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Recycling of asphalt has become a well-established practice in many countries, however the road pavement industry remains a bulk consumer of extracted raw materials. Novel solutions that find root in circular economy concepts and life-cycle approaches are needed in order to enable optimisation of infrastructure resource efficiency, starting from the design stage and spanning the whole value chain in the construction sector. Itis within this framework that the present study presents a full-scale validation of asphalt mixtures specifically designed to ensure durability of flexible road pavements and at the same time enabling the reuse of reclaimed asphalt pavement (RAP) through the incorporation of bio-materials as recycling agent. These bio-recycled asphalt mixtures have been first designed in laboratory and subsequently validated in a real scale experiment conducted at the accelerated pavement testing facilities at IFSTTAR. Four pavement sections were evaluated: three test sections with innovative bio-materials, and a reference section with a conventional, high modulus asphalt mix (EME2). Two tests were realized: a rutting test and a fatigue test and for each of them the evolution of bio-recycled asphalt mixtures properties as well as the pavement deteriorations were recorded and studied. Evolution of the bio-asphalt mixtures was monitored for a 5 months period after paving by a bespoke nondestructive micro-coring, extracting and recovering methodology developed at the Western Research Institute (WRI). The structural health of the pavement sections was monitored through periodic falling weight deflectometer (FWD) as well as with strain gages and temperature sensors. As a result the three tailored bio-asphalt mixtures performed similarly or better than the control mixture, both in terms of property evolutions and durability. [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]

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]

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]

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]

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]

• Self-cementation of recycled concrete aggregate was investigated by thermogravimetric analysis. • The unhydrated binder content in fine recycled concrete aggregate is between 6.2% and 7.9%. • The secondary hydration products form bonds and densify the microstructure. • The hydration of unhydrated binder can be divided into two phases. A key question concerning the application of recycled concrete aggregates (RCA) into pavement is the assessment of self-cementing properties of RCA, which increase the strength and stiffness of unbound base and subbase layers. In this paper, the assessment of self-cementing properties of RCA, the hydration of unhydrated binder and their influence on the microstructure and mechanical behaviour were studied by subjecting two different RCA (NRCA and ORCA, showing significantly different self-cementing properties), after curing for 0, 360 and 720 days, to the thermogravimetric analysis (TGA), scanning electron microscopic analysis (SEM) and monotonic triaxial tests. The results show that the unhydrated binder content of NRCA is low (between 6.2% and 7.9% in fines), and most of the unhydrated binder was hydrated after curing for 360 days. Besides, the sulfate attack products, ettringite, were also observed from both TGA and SEM, which could also lead to the self-cementing properties. The hydration products of unhydrated cement and sulfate attack products not only form bonds between particles, but also fill the small pores (width less than 3 μm), turning the open type of an unbound structure to a rigid dense skeleton structure. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] We model the stresses in the subgrade of a structure of High Speed Rails. [•] The levels of the stresses in the capping layer have been calculated. [•] They are compatible with mechanical fatigue of stabilized fine-grained soils. [•] A thickness for capping layers made with treated materials is proposed. [Copyright &y& Elsevier]

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]

Abstract Ballast deterioration, under dynamic loads, remains an important issue on high-speed tracks that can lead to high maintenance costs. This ballast deterioration leads to settlements. Several studies have shown that these settlements were linked to high accelerations produced in the ballast by high-speed train (HST) passages. The solution with bituminous underlayment was used since 1980s in several countries like United States, Italy, Spain, especially on high-traffic and high-speed lines (HSL). In France, the interest in this technique is recent. Following the East European HSL satisfactory behavior, a layer of asphalt concrete was used under the ballast layer of the Bretagne-Pays de la Loire (BPL) HSL. It is intended, in addition to the schedule savings and the protection of the subgrade during the construction phase, to reduce acceleration amplitudes produced at the passage of HST, to ensure moisture stability in the subgrade and thereby to decrease the maintenance costs of the tracks. BPL HSL includes 105 km of innovative track with an asphalt concrete (GB) ballast sublayer, and 77 km with a granular layer under the ballast (UGM). Out of the instrumented sections of the BPL track, 3 sections are constructed with GB subballast layer and one with a layer of UGM as a subballast layer. A total of 127 sensors that includes accelerometers, anchored displacement sensors, temperature and humidity probes, and extensometers are used. Sensors are placed at various positions and depths in the track structures. Data were first acquired during a speed up test phase, under controlled conditions, with the same train passing at speeds ranging from 160 to 352 km/h. This paper presents the different sensors used for the instrumentation as well as the acquisition system installed to collect all measurements. Data treatment and processing is explained in details. Finally, results obtained for different speeds are presented, with a focus on accelerometer and anchored displacement sensor measurements, on two sections, allowing, among others, comparisons between the response of structures with and without asphalt concrete. The role of the GB, as a subballast layer, in damping the vertical displacement of the sub ballast structure and reducing the accelerations peaks in the ballast layer for ballasted tracks is demonstrated. [ABSTRACT FROM AUTHOR]

• 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]

