Antonin Fabbri

Poroelastic Analysis of Partial Freezing in Cohesive Porous Materials

We revisit the poromechanics set up by Olivier Coussy for better understanding of the mechanical effect of partial freezing in cohesive porous materials. This approach proves to be able to quantitatively predict swelling even if the in-pore liquid does not expand when solidifying. In this case, dilation results from the so-called cryosuction process that dominates thermal shrinkage under cooling, as shown in our analysis conducted on the historical experiment run by Beaudoin and MacInnis (1974, “The Mechanism of Frost Damage in Hardened Cement Paste,” Cem. Concr. Res., 4, pp. 139–147) on benzene saturated 24-h old cement paste. Both mechanisms are also at work when freezing water saturated early age cement paste with air voids. In this case, the cryosuction process results in shrinkage and should be added to the thermal shrinkage, their respective amplitudes being temperature dependent but, a priori, of the same order of magnitude.

A Procedure to Measure the in-Situ Hygrothermal Behavior of Earth Walls

Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of these properties are known to strongly depend on the amount of water contained in wall pores and its evolution. Thus the aim of this paper is to present a procedure to measure this key parameter in rammed earth or cob walls by using two types of probes operating on the Time Domain Reflectometry (TDR) principle. A calibration procedure for the probes requiring solely four parameters is described. This calibration procedure is then used to monitor the hygrothermal behavior of a rammed earth wall (1.5 m × 1 m × 0.5 m), instrumented by six probes during its manufacture, and submitted to insulated, natural convection and forced convection conditions. These measurements underline the robustness of the calibration procedure over a large range of water content, even if the wall is submitted to quite important temperature variations. They also emphasize the importance of gravity on water content heterogeneity when the saturation is high, as well as the role of liquid-to-vapor phase change on the thermal behavior.

Historical Rammed Earth Process Description Thanks to Micromorphological Analysis

ABSTRACT Rammed earth was traditionally used in western European countries before industrial building materials replace it during 20th century. Construction strategies developed by former builders were dictated by locally available construction materials and engendered local constructive cultures. Unfortunately, this knowledge was orally transmitted and is lost today. The rediscovery of these cultures can provide answers to modern rammed earth construction processes. Micromorphological analysis of earth walls provides information to rediscover traditional rammed earth process. This methodology is applied for the first time, on a rammed earth wall of a farm located in Bresse (France). Thanks to this methodology, pedological horizon, extraction depth, and location of the material source are identified. The surface area excavated for the construction of the building is estimated. Micromorphological study gives information on mixing degree and water content at implementation time. Strain features associated with ramming effect and rammed earth boundary layer are also highlighted.

A new constitutive model of unsaturated soils using bounding surface plasticity (BSP) and a non-associative flow rule

Abstract This paper presents a constitutive model for unsaturated soils, based on the non-associate bounding surface plasticity concept under a critical state framework. With a limited number of parameters, this model allows removing the sudden stiffness reduction at the on-set of plastic strains when the stress reaches the yield surface. It also enables to reproduce smooth transitions from pre-peak hardening to post-peak softening and from contractant to dilatant behavior, which are common short comings of more classic models. The performance of this model is highlighted by a comparison between its numerical results, those from other unsaturated elastic–plastic models and experimental data.

Poroelastic Contribution to Freezing in Cement Paste

An effective pore pressure model is used to predict the mechanical effect induced by in-pore partial freezing of a liquid phase initially saturating a cohesive porous solid. This allows discussing the influence of the thermodynamic and poroelastic properties of the different constituents of the unsaturated porous material on its strain under drained or undrained conditions.

Poromechanics of salt nucleation within an unsaturated reservoir rock

The aim of this study is to estimate the stress induced by salt crystallization in a reservoir rock during an injection of supercritical CO2 operation. A ”pore-scale” model is used to calculate the nucleation and growth of salt crystals within brine solution submitted to a drying out process. The induced crystallization pressure is then estimated through a generalized Correns law. This information is finally imported into a poromechanical model that allows calculating the local strain induced by the crystallization process. The stress state within a representative elementary volume of the host rock is then estimated through the equivalent tensile stress to which the solid matrix of the rock is subjected.

Hydric characterisation of rammed earth samples for different lime concentrations

The rehabilitation of ancient rammed earth houses, as well as the use of earthen materials in modern constructions, are a growing matter of concern, especially in area such as Rhône-Alpes, France, where 40% of old constructions are in rammed earth. A current pathology observed for this type of construction is related to the rising damps, for which the water from the ground is absorbed by the wall. This situation leads to a very saturated state. As it has been proven that the compressive strength is altered by the presence of water in the pores, a better understanding on high relative humidity range is necessary to be able to predict the mechanical behavior of buildings and thus ensure a better risk assessment. The present study describes experimental results of the water uptake experiments and moisture storage at high relative humidities.

Earthen Materials and Constructions

Abstract This chapter introduces the case of the earthen constructions including most of the techniques used in the vernacular heritage and the modern green building architecture. It starts by presenting the variety of earth building techniques focusing on the common points between all of them. It then explains these particularities which are linked to the affinity with water of the earthen material and construction. This leads to a specific hygrothermal and mechanical behavior of the materials and structures. The impact of these characteristics on building design is given. A full discussion of the case of earth stabilization is then included to show their relationship with the gain (or loss) obtained in the framework of the sustainability. By the end of the chapter, an assessment of the hygrothermal, mechanical, and durability performance is proposed.