducibility of the parameters derived from the MSCR test. Nine different binders were evaluated, including unmodified, slightly and highly modified binders. The MSCR tests were conducted at 50°C, and each laboratory performed testing five times under repeatability conditions. The test results were analysed according to ISO 5725 and observations and reasons for deviating test results are discussed in detail.

Rutting and moisture damage resistance of high reclaimed asphalt pavement warm mixed asphalt: loaded wheel tracking vs. conventional methods

Abstract: An increased potential for moisture damage and rutting has been the two main problems with warm mixed asphalt (WMA) implementation. The use of high reclaimed asphalt pavement (RAP) contents (25% or more) in WMA may alleviate these problems. At present, susceptibility to the moisture damage and rutting are usually tested for independently; however, these distress mechanisms can be linked for in-service pavements. An enhanced loaded wheel tracking test performed on dry and wet specimens, the PURWheel, is investigated in this paper to evaluate the interaction of traffic and moisture. The PURWheel is also compared with conventional rutting and moisture damage tests. PURWheel results are used to evaluate the performance of 25% and 50% RAP–WMA. Rutting and moisture susceptibility of the high RAP–WMA was comparable with current practice low RAP content hot mixed asphalt.

Influence of demolition waste used as recycled aggregate on performance of asphalt mixture

Abstract: The influence of demolition waste (DW) on the performance of asphalt mixture was investigated in this paper. DW was processed into recycled aggregate of different sizes which can be divided into recycled coarse aggregate (RCA, particle size of>4.75 mm) and recycled fine aggregate (RFA, particle size of≤4.75 mm). Three types of AC-25 asphalt mixture were prepared: RCA asphalt mixture prepared with RCA and limestone fine aggregate; RFA asphalt mixture prepared with RFA and limestone coarse aggregate; and the ordinary asphalt mixture prepared with natural limestone coarse and fine aggregate. A series of laboratory tests on recycled aggregate and asphalt mixture were carried out, including scanning electron microscopy test, immersion Marshall test, freeze–thaw split test, bending test at low temperature and rutting test at high temperature. Results showed that RCA asphalt mixture has higher optimal asphalt content and greater rutting resistance than the other two types. The cracking resistance of RCA asphalt ...

Fast layered elastic response program for the analysis of flexible pavement structures

Abstract: One of the key components in analysing pavement structural behaviour is the response model which is used to estimate the stresses, strains and displacements of the pavement structure subjected to t ...

Laboratory characterisation and field validation of geogrid-reinforced asphalt pavements

Abstract: In order to improve the mechanical properties of pavements, reinforcement systems can be employed in asphalt layers. However, the presence of a grid at the interface causes an interlayer de-bonding effect. Moreover, a real challenge is related to the proper in situ installation of grids. The present research aims to evaluate the effectiveness of pavement rehabilitation with fibreglass geogrids. To this purpose, a real-scale field trial was constructed and monitored through Falling Weight Deflectometer measurements. Interface shear tests and flexural tests were also carried out on double-layered samples prepared in the laboratory reproducing real-scale field trial characteristics. Moreover, shear tests were also performed on in situ cored specimens. Results mainly showed that a proper installation of the reinforcement is fundamental in order to obtain suitable test results and good pavement performance.

Comprehensive study on the porous asphalt effects on expressways in Japan: based on field data analysis in the last decade

Abstract: Porous asphalt has spread widely across Japanese expressways as the standard surface course material since 1998, greatly contributing to the decrease in the number of traffic accidents on wet surface conditions. On the other hand, due to rainwater penetration through the porous surface, water sensitivity of the binder course layer becomes a key issue to secure its durability. This paper summarises the successful performance of porous asphalt surface courses based on a long-term survey over nearly 15 years in fields, also describing the negative impacts of porous asphalt. The experience shows that the durability of the binder course should be taken into consideration when a porous asphalt surface course is applied over old existing roads. This is vitally important if porous asphalt is to perform its excellent functions over a full service life by avoiding unexpected damage of the pavement.

Two-dimensional digital image correlation for asphalt mixture characterisation: interest and limitations

Abstract: As a practical and effective tool for quantitative in-plane deformation measurement of a planar surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. This paper presents an overview of the use of DIC-based techniques for asphalt mixture characterisation reported in the literature. 2D DIC is well suited to analyse asphalt materials mechanical properties because of their anisotropic and heterogeneous nature. Fundamentals of DIC are first briefly described. Specific advantages of using these techniques in a context of asphalt material characterisation are then highlighted. Critical issues that require further research and development are finally examined.

