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The main objective of this paper is to study the evolution of the ice content of porous media submitted to sub-zero temperatures by dielectric and ultrasonic measurements. Dielectric measurements are made by a capacitive sensor-based apparatus. The amount of ice formed within the tested sample is estimated from the global dielectric constants of the sample and of all the phases that form the tested composite material. On the other hand, ultrasonic measurements are based on the evolution of the ultrasonic wave velocity through the tested sample during a freezing-thawing cycle. These two methods lead to very close results and appear to be cheaper alternatives to low temperature calorimetry. The ice content curves are analyzed with the help of thermoporometry concepts in order to characterize the pore size distribution. Results appear to be complementary to mercury intrusion porosimetry ones. Moreover the commonly observed hysteresis of the ice content during a freezing-thawing cycle is investigated with respect to material microstructure.

A number of laboratory tests (uniaxial, triaxial and hydrostatic) have been conducted on a dry porous limestone. A conceptual model is proposed to correlate deformation and damage fields (including acoustic emission activity) with the variation of ultrasonic velocities, quality factors and energies as measures of attenuation. This correlation is presented in a stress deviator versus confining pressure diagram. In this way, the successive steps occurring in the damage process of this rock are well described. In particular, the quality factor of S‐waves distinguishes clearly the onset of the initially stable cracking, while the velocity of S‐waves and strain measurements are sensitive to dilatancy which appears later in the damage process of the limestone studied.

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This paper deals with two aspects of the characterization of the fracture process zone (FPZ) in quasi-brittle materials such as concrete. An overview is given of the possibility of using a destructive technique, such as the scanning electron microscope, and a numerical model, such as the nonlocal isotropic damage model (NLIDM), to detect FPZ characteristics, e.g., length and width of the FPZ. The fracture of concrete requires the consideration of progressive damage, which is usually modelled by a constitutive law and can be studied by a numerical method. The object-oriented finite element method (OOFEM) has recently been used in damage studies, and thus the FPZ is calculated on the basis of one of the damage models (the NLIDM). The results obtained from the experimental investigation are similar to those obtained using the NLIDM, which has proven to be a useful tool for analysis of the cracking process.Key words: object-oriented finite element method, nonlocal isotropic damage model, fracture process zone, scanning electron microscope.

This article presents a study of steel fiber-reinforced concrete (SFRC). In its first part, a four-point bending test performed on both plain concrete and SFRC is investigated. The collected nonlinear load-deflection curves are transformed into stress-strain curves with the help of an incremental method, which the authors developed in the nonlinear regime. In the second part of this article, the authors present a micromechanical approach based on Mori-Tanaka/ Voigt mean-field homogenization schemes in order to model the effective nonlinear behavior of the three-phase brittle composite materials. The first phase (concrete matrix) is assumed to obey Ju's brittle damage model. The second phase (fibers) is modeled with classical J 2 plasticity, while the third phase represents cavities. Numerical algorithms enable the simulation of SFRC within reasonable CPU time and memory requirements. The homogenization module is interfaced to the finite element package ABAQUS. A two-scale simulation of the bending test is validated against the experimental results.