• Continuous behavior of HSL with bituminous sub-layer over 4-years was observed. • The bituminous sub-layer reduces acceleration levels under the ballast even after 4 years of service. • No fatigue damage was caused in the bituminous sub-layer under high-speed train traffic. • This study underlines the very good overall behavior of the track. • Detection of track damage using accelerometers appears possible. Tamping and ballast wear, due to dynamic stresses, lead to frequent and costly maintenance operations. To mitigate the impact, an innovative track structure combining a bituminous (asphalt concrete) layer below the ballast has been built on the Bretagne-Pays de la Loire High-Speed Line (BPL HSL). The track is intended to reduce the amplitude of the accelerations produced by passing High-Speed Trains (HST) which are the main reason for the settlement of ballast. BPL HSL includes 105 km of asphalt concrete sub-layer below the ballast and 77 km of granular sub-layer. In order to study the dynamic responses of these different structures, some track sections have been instrumented with anchored deflectometers, accelerometers, strain gauges and temperature probes. The aim of this paper is to present the results achieved after four years of commercial traffic. The data processing methods developed for this acquisition phase and the measurements of the substructure deflection, the vertical accelerations under ballast, and the vertical and horizontal strain of the various sections were presented. Deflection measurements, vertical strains and vertical accelerations peaks at the top of the sub-layer are compared between the granular and the bituminous track structures and shows that there is no evolution of the measurements during the four years of monitoring. The study clearly demonstrated that the presence of the bituminous layer in the structure reduces the acceleration levels under the ballast that cause its deterioration. Such conclusions suggest that a bituminous sub-layer might contribute to lower track maintenance needs over the service life of the line, decreasing operational costs and increasing capacity. [ABSTRACT FROM AUTHOR]

Highlights: [•] The stress states in the capping layer of several HSRs structures have been modeled. [•] Results are compared with stress paths induced by several laboratory fatigue tests. [•] A test is highlighted and a design dedicated to treated/stabilized soils is proposed. [Copyright &y& Elsevier]

Abstract: Road pavement structures are generally composed of granular materials. The influence of the unsaturated state, or suction, on the mechanical behavior of unbound granular materials in roads during a large number of cycles has not been given sufficient attention and is not generally considered in models used for these materials. This article presents an experimental study on compacted natural sand in Missillac, France that used the direct shear test and the soil water retention curve (SWRC) to measure the effective stress, and repeated load triaxial tests to determine the material''s resilient behavior. The effective stress concept was used in a nonlinear elasticity model to predict the material''s resilient behavior under unfavorable moisture conditions, which are one of the most common mechanisms of deterioration in low-traffic pavements. [Copyright &y& Elsevier]

Abstract: Granular materials are generally used in unbound layers of road pavement structures. The mechanical behavior of these materials is widely studied with repeated load triaxial tests (RLTT) in which the elastic response is defined as the resilient behavior. Usually observed under total stress conditions, the effect of pore pressure changes during loading are not usually included in design. Further, the unbound layers frequently exist under partially saturated conditions. The influence of the unsaturated state, i.e., the suction, on the mechanical behavior, of unbound granular materials for roads has not been sufficiently studied and is generally not taken into account in models used for these materials. This article presents an experimental study of the repeated load response of a compacted clayey natural sand, and describes a model for the response which includes the effects of soil suction. The response of the proposed model formulated in terms of effective stress is compared with a similar model formulated in terms of total stress. The results from both the effective stress model and the total stress model are compared with the measured volumetric and deviatoric response. It is suggested that since the model parameters for the effective stress formulation are relatively constant for all values of suction (water content), the resilient response can be best captured by an effective stress model. [Copyright &y& Elsevier]

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 Chaussées. Finally, the calculation of the rut depth evolution with time is carried out. [ABSTRACT FROM AUTHOR]

• The fatigue process of aged asphalt mixtures was assessed under two-point bending fatigue tests. • Acoustic emission technique can characterize the fatigue damage and failure mechanisms. • AE-hits could reflect the onset of damage and failure stages. • New thresholds to identify damage initiation and fracture propagation were proposed. • Classical failure criteria were analyzed and compared to the acoustic emission thresholds. This paper presents a new method for analyzing experimental data stemming from the Two-Point Bending (2 PB) fatigue test conducted on French standardized trapezoidal specimens, in accordance with the European standard EN 12697-24. These tests were performed on an asphalt mix specimen sawn from an in-service road pavement, adopting a loading frequency of 25 Hz and a target temperature of 10 °C. The Acoustic Emission (AE) technique was implemented to monitor the damage and failure processes during fatigue. The fatigue life, defined as the critical number of loading cycles inducing specimen failure, is investigated herein according to several methods, including a normalized criterion, models proposed in the literature, experimental fitting, and Acoustic Emission activity analysis. First, based on the AE analysis, new damage and failure criteria are proposed (Damage Initiation and Failure Propagation Thresholds). In a second step, the mechanical behavior is fitted, in terms of strain, force, stiffness modulus, and phase angle, using four functions, namely: a polynomial function, a continuous Fourier series, a sum of sine functions, and a Gaussian function. After the fitting process, the first derivative is calculated and the singular points of the curves are detected and discussed. Lastly, a phenomenological analysis is carried out in order to understand the damage and failure process stages. [ABSTRACT FROM AUTHOR]