1,721,024 research outputs found
EXPERIMENTAL CHARACTERIZATION OF HEMP WOVEN FABRIC REINFORCED EPOXY RESIN COMPOSITES PRODUCED WITHOUT HEAT TREATMENT
Full text linkIn the field of composite materials there is growing emphasis on environmental impacts, resulting in the replacement of synthetic-based components with bio-based components, and in particular, attention to the production process. The focus of the paper is the production of a composite reinforced with natural fibers, which can find applications in the construction field as the reinforcement of wooden structural elements, or as a skin for boards or sandwich panels. In this sector, it is not neces-sary to achieve very high mechanical performance as in the automotive sector. On the other hand, the cost of the product must be kept low and the production process simple. The proposed composite was prepared with an epoxy resin matrix reinforced with a bidirectional woven fabric made of hemp fibres without any heat treatment. The composites were hand laminated and manufactured by cold moulding to reduce energy consumption. To optimize the behaviour of the composite, various specimens were manufactured, and factors such as the curing pressure, quantity of resin and layer orientation were modified. Tensile strength tests were conducted on specimens according to the ASTM D3039 standard
New set up for tensile test performed on thin bamboo
No full textThe tensile test is one of the most important and widespread tests on bamboo and materials in general. This test on bamboo presents some difficulties if performed according to International Standards, amplified in the case of thin bamboo. The aim of this study is to introduce a new tensile test set up able to improve the procedure suggested by International Standards to be applicable to all bamboo species including the thinner varieties growing in the temperate climate of Europe. Materials and techniques adopted in the procedure are easy to find and to be used. Results show the effectiveness of the procedure
On the radial variation of the transverse mechanical properties of bamboo
Full text linkBamboo is a functionally graded and axially reinforced material displaying high longitudinal mechanical properties. However, it is prone to longitudinal splitting, mainly due to tensile and shear stress components. Therefore, this experimental study was focused at determining the transverse mechanical properties of five species of bamboo using digital image correlation (DIC). Thus, two tests with parts of rings were used to independently determine the inner and outer circumferential tensile strength as well as the variation of the circumferential Young's modulus through the culm wall. In the first set-up, a semi-ring (SR test) was radially loaded at the middle section and supported on rollers at both ends such that the inner surface of the specimen was under tensile stress. In the second protocol, a specimen bigger than a semi-ring (C test) was loaded by two radially applied compression loads to generate tensile circumferential stresses on the outer surface. A closed-form solution assuming a linear variation of the Young's modulus through the culm wall was developed to analyze the experimental results. The bamboo species Phyllostachys edulis (EDU), Phyllostachys bambusoides (BAM), Phyllostachys Iridescens (IRI), Phyllostachys Violascens (VIO) grown in North of Italy, and Guadua angustifolia (GA) grown in Colombia were tested. The inner tensile failure strain (range of means for all species: 0.014–0.035) was generally higher than the outer (range of means for all species: 0.008–0.0019). The effective modulus of GA (931 MPa–1148 MPa) was lower than those of the European species (range of means for all European species: 1209–2983 MPa). The inner Young's moduli for all species except EDU (796–1694 MPa) was lower than the outer (range of means for all species: 1976–4694 MPa). The trend was different for EDU that showed an outer Young's modulus about 30% lower than the inner modulus. The outer tensile strength of BAM, IRI and GA (range of means for the three species:16.5–30.5 MPa) was significantly higher than the inner (range of means for three species: 9.9–17.6 MPa), while no signficant differences were found for VIO. A different trend was obtained for EDU, for which the inner strength was about three times higher than the outer
Mechanical characterization of five species of Italian bamboo
Full text linkHigh mechanical performance coupled with sustainability gives to bamboo a high potential to substitute conventional construction materials in various applications. In particular, there are countries in which this material has been used in construction for millennia and represents an asset, on the contrary, there are countries where there is still not enough knowledge of the structural properties of locally-grown bamboo. In these cases, it is important to extend the knowledge of the mechanical properties of local bamboo species supported by the development of suitable standardised testing procedures. In this view, the paper presents the results of an experimental study for the mechanical characterization of five bamboo species cultivated in Italy (Phyllostachys bambusoides, edulis, iridescens, violascens and vivax). For compressive tests, the used methodology is compliant with ISO Standards; for tensile test, the procedure suggested by ISO is very difficult to apply so different set ups have been proposed and in the second part of the paper a critical discussion about ISO methodology and its possible improvements are reported. The findings from this research shed light on current challenges and on the possible future steps for a wider uptake of natural materials in constructions
Poisson's ratio bounds in orthotropic materials. Application to natural composites: wood, bamboo and Arundo donax
Full text linkThe paper discusses the restrictions the positive definite character of the strain energy imposes to the values of the Poisson's ratios in a linear elastic orthotropic constitutive law. By exploiting the reciprocity principle and the conservation of energy, non-trivial constraints arise, leading to a particularly expressive form of the domain of existence, named Tetrahedron-Ellipsoid locus, in the space of three independent Poisson's ratios. The presented analysis establishes several notable restrictions for the elastic behavior of orthotropic composite materials, in all the cases in which there are great differences in the Young's moduli. For instance, near the edge of this locus, some Poisson ratios may belong to an interval not including the zero value; a very interesting peculiarity, perhaps not yet figured out in literature. In order to assess the coerciveness of the formulation, the results are applied to common wood essences, to several Italian growing species of bamboo and Arundo donax, natural composite functionally graded orthotropic materials. In the latter cases, an extensive experimental investigation is carried out to detect several Poisson's ratios, not studied in literature. Poisson ratios are obtained directly by strains measured by means of both physical strain gauges and Digital Image Correlation (DIC)
New sustainable alkali-activated composite materials reinforced with natural fiber: preliminary experimental investigations
No full textA new class of materials known as alkali-activated materials (AAM) has rapidly grown in interest in the last two decades in order to reduce the CO2 emissions for cement and ceramic materials productions. This new class of materials is based on alkali-activation of precursors able to consolidate at room or slightly higher temperatures. One of the main advantages of AAM is the possibility to use waste-based powders as for example coal fly ashes, thus promoting a circular economy approach.
