Conducted jointly by UL and UAC, this research explores the use of rice husk in concrete to reduce environmental impact.
The Essentials: Conducted jointly by UL and UAC, this research explores the use of rice husk in concrete to reduce environmental impact.
Edem Chabi, researcher at LERMAB (Université de Lorraine).
Thesis defended in 2017 at the doctoral school RP2E - Doctoral School of Sciences and Engineering of Resources, Processes, Products, Environment.
This research was carried out under a Franco-Beninese joint supervision (cotutelle), ensuring simultaneous grounding in local field realities and international academic standards.
Context and Research Question
The construction sector is the largest consumer of energy and the second-largest emitter of CO2 worldwide. This situation calls for construction materials with reduced environmental impact. Concrete, the traditionally used material, accounts for a significant share of this carbon footprint. The proposed study addresses the development of sustainable concretes incorporating alternative materials such as rice husk. This agricultural byproduct, often regarded as waste, exhibits interesting mechanical and thermal properties when incorporated into a cement matrix.
The main objective of this research is to formulate a concrete based on rice husk and to analyze its mechanical and thermal performance. This approach aims to reduce agricultural waste while improving the characteristics of construction materials, particularly in the West African context, where resources are limited and sustainability is a major challenge.
Methodology
The methodology adopted rests on several key steps. First, setting tests were carried out with a pure cement paste formulated using water from rice husk infusion. These tests aimed to determine the impact of rice husk on cement setting. The results showed no inhibitory effect, unlike other plant-based aggregates.
Next, a chemical analysis of the rice husk was performed to quantify extractive content. The results showed that the extractive content of rice husk is nearly zero, distinguishing it from aggregates such as hemp and wood. This characteristic made it possible to explore the formulation of a sustainable concrete incorporating rice husk.
The concrete formulation was based on the compactness of the plant particle skeleton and on the formulation of the binder paste that fills the intergranular pore volume. The paste consists of binder, effective water, additions and any admixtures, as well as trapped and/or entrained air. Cement and water quantities were adjusted according to Féret's law, taking into account mixing intensity and casting mode.
A numerical model was developed to estimate the residual air volume in the mix. To validate this model, the formulation method was applied to five concrete samples with target strengths of 0.5, 1, 2, 4 and 8 MPa.
Key Findings
The study results show that the mechanical performance of rice husk concrete is close to the target values. However, the curing conditions of the specimens have a significant impact on mechanical strength. Curing under desiccation conditions was observed to cause a drop in strength of up to 60%. In contrast, specimens stored at a relative humidity (RH) of 95% showed the best mechanical strength.
Regarding thermal properties, thermal conductivity measurements revealed that rice husk concrete represents a viable alternative for thermal insulation. The average thermal conductivity of the concrete varies with the binder dosage, ranging between 0.070 W/(m.K) and 0.171 W/(m.K). The evolution of this thermal conductivity as a function of density and cement dosage proved linear, suggesting a direct relationship between formulation and thermal performance.
Discussion and Outlook
Incorporating rice husk into concrete formulation offers significant environmental benefits, notably the valorization of an agricultural waste product and improved thermal properties of the material. However, the research highlights challenges related to concrete curing, where optimal humidity conditions are needed to guarantee adequate mechanical performance.
The results obtained open the way for future research on optimizing the implementation and curing conditions of rice husk concrete. A deeper exploration of additives and curing methods could also help improve the durability and strength of the material. Research on sustainable rice-husk-based concrete could also extend to other regions facing similar resource and sustainability challenges, reinforcing the importance of a local and innovative approach to construction in West Africa.
Key Data
- 60%: Reduction in mechanical strength when specimens undergo desiccation.
- 0.070 to 0.171 W/(m.K): Thermal conductivity range of rice husk concrete, indicating its insulation potential.
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Sources and Access
Edem Chabi. Étude de la formulation et des propriétés mécaniques et thermiques du béton de balles de riz. Science des matériaux [cond-mat.mtrl-sci]. Université de Lorraine; Université d'Abomey-Calavi (Bénin), 2017. Français. ⟨NNT : 2017LORR0232⟩. ⟨tel-01907795⟩