1,720,967 research outputs found
Oxyfuel Combustion Residues as Supplementary Cementitious Materials for the Production of Blended Portland Cements
No full textOxyfuel combustion represents one of the most interesting processes aimed at CO2 capture and storage to mitigate greenhouse effects ascribable to the process industry. In a different technical area, searching for new processes aimed at producing low-CO2 cements has comparable relevance, due to the huge generation of greenhouse gases related to cement production. This paper proposes an integration of these two aspects, with an approach new in the pertinent literature. The possibility of reusing ashes, issued by a pilot plant fluidized bed oxyfuel combustion process, as a source of material in the production of low-CO2 cements is investigated. Ashes were tested as substitutes for natural pozzolan in blended cements. They were mixed with an industrial Portland clinker and natural gypsum in order to evaluate their hydraulic behavior at different curing temperatures (20–40°C) and times (2–28 days). Pozzolanicity tests together with differential thermal–thermogravimetric and X-ray diffraction analyses were employed to explore the hydration behavior of oxyfuel ashes-based blended cements
Molecular and supramolecular studies on polyglycine and poly-L-proline
No full textElastin is a cross-linked protein, whose soluble precursor is tropoelastin, responsible for resilience and elastic recoil in vertebrate tissues. Glycine and proline are among the most repeated amino acids in tropoelastin primary structure, the high flexible glycine being present 222 times and the more constrained proline being present 96 times. In order to deeper investigate the role of glycine and proline residues in elastin, we studied the molecular and supramolecular structures of polyglycine and poly-l-proline homopolypeptides as significant sequences for the protein. As a matter of fact, up to now, if few conformational studies are accessible only for poly-l-proline homopolypeptide in solution and for polyglycine homopolypeptide in the solid state, limited supramolecular studies are available for both homopolypeptides. Given the self-aggregation properties of these homopolypeptides, we investigated the aggregation mechanism by turbidimetry measurements together with Congo red birefringence assay, ThT fluorescence spectroscopy, and atomic force microscopy and transmission electron microscopy studies. At molecular level, we show the dominance of the cross-β structure for polyglycine fibrils while for poly-l-proline aggregates PPII conformation prevails. At supramolecular level, the results show that polyglycine is able to self-aggregate into amyloid-like fibres while poly-l-proline aggregates by following a specific pathway ranging from protofibrils to fibrils. These findings suggest that the self-aggregation properties of elastin are influenced by tropoelastin primary structure thus explaining why glycine-rich elastin-derived polypeptide sequences are amyloidogenic (Gly-effect) while proline-rich elastin-derived polypeptide sequences (Pro-effect) are able to coacervate. © The Royal Society of Chemistry 2011
Construction and Demolition Waste as Raw Materials for sustainable Cements
No full textIn 2014 about four billion tonnes of cement were produced [CEMBUREAU, 2014]. The use of industrial by-products, as a source of raw materials in the manufacture of portland and blended cements, is a research theme of significant relevance to the construction industry. Such industrial by-products can be employed as constituents of the final product or components of the raw feed in a cement kiln. Due to their hydraulic and/or pozzolanic activity, industrial by-products are utilized worldwide. Such by-products also increase durability and reduce costs for producing blended cements.
The use of such by-products as raw mixture component for the cement production has received comparatively little attention by researchers and engineers. There is currently an increasing interest towards searching for new categories of by-products, which would be able to provide reactive calcium, silicon, aluminum, and/or iron oxides, for portland cement clinker manufacture. In this regard, construction and demolition waste (C&DW) is worthy of consideration because, when obtained from a properly selective demolition process, they could be employed as alternative raw material for portland clinker production.
The present study deals with the use of two different kinds of C&DW, namely concrete waste (CW) and masonry waste (MW). In this study, C&DW is proposed to be employed as partial or total substitute for limestone and clay, respectively, in the portland clinker generating raw mixture. Four ternary mixtures containing limestone, as well as CW and MW, were subjected to laboratory tests in order to evaluate the clinker raw mixture produced and the performance of the related portland cement. A binary mixture, composed of limestone and clay, was used as a reference. All of these different cements displayed similar hydration behavior. Detailed results are presented and discussed
Rutile microtubes assembly from nanostructures obtained by ultra-short laser ablation of titanium in liquid
Full text linkPulsed laser ablation of a titanium target in water was performed by an ultra-short laser source (Ti:sapphire, @=800nm, 1kHz, 100fs). The obtained structures were characterized by Atomic Force Microscopy, Scanning Electron Microscopy, X-Ray Photoelectron Spectroscopy, micro-Raman spectroscopy and X-ray Diffraction, revealing the presence of non-stoichiometric titanium oxide nanoparticles with a certain amount of crystalline rutile phase. Upon remaining in water the ablated species, the formation of a lamellar phase has been observed. This lamellar phase rolls up to microtubes by remaining in water for a month, through a self-assembling process. The formed microtubes, with an inner diameter of about 2 um and an outer diameter of 4 um are characterized by a smooth interior surface and aggregation of nanoparticles on the outer surface
Ultra-short pulsed laser deposition of thin silver films for Surface Enhanced Raman Scattering