Although being characterized by a lower environmental impact, AAM suffer from some drawbacks, mainly the extreme brittleness and the low dimensional stability. The most frequently used solution to these problems is the addition of fibers, such as polypropylene, steel or basalt ones. The use of natural fibers with the scope to obtain a similar improvement could provide a huge environmental benefit.
In this work, the effect of natural fibers (i.e., bamboo, Arundo, hemp and kenaf) on the properties of mortars formulated with fly ashes activated by alkaline solutions has been investigated. The length of the fibers was varied in order to obtain the best properties of the composite materials. A certain amount of water has been added in all the alkali-activated mixes to obtain a good workability. A reference mortar without fibers and the same liquid/binder and binder/sand ratio has been prepared for comparison. No heat curing has been used in all the mortars.
The consistency at the fresh state, as well as the microstructure, physical and mechanical properties at the hardened state of the obtained materials have been studied. Higher flexural strength and increased toughness have been obtained. These preliminary results foster the use of natural fibers to improve the performance of low carbon footprint building materials such as alkali-activated composites in the civil engineering applications. Further studies are necessary to better explain these preliminary results
Building retrofitting system based on bamboo-steel hybrid exoskeleton structures: A case study
Full text linkThe building heritage of many seismic regions worldwide is largely substandard and seismically deficient and would require seismic retrofitting interventions. The use of natural materials with low embedded emissions could lead to a low carbon footprint of the retrofitting intervention. In this perspective, an innovative structural sustainable retrofitting system is proposed consisting of a hybrid steel–bamboo reticular bracing system. Through a preliminary two-dimensional analysis, the capabilities of the system are assessed by varying the size and the number of the culms and inserting engineered bamboo and steel rods. Considering the constraints posed by the openings, a structure that uses steel in the first inter-storey and bamboo in the others is proposed to obtain a significative improvement of mechanical performances. The spatial behaviour of this structure is studied through a three-dimensional numerical model. The seismic analyses show that the exoskeleton structure when conveniently anchored allows to achieve an effective displacement and deformation control on the primary structure, as well as a reduction of its internal forces. The results of the presented work may provide useful preliminary insights. Further research effort is needed to generalize the results to different seismic zones. The proposed seismic retrofitting system could be easily integrated with a thermal coat to also enhance energy saving
Bamboo Scaffolding as a European Promising Opportunity: A Structural Feasibility Study
Full text linkThere is an increasing need for the use of materials with low carbon emissions, especially in the construction sector, which is responsible for a large amount of emissions. In this perspective, bamboo can play a crucial role; it grows very fast and is an effective carbon sink, having good mechanical properties. It has been used for millennia in specific contexts and territories, such as scaffolding in Asia. This paper aims to demonstrate how bamboo scaffolding can be a viable option in Europe as well. Two prototypes of scaffolding are calculated for the refurbishment of two- or three-story buildings, a common typology in European urban and extra-urban residential areas. The dimensions of the considered scaffolding are 1.8 m and 1.0 m for bay lengths and 1.5 m and 0.8 m for bay lifts. The bamboo considered in the analysis grows in temperate climates, dimensionally smaller in diameter and thickness than tropical ones. Connections play a crucial role, and this paper proposes simple steel connections that are easily removable and suitable for standardized assembly processes already available on the market
Geopolymers reinforced with natural fibers: A comparison among different sources
Full text linkThe performance of different natural fibers (hemp, kenaf and bamboo) used to formulate composites with an alkali-activated matrix based on metakaolin is evaluated. Short fibers were randomly dispersed up to about 3% of the binder weight, and the fresh and cured properties of the derived composites were determined. Up to the investigated fraction, it is still possible to obtain adequate workability without the supply of additional water or additives. Upon modification with fibers, the mechanical behavior changes from completely brittle to pseudoplastic with increased toughness. The flexural strength increases by up to 80% at the highest bamboo amount and up to 20% for kenaf. Hemp fibers have a negligible effect on flexural strength but strongly improve the materials’ toughness. Moreover, the addition of fibers does not change the manner in which the material interacts with moisture. Indeed, the water uptake of the modified samples was comparable to that of the unmodified samples, and the composites showed a decreased rate of water diffusion as the amount of fiber increased
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