Conducted jointly by UL and UAC, this research explores clay-rice straw composites for sustainable construction.
The Essentials: Conducted jointly by UL and UAC, this research explores clay-rice straw composites for sustainable construction.
Christian Enagnon Adadja, researcher at LEM3; LEMA (Université de Lorraine).
Thesis defended in 2020 at the doctoral school École doctorale C2MP - Chimie mécanique matériaux physique (Lorraine).
This research is part of a Franco-Beninese joint supervision, ensuring both grounding in the local field context and adherence to international academic standards.
Context and Research Problem
The construction sector is the world's largest energy consumer and second-largest CO2 emitter. This situation raises major concerns about the sustainability of the materials used, which have a significant impact on the climate. In response to this problem, research is turning toward the development of eco-friendly materials, with particular interest in composites based on renewable resources. Christian Enagnon Adadja's thesis, conducted at Université de Lorraine, focuses on a clay-straw composite made of clay and rice straw, a material traditionally used in rural construction. This composite offers interesting mechanical characteristics likely to encourage its adoption by building professionals in sustainable construction projects.
Methodology
The study relies on an experimental and analytical approach to evaluate the elastic properties of the clay-straw composite. Experimental tests were carried out, accompanied by microstructural analysis aimed at studying the distribution of straw fibers within the clay matrix. The objective was to determine the optimal composite formulation based on straw volume fraction. Tests showed that adding rice straw improves the composite's tensile and compressive strength up to a threshold of 25% volume proportion. Beyond this threshold, a decrease in Young's modulus was observed.
To predict the elastic behavior of the clay-straw composite, several analytical models were applied, notably the Mori-Tanaka and Hashin-Shtrikman models, as well as the Voigt and Reuss bounds. A numerical study was also carried out using Digimat software, which enabled the integration of finite element (FE) and semi-analytical (MF) modules. These tools made it possible to derive the intrinsic properties of the composite's components, notably the elastic properties of the rice straw and the clay matrix, the aspect ratio of the straw, the geometric orientation of the plant inclusions, and the volume fraction of the inclusions.
Key Findings
The experimental results reveal that the mechanical properties of the clay-straw composite are strongly influenced by the proportion of rice straw. Up to 25% straw, a significant improvement in tensile and compressive strength was observed. Young's modulus, a measure of the material's stiffness, reaches a maximum value at this volume fraction, while excess straw leads to a reduction in this property.
The analytical models applied made it possible to predict the elastic behavior of the composite with a good degree of accuracy. The Mori-Tanaka and Digimat MF models proved particularly effective in modelling the elastic properties of the clay-straw composite. They made it possible to integrate various parameters, such as fiber distribution and inclusion geometry, into the analysis.
Discussion and Outlook
The results of this research highlight the value of using local, sustainable materials such as clay-straw composites in the construction sector. Optimizing the composite formulation could lead to broader applications, contributing to a reduced carbon footprint for the sector. The implications of this study go beyond simple mechanical property modelling. They pave the way for wider adoption of eco-friendly materials in construction projects, particularly in West Africa, where local resources are often underused.
Integrating these materials into current construction standards requires concerted efforts from decision-makers and industry stakeholders. Incentives could be put in place to encourage the use of clay-straw composites, fostering a transition toward sustainable construction. Future work could further explore the long-term performance of these composites under real-world conditions, as well as their behavior in the face of climate variability. This would strengthen the position of clay-straw composites as a viable solution for environmentally responsible construction.
Key Data
- 25%: Straw volume fraction at which the composite's strength improves.
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Sources and Access
Christian Enagnon Adadja. Modélisation multi-échelles des propriétés élastiques du composite argile-pailles de riz. Mécanique des matériaux [physics.class-ph]. Université de Lorraine; Université d'Abomey-Calavi (Bénin), 2020. Français. ⟨NNT : 2020LORR0067⟩. ⟨tel-02958887⟩