Rachel Raïssa Ngono Mvondo

Development and Characterization of a Micro-Concrete Based on Wood Waste from Sawmills

Rachel Raïssa Ngono Mvondo, René Oum Lissouck, Sophie Grigoletto

Key engineering materials

An experimental study was carried out to evaluate the feasibility of using concrete compositions containing waste wood for structural and non-structural building applications. First, the inert and wood aggregates used in the composite design were characterized. Five compositions containing a reference, 50% and 100% of wood particles were then produced and characterized in terms of physical and mechanical performance (e.g., apparent density, abrasion, compressive strength, and flexural strength). The selected specimens were used for additional experimental tests. These included water absorption and thermal tests. Increasing wood waste content considerably lower compressive and flexural strengths while improving the thermal insulation quality of wood waste-cement composite. The durability assessment of selected compositions further showed that the abrasion resistance of manufactured specimen decreased by adding wood waste in the cement matrix while there was an increase of the capillarity absorption coefficients. It appears that the incorporation of waste wood particles into mortars decrease their thermal conductivities to 0.3 W/mK. The use of wood waste treated by a lime solution improves the studied properties.

• #innovations in concrete and construction materials
• #recycling and utilization of industrial and municipal waste in materials production
• #hygrothermal properties of building materials
• #characterization (materials science)

Physical and mechanical properties of two tropical wood ( Detarium macrocarpum and Piptadeniastrum africanum) and their potential as substitutes to traditionally used wood in Cameroon

Stéphane Kenfack Kana, Achille Bernard Biwôlé, Paul William Huisken Mejouyo, Bernard Morino Ganou Koungang, Rachel Raïssa Ngono Mvondo, Marlène Ngansop Tounkam and 1 more

International Wood Products Journal

This study aimed to characterise two little-known woods and discuss their potential to replace those heavily exploited in Cameroon's forests. Amouk (Detarium macrocarpum) and Dabema (Piptadeniastrum africanum) were characterised for their physical and mechanical properties. Density, shrinkage, desorption kinetics, shear strength, tensile strength and modulus of elasticity (MOE) in compression and flexion were determined. A Weibull analysis was performed to predict their failure. It was found that Amouk and Dabéma can be classified as medium-heavy wood with low shrinkage and desorption, following Midilli's empirical model. The physical and mechanical characterisations show that the density, strength and MOE parameters of the woods are close to each other and enable them to be classified as medium-strength woods. The probability of failure in compression follows Weibull's law. These woods can, therefore, be used in structural applications such as construction, replacing common woods.

• #tree root and stability studies
• #african botany and ecology studies
• #wood treatment and properties
• #weibull distribution

Thermal properties and water content of two tropical wood species as a function of the air relative humidity.

Francklin Bobda, Rachel Raïssa Ngono Mvondo, Malick Diakhaté, Pierre Meukam

Heat and Mass Transfer

• #wood treatment and properties
• #natural fiber reinforced composites
• #bamboo properties and applications
• #relative humidity

Investigation of green-glued laminated timber from the Congo Basin: durability, mechanical strength and variability trends of the bondlines

René Oum Lissouck, Rachel Raïssa Ngono Mvondo, François René Ateba, Régis Pommier

Southern Forests a Journal of Forest Science

The development of glulam may give complementary, added-value to an important part of the timber production in the Congo Basin. Nevertheless, the high humidity in which these timbers operate may cause problems such as cracks and severe deformations if they are not suitably bonded. Moreover, there is a lack of knowledge concerning the refined design of the bondlines of glulam assembling from the Congo Basin hardwoods. We investigated the durability, mechanical strength, and variability features of the bondlines, manufactured under higher moisture conditions. Eight hardwood species with very different properties were selected. A one-component polyurethane adhesive was used. Industrial gluing parameters were kept constant. Delamination, shear tests and analysis of bondlines thickness were carried out. Multivariate analysis and a goodness-of-fit test of the strength variability of the bondlines were performed. Optimum bondlines thicknesses were obtained. Their durability exhibited satisfactory trends up to a density of 750 kg/m3. The behaviour of the bondlines can operate in three homogeneous groups. In each of them, the variability of the shear strength can be properly modelled using a 3-parameter Weibull probability. Wood failure trends were in accordance with several international requirements. The density value of 750 kg/m3 appeared as critical for the compatibility between the shear strength, the durability and the bondlines thickness. The overall results showed the ability of several tropical timber species to be valorised in green-glulam applications. Moreover, the findings unlock new trends concerning a reliable and safe design of tropical glulam as a structural wood-based product.

• #bamboo properties and applications
• #wood treatment and properties
• #natural fiber reinforced composites
• #durability

Effect of neem (Azadirachta Indica) fibers on mechanical, thermal and durability properties of adobe bricks

Colbert Babé, Dieudonné Kaoga Kidmo, Ahmat Tom, Rachel Raïssa Ngono Mvondo, Bernard Kola, Noël Djongyang

Energy Reports

Neem fibers are traditionally added as reinforcements in adobes. Laboratory experiments including, compressive strength, three-point bending strength, water absorption, erosion and thermal conductivity were carried out on adobes made with soil and reinforced with two neem fibers types (straw and leaves) at 0, 1, 2, 3 and 4%. It has been found that mechanical, thermal, and durability properties of adobes were globally improved. Furthermore, leaves neem fibers contribute strongly in comfort thermal, but their use has a negative effect on durability. Nevertheless, adobes reinforced with neem fibers are suitable as building materials with substantial thermal comfort and environmental benefits.