Water impact on the behaviour of flexible pavement structures in an accelerated test

Abstract: Two flexible test road structures were built and tested in an accelerated pavement test using a heavy vehicle simulator, with the aims of investigating their performance behaviour for a validation in a mechanistic performance scheme and the accuracy of repeated tests. In the test more than one million load cycles were applied, but after the first half million the water table was raised. The structures were therefore analysed in ‘moist’ and ‘wet’ states, before and after raising the water level. The increased water level had a significant effect on the structure with decreased resilient modulus and increased permanent deformation. Numerical analyses have been carried out to simulate the pavement responses, where the material properties used in the response analyses were based on field and laboratory testing. The observed accumulation of permanent deformation of the unbound layers was modelled using work hardening material models. Generally good agreement was established between the measurements and calcula...

Effect of long-term ageing on RAP mixtures: laboratory evaluation of plant-produced mixtures

Abstract: As the use of reclaimed asphalt pavement (RAP) in asphalt concrete mixtures increases, it is important to understand how the addition of already aged asphalt binders affects the overall properties and performance of the mixture. In this study, four plant-produced mixtures containing 0%, 20%, 30%, and 40% RAP were long-term oven aged in the laboratory to three levels. Mixture testing included uniaxial complex modulus and fatigue. Recovered binder testing included performance grading (PG) and rheological characterisation. The mixture testing showed that the RAP mixtures stiffen due to laboratory ageing at a slower rate than virgin mixtures and that the impact of the presence of RAP on material properties decreases with ageing time. The relative fatigue performance of the mixtures changes dramatically in stress versus strain control, indicating the importance of linking mixture and pavement design. The recovered binder properties show increase in the high continuous PG, minimal impact at the intermediate con...

IlliTC – low-temperature cracking model for asphalt pavements

Abstract: Low-temperature cracking (LTC) is a major distress and cause of failure for asphalt pavements located in regions with cold climate; however, most pavement design methods do not directly address LTC. The thermal cracking model (TCModel) utilised by American Association of State Highway and Transportation Officials Mechanistic-Empirical Pavement Design Guide relies heavily on phenomenological Paris law for crack propagation. The TCModel predictions are primarily based on tensile strength of asphalt mixture and do not account for quasi-brittle behaviour of asphalt concrete. Furthermore, TCModel utilises a simplified one-dimensional viscoelastic solution for the determination of thermally induced stresses. This article describes a newly developed comprehensive software system for LTC prediction in asphalt pavements. The software system called ‘IlliTC’ utilises a user-friendly graphical interface with a stand-alone finite-element-based simulation programme. The system includes a preanalyser and data input gene...

Thermo-mechanical behaviour of mixtures containing bio-binders

Abstract: The objective of the presented study is to develop an approach to assess the linear viscoelastic (LVE) properties and the low-temperature behaviour during thermal ageing of semi-coarse asphalt concrete (SCAC) containing bio-binders. The investigation is part of a wider ongoing research project in EIFFAGE Travaux Publics Research Center. Tension/compression complex modulus tests, direct tensile strength tests at low temperatures and thermal stress-restrained specimen tests were performed on SCAC, containing three different clear binders. The first one is a reference petroleum-based clear binder, the two others are bio-binders, manufactured from renewable raw materials and fit in with the ideas of sustainable development. The analogical LVE 2S2P1D model (2 springs, 2 parabolic elements, 1 dashpot) was used to fit experimental data for the three mixtures. This method seems to be very relevant to compare rheological properties of mixtures made with bio-binders, for which evolution of low-temperature behaviour...

Laboratory simulation of the clogging behaviour of single-layer and two-layer porous asphalt

Abstract: The permeability of porous asphalt (PA) reduces after a few years in service due to clogging. The two-layer porous asphal (TLPA) was developed to mitigate this problem. This paper presents a laboratory-simulative clogging test of single-layer and TLPA using a falling-head water permeameter. The resistance to clogging of the PA specimens was evaluated by subjecting specimens to five clogging and cleansing cycles. All clogging tests were carried out at an ambient temperature. To evaluate the effects of temperature on clogging resistance, the clogging test procedure was also conducted on selected specimens but conditioned at 10°C, 30°C and 50°C. The test results showed that a significant permeability loss took place during the first few clogging and cleansing cycles, beyond which it asymptotes. The TLPA specimens can better resist clogging compared with the single-layer PA specimens. Binder content significantly affects clogging behaviour, while specimens conditioned at higher temperature were more susceptib...

