Geneviève Foray

Influence of Diffuse Damage on the Water Vapour Permeability of Fibre-Reinforced Mortar

The study of moisture transfer inside building materials is an important issue in building physics. The hygric characterization of such materials has become a common practice for the estimation of the hygrothermal performance of buildings. However, their aging caused by mechanical loading and environmental factors inevitably affects their permeability to moisture ingress, and the knowledge of how this permeability is affected by damage and cracks is still incomplete. The effects of diffuse damage caused by mechanical loading on the water vapour permeability of fibre-reinforced mortar were studied. A full experimental setup is presented including observation of the porous structure, mechanical, and hygric characterization. Uniaxial tensile loading was applied on prismatic samples while their damage level was measured. Then, the moisture content of damaged and undamaged samples was monitored during variations of ambient relative humidity. Two numerical methods are presented and used for the comparison of the water vapour permeability of multiple samples presenting various levels of damage. By this methodology, diffuse damage caused by mechanical loading is shown to have an impact on the water vapour transfer inside the material.

Characterisation of concrete and mortar cracking by digital image correlation and acoustic emission

Cracks and defects in construction materials can cause an increase in their moisture permeability, and accentuate their degradation. In order to accurately assess the durability and the overall performance of building facades, one must dispose of a reliable method for the identification of the damage state of such materials. The present work aims at developing a methodology for the detection and monitoring of damage and fractures in building materials. Digital image correlation and acoustic emission monitoring were simultaneously performed during tensile loading tests of fibre-reinforced mortar samples. The optical technique was found able to reveal all ranges of cracks, from microscopic to macroscopic, and an image-processing procedure was conducted as to quantify their evolution in the course of the degradation of the samples. It was also found that the acoustic activity could be related to the optical measurements in terms of damage quantification and localisation.

Analysis of liquid suspensions using scanning electron microscopy in transmission: estimation of the water film thickness using Monte–Carlo simulations

Environmental scanning electron microscopy (ESEM) allows the observation of liquids under specific conditions of pressure and temperature. Moreover, when working in the transmission mode, that is in scanning transmission electron microscopy (STEM), nano‐objects can be analysed inside a liquid. The contrast in the images is mass‐thickness dependent as in STEM‐in‐TEM (transmission electron microscopy) using closed cells. However, in STEM‐in‐ESEM, as the liquid–vapour equilibrium is kept dynamically, the thickness of the water droplet remains unknown. In this paper, the contrasts measured in the experimental images are compared with calculations using Monte‐Carlo simulations in order to estimate the thickness of water. Two examples are given. On gold nanoparticles, the thickness of a thick film can be estimated thanks to a contrast inversion. On core‐shell latex particles, the grey level of the shell compared with those of the core and of the water film gives a relatively precise measurement of the water film thickness.

Study of the surfactant role in latex–aerogel systems by scanning transmission electron microscopy on aqueous suspensions

For insulation applications, boards thinner than 2 cm are under design with specific thermal conductivities lower than 15 mW m−1 K−1. This requires binding slightly hydrophobic aerogels which are highly nanoporous granular materials. To reach this step and ensure insulation board durability at the building scale, it is compulsory to design, characterise and analyse the microstructure at the nanoscale. It is indeed necessary to understand how the solid material is formed from a liquid suspension. This issue is addressed in this paper through wet‐STEM experiments carried out in an Environmental Scanning Electron Microscope (ESEM). Latex–surfactant binary blends and latex–surfactant–aerogel ternary systems are studied, with two different surfactants of very different chemical structures. Image analysis is used to distinguish the different components and get quantitative morphological parameters which describe the sample architecture. The evolution of such morphological parameters during water evaporation permits a good understanding of the role of the surfactant.

3D Multiscale Characterization of Silica Aerogels Composites

New composites based on a matrix of silica aerogel grains are currently being developed to answer the expectations of thermal renovation. One of the key parameters for their commercial use is the control of their porous network. In this study, we aim to propose a three-dimensional characterization from the nanometer to the millimeter scale of the silica aerogel particles themselves. Transmission electron microscopy (TEM) is used to characterize the mesoporous network within the aerogel grain. The arrangement in three dimensions of the grains and the voids within the aerogel grain pileup is investigated at the micron scale by X-ray tomography.