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A laboratory study was done on three bitumen of penetration grade 50/70 from three sources and three corresponding mastics made using these three base bitumen and one filler – Limestone. The tests ...

Utilisation of recycled construction and demolition waste (CDW) within pavements is a beneficial substitution technique towards sustainability. Following this approach, this research investigates t...

In recent years, crumb rubber (CR) has become an attractive option to modify bitumen. In this research, a set of Dynamic Shear Rheometer (DSR) tests were used were used to gauge the effect of two t...

After premature de-bonding failures of several roads in Germany, researchers at the Technische Universität Dresden developed a new testing device, the Dresden Dynamic Shear Tester (DDST), for quality control and characterization of the interlayer bond. The DDST is used to quantify the shear stiffness of the interlayer bond between asphalt layers at different temperatures, stress levels, and frequencies. The DDST was designed to avoid some limitations of common interlayer bond static tests (i.e., Leutner tests, torque bond tests, etc.) by simulating the dynamic loads experienced by real pavements and determining material parameters which can be used within mechanistic models. The paper presents the philosophy and methodology behind the DDST as well as the post-processing of the test data to obtain a master curve of shear stiffness of the interlayer bond. The master curve is determined by back-calculation of testing data by coupling a Fourier assisted finite element method with an optimization algorithm. The results of experiments showed that the shear stiffness at the interlayer zone was strongly influenced by the temperature, frequency, and normal load. At high temperatures the adhesion of the tack coat did not contribute to the layer bond. It was deduced that at high temperature and with no axial load shear stiffness was achieved only through aggregate interlocking and, when normal pressure was applied, through friction between the surfaces of the asphalt layers.

An innovative consistent simulation chain is used in this chapter for the combination of the advantages of a microstructure finite element (FE) model of asphalt composites with a macrostructure FE model of pavement under tire rolling load. For this study, an existing microstructural FE model of a Stone Mastic Asphalt including coarse aggregates, asphalt mortar, and air voids was parameterized and validated beginning with experimental tests of asphalt mortar. In order to identify the macroscopic (homogenized) material properties of the asphalt mixture for use in the FE computations of two pavement structures under rolling tire load, this validated microstructural model is applied. These calculations are then evaluated using a new macro-micro-interface, which represents the rolling tire loading conditions for the microstructural model by generating time-dependent displacement boundary conditions. The results indicate that the introduced simulation chain allows for the investigation of the processes, stresses and strains inside the asphalt composite at realistic loading conditions. The experimental tests on the component level can be improved and a better comprehension of the interacting processes in asphalt mixtures under rolling tire load can be obtained by using the results.

In this chapter, a simulation chain is described and applied to an asphalt test track and a highway pavement structure. The simulation chain consists of different modules reaching from the experimental identification of the asphalt material, its numerical modeling on the material scale via adequate models to finally the structural scale of the pavement and the vehicle-tire system, which is numerically assessed in the framework of a coupled vehicle-tire-pavement system. Relative dynamic effects of vehicle-tire-pavement interaction have been investigated based on a multibody analysis of the vehicle driving on a rough pavement surface (external stimulus). For the pavement simulation, equivalent tire loads are used in an arbitrary Lagrangian Eulerian framework for tire and pavement. Finally, the rut formation is computed by varying different influence factors (climate temperature, vertical tire force, type of asphalt material of the surface layers etc.). With the help of the simulated deformed pavement geometry (whole service life), surface drainage characteristics are finally analyzed and assessed via a surface drainage module, e.g. to compute and predict the alteration of the pavement runoff during the service life of the pavement.

