Behaviour Of Bituminous Mixtures Research Articles

Towards improved correlations between bitumen properties and rutting resistance of bituminous mixtures – FunDBitS literature review

Bitumen is the most common binder used in the production of bituminous mixtures for road paving, having a fundamental influence on the performance of the pavement. However, it is not yet fully understood which bitumen properties have a significant influence on the behaviour of bituminous mixtures. In this context, the FunDBitS project was developed. Its main objective was to prepare recommendations on the properties of the bitumen to be specified in order to obtain suitable bituminous mixtures, namely in what concerns to its resistance to permanent deformation (rutting), stiffness, low temperature cracking, fatigue cracking and binder/aggregate interaction. In this framework, the research studies that have become internationally available since the BiTVal project were reviewed in order to assess performance-based bitumen characteristics, which may be introduced into bitumen specification standards. This paper specifically presents the main conclusions regarding the properties of bitumen related to the behaviour to permanent deformation of bituminous mixtures. It was concluded that the most promising test is the “non-recoverable creep compliance” (Jnr) from the Multiple Stress Creep and Recovery (MSCR) test method, although Zero/Low Shear Viscosity (ZSV/LSV) by creep or oscillation test method can also give good correlations with permanent deformation of bituminous mixtures.

Influence of Moisture Conditioning on Linear Viscoelastic Behaviour of Bituminous Mixtures Used For Railway Trackbeds

Abstract The influence of moisture on the linear-viscoelastic properties of bituminous mixtures with and without polymer modified bitumen (PMB) to be used for railway trackbeds was addressed in this paper. Nowadays, the use of bituminous mixtures in railway trackbeds, particularly for new high-speed lines, is a common practice. The variation of the thermomechanical properties of bituminous mixtures needs to be characterized considering railway loading, circulation speed, and environmental exposure conditions. For this purpose, improved 3D complex modulus tests were performed on base-course type mixtures. A tri-dimensional constitutive model, called 2S2P1D (2 Springs, 2 Parabolic creep elements and 1 Dashpot), was used to model the viscoelastic behavior of the materials. A moisture conditioning procedure was used to induce moisture damage to the mixtures. The thermomechanical properties of the materials are compared for the conditioned and non-conditioned states. Low variation of the linear viscoelastic behavior of the studied materials after moisture conditioning was observed. The results allowed assessing the interest of using polymer modified bitumen for bituminous mixtures to be used in railway trackbeds.

Crack propagation characterisation of bituminous mixtures using a four-point bending notched specimen test

Fracture behaviour of bituminous mixture has been increasingly studied in the last decade for a more comprehensive and detailed approach which could be taken into account in the pavement design process. This study presents an investigation at the Université of Lyon/Ecole Nationale des Travaux Publics de l'Etat (ENTPE) on fracture behaviour of bituminous mixtures during crack propagation. The four-point bending notched fracture test which has been designed at ENTPE was used. A quite new methodology, which makes it possible to characterise fracture behaviour of tested mixtures during crack propagation tests, has been proposed and applied for these tests thanks to an improved crack length determination approach based on inverse analysis. According to this methodology, different fracture parameters such as fracture toughness and fracture energy can be evaluated at different moments during the crack propagation test for a given advancement of the crack tip.

Three‐dimensional analysis of fatigue tests on bituminous mixtures

AbstractA tension–compression test on cylindrical specimens was used to study the three‐dimensional behaviour of bituminous mixtures during fatigue tests. The tests were carried out at 10 °C, 10 Hz at constant strain amplitude mode. The axial strain, radial strain and axial stress were measured using a prototype apparatus developed at the University of Lyon/“Ecole Nationale des TPE” (ENTPE). In addition to axial stress and strain analysis, the measurements of the radial strain made it possible to obtain the complex Poisson ratio and the volumetric strains during the tests. The results showed good correlations between the volumetric strains and global damage. The effects of the change of temperature due to viscous dissipation on the volumetric strain and on the complex modulus were also analysed.