• #hygrothermal properties of building materials
• #bamboo properties and applications
• #natural fiber reinforced composites
• #durability

Investigation on mechanical and thermal properties related to hygroscopicity of two African hardwoods

Rachel Raïssa Ngono Mvondo, René Oum Lissouck, Serge Bell, Pierre Meukam

Wood Material Science and Engineering

This paper aims to study the mechanical, thermal and hygroscopic behavior of Okan (Cylicodiscus gabunensis) and Ayous (Triplochiton scleroxylon), two African hardwood species grown in southern Cameroon. The mechanical characterization of wood at 10%, 15%, 20%, 25% and 30% was investigated using tensile and bending tests. The thermal parameters were measured at the same moisture content levels by using the asymmetrical hot plate method. Sorption isotherms were obtained using the static gravimetric method. Mechanical properties decreased with moisture content. Okan wood, which Guitard and Brazilian models was not suitable for, presented very good properties compared to Ayous wood. Its flexural strength varied between 100 and 140 MPa and was 2.5 times higher than Ayous wood. Thermal conductivity increased with moisture content and was ranged from 0.1 to 0.56 W/mK. There was no significant difference between the radial thermal conductivities of the two species. The volumetric heat capacity was not influenced by the heat flow and the species. Experimental data showed a good fitting with the GAB model concerning sorption isotherms. Okan wood was less hygroscopic than Ayous wood. The annual equilibrium moisture content of the two species was determined and the cities of Bafoussam and Douala presented the best stabilization trend.

• #wood treatment and properties
• #tree root and stability studies
• #forest ecology and management
• #equilibrium moisture content

Thermomechanical characterization and durability of adobes reinforced with millet waste fibers (sorghum bicolor)

Colbert Babé, Dieudonné Kaoga Kidmo, Ahmat Tom, Rachel Raïssa Ngono Mvondo, Raphaël Belinga Essama Boum, Noël Djongyang

Case Studies in Construction Materials

Artisans in the Sudano-Sahelian zone of Cameroon make abundant use of adobes formulated from red millet fibers for the construction of houses. However, scientific data are missing in the literature to provide necessary information for the understanding of thermomechanical characteristics and durability of these materials. Adobe bricks used in this paper are formulated from the soil with 0, 1, 2, 3, and 4 % of millet waste. The samples are characterized by geotechnical, mechanical, thermal, and durability laboratory tests. Experimental measurements of mechanical and thermal characteristics show that millet fibers can contribute to the improvement of compressive strength and thermal conductivity by 38 and 23 % corresponding respectively to the incorporation of 2 and 4 % of millet fibers. Moreover, to understand the durability of the samples, the assessment of the behavior of adobe bricks exposed to water and friction (abrasion) shows that the incorporation of 2–4 % of millet fibers in the clay matrices, enabled us to obtain more resistant composites compared to the pure matrix. As a result, millet fibers, by their good adhesion to the clay matrix, act as reinforcement by contributing to the improvement of the thermomechanical characteristics and the durability of adobe bricks. Thus, adobe bricks reinforced with millet fibers can be used without damage, and cheap as building materials with a contribution to thermal comfort.

• #hygrothermal properties of building materials
• #masonry and concrete structural analysis
• #urban heat island mitigation
• #durability

Influence of moisture content on the thermophysical properties of tropical wood species

Rachel Raïssa Ngono Mvondo, Jean Claude Damfeu, Pierre Meukam, Yves Jannot

Heat and Mass Transfer

• #wood treatment and properties
• #natural fiber reinforced composites
• #bamboo properties and applications
• #thermal diffusivity

Influence of water content on the mechanical and chemical properties of tropical wood species

Rachel Raïssa Ngono Mvondo, Pierre Meukam, Jena Jeong, Domingos De Sousa Meneses, Elambo George Nkeng

Results in Physics

This paper aims to study the mechanical behavior and surface chemistry in relationship with moisture content of Iroko (Milicia excelsa), Bilinga (Nauclea diderrichii), and Tali (Erythrophleum suaveolens). Mechanical characterization was done experimentally using tensile and bending tests. Chemical semi quantitative analysis of the wood at 10%, 15%, 20% and 30% of moisture content was investigated using attenuated total reflectance Fourier transform infrared spectroscopy. The main chemical functions involved by the presence of water were identified as well as the other functional groups. The ratio between lignin and carbohydrates was estimated for all the wood species. The results indicated a negative correlation in the relation between moisture content and mechanical properties. Tali had the higher bending strength while Iroko had the lowest value. The average percentage change rate of the Young’s moduli induced by 1% of moisture content changes, especially between 10% and 20%, varied with the wood species: 1.69% in Tali, 1.65% in Bilinga and 2.54% in Iroko approximately. The infrared spectra obtained differed among species. The results also showed that Iroko contained higher lignin and were the least sustainable according to mechanical properties. The bands at 3340 cm−1 and 1635 cm−1 were more impacted by moisture content.

• #wood treatment and properties
• #natural fiber reinforced composites
• #bamboo properties and applications
• #water content