This chapter presents a comprehensive characterization of asphalt concrete at different scales of observation. State-of-the-art characterization procedures for bitumen, mastic, mortar and asphalt are described in detail. The procedures were envisaged to provide experimental data for parameter identification and validation of constitutive numerical models. The validation of numerical models against experimental data is a prerequisite for the use in any application. The temperature-frequency dependency of the rheological properties of bitumen and mastic was characterized using temperature sweeps in the dynamic shear rheometer. The results showed that the bitumen provenance and the filler’s mineralogy have a major impact on the rheological response of the asphalt. A new rheometer, known as Dresden dynamic shear tester, was developed with the aim of characterizing the thermo-viscoelastic properties of mortar. This novel equipment was also used to identify the stiffening effect of the aggregates by comparing the results of bitumen, mortar and asphalt. Finally, the short and long term behavior of different asphalt mixtures were characterized with the repeated load triaxial tests and with the indirect tensile tests. The results showed that the performance of asphalt is highly affected by the bitumen type and the aggregate gradation.

Understanding the structural behaviour of layered asphalt pavements at loading by rolling tyres is a fundamental requirement for the future design of more durable pavements. The paper presents the ...

Currently, many efforts are undertaken to reach asphalt performance from binder performance in order to reduce costly and time consuming laboratory tests on asphalt materials. In this context, it is important to use and develop appropriate testing methods for a comprehensive binder characterisation, which requires suitable material models. Depending on the application, different models can be used to model rheological bitumen behaviour. This paper focuses on the applicability of the Christensen and Anderson model (CA model) and the Olard-Di Benedetto (2S2P1D) model for bitumen samples containing different amounts of recycled components using various objective functions in the optimisation process. The purpose is to analyse the influence of the reclaimed asphalt rate on the parameters of the investigated models. Dynamic Shear Rheometer tests are conducted on binder samples extracted from Stone Mastic Asphalt mixes with polymer modified bitumen and Asphalt Concrete mixes with paving bitumen, each co...

Bitumen of penetration grade 50/70 is the most commonly used binder in asphalt pavements of Europe. This research attempts to differentiate between three bitumen of penetration grade 50/70 that have been acquired from three sources. The rheological properties, fatigue and rutting resistance were analyzed and compared using the results of Dynamic Shear Rheometer (DSR) tests. The rheological test data acquired were modelled and further approximated using the 2S2P1D model. Additionally, to understand the changes in performance due to ageing, all the DSR tests were repeated for Rolling Thin Film Oven Test (RTFOT) aged and Pressure Aging Vessel (PAV) aged bitumen. Finally, the tests results were summarized in a performance diagram to aid in overall ranking of the bitumen taking into consideration relevant parameters.

Computer-aided civil and infrastructure engineering (2020). doi:10.1111/mice.12535, Published by Blackwell, Boston, Mass. [u.a.]

Fatigue performance of bitumen holds great importance in the design and durability of asphalt pavements. However, there are still gaps in knowledge on the influence of specific experimental conditions on the degradation of bitumen under cyclic loading. Stress-controlled fatigue tests at three temperatures (-10 °C, 15 °C and 20 °C) and two loading frequencies (10 Hz and 20 Hz) were performed on cylindrical specimens of a 50/70 grade bitumen, using a recently developed fatigue testing protocol in the Dynamic Shear Rheometer (DSR) equipment. Experimental data were analysed through multiple analysis approaches, including a novel ‘failure lines’ method that uses the dissipated energy (DE) of the material and the number of cycles to failure (Nf). Experimental results corroborated the impact of temperature and frequency testing conditions on the fatigue response of the bitumen. For example, at 200 kPa and 20 °C, the bitumen dissipated 3.07 times more energy at failure at 10 Hz than at 20 Hz; while at 400 kPa and 10 °C, the bitumen only dissipated 1.07 times more energy at 10 Hz than at 20 Hz. Also, depending on the applied stress, the bitumen tested at 10 Hz dissipated between 2.45 and 4.02 times more energy at 20 °C than at 15 °C, and between 4.11 and 6.52 times more energy at 15 °C than at 10 °C. Additionally, 15 °C was identified as a ‘frequency-free transition temperature’ for this bitumen, as the ‘failure lines’ at both frequencies overlapped. Finally, a new temperature and frequency independent fatigue representation was identified when analysing the initial DE and Nf data.

