A Bamboo Treatment Procedure: Effects on the Durability and Mechanical Performance

Bamboo is a natural material having a fast reproduction and high mechanical strengths. However, when a bio-based material in general, and bamboo in particular are expected to be a construction material, their sensitivity to moisture and their durability are usually questionable. Indeed, it is well known that these materials do not possess the same performance in the long-term, when compared to industrial materials. Sustainable solutions for the bamboo treatment still need to be investigated. The present study explores the oil-heated treatment with different types of oils, like flax or sunflower oils. The present investigation concentrates on mechanical properties and durability of treated bamboos to assess the effectiveness of these kinds of treatment. First, bamboo specimens were treated to decrease their sensitivity to moisture and improve their durability. Different conditions of treatment were tested: treatment at 100 °C or 180 °C; with flax oil, sunflower oil, or without oil; treatment durations of 1 h, 2 h, or 3 h; and, different cooling methods and cooling durations. Then, mechanical and durability tests were carried out on untreated and treated bamboos: uniaxial compression tests, 3 points bending tests, water immersion tests, and humidity tests. The results showed that some tested treatment methods could increase both the durability and the compressive strength of treated specimens, compared to untreated bamboo. The best results were observed on specimens treated at 180 °C during 1 h or 2 h without oil, and then cooled in 20 °C sunflower oil

Matériaux composites à fibres naturelles / polymère biodégradables ou non

Les fibres naturelles ont récemment attiré l'attention des scientifiques en raison de leurs propriétés : faible coût, faible densité, renouvelables, biodégradables et non abrasives. Dans cette étude, trois types de fibres de bambou sont étudiées. La modification chimique des fibres par la soude est utilisée pour enlever l'hémicellulose et la lignine. Puis, la surface de la fibre est modifiée par acétylation ou silane avant élaboration de composites PP. Les propriétés mécaniques des composites augmentent avec le diamètre des fibres et avec l'utilisation d'un agent d'ensimage. Des mélanges amidon/PVA/plastifiant/agent de couplage sont également étudiés. Les composites préparés par réticulation avec l'acide citrique ont d'excellentes propriétés mécaniques. La résistance à la traction et la déformation à rupture de ces composite augmentent avec la teneur en PVA. La présence d'argile et de fibres ont toutes deux un effet considérable sur les propriétés mécaniques des composites.Natural fibers have recently attracted the attention of scientists because of their properties of low-cost, low density, renewable, biodegradable and nonabrasive. In this study, three types of bamboo fibers are prepared. Chemical modification of fibers by alkali is used to remove hemicellulose and lignin. Then, fiber surface is modified by acetylation and silane before processing composite materials with polypropylene. As expected, the mechanical properties of the composites increase with the average fibre diameter. Tensile strength and Young's modulus increase when using a coupling agent. Starch/PVA blends are also prepared with glycerol and water as plasticizer. The composite prepared by citric acid crosslinking has excellent mechanical properties. Tensile strength and elongation at break of starch/ PVA composite increase with the content of PVA. The presence of clay and fiber are both found to have considerable effect on the mechanical properties of the composites.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Microstructural Characterization of Porous Clay-Based Ceramic Composites

Clay-based materials are the most traditional components of buildings. To improve their performance in a sustainable way, agents can be mixed to fired clay acting as a pore-forming factor. However, firing temperatures highly influence their microstructure which is closely linked to a material’s final performance as a ceramic block. To highlight the influence of the firing temperature on microstructure, and more specifically on the pore size distribution of clay-based materials, three innovative porous materials were manufactured. These materials were produced by mixing clay and pore-forming agents. They were characterized by optical and scanning electronic microscopy, x-ray diffraction, mercury intrusion and nitrogen adsorption. These techniques allow the phase identification of materials, show sample microstructure and quantify the pore size distribution at different scales. Furthermore, geometric parameters of sample microstructure such as grain diameter and roundness are estimated by using computer software. To conclude, results provide an enlightenment about the influence of material microstructure on the pore size distribution at two firing temperatures. These results can be useful to allow the tune of porous characteristics and, therefore, contribute to the production of more sustainable construction materials

Uncertainty and sensitivity analysis applied to a rammed earth wall: evaluation of the discrepancies between experimental and numerical data

