1,720,997 research outputs found
DURABILITY AND MECHANICAL PROPERTIES OF NANOCOPOSITE FIBER REINFORCED CONCRETE
Full text linkIn this study we investigated the influence of polypropylene/organoclay fibers on durability and mechanical behaviour of concrete. Pure polypropylene fibers and polypropylene nanocomposite fibers of two different lengths (20 and 60 mm) have been mixed in concrete at two volume fractions (0.1% and 0.3%). Nanoclay addition increases fibers elastic modulus (about 27%) reducing ductility. Workability of concrete is greatly influenced by fibers length and volume fraction: increasing these two values workability decreases. Fibers are not influent on compressive and flexural strength while post-cracking toughness is increased. Nanocomposite fibers have a better pull-out strength due to a better friction during slipping, but this doesn’t ensure a better adhesion. Water absorption, freeze/thaw cycles and sulfate attack test demonstrate that increasing fibers volume fraction, durability of concrete increases
Digital light processing of high-strength hydroxyapatite ceramics: Role of particle size and printing parameters on microstructural defects and mechanical properties
Full text linkDense hydroxyapatite (HA) bars were fabricated using digital light processing. The roles of HA median particle size (MPS), curing depth-to-layer thickness ratio (CD/LT), and debinding process on the printing/debinding flaws and flexural strength of the sintered parts were investigated. Commercial HA was milled for different times to provide powders with an MPS ranging from 0.3 to 2.7 μm. Thermal debinding led to delamination and vertical cracks, which decreased with increasing MPS; the minimum value required to fabricate specimens with appreciable flexural strength was 0.9 μm. At a given MPS (2.7 μm), the CD/LT varied between 1.4 and 3.3, indicating a progressive disappearance of the above major flaws. Finally, the positive effect of water debinding prior to thermal debinding on reducing crack formation was demonstrated. After optimisation, the bars achieved a flexural strength greater than 100 MPa, which is the highest value among dense HA fabricated using lithography-based techniques
Durability and mechanical properties of nanocomposite fiber reinforced concrete
No full textIn this study we investigated the in uence of polypropylene/organoclay bers on durability and mechanical behaviour of concrete. Pure polypropylene bers and polypropylene nanocomposite bers of two di erent lengths (20 and 60 mm) have been mixed in concrete at two volume fractions (0.1% and 0.3%). Nanoclay addition increases bers elastic modulus (about 27%) reducing ductility. Workability of concrete is greatly in uenced by bers length and volume fraction: increasing these two values workability decreases. Fibers are not in uent on compressive and exural strength while post- cracking toughness is increased. Nanocomposite bers have a better pull-out strength due to a better friction during slipping, but this doesn’t ensure a better adhesion. Water absorption, freeze/thaw cycles and the sulfate attack test demonstrate that concrete durability increases with the volume of the ber fraction
DLP Fabrication of Zirconia Scaffolds Coated with HA/β-TCP Layer: Role of Scaffold Architecture on Mechanical and Biological Properties
Full text linkIn order to merge high-mechanical properties and suitable bioactivity in a single scaffold, zirconia porous structures are here coated with a hydroxyapatite layer. The digital light processing (DLP) technique is used to fabricate two types of scaffolds: simple lattice structures, with different sizes between struts (750, 900 and 1050 µm), and more complex trabecular ones, these latter designed to better mimic the bone structure. Mechanical tests performed on samples sintered at 1400 °C provided a linear trend with a decrease in the compressive strength by increasing the porosity amount, achieving compressive strengths ranging between 128–177 MPa for lattice scaffolds and 34 MPa for trabecular ones. Scaffolds were successfully coated by dipping the sintered samples in a hydroxyapatite (HA) alcoholic suspension, after optimizing the HA solid loading at 20 wt%. After calcination at 1300 °C, the coating layer, composed of a mixture of HA and β-TCP (β-TriCalcium Phospate) adhered well to the zirconia substrate. The coated samples showed a proper bioactivity, well pronounced after 14 days of immersion into simulated body fluid (SBF), with a more homogeneous apatite layer formation into the trabecular samples compared to the lattice ones
Production and characterization of polyethylene/organoclay oriented fiber
No full textThe aim of this work was to study the influence of drawing process on the mechanical properties of polyethylene/clay fibers. To this extent, three different PE/clay blends (3, 5 and 10 wt.%) were prepared by melt compounding in a twin-screw extruder. The investigated clay was a commercial organically modified montmorillonite (Dellite 67G). After compounding fibers were produced by a single-screw extruder and drawn at different draw ratios. At increasing draw ratio an increase of elastic modulus and tensile strength was attained. The presence of clay layers increases fibers ductility hindering fibrils formation during the drawing process. Moreover, at increasing clay contents a decrease of tensile strength for high draw ratios was observed. These results demonstrated that the dispersed clay layers can be re-aggregated by the uniaxial flow induced by the drawing process resulting in a decay of mechanical properties at high draw ratios
