Consultation des offres

PhD Position: Multiscale modeling of the thermo-hygromechanical response of concrete informed by the molecular scale CDD

Contact

Tulio Honorio De Faria

91190 Gif sur Yvette

France
0147406827
tulio.honorio-de-faria@ens-paris-saclay.fr

Descriptions

Laboratoire :
LMT - Laboratoire de Mécanique et Technologie
Date de début :
01/09/2020
Date de fin :
31/08/2023
Date limite pour postuler :
30/04/2020
Descriptif :

Profile and skills required:
- Notions about porous materials, or more specifically cement-based materials
- Motivation to perform simulation and modeling research
- Knowledge of (or motivation to learn) classical molecular simulation techniques
- Knowledge of (or motivation to learn) micromechanics
- Scientific communication and advanced English
- Motivation to carry out fundamental research at fast pace
Thesis detailed overview
Thermal deformations are one of the major causes of cracking of cement-based materials [1]. These deformations may have negative impacts on the performance and durability of built infrastructures for transport, sanitation and security; infrastructures for energy production, and building envelopes. Understanding, predicting and controlling the thermal deformations in cement systems is crucial: (1) to better manage the resilience and vulnerability of (infra-)structure as well as extent the service life of existing infrastructures, which represents a reduction in the environmental impact of using concrete; and
(2) to ensure the performance specifications related to the confinement and insulation capacity of cement systems, contributing to a better formulation of cement-based materials and design of concrete structures tailored to such performances specifications.
The prediction of thermal deformations relies on an accurate description of the thermal properties, namely the coefficient of thermal expansion (CTE), the heat capacity and the thermal conductivity. For cement-based materials, these properties are reported to be composition, time, temperature and relative humidity (RH) dependent [2]. Sensitivity analysis shows that relatively small variations in the heat capacity and in CTE may significantly affect the thermal response of concrete structures [3].
The goal of this project is to provide models of the thermal expansion and heat capacity
of cement-based materials that are informed by the relevant physical phenomena in a
multiscale framework and that can be used in the engineering practice. The target
applications are concrete infrastructures and building envelopes made of cement-based
materials that are subjected to thermal loads in an environment with a given RH. We will focus on the elucidation of the physical origins as well as the temperature and RH-dependency of the CTE and the heat capacity. Aspects related to drying or deformations related to RH variations will only be considered if they contribute to the understanding of the RH-dependency of the CTE and the heat capacity. We assume that accounting for the multiscale nature of cementbased materials is crucial to understand thermal deformations.
Research efforts have been devoted to correlate composition, structure, property and
performance of civil engineering materials by means of multiscale modelling and simulations.
Much of this effort is focused on mechanical properties [4–7], whereas only few studies cope
with thermal properties [2, 8–10]. Critical questions regarding the thermal behavior of cementbased materials remain unanswered. In particular, the physical origins of the following aspects are still to be addressed:
1. Concerning the thermal expansion, cement-based materials exhibit at least two non-trivial
behaviors: (i) the CTE is a non-monotonous function of the relative humidity, reaching
a maximum value at approximately 70% RH (Fig. 1); and, (ii) the CTE often reach a
minimum value at the first days.
2. The effective heat capacity of heterogeneous materials is expected to be the average of the heat capacities of all phases weighted by their (volume or mass) fractions, i.e. described by a mixture law [10]. However, estimations of heat capacity of cement-based materials
using mixture laws are not in a reasonable agreement with experimental data [9].
Modeling strategies that can describe these peculiar behaviors of cement-based materials from the underlying physics will represent an advance in the field by enhancing the confidence on the predictions of the performance and durability of cement-based materials. Additionally, in a more ambitious perspective, the knowledge obtained from modelling can be used to advance in the design cement-based materials with tailored thermal properties, following the example of the research on other micro- and mesoporous materials [11].

Financial support
Financial support of the French National Research agency (ANR) via the project ANR JCJC
THEDESCO (ANR-19-CE22-0004-01). The participation in national and international conferences (2 to 3) is comprised.

Mot(s)-clé(s)

  • Béton
  • Comportement physique et mécanique
  • Matériaux
  • Milieux poreux
  • Modélisation
  • Thermique du Bâtiment