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The strength and stiffness of unbound pavement base and subbase layers built with recycled concrete aggregates (RCA) can increase due to the self-cementing properties of RCA. While the effect of different levels of self-cementing properties on resilient deformation behaviour has not been thoroughly studied. In this research, the self-cementing properties, microstructure and resilient deformation behaviour of two different RCA, NRCA (New RCA, crushed recently) and ORCA (Old RCA, crushed long time ago), showing significantly different levels of self-cementing properties, after curing for different times (1, 180, 360 and 720 days), were studied by calorimeter tests, mercury intrusion porosimetry (MIP) tests and repeated load triaxial tests (RLTT). The results indicate that long-term resilient behaviour is influenced by the level of self-cementing properties. For NRCA, showing strong self-cementing properties, the microstructure and resilient deformation behaviour were improved after curing for 720 days, which were comparable to those of lightly treated materials. On the contrary, for ORCA, showing negligible self-cementing properties, the resilient behaviour is not affected by curing. [ABSTRACT FROM AUTHOR]

This paper presents part of the studies developed in the European project ENSEMBLE. (ENabling SafE Multi-Brand pLatooning for Europe). The first part of the paper describes the validation of a numerical model based on comparisons with experimental results obtained from a test section subjected to the pass of 3 human-driven trucks simulating a platoon configuration. The numerical model is then used to predict the maximum and accumulated strains produced by the passage of each truck on the same test section at two different temperatures when the following platoon parameters are varied: (1) inter-truck time gap, (2) truck speed and (3) lateral deviation (wandering). The results confirm that the proper control of these parameters can help to keep the same level of fatigue damage as with trucks in individual configurations. In this way, the environmental, social and economic benefits of platooning can be attained without compromising the existing pavement structures. [ABSTRACT FROM AUTHOR]

A better understanding of the changes in binder chemistry and microstructure triggered by aging is fundamental as it increases the cracking susceptibility of asphalt materials and reduces pavement durability. In this context, this paper presents the findings of a collaborative study that delves further into the alterations in binder chemistry, microstructure, and rheology of laboratory – and field-aged binders using innovative experimental and fundamental theory techniques. An increase in polarity leading to a shift in the apparent molecular weight distribution (AMWD) towards higher molecular weights, which implies molecular agglomerations, could be observed as a result of aging via Saturates, Aromatics, Resins, and Asphaltene Determinator (SAR-AD) and Size Exclusion Chromatography (SEC), respectively. As for the theoretical methods, the δ-method and Molecular Agglomeration Index (MAI) that estimate the AMWD and incidence of molecular agglomeration, respectively, show satisfactory relationship with the SAR-AD and SEC results. This reinforces the soundness of the δ-method and MAI. [ABSTRACT FROM AUTHOR]

Partially/fully self-driven trucks in platoon configurations promise to increase transport efficiency, reduce fuel consumption/gas emissions and improve road safety through the use of connectivity technologies and automated driving support systems. However, truck platooning means the introduction of new types of loads on pavements which are characterised by: multiple loads, generated by the multi-axle configurations of the different trucks forming the platoon, traffic channelisation by the reduction of the lateral deviation of the trucks, and reduced inter-truck time gaps, which may reduce the self-recovery capacity of asphalt concrete materials, reducing the pavement service life. In this context, this study presents a parametric analysis carried out to evaluate a pavement structure subjected to several platoon truck configurations. The results of the study indicated that to keep the same pavement structural response as for individual trucks, it is possible to act on the following parameters in the platoon configuration: traffic distribution along the year and along the time of the day (avoiding traffic at higher temperatures), percentage of platoon penetration in the daily and annual traffic, level of loading of the trucks, number of trucks in platoon configuration, wandering, and inter-truck time-gaps/distances. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the permanent and resilient deformation behaviour as well as the shear and physical properties of different RCA, sourced from demolished buildings (RCAB1 and RCAB2) and concrete pavement (RCAP). Monotonic triaxial tests and repeated load triaxial tests (RLTT) were performed to determine respectively their failure resistance and the cyclic behaviour, modelled with the Boyce model and the DBGSP model. In addition, the physical properties and water absorption kinetics of aggregates were studied and compared with the existing standard. The results indicated that all RCA have admissible physical properties and can be used in pavement base and subbase layer. However, the RLTT revealed that the use of concrete wastes with low strength and containing high amount of rounded particles (RCAP in this study) can lead to poor performance of pavement, which should be limited in the pavement construction. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms for road surface degradation requires an examination of asphalt layer responses under realistic rolling tire loads. In this study, we proposed a novel tire-sensor-pavement coupling chain for integrating the realistic distribution of tire contact stress into the mechanical modelling of the asphalt layer. The tire contact stress distributions under different tire loading conditions including tire loads and tire inflation pressures are obtained by using a sensor measuring system. The temperature- and frequency-dependent material behaviour of asphalt mixes is described through the VENoL (NOnLinear Viscoelastic) model. The model reliability is validated by numerical/experimental confrontation via a series of complex modulus tests. A new algorithm is developed to achieve the coupling simulation of the tire–pavement interaction system. Finally, the dynamic responses of the asphalt mixture including external force, displacement fields and surface deflection were investigated depending on rolling tire loads. The proposed method provides a fundamental requirement for understanding the structural behaviour of asphalt pavement loaded by rolling tires, which can be used to get insights into asphalt pavement surface design. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate a source of reclaimed asphalt aggregates without binder addition. To this end, a series of triaxial tests was performed. First, monotonic triaxial tests allowed to determine failure resistance of the material at 20°C, 50°C and at 20°C with a prior preheating at 50°C. Then, the resilient and permanent behaviours at 20°C were studied thanks to Repeated Load Triaxial (RLT) tests with different levels of loading. The results show that increasing the temperature test implies a drop of failure resistance but a higher cohesion. RLT tests reveal a stress dependent resilient behaviour. Finally, the experimental results were compared with calibrations of the non-linear elastic Boyce model.

