Characterization of fracture patterns and hygric properties for moisture flow modelling in cracked concrete

Abstract

International audienceSeveral years after their installation, building materials such as concrete present signs of ageing in the form of fractures covering a wide range of sizes, from microscopic to macroscopic cracks. All sizes of fractures can have a strong influence on heat and moisture flow in the building envelope, but their distribution is difficult to predict due to the variety of environmental factors which cause them. This paper aims at applying experimental non-destructive techniques for the observation of fracture patterns and of fluid flow in fractures, in order to provide this data to models for fluid transfer in fractured porous media. Digital image correlation was performed during the fracturing of concrete samples, in which moisture uptake was then monitored using X-ray radiography. Finite-element simulations were then performed based on the measurements of the fracture patterns, in order to recreate the measured moisture concentration profiles. Digital image correlation was found suitable as a mean to obtain a complete mapping of the deformations at the surface of the samples, and a first step was made towards the use of non-destructive fracture characterization for the purpose of moisture transfer modelling

Acoustic Emission Analysis of Cement Mortar Specimens During Three Point Bending Tests

“…It is evident that during the first three loading loops the Ib-values exhibit a noticeable increase indicating prevalence of microcracks (Rouchier et al, 2012). For the three initial loadings high Ib-values (Ib between 1 and 1.1) are obtained due to a large number of low amplitude AE events.…”

Influence of concrete fracture on the rain infiltration and thermal performance of building facades

“…Two aspects must be considered when evaluating the accuracy of the calculations: the prediction of water infiltration in the fractures and of the overall fluid flow in the porous medium resulting from their presence. This latter concern was addressed in a previous study [31], in which a first version of the simulation code was developed and tested: two-dimensional moisture content distributions were measured by X-ray radiography in cracked concrete samples, and the simulation code was used to recreate these distributions based on the knowledge of the crack geometry, measured by digital image correlation. Fracture flow was not calculated, as cracks were considered initially water-filled: this assumption coincides with the observation that water infiltration in cracks occurs in a much smaller time frame than in the porous medium.…”

“…1 for the prediction of moisture flow requires the knowledge of the material's equilibrium moisture content w = f p c , as well as its unsaturated moisture permeability. Simulations performed in the present work involve five different materials, two of which have undergone hygric characterisation in previous papers [31,29], while the properties of the three other materials have been extracted from the literature. The geometries of the simulation cases, along with the corresponding references for material properties, are defined in Sec.…”

“…1 and 11 was performed with the finite-element method (FEM), mainly following the methodology presented by [13]. A simulation code was recently developed [31], and adapted so that experimental measurements of fracture geometries can be automatically integrated in a 2-dimensional FE mesh. The capillary pressure p c and the temperature T were respectively chosen as driving potentials for moisture and heat flow.…”

“…In a recent study [28], digital image correlation and acoustic emission monitoring were found reliable for the quantification and localisation of all scales of fissures, from micro-cracks to macroscopic fractures. A numerical code was then developed [31], that may include these measurements into a finite-element frame for the prediction of coupled heat and moisture flow. The next step of this procedure, and topic of the present paper, is the application of this simulation code in order to estimate the consequences of cracking on the moisture accumulation and thermal performance of building facades, subjected to realistic climatic conditions during long periods of time.…”