1,721,370 research outputs found
Carbon Nanotubes Strengthened Interphase in Textile Reinforced Mortar (TRM) Composites
No full textPerformance of inorganic matrix composite materials for structural purposes is strongly dependent on the matrix-to-fabric interphase bond strength. Consequently, owing to lack of congruence between the fabric and the matrix, design performance parameters are strongly penalised. Besides, yarn inner filaments (the core) easily slide over outer filaments (the sleeve) in the so-called telescopic failure. Broad experimental evidence supports the adoption of epoxy coatings to improve matrix-to-fabric strength and prevent telescopic failure, although the presence of the organic phase partially impairs the remarkable advantages associated to the inorganic matrix, such as thermal stability and water vapour permeability. Silica coatings appear as a promising alternative to traditional epoxy, by inducing localised pozzolanic reactivity, firmly linking synthetic fibres and hydraulic lime through the formation of highly cementing products at the interphase. In this work, the effect of a dispersion of multi-walled carbon nanotubes (MWCNT) in a silica nano-coating is assessed in uni-axial traction tests. The silica coating is prepared through sol-gel deposition in which carbon nanotubes are dispersed. The overall amount of carbon nanotubes in the silica sol is fixed at 0.5% wt. Silica-coated AR-glass and carbon fabric composite specimens, embedded in a commercially-available lime mortar matrix, are tested and compared. Carbon nanotubes provide a remarkable enhancement in both ultimate strength and elongation for AR-glass TRM, yielding an impressive two-fold increase in terms of strength. Differently, coated carbon fabrics composites show an increase up to 31% in terms of ductility, in view of an unexpected strength loss
Durable and highly dissipative fibrous composites for strengthening coastal military constructions
No full textReinforced concrete strategic structures for military purposes are often established in coastal or offshore areas, widely subjected to chemical attacks, mainly due to an aggressive saline and acid environments. Porosity of cementitious conglomerates favour penetration of chlorides, which tend to corrode the internal metallic rebar. The reinforcement of structures with fibrous composite materials is a viable solution to restore the initial requirements of the building, especially when it exerts defence purposes. Among synthetic fibres, polyphenylenebenzobisoxazole (PBO) is an organic fibre based on linked aromatic structures with high elastic modulus and tensile strength and highly dissipative attitudes. In this work, the assessment of durability of continuous fibre-reinforced cementitious mortar (FRCM) composites is carried out comparing the mechanical performance of laminates subjected to uni-axial tensile tests. It is found that PBO-FRCM presents high resistance against aggressive environments and specifically preserve its mechanical strength in the presence of salt-water, where other reinforcing materials undergo a dramatic degradation process
Targeting functionalised carbon nanotubes at the interphase of Textile Reinforced Mortar (TRM) composites
Full text linkTensile performance of textile reinforced inorganic matrix composites strongly depends on the matrix-to-fabric bond strength, that is the weak chain in the system. In this work, we investigate the role of multi-walled carbon nanotubes (MWCNT) dispersion in an amorphous silica nano-coating for AR-glass and carbon fabric Textile Reinforced Mortar (TRM) composites. Two lime mortars are considered at 56-day curing. Comparative mechanical testing in uni-axial tension show remarkable enhancements in terms of mean ductility, strength and energy dissipation capabilities. Besides, coating successfully hinders telescopic failure and delamination, which significantly narrows data scattering and benefits design limits. Crack pattern analysis reveals that coating promotes diffuse cracking in the specimen, with gradual and progressive damage buildup. Indeed, mean crack width and mean crack spacing are consistently reduced. BET, optical and E-SEM microscopy supports the action mechanism of the coating, that promotes wettability, surface roughening and imparts a remarkable increase in the specific surface area of the reinforcement
Comparing durability of steel reinforced grout (SRG) and textile reinforced mortar (TRM) for structural retrofitting
Full text linkWe assess tensile performance of Steel Reinforced Grout (SRG) and Fabric Reinforced Cementitious Matrix/Textile Reinforced Mortar, upon exposure to aggressive environments. Galvanized and brass-coated Ultra High Tensile Strength Steel fabrics are considered for SRG, while carbon, AR-glass, basalt and PBO fabrics are investigated for TRM, in a common cement mortar. Exposure to the aggressive environments is realized by specimen immersion for 1000 h (41.6 days) at controlled temperature in distilled water as well as alkaline, saline and acid solutions. Mechanical performance of rectangular 1-ply coupons is assessed in uni-axial traction: Ultimate strength and elongation, dissipated energy at failure and environmental conversion factors for design values are calculated and compared. It is found that significant performance difference exists in dependence of the aggressive environment under consideration. As a result, careful selection of the reinforcing fabric leads to substantial advantage in terms of durability, that should be capitalized upon at the design stage. A simple material selection matrix is presented which suggests the best reinforcing textile/aggressive environment combination for design purposes
Assessment of the Behaviour of Low-Modulus Polyurethane Foams Subjected to Severe Shear Deformation Conditions
