Thesis defence A. Alipour: asphalt

19 June 2017 | 10:00
location: Aula, TU Delft
by Webredactie

Computational Modelling of Compaction in Asphaltic Mixtures and Geomaterials. Promotor: Prof.dr. A. Scarpas (CiTG).

Asphaltic mixtures are heterogeneous composite materials consisting of aggregates coated and bound by asphalt binder. The long term performance of asphaltic pavements is highly dependent on the mechanical behaviour of the asphaltic mixture during construction (mixing and compaction) and operation; inadequate mixture compaction leads to faster moisture and oxygen diffusion, ravelling, rutting and poor fatigue life.

Generally, the decision making process by pavement constructor for compaction of asphaltic layer is based on past experiences and laboratory results. Both approaches have uncertainty and will not necessarily provide the optimum solution in terms of time, cost and quality. Alternatively, utilizing a model that predicts the compaction curve before construction can help the constructor to estimate the influence of each of the influential parameters on the compaction curve. As such, he/she can plan for a more realistic compaction pattern.

This thesis focuses on developing new constitutive models applicable for simulation the (a) compaction process of asphaltic materials and (b) no-tension characteristics of unbound aggregates. The research methodology for developing the compaction model is chosen as a spiral methodology with four major stages. Within these stages, various aspects that the asphaltic mixture experiences during compaction process are taking into account (Chapter 1). This approach is the most significant feature that differentiates the compaction model from previous works in the same field of research.

The first stage of developing the compaction model addresses the elastoplastic behaviour of aggregates as the main structure of the asphaltic mixture. In this regard, a new yield surface that can capture the pressure dependency and shear failure of aggregates is formulated and implemented in an elastoplastic algorithm. In addition, an isotropic hardening law is derived to consider the expansion of the yield surface and material hardening (Chapter 2).

The second stage of developing the compaction model focuses on the response of aggregates when subjected to cyclic loading. In this respect, a similar formulation for the yield surface in Chapter 2 is utilized for the boundary surface and is implemented in the cyclic plasticity algorithm (Chapter 3).

The third stage of developing the compaction model is related to the viscoelastic characteristics of asphalt binder as a component of asphaltic mixture. In this context,based on Quasi Linear Viscoelasticity, an algorithm in a large strain framework is developed that simulates the response of asphalt binder under various temperatures (Chapter 4).

The fourth stage of developing the compaction model combines the elastoplasticity, cyclic plasticity and viscoelasticity algorithms according to the theory of mixtures. Additionally, the influence of temperature on the mechanical characteristics of the components of asphaltic mixture and various types of hardening that the mixture experiences during compaction are reviewed (Chapter 5).

The no-tension characteristics of unbound aggregates are simulated by modifying the strain energy function of a hyperelastic material. The results indicate that utilizing the no-tension model instead of common elastic models for predicting the behaviour of unbound aggregates in base layer influences the overall response of flexible pavement (predicted by simulation) significantly (Chapter 6).

In conclusion, this thesis opens a new gate towards formulating new constitutive models for asphaltic materials and geomaterials (Chapter 7). These models can contribute in developing software packages for simulation the mechanical behaviour of flexible pavements during construction phase.

More information?
For access to theses by the PhD students you can have a look in TU Delft Repository, the digital storage of publications of TU Delft. Theses will be available within a few weeks after the actual thesis defence. 

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