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6th International Conference on Accelerated Pavement Testing , NANTES, FRANCE, 27-/09/2021 - 29/09/2021; The concept of truck platooning is to take advantage of the connectivity technologies and automated driving support systems to link trucks in close formation (convoy) in order to increase transport efficiency, reduce fuel consumption and gas emissions while improving road safety. However, closely guided trucks following each other could have a different impact on road structures than the usual truck traffic. Notably, different studies with traffic simulators highlight the significant effect of the wander pattern of traffic on the damage observed on test road structures. On the other hand, the positioning systems could offer the opportunity to choose an optimized wander pattern of the trucks within the platoons, especially designed to mitigate the overall damage. In this context, the study reported in this paper addresses, through numerical simulations, the multi-loading effects of truck platoons on road structures for different configurations of wander patterns. The aggressiveness of these patterns is evaluated on the basis of the viscoelastic response of the pavement structures (strain field) computed using software ViscoRoute\textcopyright 2.0. Finally, recommendations on the choice of wander pattern configurations to be tested on APT facilities are proposed.

Dynamic on-road charging of vehicles can be done by conductive means, whose implementation require the presence of elements in the pavement, potentially affecting its durability. Some prototypes tested on site and in laboratory showed different mechanisms of damage: rutting, interface debonding and thermal cracking. Including different materials in an asphalt concrete (AC) can generate differential stress fields that can lead to premature failure. A thermal test was developed to simulate the behaviour of AC under daily thermal solicitations. This paper focuses on the development of a numerical simulation able to represent the stress field evolution in the AC. A Generalized Maxwell model coupled to WLF equation represented the thermo-viscoelastic behaviour of the AC under such conditions. This model was implemented into a FEM software named Cast3m®. First results show a stress concentration in the AC just under the groove. According to the design used for implementing ERS infrastructures, stress levels remain under acceptable values as to avoid damage.

Nowadays, the development of electric heavy goods vehicles is hindered by the limited capacity of batteries. An alternative solution to batteries is to develop electrified road systems, capable of supplying and/or recharging electric vehicles while they are driving. In this project, an Electric Road System (ERS), i.e. a solution for electric supply by a feeding track embedded in the pavement, is studied. The system consists of metallic conductive segments, fixed on a rubber support, installed in a groove in the middle of the pavement. Laying such a device in a bituminous pavement requires an efficient bonding of the rubber with the pavement materials, and a good resistance to traffic and climate. Studies were made at laboratory scale and at full scale to select appropriate joint materials and assess the load resistance and durability of the rail/pavement system. Two types of laboratory tests were performed on asphalt concrete samples integrating the rubber elements: wheel tracking tests, at temperatures of 20, 40 and 60 °C, and climatic tests (temperature cycles between −20 °C and 20 °C). Modelling of the tests was also carried out. After evaluation of different products, an appropriate joint material was selected. Then, an accelerated test was performed with the FABAC traffic simulator, to validate the behavior of the electric supply system inserted in a bituminous pavement, at full scale. The pavement structure was instrumented, submitted to 500 000 dual wheel load cycles at 65 kN, and monitored using deflection measurements and profile measurements. The test confirmed the satisfactory behavior obtained at laboratory scale.

Recycling of old pavements is becoming a widespread technique; in order to preserve the natural resources of aggregates and binder, the materials reclaimed from the damaged layers of the pavements maintained are generally reincorporated in the material for new maintenance layers. However, recycling induces some technical challenges. In the case of the Hot mix asphalt (HMA), the most commonly used road construction material, one of the main concerns is ageing. Along with the heterogeneity of the RA properties in stockpiles, it is one of the main factors limiting the recycling rates in HMA. Therefore, the characterisation of ageing through reliable ageing indexes and of its impact on the bitumen physical properties is of paramount importance to improve the recycling techniques. The RILEM TC 237 SIB TG5 inherited a database from the previous work of the RILEM TC 206 ATB TG5 on a protocol for bituminous mixture ageing in laboratory. Taking advantage of these data, the work of the Task Group was first dedicated to a state of the art and an evaluation of the chemical ageing characterization through indexes based on Fourier Transform Infrared Spectroscopy (FTIR). In a second step, an attempt was made, in order to bring out the essential trends of the rheological data with ageing, by using a Huet modified rheological model. Then, exploring the potential of a recently developed method, an interpretation of these trends in terms of asphalt structure is suggested. Finally, possible empirical relationships between the chemical ageing indexes and the rheological parameters are investigated.

Within the framework of a sustainable development, manufacturing bituminous mixtures while reducing energy and using less new aggregates and new bitumen may be considered as an important topic, according to the quantities of asphalts mixtures produced for creating and maintaining road networks. This work aims to study the interest and the potential problems when coupling the warm mix asphalt technology (WMA) and the use of high ratio of reclaimed asphalt pavement (RAP) in the mixture. Initially, a study on managing RAP is performed, aiming to show that separating RAP aggregates in several fractions leads to a higher control of RAP in terms of homogeneity. Homogeneity of RAP is a key point for increasing recycling rates. The present study coupling WMA and RAP is based on the French design method for manufacturing asphalt concretes, which includes gyratory compaction tests, French wheel tracking tests, complex modulus tests and fatigue tests. However, the French design method does not take into account the physical and chemical aging of bituminous mixtures with time. As we consider that coupling WMA and RAP may lead to aging problems, it was decided to use an aging process before performing the standard tests. The results show that a WMA containing a high ratio of RAP has good performances according to the standard relative to this material, whatever the test. However, this material tends to be more sensitive to fatigue than hot and warm mixes without RAP.