In this contribution, a physically motivated continuum mechanical model for asphalt concrete and stone mastic asphalt (asphalt material) at large deformations is proposed. The rheological model consists of a short-term and a long-term part connected in series governing the description of the short-term and the long-term behavior (volume preserving) of the asphalt material, respectively. The rheological element assembly of the short-term part is physically motivated by the particle size distribution of the asphalt material under investigation (choice of several networks formed by different size fractions of the aggregate mixture) and represents the asphalt material’s mainly viscoelastic behavior to short-term loading, e.g. during contact with a rolling tire. The long-term part captures large inelastic (accumulated) deformations due to repetitive loading and enables to represent e.g. rut formation during a structural pavement analysis. An experimental testing program including digital image correlation (DIC) for strain measurements on cylindrical samples was set up and enabled the identification of the model parameters. Furthermore, specific model parameters have been identified from the information provided by the manufacturer’s data sheet of the asphalt material based on the particle size distribution of aggregates, the binder content and the void content.

The motivation for this research comes from the inadequacy of the methods currently used for sizing and optimization of building materials used in pavement construction based on increasing traffic loading and changing climatic conditions. Using examples, the paper highlights how deficits can be identified by a detailed investigation of the relationships in order to form a foundation for solving these deficits.

The paper discusses the effect of the amount and particle size of rubber on the properties of rubber-modified bitumen. Therefore, rubber-modified bitumen with rubber contents of 10, 15 and 20 % and a variation of the particle size from small (0.4 mm) to middle (0.8 mm) and up to big (1.0 mm) were prepared in laboratory by using a paving bitumen 50/70 as reference bitumen. Additionally, a polymer-modified bitumen (PmB 25/55-55), which is commonly used in asphalt wearing and binder courses, was involved in the investigations to verify the modification states. Different laboratory tests were conducted to evaluate the influence of the selected rubber particles. At first, the impact of the rubber modifications on conventional bitumen tests are presented. Furthermore, DSR tests were conducted to determine performance related bitumen properties. DSR results have also been used to determine the rutting susceptibility. In addition, the binders were rated to their fatigue damage resistance by applying repeated load cycles using the DSR test device as well. Following, the paper gives recommendations in terms of the use of rubber-modified binders for asphalt pavements.

A good and durable interlayer bond is of high importance for the service life of asphalt pavements. Accordingly, the interlayer bond has long been the subject of active investigation. This paper describes a new test device for cyclic testing of the interlayer bond in double-layered asphalt laboratory specimens. Experiments were carried out to determine the shear stiffness at five temperatures, five normal stresses, and six loading frequencies. All three parameters had a strong influence on the shear stiffness and, therefore, on the operation of the interlayer bond. At low temperatures, high tack coat stiffness as well as good adhesion and aggregate interlocking was present. In contrast, rapid decrease in bonding stiffness occurred at rising temperatures because of the loss of adhesion. In addition, a total loss of interlayer bond occurred at low loading frequencies when no normal force was applied. Furthermore, it was observed that the tack coat amount applied at the interface had a significant effect on the shear stiffness. A numerical model based on the finite element method was developed to simulate the test. With the aid of sigmoidal regressions built for the lowest and highest test temperatures, it was possible to predict the shear stiffness analytically at any shear force and shear displacement and to compare the stiffness with the experimentally determined one.

Unbound Granular Materials (UGM), used in base and subbase layers, play an important role in the structural performance of low volume roads with thin asphalt surface layers. They show complex stress dependent elasto-plastic behavior under cyclic loading. A proper understanding of the elastic and permanent deformation behavior of UGM is crucial to assess their suitability for the particular service. Full understanding of the material behavior is only possible by means of sophisticated test procedures such as the repeated load triaxial test. This testing method is quite complicated and the human and technological resources needed usually exceeds the budget of low volume road projects. Therefore, there is a need for simple and economical test methods to characterize the mechanical behavior of UGM under the action of high traffic loads. The paper shows the results of a test campaign using two different testing methods: a simple repeated load volumetric compression test and a more advanced repeated load triaxial test. The results of both tests showed a strong dependency of the bearing capacity and the permanent deformation behavior on the amount of water and stress level. The tests results are also used to develop a classification method for UGM.