Rutting, due to permanent deformations of unbound materials, is one of the principal damage modes of low traffic pavements. Flexible pavement design methods remain empirical; they do not take into account the inelastic behavior of pavement materials and do not predict the rutting under cyclic loading. A finite-element program, based on the concept of the shakedown theory developed by Zarka for metallic structures under cyclic loadings, has been used to estimate the permanent deformations of unbound granular materials subjected to traffic loading. Based on repeated load triaxial tests, a general procedure has been developed for the determination of the material parameters of the constitutive model. Finally, the results of a finite-element modeling of the long-term behavior of a flexible pavement with the simplified method are presented and compared to the results of a full-scale flexible pavement experiment performed by Laboratoire Central des Ponts et Chaussees. Finally, the calculation of the rut depth evolution with time is carried out. DOI: 10.1061/(ASCE)EM.1943-7889.0000165 CE Database subject headings: Elastoplasticity; Triaxial tests; Full-scale tests; Highways and roads; Predictions. Author keywords: Elastoplasticity; Elastic shakedown; Plastic shakedown; Repeated load triaxial tests; Full-scale experiment.

The objective of this study is to assess the impact of climate on the performance of bituminous pavements with two different methods, and then to examine their impact on actual design scenarios. Three climate cases were selected for the comparisons involving the effect of temperature: one in France (Bordeaux) and two in the United States (Seattle and Phoenix). The case of an experimental site in Québec was also used for comparisons concerning consideration for seasonal variations in ground bearing capacity. The analyses were based on French (Alizé-LCPC) and US (AASHTOWare Pavement ME Design) mechanistic-empirical pavement design approaches. Interesting features of the two design methods are outlined and their fatigue cracking models are linked together. The results of the study highlight the importance, for design purposes, of the empirical fatigue equations as a function of temperature. For the site studied in France, the design results in terms of AC base layer thicknesses indicate that both methods show a similar trend with an increase in temperature. For the site in Québec, which is submitted to severe freeze/thaw cycles, the results show that taking temperature and moisture into account for unbound materials leads to a prediction of more severe permanent deformation. Highlights Presentation of two mechanistic-empirical (ME) methods for pavement design Description of the fatigue equations governing asphalt mixes for design purposes Identification of the parameters used in the design of pavement structures Study of the influence of the climate in France and Québec on pavement performance Comparison of the French and US methods for pavement design and correspondence between them [ABSTRACT FROM AUTHOR]

Because bitumen aging is behind the major pavement distresses, a better understanding of it is of utmost importance for tailoring longer-lasting roads and developing more effective maintenance strategies. For this purpose, this paper presents an in-depth review of the relevant literature on the aging phenomenon of neat (unmodified) bitumen. The main accelerated laboratory aging procedures as well as some recent ones, for both bitumen and asphalt mix, are presented, and their effectiveness in reproducing the effects corresponding to field aging are discussed. Then, the main laboratory tests used to track the evolution of bitumen aging and some end-of-life criteria that reflect poor pavement performance are outlined. Finally, a promising method whereby the colloidal structure of bitumen can be estimated from its rheological behavior is presented. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) arises from the demolition of asphalt road layers. The Optimal Recycling of Reclaimed Asphalt Pavements Project concerns the cold recycling of 100 % RAP without binder addition in base and subbase layers of low-traffic roads. In this context, a test program was performed with Rhine region materials to evaluate the impact of the mastic coating of untreated RAP. A source of reclaimed asphalts with 4.4 % of bitumen is tested before (RAP) and after binder extraction (RAP-BE) and then is compared to an unbound granular material (UGM) with a similar particle-size distribution. Repeated load triaxial tests were conducted at several frequencies to study the permanent and resilient behaviors. The results show that the RAP before binder extraction and the UGM present similar permanent behaviors, while the aggregates without binder reveal low strains. Concerning the resilient phase, the RAP and the RAP-BE show similar levels of strains, but the resilient moduli of the UGM are significantly lower than those of the RAP. From the experimental results, the nonlinear elastic Boyce model was fitted and brings out a highly anisotropic mechanical behavior of the RAP. Finally, the RAP shows a frequency-sensitive viscous behavior because of the bitumen in the mastic, while the effect of the frequency is negligible for the RAP-BE. [ABSTRACT FROM AUTHOR]