Sustainable development policies currently in effect in civil engineering serve to promote techniques capable of saving both energy and raw materials; such techniques use a combination of warm mix asphalt (WMA) concretes with reclaimed asphalt pavement (RAP). One issue raised when combining WMA and RAP involves determining the potential lack of RAP binder remobilisation during blending with the new binder, i.e. the so-called double-coating phenomenon. This paper aims to present the results of an Attenuated Total Reflection (ATR) imaging by means of infrared microspectrometry on asphalt mixtures featuring high RAP content. In the context of a Ph.D. thesis program, this analysis is combined with a study of the mechanical performance of these materials (not presented herein). The main objective of this research work is to assess the blending and coating quality of the materials at the microscopic scale. The experimental program consists of evaluating raw aggregates, binders, RAP and asphalt mixtures by ATR-FTIR microspectrometry in order to generate pictures for analysis and interpretation according to two distinct methods, namely Principal Component Analysis (PCA) and Independent Component Analysis (ICA). This analysis protocol introduces markers inside asphalts, like SBS or EVA copolymers or carbonyl and sulfoxide indices. The first main result of this study is improved control over the ATR imaging tool and its enhanced potential for analysing bituminous mixtures. A protocol for preparing samples and interpreting their results can now be proposed; an actual asphalt concrete has been analysed, not merely a laboratory-produced sample, as indicated in the literature. As a second result, tracers have been set up to distinguish raw and RAP materials (aggregates and binders), thus representing an initial step to studying the double coating, although it would seem difficult to generalise this study to a wide array of mixtures. Lastly, let’s point out that ATR-FTIR imaging is a “localised” study, making the determination of bituminous material homogeneity at specimen or even stockpile scale a real challenge for the future.

Setting a method to evaluate the mechanical properties of an aged asphalt mix using a rapid chemical measurement from small samples, would be of high interest at different steps of a road structure life cycle: at the design step, to optimise the estimates of the service lifetime usually based on the properties of unaged materials; during the service life, to update the residual lifetime expectation of an existing structure according to the actual properties of the in situ aged materials; and at the end of the service life or for maintenance management, to evaluate the recyclability of the materials of the structure. This study was carried out aiming at comparing results from Fourier Transform InfraRed and Dynamic Shear Rheometer tests. Experimental data came from an international round robin test, organised by the RILEM TC ATB, designed to set an ageing protocol on loose bituminous mixtures. The evolutions of the carbonyl index (ICO) calculated from the FTIR spectra are compared to the evolutions of the parameters of a modified Huet Rheological Model (1S2P1D) fitted on the experimental linear viscoelastic data measured on the recovered binder. A significant relationship is observed suggesting that chemical and rheological properties could be correlated. Based on this observation, a method is proposed for predicting the G* values of a binder aged at a given ΔICO level. Subsequently, this method could be used to predict the complex modulus E* of a given mix from the shear modulus G* of the binder using existing binder/mix transfer models.

In the framework of a study on rutting of bituminous layers, thermo-controlled triaxial tests under constant confining pressure on homogeneous asphalt concrete specimen have been performed. These tests are cyclic sinusoidal tests, with the aim to reproduce in some way the loading and unloading phases due to traffic on roads. The influences of confinement and load frequency have been studied. Tests have highlighted that confinement notably decreases the strain rate as well as the level of strain reached at the end of the test. The tests did not allow to clearly observe the influence of frequency on the response of the material, due to problems of repeatability. In order to avoid such problems, another test procedure was adopted. It consisted in changing either confinement or frequency during the test, with the purpose to see an evolution of strain rate, and to establish correlations. These tests have clearly shown the influence of cyclic loading and the relative influence of loading frequency on the response of asphalt concrete. The main objective of this triaxial programme is to develop a numerical model, based on rheological laws, able to predict the behaviour of bituminous layers.

This chapter focuses on permanent deformation, which is at the origin of pavement rutting. First experimental laboratory tools and associated analyses related to permanent deformations are presented. It is either material tests, that can be homogeneous or giving a simple empirical characteristic, or non-homogeneous Structural/Specimen tests.

This chapter first presents the results of a survey perfomed on the practices used in Europe. This survey is first report on the subject and could be usefully completed by the states of the art prepared in the framework of the Re-road and Direct-Mat European projecys.

In the framework of the RILEM TC 206-ATB TG3, a Round Robin Test (RRT) has been performed in order to evaluate the reproducibility of the French Wheel Tracking Test (FWTT) on a mix made with Polymer Modified Bitumen (PmB). For this mixture, some particular problems had been reported, such as heating of the sample due to friction and sticking of the binder to the wheel. Two procedures, called anti-overheating and anti-sticking procedures, have been proposed by the group in order to improve the reproducibility of the wheel tracking tests. These procedures are assessed. Causes of scattering are discussed. Differences between the tyres used during this RRT as a possible origin of scattering are discussed, as well as temperature peaks and over-compaction of specimens.