As basis for the subsequent numerical modelling of tyre–pavement-interaction phenomena, an adequate representation of asphalt material behaviour is required. Therefore, in the present publication, experimental investigations by the repeated load triaxial test and a new approach of the interpretation of the test results are presented. Based on these results, an appropriate asphalt material model that considers elastic, viscous as well as plastic properties and that allows for large strain theory is selected for the numerical modelling by finite element method. The related material parameters are identified based on the experimental data by an optimisation procedure. Exemplarily, the numerical simulation of data points of the Cole–Cole-plot and the computation of an asphalt test sample in triaxial stress state are conducted. The comparison of experimental and numerical results shows good agreement. Therefore, the material model and the parameters may be used subsequently for structural pavement computations.

This paper compares the rheology properties and mechanical performance of four mastics fabricated with the same base bitumen and four different fillers (dolomite, granodiorite, limestone and rhyolite). The main objective of the investigation was to measure the impact that the filler exerts on the mechanical response of the bitumen. An experimental campaign using the dynamic shear rheometer was performed to quantify rheological properties of the different mastics under both, unaged and aged conditions, as well as their fatigue, rutting and low-temperature cracking susceptibility. A main finding is that the specific surface area of the filler was the most sensitive parameter affecting the mechanical response of the mastics. Also, it was observed that the mastic prepared with granodiorite filler showed the best fatigue and rutting resistance. The results of the investigation were synthesized through a ‘performance diagram’ that can be used for ranking and characterising bituminous mastics.

The sustainability of asphalt pavements is highly depending on the quality of the interlayer bond (IB) between the different asphalt layers. In this project a complicated apparatus for cycling testing of the interlayer bond has been developed in order to determine the shear stiffness at the interface between asphalt layers taking into account the combined effect of varying and repeated traffic loading, acceleration and braking processes and temperature. A universal master function for analytical assessment of the IB shear stiffness has been established for any IB condition using the experimental results. Another function for completely fatigued IB has been developed as well. Both functions have been implemented into a finite element program to estimate the fatigue status of asphalt pavements for different bond qualities over a service life of 30 years using the German method for computational design according to RDO Asphalt 09. It has been succeeded to make a monetary evaluation of the reduced service life of asphalt pavements caused by interlayer bonds of different quality and to assess the construction cost penalty.

The corresponding paper presents selected results of a research on the feasibility of going toward 100% recycling of asphalt pavements into surface courses through an increasing percentage of RA within the mixes. The research is carried out within a two-year CEDR Transnational Road Research project, AllBack2Pave, led by the Technische Universitaet Dresden (Germany), together with the University of Nottingham (UK) and the University of Palermo (Italy), and finalised in January 2016. The main objectives of the project are - to establish, through laboratory tests on binders and asphalt mixes, whether the use of high rates of RA is feasible in developing mixes with high level of durability, and - to develop a "AllBack2Pave end-user manual” on how to best produce cost-effective and high-quality asphalt mixes with high RA content followed by a sustainability assessment of the practice of using asphalt surface mixes with high recycling rates based on chosen European case studies to identify the most cost-effective solutions, together with their environmental impact over the whole lifecycle of selected road pavements. The paper focus on selected results of laboratory tests conducted for different types of representative asphalt surface mixes with different amounts of reclaimed asphalt as well as for the bitumen extracted from the investigated asphalt mixes. In detail, the thermal cracking resistance of the used bitumen will be analysed and critical temperatures will be given. Regarding the asphalt mixes, the stiffness behaviour and the rutting resistance of all materials will be discussed.

