Anne Millien

Mechanical Testing of Interlayer Bonding in Asphalt Pavements

Steadily increasing requirements on pavement performance properties, in terms of bearing capacity and durability, as well as new innovative developments regarding pavement materials and construction, are observed worldwide. In this context interlayer bonding at the interfaces of multi-layered bituminous systems is recognized as a key issue for the evaluation of the effects, in terms of stress-strain distribution, produced by traffic loads in road pavements. For this reason a correct assessment of interlayer bonding is of primary importance, and research efforts should be addressed in order to improve the lack of correlation and/or harmonization among test methods. Following this principle RILEM TG 4 organized an interlaboratory test in order to compare the different test procedures to assess the interlayer bonding properties of asphalt pavement. The results of the experimental research are presented with a preliminary overview of basic elements, test methods and experimental investigations on interlayer bonding. Then the RILEM TG 4 experimental activities, based on the construction of three real- scale pavement sections, are presented in detail. Each pavement section was composed of two layers, and three different interface conditions were chosen. The first pavement was laid without interface treatment and the others with two different types of emulsion. Fourteen laboratories from 11 countries participated in this study and carried out shear or torque tests on 1,400 cores. The maximum shear or torque load and the corresponding displacement were measured, and the shear or torque strength was calculated as a function of the following parameters: diameter, test temperature, test speed, stress applied normal to the interface and age of the specimen. The results of this study are presented in terms of precision and correlations regarding the parameters which results in useful information on asphalt pavement interlayer bond tests.

Geogrid Interlayer Performance in Pavements: Tensile-Bending Test for Crack Propagation

The roads durability is an objective that gains more and more importance because of the economical – environmental factors. A durable road surface should be provided in the course of repair operations. Geogrids (carbon, glass or steel fibbers) are used for increasing the durability of overlaid asphalt surfaces. They reduce fatigue cracks as well as thermal cracking and prevent structural deformation. This article presents experimental results based on the thermal shrinkage-bending test. The mechanical performances of two double layers complexes (unreinforced or reinforced by grids) are discussed and analysed. In terms of durability, ecology and economical reasons, the three solutions presented in this article, wants to expose the behaviour of a mixture that is reinforced (in three ways) to improve the consumption of eco-elements (like stone and bitumen) and also to improve the life time of the future work. After analyse the three solutions UN, FP and CF we can conclude that a weak mixture (in eco-elements) can be very well improved in using the two reinforcing solution, presented below.

Shear test to evaluate the fatigue of asphalt materials

The analysis and interpretation of fatigue on bituminous materials has already been the objective of a body of research. This paper presents an experimental campaign conducted on two materials, AC6 and AC10, involving the use of a double-shear test. The fatigue test results are analysed according to both the classical and energy approaches. The classical approach depends on the mixture and mode of loading: in this approach, the cumulative dissipated energy remains independent of the mode of loading and temperature, yet dependent on mix design. On the other hand, the ratio of dissipated energy method is dependent on the mode of loading while independent of the type of materials and temperature. Its results are analysed within an energy approach that allows one to compare the results.

Surface roughness: a key parameter in pavement interface design

Abstract The mechanical behaviour of the first interface under a surface layer is critical to pavement durability. Several of the distresses observed are mainly due to traffic loading or repetitive loading; they may also be related to the tack coat, which is often used to bond both layers, as well as to the application rate, curing time and cleanliness. The roughness effect however has not been heavily emphasised in pavement design. Out of such concerns, the interface model proposed in this paper makes use of a meso- and macro-scale cohesive zone model, thus making it possible to take into account roughness and damage behaviour of the interface in either pure or mixed mode. The objective of this study is to propose an innovative method to identify these model parameters during in situ operations for practical engineering perspective. In this paper, an Interface Damage Model is analysed at the meso-scale with the actual roughness and idealised periodic roughness profiles. The parametric numerical analysis performed clearly shows the influence of roughness of these structures in shear mode. Moreover, a macro-scale interface damage model, which includes roughness as an internal variable, is proposed for pavement structures with smooth interfaces

Pavement Design for Curved Road Sections

ABSTRACT This paper focuses on damage processes other than the main one observed and studied in pavement design. Previous research has targeted the experimental fatigue performance of tack coats. The French Pavement Design method has been chosen herein to illustrate how interface fatigue performance can lead to improved design, especially when pavements are subjected to repeated horizontal loadings. In a curved pavement section, longitudinal top-down cracking is observed, and this damage process may also be taken into account during the design approach. A 3D finite element model has been derived to assess pavement lifetime. In conclusion, it is proposed to include the fatigue performance of interfaces when designing pavements with horizontal loadings and thin surface layers.

Analyzing of Wedge Splitting Test on Asphalt Pavement Using Optical Measurements

This paper dealt with the characterization of opening mode fracture using Digital Image Correlation, coupled with a kinematic approach. Tests were carried out using a Wedge Splitting sample made in asphalt concrete AC12. The asphalt concrete was provided in the RILEM-SIB. The samples were a bi-layered asphalt concrete with or without a carbon fiber grid at interface. During experimentation, the sample deformation was recorded by using Digital Image Correlation. Based on the optical measurements coupled with the analytical approach, the energy release rate was performed by means the crack relative displacement and stress intensity factors. Using an adjustment procedure, based on an iterative Newton–Raphson algorithm, the crack relative displacement factor was calculated from optical measurements. the stress intensity factor was estimated from an analytical approach. Furthermore, the crack opening displacement was measured from the mark tracking method. This approach allowed the assessment of fracture parameters for the real structures to be considered.

Damage Modeling of Asphaltic Pavement Rough Interfaces Under Tensile and Shear Loading

The interface mechanical behavior in asphaltic pavement structures represents a key parameter for the computational design. Several degradation mechanisms are observed in surface layers due to the de-bonding despite the implementation of tack coats or reinforcing systems. The interface modeling becomes more important in the pavement field during the last ten years, even if this concept is widely studied in composites, masonry structures… Furthermore, the experimental research highlights the sensitivity of the imperfect interface behavior in respect to the underlayer roughness. Due to these concerns, parametrical studies are proposed in this paper, by using a macro scale cohesive zone model. This model allows taking into account the damage behavior of the interface, in pure or mixed mode. Damage mechanisms are governed by internal variables. The numerical results based on a finite element method are compared with experimental tensile and shear data. The geometrical periodic roughness (triangular, crenel) and the mixed mode failure are investigated under monotonic loading. A parametric numerical analysis is presented and shows clearly the roughness influence of these structures.