Multiscale modeling of the thermorheological behavior of building materials : application to bituminous mixtures in the context of performance assessment of flexible pavements and to frozen ground as temporary supports in underground excavation

Abstract

Due to the possibility of realistic prediction of material- and structural behavior, reliable models for the description of the mechanical behavior of composite materials got more important during the last years. For this purpose, different material models for the numerical description of macroscopic behavior of composit materials are investigated within this thesis.<br />For the identification of model parameters, multiscale models are introduced, aiming to relate the macroscopic behavior of composite materials to the material composition and the properties of constituents at finer scales of observation. Hereby, methods for the experimental investigation of properties of material phases, on the one hand, and for validation of multiscale models, on the other hand, are applied.<br />This thesis, comprising four publications, deals with identification of material properties at different observation scales, as well as with the development and prediction of material properties of composite materials and the implementation into numerical calculation programs.<br />Whereas Publications A, B, and C focus on the description of asphalt concrete, dealing with: (i) macroscopic material modeling and (ii) multiscale modeling of viscoelastic and viscoelastic-viscoplastic properties, Publication D is concerned with the determination of creep and strength behaviour of frozen ground: Publication A ("Integration schemes and parameter identification in viscoelastic modeling of asphalt: application to low-temperature assessment of flexible pavements") deals with the implementation of rheological models into a finite element program which is applied to numerical simulation.<br />Publication B ("Multiscale prediction of viscoelastic properties of asphalt concrete") comprises the incorporation of finer-scale information. Hereby, four additional observation scales are introduced below the macro-scale, allowing us to relate the rheological behavior of asphalt concrete to the bahavior of bitumen. In Publication C ("Multiscale viscoelastic-viscoplastic model for the prediction of permanent deformation in flexible pavements") the multiscale model for asphalt concrete is extended towards viscoplastic deformation. Publication C comprises a new material model taking plastic deformation into account, in order to capture the thermorheological bahavior of asphalt concrete at elevated temperatures.<br />In Publication D ("A micromechanics-based model for frozen soil during artificial ground freezing") an additional application of the multiscale model on frozen ground is investigated . Within Publication D, the homogenization methods introduced so far are extended and methods for homogenization of strength are presented. The obtained material parameters for the different composite materials serve as input for numerical simulations, which, in turn, uses macroscopic material models for the preparation of predictions.