No full textNanostructured thin films have been obtained by ultra-short Pulsed Laser Deposition (PLD) of silver performed in vacuum. The ablation source used in these experiments was a frequency doubled (λ = 527 nm) Nd:glass laser with a pulse duration of 250 fs. The films have been characterized by UV-vis spectroscopy, Atomic Force Microscopy and Transmission Electron Microscopy. The Surface Enhanced Raman Scattering activity, investigated by Raman scattering of rhodamine B adsorbed onto rough silver substrates, results strongly related to the Effective Surface Area (ESA) of the silver surfaces. Surprisingly, silver films obtained by ultra-short PLD are very similar to those obtained by short PLD. With the aim of explaining this likeness, the dynamics of plasmas induced by short and ultra-short laser pulses have been studied by Optical Emission Spectroscopy and fast imaging. Composition, velocity, excitation temperature and density of short and ultrashort plasmas are quite similar, showing that film properties are strongly related to the plasma features
Solar-driven production of lime for ordinary Portland cement formulation
No full textCement production is an energy-intensive manufacturing process with potentially large environmental burdens. Among the others, it is one of the largest industrial sources of CO2 emission. Limestone calcination is the stage responsible for most of CO2 emissions and energy requirement. This article aims at supporting the use of solar energy as non-carbogenic renewable source to sustain limestone calcination, with advantages on both the economic and environmental aspects of the process. A directly irradiated Fluidised Bed (FB) reactor was used as limestone precalciner for clinker production. Concentrated solar radiation was simulated with an array of three short-arc Xe-lamps of 4 kWel each, coupled with elliptical reflectors, capable of producing a peak flux of about 3 MW m−2 at the centre of the reactor. The total irradiated power is of approximately 3.2 kWth. Thermocouples and an IR camera were used for the analysis of the FB thermal profiles. Calcination was carried out at a nominal bulk bed temperature of 950 °C, in an atmosphere containing about 70% CO2. The reactivity of lime generated by the solar-driven calcination process has been characterised. Lime produced by the solar-driven process was used together with commercial clay as kiln feed components for the formulation of Portland cement samples. A binary mixture composed by fresh limestone and the same clay as above was employed as a reference. The key focus of the investigation was the assessment of the reactivity of the solar-generated lime toward the main clay components in the clinker production process, as compared to lime from ordinary calcination. An aspect that is specifically scrutinised is whether the different, and possibly more severe, thermal history to which limestone particles undergo during solar-driven calcination in directly irradiated FB reactors may compromise lime reactivity. Portland clinkers were produced by burning the raw meals at 1500 °C for 15 min. Clinkers were mixed with 5% natural gypsum to prepare the related Portland cements, which were then paste hydrated for times ranging from 2 to 28 days (water/cement mass ratio = 0.5, 20 °C, 95% relative humidity). Parameters as lime saturation factor, burnability, phase composition of clinkers and hydration behaviour of cement pastes were taken into consideration. Techniques as X-ray fluorescence and diffraction, and simultaneous differential thermal–thermogravimetry were used to study the materials
Use of Fluidized Bed Combustion Residues and Alumina Powder as Components of Ettringite-Based Aerated Building Elements
No full textThe use of industrial wastes and by-products for making construction materials unequivocally gives a
pronounced environment-friendly character to their manufacturing process. Two binary (M1, M2) and one
ternary (M3) mixtures, based on alumina powder, fluidized bed coal combustion fly- and/or bottom-ash were
submitted to hydrothermal treatments in order to generate aerated building elements based on ettringite
(6CaO·Al2O3·3SO3·32H2O); ettringite is a compound characterized by low density, water insolubility, high fire
resistance and significant mechanical strength. The M1 – M3 systems were hydrated in a thermostatic bath
(100 % R.H) at 55 °C and 70 °C for aging periods ranging from 2 h to 28 d; the hydrated samples were
submitted to both differential thermal–thermogravimetric and X-ray diffraction analyses for assessing the
formation of the hydration products. In this regard, the ettringite generation, being also dependent on the
operating temperatures and times, was observed within all the investigated systems. Furthermore, the best
results in terms of both ettringite concentration and formation rate were exhibited by the M2 system at 70 °C
after 2 d of curing
Nanoparticles and thin films formation in ultra-short pulsed laser deposition of vanadium oxide
No full textThe ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by Ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V2O5 and VO2 is discussed
Investigating by circular dichroism some amyloidogenic elastin-derived polypeptides
No full textTamburro and coworkers have demonstrated that some elastin-derived polypeptide sequences are able to give rise, in vitro, to amyloid-like fibers. The biological relevance of this finding could be explained by the recent detection of some amyloidogenic material found in arteries of old patients affected by atherosclerosis and demonstrated to be elastin derived. In this context, the comprehension of the mechanism responsible for the amyloid-like fibrillogenesis of elastin-derived sequences is of crucial importance for the design of drugs that could inhibit the amyloidogenic process. To gain further insights into the elastin amyloidogenic process, we studied the polypeptide sequences encoded by Exon 7 and Exon 32 of the human tropoelastin gene, and we demonstrated that only Exon 32 is able to aggregate in amyloid-like fibers. Vis-UV Thioflavin T circular dichroism (CD) spectroscopy rapidly and unambiguously detected the amyloidogenic propensity of the polypeptides. To gain additional insights into the aggregation mechanism of elastin-derived amyloidogenic peptides, we carried out the kinetics of EX32 amyloid-like aggregates by using ThT dye. CD spectroscopy was also used for investigating the secondary structure of the polypeptides, thus giving useful insights into the conformations involved in amyloid-like fiber formation. Furthermore, complementary techniques such as fluorescence spectroscopy, spectral shift, and binding Congo red UV assays as well as atomic force microscopy were also used to confirm the amyloidogenic behavior of the studied polypeptides
- …