The paper presents tests performed on an instrumented motorway section, to monitor traffic and pavement deflections using geophones. Geophones are sensors used to measure displacement velocities, and by integrating their signal, it is possible to monitor vertical displacements. In this study, 4 geophones have been installed in the base layer of the pavement, and their measurements have been recorded under real traffic, during a period of approximately 18 months, using a remote control data acquisition system, transferring the data to a server. Different methods of treatment of the geophone measurements have been proposed: the first application concerns the detection of different heavy vehicle silhouettes, by analysing the number of peaks of the displacement signals; the second application concerns the measurement of vehicle speeds, by determining the time difference between the measurements of two geophones. The third application concerns the measurement of pavement deflections. To measure accurately the deflection, a procedure has been developed, to correct the geophone response, which is attenuated in the low frequency range. This procedure has been validated by measurements under controlled loading conditions, on the IFSTTAR accelerated pavement testing facility, and then applied to in situ measurements. In conclusion, the study shows that geophones, which present the advantage of being relatively inexpensive and robust sensors, offer interesting possibilities for pavement monitoring. [ABSTRACT FROM AUTHOR]

When reinforcing existing cracked asphalt pavements, the design and evaluation of the durability of the reinforced structure are quite different from those of a new pavement generally based on fatigue criteria deduced from stress and strain fields computed for the undamaged pavement. For the design of reinforcement solutions, the presence of cracks and their propagation must be considered explicitly. To move in this direction, the present article aims at improving the understanding of bottom-up crack propagation in asphalt pavements. Some investigations relying on the interpretation of an accelerated full-scale fatigue test are presented as well as the numerical analysis of this test through the theory of linear elastic fracture mechanics and the Paris law. The tested pavement section is composed of four layers. The two uppermost layers are made of asphalt concrete (AC) materials whose modulus and fatigue performances are different. The pavement is subjected to repeated loads applied by the Fatigue du Béton Armé Continu (FABAC) traffic simulator of the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR), and the development of cracking in the AC layers is monitored using embedded instrumentation and Falling Weight Deflectometer (FWD) test campaigns. To better control the crack pattern that develops during the fatigue test, an artificial flaw (metal angle) is purposely placed at the bottom of the AC layers (in the transverse direction to the moving loads) to localize the initiation of cracking. A bottom-up crack is supposed to grow vertically from this defect in the AC layers. This is effectively detected and followed by the experimental measurements, which are combined to model for the analysis of the test. Finally, the kinetics of crack growth deduced from the Accelerated Pavement Test (APT) results and those computed using the Paris law calibrated from fatigue tests performed in the laboratory are compared. [ABSTRACT FROM AUTHOR]

The phenomena of settlement and wear of the ballast under dynamic stresses lead to high frequencies and high maintenance costs on high-speed railway lines. Studies have shown that these settlements are linked to high accelerations produced in the ballast by the passage of high-speed trains (HST). A layer of asphalt concrete (GB) was introduced under the ballast layer on the high-speed line Bretagne-Pays de Loire (BPL HSL). It is intended, among other things, to reduce the amplitude of accelerations produced at the passage of the HST and thus improve the durability of the track. The BPL HSL spans 105 km, with a sublayer of asphalt concrete under the ballast and 77 km with a granular sublayer (UGM). To evaluate the performance of the structures with bituminous sublayer and to compare it with traditional structures with granular sublayer, four track sections have been instrumented during construction. This article presents the different sensors of the instrumentation, as well as the acquisition system installed to collect measurements. The focus, in this study, concerns the temperature, water content, and vertical settlement measurements made on the instrumented sections. Temperature variations recorded during two years on the railway structure with bituminous sublayer were analyzed and compared with those measured on a classical bituminous pavement. Influence of the bituminous layer on water infiltration and track settlements has also been studied. [ABSTRACT FROM AUTHOR]

