Naima Belayachi

Physical Characterization of Natural Straw Fibers as Aggregates for Construction Materials Applications

The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw.

Thermo-Mechanical Behaviour of an Innovant Straw Lime Composite for Thermal Insulation Applications

This paper presents an investigation on the use of new light-weight construction material, composed of lime, water and cereal straw fiber. Two types of fibers were used: wheat and barley straw. The influence of some parameters such as fiber types, binder types (lime and/ or lime-cement), fiber to binder ratio (F/B) and Water to Binder ratio (W/B) on the mechanical and thermal properties is studied. Compressive strength, thermal conductivity and density of the material were investigated. The results indicated that the thermal conductivity of the straw-lime composites decreased with increasing straw content. The result comparisons also revealed that the composite reinforced by wheat straw fibres has the highest compressive strength.

Thermo-hydro-mechanical behaviour of tuffeau stone masonry

This paper deals with thermo-hydromechanical behaviour of a stone masonry wall assembled with mortar. Macroscopic modelling is proposed that allows an evaluation of the impact of everyday thermal and hydraulic variations on the generation of variations in effective stress. The thermo-hydromechanic parameters of the unsaturated stone have been estimated by experimental tests for tuffeau, such as that found in the Chambord monument. An inverse identification has been used for the optimisation of these parameters based on in- situ measurements, before using the model for long-term analysis. The results of this numerical study show that the contrast between the properties alone is not sufficient to generate a stress that is superior to the stone strength. Otherwise, the variations in thermal and hydraulic conditions on the surface of the stone could lead to a fatigue-like degradation of historic monuments. Cet article s’intéresse au comportement thermo-hydromécanique d’un mur maçonné en pierre liée avec un mortier. Nous proposons une modélisation macroscopique qui permet d’évaluer l’impact de la variation quotidienne hydromécanique à la génération des variations des contraintes effectives au sein de la pierre. Les paramètres utilisés dans le modèle sont ceux identifiés au cours d’essais de laboratoire sur des échantillons de pierres similaires à ceux du château de Chambord. Une identification inverse a été utilisée pour les paramètres inconnus basée sur les mesures in situ. Les résultats de nos modélisations montrent que seul le contraste des propriétés ne conduit pas à des valeurs de contraintes suffisantes pour générer la rupture de la pierre. En revanche les variations cycliques d’hygrométrie et de température conduisent à des variations cycliques de la contrainte effective et la contrainte totale susceptibles d’endommager la pierre par fatigue.

Properties of cementitious mortars reinforced with natural fibers

Abstract The purpose of this study is firstly to investigate the effect of various treatments on the chemical and morphological properties of the fibers of two xerophyte plants (Doum ‘Chamaerops humilis’ and Diss ‘Ampelodesmos mauritanicus’), in order to improve the adhesion between fibers and cement matrix, secondly the effect of increasing inclusion rates of these two fibers on the physical, mechanical and thermal properties of cementitious composites. Obtainable results by infrared spectroscopy, X-ray diffraction and scanning electron microscopy revealed that the alkaline treatments of the Doum and Diss fibers with 1 and 3% NaOH for 30 min at room temperature resulted in an optimal improvement of the crystallinity index and alter the characteristics of the surface topography. The reinforcement of mortars with these two fibers caused a decrease in their bulk density and consequently the compressive strength, as well as an increase in their porosity and thus their capacity of water absorption. Moreover, the mortars reinforced with 2% of treated Diss fibers and 1.5% of treated Doum fibers show the high flexural strengths. Also, thermal conductivity measurements were carried out for different drying durations to assess the effect of water content on the thermal properties. Thermogravimetric Analysis coupled with differential scanning calorimetry are also performed to study the degradation and mass loss of composites at high temperature. The results reveal that the incorporation of these fibers reduces the thermal conductivity and increases the heat absorption of the composites.

Modelling of two-phase flow in capillary porous medium by a microscopic discrete approach

The aim of this work is to study the fluid flow in porous media by a microscopic approach. For that, the microstructure of a porous material is represented by a network of capillary pipes with geometric and flow characteristics chosen in such a way as to fit both the pore volume and water saturated hydraulic conductivity of a studied porous material. In saturated state, a pipe is supposed to have a Kozney–Carman hydraulic conductivity. In partially saturated conditions, the “menisci model” as proposed by has been used. Such a representation is sufficient to satisfactory reproduce mostly of laboratory results on flow properties of a porous material in saturated and partially saturated conditions as demonstrated by our numerical results on a porous stone.