Due to the environmental impact of building materials, researches on sustainable materials, such as bio-based and earth materials, are now widespread. These materials offer numerous qualities such as their availability, recyclability and their ability to dampen the indoor relative humidity variations due to their hygroscopicity. As these materials can absorb large amount of humidity, numerical and experimental studies of their hygrothermal behaviour are crucial to assess their durability. To validate a hygrothermal model, numerical and experimental data have to be confronted. Such confrontation must take into consideration the uncertainties related to the experimental protocol, but also to the model. Statistical tools such as uncertainty and global sensitivity analysis are essential for this task. The uncertainty analysis estimates the robustness of the model, while the global sensitivity analysis identifies the most influential input(s) responsible for this robustness. However, these methods are not commonly used because of the complexity of hygrothermal models, and therefore the prohibitive simulation cost. This study presents a methodology for comparing the numerical and experimental data of a rammed earth wall subjected to varying temperature and relative humidity conditions. The main objectives are the investigation of the uncertainties impact, the estimation of the model robustness, and finally the identification of the input(s) responsible for the discrepancies between numerical and experimental data. To do so, a recent and low-cost global variance-based sensitivity method, named RBD-FAST, is applied. First, the uncertainty propagation through the model is calculated, then the sensitivity indices are estimated. They represent the part of the output variability related to each input variability. The output of interest is the vapour pressure in the middle of the wall to confront it to the experimental measurement. Good agreement is obtained between the experimental and numerical results. It is also highlighted that the sorption isotherm is the main factor influencing the vapour pressure in the material

Control of the morphology of waterborne nanocomposite films

International audienc

Rammed Earth incorporating Recycled Concrete Aggregate: a sustainable, resistant and breathable construction solution

Construction and demolition debris, mainly concrete and masonry rubble, represent a significant share of municipal waste. Recycling crushed concrete aggregates and using them as substitutes for natural ones might therefore be determinant in reducing landfilling and mineral resource depletion. An innovative way to give new value to Recycled Concrete Aggregates (RCAs) is to ram them in layers to form load-bearing walls for stabilised Rammed Earth (RE) applications. However, the success of those few existing RE projects using RCA is mainly due to the knowledge and experience of the contractors rather than official standards or guidelines or scientific literature. The objective of this study was to further the knowledge of this building technique by determining the effect of different RCA replacements on the material’s mechanical resistance, sustainability and hygroscopic properties: indicative of the structure’s structural, environmental and hygrothermal performance. Mechanical resistance was assessed by means of the Unconfined Compressive Strength (UCS, commonly used for rammed earth-like materials), hygroscopic properties via Moisture Buffer Value (MBV) and sorption isotherms while the sustainability was assessed via consequential Life Cycle Assessment (LCA). Microstructural investigations via mercury intrusion porosimetry, nitrogen adsorption-desorption isotherms, scanning electron microscopy and Xray diffraction were performed to understand and explain material mechanical and hygroscopic behaviour. The building technique, already proven to be durable, was demonstrated to be resistant (from 4 to 12 MPa at 28 days depending on the RCA replacement and cement content), sustainable (down to 25 kg CO2-eq. of embodied carbon per square meter of load-bearing wall) and to have good moisture buffering abilities (0.88 g/(m2%RH) for mixtures containing only RCA). Strength appeared to be more related to the particle size distribution of the mix rather than to the percentage of RCA added. The amount and type of stabiliser added to the mix and the distance covered by the RCA during its lifetime strongly affected the environmental sustainability of the mixture; to maximise the potential of this building technique, reducing the amount of cement in the mixture by using alternative stabilisers should be the main priority

Memory B cell compartment constitution and susceptibility to recurrent lower respiratory tract infections in young children

A proportion of children have recurrent LRTIs, mostly as a result of Spn, which persist after 2 years of age. Here, we investigate, by flow cytofluorometry, the constitution of the memory B cell compartment in 90 healthy children and 49 children with recurrent LRTIs to determine if an increased susceptibility to recurrent LRTIs results from a delayed or abnormal ontogeny with poor antibody-mediated protection. Total IgA, IgM, IgG, and IgG subclasses were measured by nephelometry, as well as antipneumococcal antibodies by ELISA. Pneumococcal vaccination status was obtained. We show that the memory B cells increase between birth and 2 years of age (1.6% vs. 21.1%, P0.40) to reach adult-like values (31.8±11.8%, P=0.08). Proportions of switched and IgM memory B cells were similar in children and adults. Comparatively, LRTI children had no delay in the constitution of their memory B cell compartment (2-3 years old: 26.9%; 3-4 years old: 18.2%; 4-5 years old: 26.8%, P>0.05). Their switched and IgM memory B cells were similar among age categories, and the distribution was overall similar to that of healthy controls. LRTI children had normal total and pneumococcal serotype-specific antibody values but showed a rapid waning of antipneumococcal antibody levels after vaccination. In summary, our results show that the memory B cell compartment is already similarly constituted at 2 years of age in healthy and LRTI children and thus, cannot explain the increased susceptibility to bacterial pneumonia. However, the waning of antibodies might predispose children to recurrent infections in the absence of revaccination

Characterization of hygrothermal insulating biomaterials modified by inorganic adsorbents

International audienc