To evaluate the anti-fatigue performance of asphalt pavement affected by temperature and solve the problem of an inaccurate estimation of fatigue damage by adopting a single fixed temperatu...

The paper describes the accepted understanding of the shakedown concept. The results of several repeated load triaxial tests performed on crushed rock aggregates at different stress levels for a large number of repetitions of loading are given. The development of the resulting permanent deformation which accumulates with the repeated loading is depicted and compared with the types of responses usually described by the shakedown approach. It is shown that the existing shakedown approach can represent some, but not all, of the observed responses. Thus a modified set of possible responses is defined in shakedown terms and some explanation of the differences from the conventional approach are given. It is concluded that the method of description could give a powerful material assessment and pavement design tool for the engineering of unbound pavement bases. A design chart is derived from the data described, so as to illustrate a possible design approach.

This paper reports the results of several repeated load triaxial tests performed on a crushed rock aggregate at different stress levels. The development of the resulting permanent deformation that accumulates with the repeated loading is described and compared with the types of responses usually described by the shakedown approach. It is shown that the existing shakedown approach can describe some, but not all, of the observed responses. Thus, a modified set of possible responses is defined in shakedown terms and some explanations of the differences from the conventional approach are given. The elastic shakedown limit can be used to predict whether or not stable behavior occurs in the unbound granular material layer of a pavement construction or whether rutting will occur. With this information a pavement's granular base may be dimensioned. The elastic shakedown limit of a Granodiorite has been used in this manner and the resulting design compared with an empirical German design procedure. The paper concludes with an assessment of the benefits and limitations of the new approach.

A new simple design approach that uses test results from the repeated load triaxial apparatus to establish the risk level of permanent deformations in the unbound granular layers (UGL) in pavement constructions under consideration of the seasonal effects was developed. From these data, a serviceability limit line (plastic shakedown limit) stress boundary for the unbound granular materials (UGM) was defined for different moisture contents. Below this line, the material has stable behavior. The serviceability limit line was applied in a finite-element (FE) program, FENLAP, to predict whether stable behavior occurs in the UGM. To calculate the stress in the UGL, a nonlinear elastic model (Dresden Model) was implemented into the FE program. The effects of changing moisture content during spring thaw period and asphalt temperature on pavement structural response were investigated. Additionally, permanent deformation calculations for the UGL were performed taking the stress history into consideration. The results clearly demonstrate that, for pavement constructions with thick asphalt layers, there is no risk of rutting in the granular base, even at a high number of load repetitions. The proposed design approach is a very satisfactory simple method of assessing the risk of rutting in the UGL, even without the calculation of the exact permanent deformation of the pavement construction.

The shakedown concept has been used to describe the behavior of conventional engineering structures under repeated cyclic loading. The possibility has been raised that a critical stress level exists between stable and unstable conditions in pavement. According to the “shakedown” concept, this level is termed the “shakedown limit.” Several repeated load triaxial tests were performed on crushed rock aggregates at different stress levels. The resulting permanent deformation, which accumulated with the repeated loading, was described and compared with the types of responses usually described by the shakedown approach. The existing shakedown approach can describe some, but not all, of the observed responses. Thus, a modified set of possible responses was defined in shakedown terms. The method of description could provide a powerful material assessment and pavement design tool for engineering unbound pavement bases. A design chart derived from the data illustrates a possible design approach.

Workshop 2: Harbour Geotechnics : extended abstracts book : 3rd International Conference on Transportation Geotechnics, 4-7 September 2016, Guimarães, Portugal / organized by University of Minho (UM), Portuguese Geotechnical Society (SPG), International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) ; edited by Yoshiaki Kikuchi, Alexandre Pinto and José Cerejeira 3rd International Conference on Transportation Geotechnics, ICTG 2016, Guimaraes, Portugal; Amsterdam : Elsevier, Procedia Engineering, 143, 844-853 (2016). doi:10.1016/j.proeng.2016.06.138, Published by Elsevier, Amsterdam