Processability, morphology and mechanical behavior of polypropylene/clay nanocomposite fibers
No full textInfluenza di fibre nanocomposite in polipropilene sul comportamento di una malta cementizia
No full textVat-photopolymerization of ceramic materials: exploring current applications in advanced multidisciplinary fields
Full text linkAdditive manufacturing has brought about a real revolution in the manufacture of objects in a variety of application areas, overturning the traditional paradigm based on subtractive approaches. The potential benefits deriving from the application of these techniques in the field of ceramic materials extend to different industrial sectors, leading to shorter, more accurate and cost-effective manufacturing processes. Within the present review, we provide a transversal analysis of the state-of-the-art of the applications of vat-photopolymerization technologies, namely, stereolithography and digital light processing in relevant technological industrial/research fields of our times, including biomedicine, energy, environment, space and aerospace, with a special focus on current trends and project-specific requirements. Unmet challenges and future developments will be discussed as well, providing readers a transfer of knowledge and “lessons learned” from one field to the other, being this approach aimed at the further growth of the technology towards its industrialization and market uptake
Mechanical properties, life-cycle assessment, and costs of alternative sustainable binders to stabilise recycled aggregates
Full text linkCement-stabilised subbases provide superior bearing capacity and durability to road pavements compared to unbound aggregate layers. However, stabilisation reduces the environmental benefits derived when recycled aggregates are used. This research compares alternative binders to Portland cement to highlight mechanical, environmental, and economic advantages and disadvantages in a cradle-to-production scenario. Three low-clinker cements with different proportions of pozzolana and three alkali-activated (AA) binders derived from (i) construction and demolition waste fines, (ii) municipal incinerator bottom ash and (iii) waste clay, were compared to Portland limestone cement. The compressive strength of binder pastes was measured after 7 and 28 curing days.
Pozzolanic cements proved viable alternatives to Portland ones, while AA pastes exhibited lower strengths. The crystallinity of alkali-activated silica- and alumina-rich waste precursors was responsible for their limited strength. The life cycle assessment indicated that the replacement of clinker with pozzolana significantly reduces the environmental impact. AA binders with waste precursors can reduce the environmental impact only with a limited quantity of alkaline solution. If the lower strength achieved by AA binders is compensated by adding higher quantities to recycled aggregate, the increase in environmental impact and cost would make them less competitive. The option of using AA binders would be further strengthened with the production of environmentally friendly alkaline solutions and greater local availability of amorphous precursors. At present, cements are cheaper than AA binders due to the current massive production, widespread availability, and competition between producers
Morphology Development and Mechanical Properties Variation during Cold-Drawing of Polyethylene-Clay Nanocomposite Fibers
Full text linkpeer reviewedIn this work, the influence of composition and cold-drawing on nano- and micro-scale morphology and tensile mechanical properties of PE/organoclay nanocomposite fibers was investigated. Nanocomposites were prepared by melt compounding in a twin-screw extruder, using a maleic anhydride grafted linear low density polyethylene (LLDPE–g–MA) and an organomodified montmorillonite (Dellite 67G) at three different loadings (3, 5 and 10 wt %). Fibers were produced by a single-screw extruder and drawn at five draw ratios (DRs): 7.25, 10, 13.5, 16 and 19. All nanocomposites, characterized by XRD, SEM, TEM, and FT-IR techniques, showed an intercalated/exfoliated morphology. The study evidenced that the nanoclay presence significantly increases both elastic modulus (up to +115% for fibers containing 10 wt % of D67G) and drawability of as-spun nanocomposite fibers. Moreover, at fixed nanocomposite composition, the cold-drawing process increases fibers elastic modulus and tensile strength at increasing DRs. However, at high DRs, “face-to-edge” rearrangement phenomena of clay layers (i.e., clay layers tend to rotate and touch each other) arise in fibers at high nanoclay loadings. Finally, nanocomposite fibers show a lower diameter reduction during drawing, with respect to the plain system, and surface feature of adjustable roughness by controlling the composition and the drawing conditions
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