Influence of reclaimed asphalt content on the mechanical behaviour of cement-treated mixtures

Abstract: For the rehabilitation of asphalt pavements the upper distressed layers are usually milled before overlaying to eliminate reflection cracking–related problems and to preserve the pavement geometry. This maintenance technique generates a large amount of reclaimed asphalt (RA) as a product of the milling operation. The recycling of RA in cement-treated base and subbase courses represents a valuable solution in terms of technical, economic and environmental benefits. However, the influence of RA on the mechanical properties of cement-treated materials (CTMs) is still not completely understood. As a consequence, CTMs using a high content of RA have not yet been widely applied. The present paper shows the findings of an experimental analysis on CTMs including 50% and 80% RA in comparison with the reference CTM consisting of 100% mineral aggregates. In particular, indirect tensile tests and unconfined compressive tests were conducted to evaluate the resistance characteristics of the CTMs. In addition, complex m...

Porous asphalt mixture with 100% recycled concrete aggregate

Abstract: Recycling of construction debris in Singapore is an important practice given the large amount generated annually. In order to maximise the rate of recycled concrete aggregate (RCA) generated from construction debris, porous asphalt mixture (PAM) made of 100% RCA was studied in both mechanical and functional aspects. Altogether, three designs of PAMs were evaluated, namely (a) PAM–RCA mixture comprising 100% RCA, (b) PAM–RCA–TAFPACK-Super (TPS) mixture comprising 100% RCA with enhanced asphalt binder, and (c) PAM–granite mixture comprising 100% granite, with PAM–granite mixture serving as the control. A series of laboratory tests were conducted, namely the draindown test, Cantabro test, Marshall test, permeability test, and ageing test. The results showed that PAM made of 100% RCA (PAM–RCA mixture) can offer the basic drainage function and possesses potential for low-strength application, i.e. pedestrian/cyclist pathways. Meanwhile, PAM made of 100% RCA and modified by specific additive TPS (PAM–RCA–TPS mi...

Improving the rheological properties of crumb rubber modified binder using hydrogen peroxide

Abstract: To overcome the problems of segregation between the rubber particles and the asphalt binder in the crumb rubber modified asphalts (CRMAs) different solutions were tested, including the establishment of chemical bonds between the different components of CRMA and the asphalt materials. In this research, a chemical method was employed to treat variously manufactured (ambient and cryogenic grinded) crumb rubbers’ surfaces in order to graft functional groups and improve bitumen-rubber compatibility and reduce segregation. In general, 400 g of crumb rubber was heated to 80±2°C and was continuously stirred with 100.1 ml of hydrogen peroxide and 90.1 ml of FeSO4 for 30 min. Then the activated crumb rubber was processed into asphalt for 60 min at 177±2°C. Hydrogen peroxide treatment significantly reduced phase separation; it produced even more stable suspension when FeSO4 catalyst was employed. The surface differences of cryogenic and ambient grinded rubbers resulted differences in the flow properties, especially ...

Effect of particle mobility on aggregate structure formation in asphalt mixtures

Abstract: During compaction of asphalt mixtures, aggregate structure starts building up by proximity and direct contact of aggregates. In the previous studies, it has been shown that the aggregate structure directly affects the service performance. However, the mechanisms of the aggregate structure formation are not clearly understood. This study is focused on the mechanisms affecting aggregate mobility during compaction and the effect of material properties on the aggregate structure formation. At the initial stages of compaction, there is a relatively thick layer of mastic (i.e. mix of binder and filler) between aggregates, which allows for a shearing mobility in the mix, if the mastic viscosity is sufficiently low. However, as compaction proceeds, the mastic layer at proximity zone of aggregates becomes thinner due to high stress intensity and the higher viscosity of thin mastic film or the aggregates dry contact effect increases the shearing resistance against compaction (i.e. mix becomes locked). In this study...

Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests

Abstract: Mechanistic-empirical (M-E) pavement design methods have become the focus of modern pavement design procedure. One of the main distresses that M-E design methods attempt to control is permanent def ...