Effect of Fatigue Cyclic Loading on the Linear Viscoelastic Properties of Bituminous Mixtures

AbstractThis paper focuses on the three-dimensional (3D) linear viscoelastic (LVE) behavior of bituminous mixtures and the damage occurring after a great number of cyclic loadings. Two complex modulus tests were carried out before and after a fatigue test. The complex modulus E* and complex Poisson’s ratio ν* were measured for large ranges of temperatures (from −25 to 30°C) and frequencies (from 0.03 to 10Hz). First, it is shown that the time temperature superposition principle (TTSP) is verified and applicable in the 3D case. Then, the change of the complex modulus created by fatigue test was analyzed. Lastly, a model with a continuum spectrum called two springs, two parabolic elements, one dashpot (2S2P1D), developed at the Ecole Nationale des Travaux Publics de l’Etat (ENTPE), was used to simulate the 3D linear viscoelastic behavior of the tested bituminous mixture before and after fatigue damage.

Validation of the time–temperature superposition principle for crack propagation in bituminous mixtures

The time–temperature superposition principle (TTSP) is known to be valid in the small strain domain where the behaviour of bituminous mixtures is linear viscoelastic (LVE). The behaviour is then called thermorheologically simple. In this work, an experimental campaign was performed at University of Lyon/ENTPE (France) to check the validity of the TTSP in the linear domain in the tridimensional case and also when cracks occur and propagate in bituminous mixture. A four-point bending test, which has been designed at University of Lyon/ENTPE, was used as crack propagation test. First, a complex modulus test is performed on cylindrical specimen in the LVE domain. Then, a series of crack propagation tests are carried out at different temperatures and different imposed displacement rates. The same shift factors obtained for master curve of complex modulus is also applied for the crack propagation tests analysis. The results allow obtaining a unique curve, for identical loadings when plotting as a function of reduced time. This result confirms that the TTSP is also valid for crack propagation in bituminous mixtures.

Analysis of the effect of wax content on bitumen under performance grade classification

This paper describes an analysis of the effect of wax content on bitumen under performance grade (PG) classification. Wax content affects the performance and rheological behavior of bitumen. Bituminous mixtures with bitumen of high wax content tend to become very soft at high temperatures leading to rutting problem on pavement. Also the rheological behavior of bitumen has a great influence on the behavior of bituminous mixtures. To address the potential adverse effect of wax on bitumen, countries in Europe limit the wax content to 2.2% (BS EN 12606-1). In Mainland China, the standard (JTG F40-2004) classifies bitumen into three grades (Grades A, B and C). Grade A, with wax content below 2.2%, is used for highway pavement construction. Grades B and C, with wax content limits of 3.0% and 4.5% respectively, can only be used on roads with relatively lower traffic. The current binder specifications in Hong Kong Special Administration Region is based on penetration testing, which does not properly account for pavement performance. This paper assesses the effects of wax content and the rheological properties of seven types of bitumens and provides the basis for a performance grading binder standard for Hong Kong.

Studies on creep and recovery of rheological bodies based upon conventional and fractional formulations and their application on asphalt mixture

Traditionally, the time-dependent behaviour of bituminous mixtures has been modelled using linear visco-elastic theory described by creep and relaxation functions. Research, however, has shown that parameter identification for functions with linear time derivatives becomes problematic when the behaviour of asphalt mixtures needs to be matched for both the loading and unloading responses. The research introduced in this paper explored the possibility of using fractional creep functions for modelling. Furthermore, the possibility of using fractional creep functions for various rheological bodies to investigate the fractional time derivatives for strain is discussed. It is shown that, by means of these creep functions, the time-dependent deformation behaviour of bituminous material in terms of the retarded creep during loading and the relaxation behaviour during unloading may be described more realistically than by using time derivatives of integer order. The fractional creep functions allow for the development of non-linear viscous strain during the creep process and to better match the observed behaviour of asphalt mixtures, compared to the use of conventional linear models. This study specifically investigated the retardation and relaxation times in creep and recovery, and examined how these can be influenced by the choice of the fractional derivatives. The constitutive relationships developed in this paper are implemented in a non-linear computational model based on the finite element method. Modelling of the above-mentioned phenomena is presented and discussed with the help of numerical simulations and determination of model parameters with the help of actual test data.