No full textPolymeric materials are broadly employed as buildings materials because of a number of interesting properties for specific applications. Among them, polyurethane (PU) takes advantage of outstanding mechanical properties, such as high deformability and dissipation, as well as remarkable thermal and chemical stability. As a foam, PU is arguably the most popular insulating materials, used as a supplementary layer in precast concrete panels, infill walls and roofs. Experimental assessment of the mechanical behaviour of PU foams is therefore a long-standing issue, which is demanded to validate analytical models and provide reliable parameters in FEM modelling. In particular, reliable experimental assessment to large deformations is still difficult to attain. In the present study, we carry out a preliminary mechanical characterisation of a single low-modulus PU foam by means of a testing machine prototype, which performs simple shear and shear-per-traction deformations of a square-shaped sample, according to the restraining system adopted. Simple curve-fitting of the response leads to different mechanical parameters for the same material. Shear test results are related to compressive tests and microstructural investigation of the PU foam, through Scanning Electron (SEM) microscopy. The proposed polynomial laws for the tangential and normal net forces are applicable for calibrating FEM models aimed to predict the behaviour of soft materials subjected to high deformations
Evaluation of Preventative Methods against Rebar Corrosion in Concrete
Full text linkPrevention of rebar corrosion is achieved in the design and construction phases, by means of suitable mix design, casting and curing, and adequate cover depth; this approach has been introduced in international standards (EN 206) and design codes (Eurocode 2). Additional protection methods (cathodic protection, stainless steel or 1alvanized rebars, corrosion inhibitors, concrete coatings) can be used in very aggressive environment, especially in presence of chlorides, or when increased service life is required. In this work a simplified performance-based approach, based on Monte Carlo simulation, has been used to evaluate the service life (initiation time of corrosion) in chloride containing environments. The results confirmed that cathodic prevention and stainless steels are the most effective protection methods to guarantee a safe working condition in a severe environment. The use of pozzolanic or slag cement is confirmed as an effective way to slow chloride transport and by this way to increase the service life
A new Rayleigh-like wave in guided propagation of antiplane waves in couple stress materials
Full text linkMotivated by the unexpected appearance of shear horizontal Rayleigh surface waves, we investigate the mechanics of antiplane wave reflection and propagation in couple stress (CS) elastic materials.
Surface waves arise by mode conversion at a free surface, whereby bulk travelling waves trigger inhomogeneous modes. Indeed, Rayleigh waves are perturbations of the travelling mode and stem from its reflection at grazing incidence. As well known, they correspond to the real zeros of the Rayleigh function.
Interestingly, we show that the same generating mechanism sustains a new inhomogeneous wave, corresponding to a purely imaginary zero of the Rayleigh function. This wave emerges from "reflection"
of a bulk standing mode: This produces a new type of Rayleigh-like wave that travels away from, as opposed to along, the free surface, with a speed lower than that of bulk shear waves. Besides, a third zero of the Rayleigh function may exist, which represents waves attenuating/exploding both along and away from the surface. Since none of these zeros correspond to leaky waves, a new classification of the Rayleigh zeros is proposed. Furthermore, we extend to CS elasticity Mindlin’s boundary conditions, by which partial waves are identified, whose interference lends Rayleigh-Lamb guided waves. Finally, asymptotic analysis in the thin-plate limit provides equivalent 1-D models
Study of cytoskeleton from microscopic point of view: Our experience
Full text linkThe manuscript deals with our studies and experiences in the assessment of cytoskeleton in different cellular models and situations. The immunofluorescent study of several cytoskeletal proteins was relevant in the evaluation of a therapy for osteoarthritis, in case of alkaptonuria and in testing the efficacy of docetaxel in neuroblastoma cancer cells leading to apoptosis. A relevant part of our experience focus on the study of cytoskeleton in seminiferous epithelium and spermatozoa, identifying alterations affecting blood-Testis barrier after a silver nanoparticle treatment, chromosomal segregation in case of varicocele, sperm motility and diagnosing systematic sperm defects as "Primary ciliary dyskinesia" and "Dysplasia of the fibrous sheath". The evaluation of cytoskeleton represents a specific and sensitive analysis in establishing the health status of different cells
Antiplane Stoneley waves propagating at the interface between two couple stress elastic materials
Full text linkWe investigate antiplane Stoneley waves, localized at the discontinuity surface between two perfectly bonded half-spaces. Both half-spaces are elastic linear isotropic and possess a microstructure that is described within the theory of couple stress materials with micro-inertia. We show that the microstructure deeply affects wave propagation, which is permitted under broad conditions. This outcome stands in marked contrast to classical elasticity, where antiplane Stoneley waves are not supported and in-plane Stoneley waves exist only under very severe conditions on the material properties of the bonded half-spaces. Besides, Stoneley waves may propagate only beyond a threshold frequency (cuton), for which an explicit expression is provided. For a given frequency above cuton, this expression lends the admissible range of material parameters that allows propagation (passband). In particular, significant contrast between the adjoining materials is possible, provided that Stoneley waves propagate at high enough frequency. Therefore, micro-inertia plays an important role in determining the features of propagation. Considerations concerning existence and uniqueness of antiplane Stoneley waves are given: it is found that evanescent and decaying/exploding modes are also admitted. Results may be especially useful when accounting for the microstructure in non-destructive testing (NDT) and seismic propagation
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