1,721,113 research outputs found
Thermal properties of fly ash based geopolymers containing refractory powder
No full textAbstract from the Young Researchers’ Forum, XIII AIMAT Congress and SIB Congress - Ischia, Italy, July 2016. Geopolymers are a new class of material synthetized through the alkali activation of a low-calcium aluminosilicate precursor. Several studies highlighted their remarkable thermal stability. However, the majority of the research focus on metakaolin-based geopolymers and, in most of the cases, a thermal curing is performed. This study, instead, aims to investigate the thermal properties of fly ash-based geopolymers containing refractory powder, cured both at room and high (70°C) temperature
Experimental study on the physical-mechanical durability of innovative hemp-based composites for the building industry
Full text linkFor reducing the environmental impact of the building sector, novel sustainable composites have recently been developed, by bonding hemp hurds with a new hybrid organic-inorganic binder. These composites, designed as substitutes for traditional insulating materials or as substitutes for formaldehyde-bonded wood particle boards, exhibit very promising thermal, physical and mechanical properties. To ensure that the panel performance is maintained during the building operation phase, durability needs to be specifically evaluated as well. Therefore, in this study three composite types with low, medium and high density (LD, MD and HD, respectively) were subjected to accelerated ageing and the alterations in their physical-mechanical properties were evaluated. Composite resistance to accelerated ageing is strongly correlated with bulk density. HD composites, the only ones actually designed to be directly exposed to rainfall, exhibited almost negligible decreases in mechanical properties and hence a substantially satisfactory behavior. MD and LD composites, designed to provide thermal insulation and hence to be sheltered by HD panels, were affected to a larger extent by accelerated ageing, which however was definitely more severe than the real exposure conditions of the composites during their service life. Further studies are currently in progress to optimize the composites formulation and physical-mechanical durability
Superplasticizer addition to carbon fly ash geopolymers activated at room temperature
Full text linkPresent concerns about global warming due to the greenhouse emissions in the atmosphere have pushed the cement industry to research alternatives to ordinary Portland cement (OPC). Geopolymer binder may constitute a possible breakthrough in the development of sustainable materials: understanding the effectiveness and the influences of superplasticizers on geopolymer systems is one of the essential requirements for its large-scale implementation. This study aims to investigate the possibility of using commercially available chemical admixtures designed for OPC concrete, to improve fresh properties of fly ash-based geopolymers and mortars. A special emphasis is laid upon evaluating their influence on mechanical and microstructural characteristics of the hardened material realized under room-temperature curing conditions. Results indicate that the addition of a polycarboxylic ether-based superplasticizer, in the amount of 1.0 wt. % by mass of fly ash, promotes an improvement in workability without compromising the final strength of the hardened material. Moreover, the addition of the polycarboxylic ether- and acrylic-based superplasticizers induces a refinement in the pore structure of hardened mortar leading to a longer water saturation time
Self-compacting concrete with recycled concrete aggregate: Study of the long-term properties
Full text linkThis paper investigates the shrinkage and creep of self-compacting concrete prepared with coarse and fine recycled concrete aggregates (up to 40% of total amount of aggregates). Physical properties and porosity measurements are studied and related to the mechanical properties. Results highlight that self-compacting characteristics are maintained when recycled aggregates are utilized and their good quality promotes high mechanical properties. Creep behavior and pores size distributions are more influenced by the content and assortment of recycled aggregates, although their effect is more limited compared to what occurs in traditional concrete with recycled aggregates
PLA composites formulated recycling residuals of the winery industry
No full textParticulate composites with polylactide (PLA) as a matrix and wastes deriving from the wine production have been formulated at different compositions. The microstructure and the mechanical properties of the composites, as well as the thermal stability and water uptake have been evaluated. The results showed that the wine waste residue does not compromise the thermal stability of the matrix while improves the impact strength and influences tensile properties. Specifically, tensile strength progressively decreases on addition of the winery waste, while the elastic modulus slightly increases. This behavior was attributed to the inhomogeneity of the filler particle size and morphology, which can partially induce a discontinuous interface at high filler loading and affect the water uptake. An increase in the value of the water contact angle is obtained below a 10% wt content and the mechanism of water uptake is not modified below the 20 wt% of filler. In any case, up to a content of 15 weight percent, winery wastes can be used in the plain matrix as an extender. Since simple and low cost operations are requested to obtain suitable fillers, an overall decrease in the material cost can be envisaged thus partially solving the drawbacks of PLA exploitation in the packaging industry, and leading to cost-effective application. Moreover, the conversion of lignocellulosic wastes as filler in biocomposites would be in favor of waste reduction while adding value to the agro-food chain
Epoxy composites containing wastes from wine production as fillers
No full textComposites formulated with an epoxy matrix, kenaf fibers, and the residuals of the wine industry are investigated at different compositions. The microstructure and the mechanical properties of the composites have been studied, as well as their moisture uptake. A proper mix design of the composite can allow the waste inclusion as filler either increasing or providing mechanical properties equal to those of the plain matrix. The increase in the water permeability induced by the waste is lower than that of induced by the kenaf fibers. Because of the simple mixing and pretreatment operation, this easy-to-handle recycling route may decrease the overall cost of the material reducing the amount of polymer matrix and offers a valuable alternative to damping. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46234
Geopolymer mortars for strengthening existing reinforced concrete structures
No full textThis paper aims to investigate the suitability of geopolymer mortars for strengthening existing reinforced concrete structures. Mortars were realized by mixing carbon fly ash with sodium silicate and sodium hydroxide solutions and sand. Several mixtures were prepared by varying the molar concentration of sodium hydroxide solution. Physical and mechanical properties of the hardened mortars were evaluated after 7 and 28 days of curing at room temperature. Geopolymer mortars were then used as matrix to cast fiber reinforced geopolymer matrix (FRGM) composites, comprised of high-strength steel fibers. The composites were applied on one face of concrete prisms and the bond behavior of the FRGM–concrete joints was investigated using single–lap direct shear test setup. Results show that geopolymer mortars can potentially replace cementitious mortar used in fiber reinforced inorganic matrix composites for strengthening applications of existing reinforced concrete structures
Valorization of organic additions in restorative lime mortars: Spent cooking oil and albumen
No full textAir- and formulated lime mortars with pulverized brick waste were synthesized with addition of two organic waste-based additives: spent cooking oil and albumen. The addition of spent oil in the mortar induced significant hydrophobic effects, but decreased permeability values and setting kinetics. Parallel additions of oil and albumen in lime mortars significantly increased their hydrophobicity and superficial durability without retarding their setting time thanks to role of fatty acids and unfolded proteins under alkaline conditions. The parallel valorization showed high potentials in synthesis of restorative mortars design with low environmental impact and high respect to the feature of historic mortars
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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