Hydromechanical Properties of some Mortars Used in some Ecologic Construction Techniques

This paper presents results of hydromechanical characterization tests performed on some mortars used in eco-construction practice. Typically, such mortars could be found in buildings constructed following so called GREB technique that uses straw bales as structural and insulating elements in addition to a wood frame. The full experimental program includes thermal, mechanical and hydraulic – hygroscopic tests. Mechanical tests, including uniaxial compression test and three point bending test and hydraulic tests including water and vapor water permeability, retention curve and unsaturated water permeability have been performed on three earth-cement mortars with sawdust additive. Tests were performed in age of 7, 14, 28 and 120 days. For retention curve and so called relative permeability a simple method has been used based on measurements of masse variations of samples on a controlled humidity environment and an inverse problem approach. Using of sawdust improves hydraulic properties of these mortars but the early age strength of these mortars has to be improved by cement additives.

On the Modeling of Transition from a Diffuse to a Localized Damage

An approach to model long term hydromechanical behavior of rock masses around underground excavations is proposed. Implemented in a classical finite element numerical code this approach combine in one hand a continuum model to describe the progressive damage and strain localization and a fracture mechanics XFEM based numerical procedure to model the behavior of fractured mass once the macrofracturing takes places.

Hygrothermal Behavior of Clay - Sunflower (Helianthus annuus) and Rape Straw (Brassica napus) Plaster Bio-Composites for Building Insulation

The aim of this experimental investigation is to study and compare hygrothermal properties of different materials based on vegetable aggregates and clay in order to prove the performance of the developed composite in the framework of BIOCOMP project. Crude earth is known to have very high capacities to regulate indoor humidity. Vegetable aggregate is characterized by high porosity leading also to very effective natural indoor climate regulators. Then, we expect the mix of these two material will to produce an insulation bio-composite with enhanced thermal and hygroscopic performance. Sunflower stem, rape straw and clay used in this investigation are considered as a very low carbon footprint because they are real local agricultural byproducts. Clay-sunflower and rape bio-composites seem to be appropriate and effective biobased insulating plasters, further investigations must be performed in order to characterize more accurately their interesting hygrothermal properties as long as the acoustical and mechanical aspects. Samples have been manufactured with four different vegetable aggregates (rape straw, sunflower bark, sunflower pith and a mix of sunflower pith and bark) at a same binder/aggregate ratio. The same clay soil is used as a binder for the four bio-composites. The thermal properties for the different bio-composites were obtained from the thermal conductivity measurements after various relative humidity, in order to evaluate the impact of the water content on the thermal parameters. For the hydraulic properties, the sorption-desorption isotherms for the four composites are obtained. The results show a significant effect of the different aggregates on the hygrothermal behavior of the bio-composite based on clay.

A Comparative Study of Hydromechanical Properties in Saturated and Partially Saturated Conditions of Two Soils from the Runway of Oran Airport

This study concerns the ground soils of the second runway of the Es-Sénia airport in Oran (Algeria). This airport was built on a very complex hydro geotechnical site when underground cavities, following the dissolution of gypsum soil, were found during the before-construction geologic studies. Several, techniques are used in laboratory (Permeability, triaxial compression tests at various confining pressure, and hydric tests in saturated and unsaturated conditions) and for in situ it’s used the results of SPT and pressure-meter tests. A comparison of parameters of two soils identified in saturated and partially saturated conditions by in situ and laboratory tests was performed in order to respond to questions of the similarity of hydro mechanical properties of two soils as well as their statistical representativeness of the in-situ reality. It is found that, in respect to the studied parameters, laboratory results are statistically significant and reconstituted soils is statistically representative of natural soil reconstitution.

Evaluation of Classical Models for Thermal and Moisture Transport in Stone Walls of Historical Buildings

This paper concerns the evaluation and the validation of a heat and moisture transfer models in stone walls using in situ measurements on an instrumented wall. Firstly, a pure thermal (respectively moisture) diffusion problems are considerate, then this problem was combined with convection on the external edge of model. It is found that, despite of an uncoupled approach, the nonlinear thermal diffusive model performs quite well and reproduces perfectly the measured temperatures. It is the same for the convective-diffusive thermal problem, where the temperature on the surface wall is also reproduced quite well. An improvement of this second type problem results could be expected by taking into account the radiation. Otherwise, the both cases of moisture transfer problem (purely diffusive or diffusive-convective problem) are ill-simulated by the Kunzel’s model.