Geogrids are used for the rehabilitation of cracked pavements. To ensure an efficient reinforcement, it is required to know the residual mechanical properties of the geogrid after its implementation and compaction of the above asphalt concrete layer and the level of damage of the grid. This article presents the results of the national French project SolDuGri dealing with pavement reinforcement by geogrids and more precisely the reproduction in laboratory of the in situ damage. In this project, full-scale tests have been performed to evaluate the in situ damage of four different types of geogrids in asphalt concrete pavements. Then, after construction, the geogrids have been recovered from different locations on the field sections, where they had been subjected to compaction. These grids have been subjected to direct tension tests in the laboratory. Laboratory analyses like scanned asphalt concrete and greogrid surfaces have been performed to evaluate indenter shapes. Different sets of indenters have been made, and a laboratory complete study of greogrid indentation tests has been performed with different sets of temperature, indenter shapes, and indentation forces. The first conclusions are that the indenter geometry and the temperature have the main influence on the strength resistance and elastic modulus of the grid. Results obtained after indentation performed in laboratory can be compared to those measured on in situ recovered grids. [ABSTRACT FROM AUTHOR]

Classically, measurements on instrumented pavements are performed on site, under known load conditions. In such conditions, data interpretation and modelling of the pavement are relatively easy. However, on-site measurements are time consuming and costly to perform, because they require using a dedicated vehicle and closing the lane to traffic. This paper presents an experiment, where an instrumented bituminous pavement motorway section has been followed by remote monitoring, under normal traffic. The section, instrumented with strain gages, temperature probes and geophones, has been monitored continuously during 18 months. Signal sorting procedures have been developed for reducing the quantity of recorded data, and for analysing the structural response of the pavement, under highly variable loading conditions. The results of the strain gage measurements, made at different depths within the pavement, have shown that the response of the pavement presents large variations with temperature, and in particular, that the degree of bonding between layers can decreases at high temperatures, leading to sliding between pavement layers. The mechanical response of this section has been analysed using a classical multi-layer linear elastic pavement model and also a viscoelastic model. The best predictions have been achieved with the viscoelastic model. Different approaches for describing the behaviour of pavement layer interfaces have also been evaluated. [ABSTRACT FROM AUTHOR]

Since users expect long-lasting roads, road system managers must maintain infrastructures that are tailored to the needs of traveling, offer a growing number of services, are meticulously maintained, and are resilient to weather events. However, with societal issues and budget constraints, it becomes difficult for managers to ensure the optimal operation of their networks. To tackle this huge challenge, The French institute of science and technology for transport, development and networks (IFSTTAR) has launched the 5th Generation Road program. This program aims to design full scale demonstrators, which integrate the numerous innovations that are already available in research centers, and to demonstrate the synergy among them. After presenting the general objectives of the 5th Generation Road program, this paper presents one example of a demonstrator that concerns remote monitoring of an instrumented motorway section. [ABSTRACT FROM AUTHOR]

The constitutive modeling of cyclic plasticity of soils has made great progress, especially in the area of sands liquefaction modeling. Nowadays, the problem of rutting of flexible pavements linked to permanent deformations occurring in the unbound layers is taken into account only by empirical formulas. This paper presents an elastoplastic model with both isotropic and kinematic hardening. The yield surface, plastic potential, and isotropic hardening are based on a model for sands, which takes into account the influence of the initial void ratio and of the mean stress on the mechanical behavior. A kinematic hardening has been added in order to take into account the mechanical behavior of the material for large cycle numbers. A complete model is then developed, simulations are presented, and comparisons with repeated load triaxial tests carried out on a subgrade soil (clayey sand), have been made. These comparisons underline the capabilities of the model to take into account the monotonic, cyclic, and ratchetting behavior of unbound materials for roads. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

• Recycled concrete aggregate. • Self-cementing properties. • Unhydrated cement content. • Unbound granular material. • Monotonic triaxial test. Recently, the use of recycled crushed concrete aggregates (RCA) as a substitution of natural aggregates in pavement base and subbase layers has become more popular. Occasionally, a growth of stiffness and strength in unbound base and subbase layers built with RCA can be observed, which can be considered as self-cementing properties of RCA. In this study, the potential self-cementing properties and the long-term mechanical behaviour of two different RCA (NRCA and ORCA), with significantly different self-cementing properties, were studied by pH value, thermogravimetric analysis (TGA) and monotonic triaxial tests under varying confining pressures (20/40/70 kPa) and varying curing times (1/28/360 days). Results show that the long-term storage can largely reduce the self-cementing properties of RCA (ORCA), while the RCA crushed recently (NRCA) exhibits much stronger self-cementing properties. Besides, the long-term mechanical behaviours are influenced by self-cementing properties and confining pressure as well as curing time, so that the strength and stiffness of RCA specimen, with stronger self-cementing properties (NRCA), increase more under low confining pressure and long curing time. The experimental results also indicate that the long-term mechanical behaviours of NRCA are consistent with cement treated materials, whose ductile stress–strain response gradually turns to stiff brittle behaviour as curing time increases. [ABSTRACT FROM AUTHOR]