Deformabilidad en hormigones con agregados reciclados

Diversos trabajos han demostrado la factibilidad de elaborar hormigones con agregados reciclados, sin embargo sobre algunos aspectos poco explorados aún existen informaciones contrapuestas. Entre ellos se destacan el comportamiento diferido del hormigón (contracción y fluencia) y la capacidad de deformación en tracción (extensibilidad). Estas propiedades afectan directamente el grado de fisuración que puede tener una estructura de hormigón, lo que adquiere una significativa relevancia en la práctica, al considerar su vida en servicio. En este trabajo se presenta un estudio de la deformabilidad de hormigones que contienen 50 o 100 % de agregado grueso obtenido a partir de la trituración de losas de pavimento. Los resultados se comparan con los de otros dos hormigones elaborados con idénticas proporciones de materiales componentes variando el tipo de agregado grueso, piedra partida granítica o piedra partida cuarcítica. Se evaluaron la resistencia a tracción, la extensibilidad en flexión bajo cargas rápidas, y la fluencia en compresión. Bajo cargas de corta duración se encontró una deformabilidad creciente en el hormigón con mayor contenido de agregados reciclados, tanto en flexotracción como en compresión; también se midieron mayores valores de contracción libre y de fluencia. A partir de los resultados surge que es posible estimar la deformabilidad del hormigón con agregados reciclados siguiendo criterios similares a los aplicados en hormigones con agregados naturales; las diferencias de deformabilidad se pueden justificar considerando la menor rigidez del agregado reciclado.Different works have demonstrated the feasibility of elaborating concrete with recycled aggregates, nevertheless there is still opposite information about some aspects that have not been widely studied. The differed behaviour (shrinkage and creep) and the deformation capacity in tension (extensibility) of concrete are among them. These properties have a direct effect over the degree of cracking that can have a concrete structure so, considering its service life, they acquire a significant relevance in practice. This paper presents a study on the deformability of concretes that contain 50 or 100 % of coarse aggregate obtained from crushed pavement slabs. The results are compared with those obtained on other two concretes prepared with the same mixture proportions varying only the type of coarse aggregate, granitic crushed stone or quartzitic crushed stone. The tensile strength, extensibility in flexure under rapid rate of loading and creep in compression were evaluated. It was found that under short term loads the deformability of concrete increases with the content of recycled aggregates, both in flexure and in compression, grater values of free shrinkage and creep were also measured. From the obtained results it appears that the deformability of concrete with recycled aggregates can be estimated following the same criteria applied to concrete with natural aggregate, the differences in deformability can be justified considering the lower stiffness of the recycled aggregate

Catalysing sustainable fuel and chemical synthesis

Concerns over the economics of proven fossil fuel reserves, in concert with government and public acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change from such combustible carbon, are driving academic and commercial research into new sustainable routes to fuel and chemicals. The quest for such sustainable resources to meet the demands of a rapidly rising global population represents one of this century’s grand challenges. Here, we discuss catalytic solutions to the clean synthesis of biodiesel, the most readily implemented and low cost, alternative source of transportation fuels, and oxygenated organic molecules for the manufacture of fine and speciality chemicals to meet future societal demands

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

International Consensus Statement on Rhinology and Allergy: Rhinosinusitis

Background: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR‐RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR‐RS‐2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence‐based findings of the document. Methods: ICAR‐RS presents over 180 topics in the forms of evidence‐based reviews with recommendations (EBRRs), evidence‐based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary. Results: ICAR‐RS‐2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence‐based management algorithm is provided. Conclusion: This ICAR‐RS‐2021 executive summary provides a compilation of the evidence‐based recommendations for medical and surgical treatment of the most common forms of RS

Small ion effects on self-coacervation phenomena in block polyampholytes

Self-coacervation is a phenomenon in which a solution of polyampholytes spontaneously phase separates into a dense liquid coacervate phase, rich in the polyampholyte, coexisting with a dilute supernatant phase. Such coacervation results in the formation of membraneless organelles in vivo and has further been applied industrially as synthetic encapsulants and coatings. It has been suggested that coacervation is primarily driven by the entropy gain from releasing counter-ions upon complexation. Using fully fluctuating field-theoretic simulations employing complex Langevin sampling and complementary molecular dynamics simulations, we have determined that the small ions contribute only weakly to the self-coacervation behavior of charge-symmetric block polyampholytes in solution. Salt partitioning between the supernatant and coacervate is also found to be negligible in the weak-binding regime at low electrostatic strengths. Asymmetries in charge distribution along the polyampholytes can cause net-charges that lead to "tadpole" configurations in dilute solution and the suppression of phase separation at low salt content. The field and particle-based simulation results are compared with analytical predictions from the random phase approximation (RPA) and postulated scaling relationships. The qualitative trends are mostly captured by the RPA, but the approximation fails at low concentration

Evaluation of Alkylimidazoles as Physical Solvents for CO₂/CH₄ Separation

1-<i>n</i>-Alkylimidazoles are a class of tunable solvents with low volatility and low viscosities. Although imidazoles have been known for some time in the pharmaceutical industry, and as convenient precursors for synthesizing imidazolium-based ionic liquids (ILs), only recently have they been given consideration in some of the same solvent-based separations applications that ILs have been studied for, such as post-combustion CO₂ capture and natural gas treating. “Sweetening”, the removal of CO₂, H₂S, and other “acid” gases from natural gas (CH₄), is an existing industrial application where low volatility, low viscosity physical solvents are already applied successfully and economically at large scale. Physical solvents are also used for syngas cleanup and in the emerging application of pre-combustion CO₂ capture. Given the similarities in physical properties between 1-<i>n</i>-alkylimidazoles, and physical solvents currently used in industrial gas treating, the 1-<i>n</i>-alkylimidazole class of solvents warrants further investigation. Solubilities of CO₂ and CH₄ in a series of 1-<i>n</i>-alkylimidazoles were measured under conditions relevant to the use of physical solvents for natural gas treating: ∼5 atm partial pressure of CO₂ and temperatures of 30–75 °C. Solubilities of CO₂ and CH₄ were found to be strongly dependent on temperature, with the solubility of each gas in all solvents diminishing with increasing temperature, although CO₂ exhibited a stronger temperature dependence than CH₄. Ideal CO₂/CH₄ solubility selectivities were also more favorable at lower temperatures in 1-<i>n</i>-alkylimidazole solvents with shorter chain lengths. CO₂ solubility decreased with increasing chain length, while CH₄ solubility exhibited a maximum in 1-hexylimidazole. The solubility trends observed with temperature and chain length can be explained through calculation of solution enthalpies and solvent fractional free volume as approximated from van der Waals volumes as calculated via atomic contributions. Of the solvents examined, 1-methylimidazole displays the most favorable CO₂ solubility and CO₂/CH₄ selectivity, and has the lowest viscosity. A comparison of 1-methylimidazole to commercially used solvents reveals similar physical properties and the potential for use in industrial gas processing. Imidazolium-based ILs are also compared, although they appear less favorable for use within established process schemes given their higher viscosities and reduced capacity for CO₂

Properties and Performance of Ether-Functionalized Imidazoles as Physical Solvents for CO₂ Separations

Previously, we investigated 1-<i>n</i>-alkylimidazoles as low viscosity, low vapor pressure physical solvents for CO₂/CH₄ separation and noted a decrease in performance as the length of the <i>n</i>-alkyl chain was extended. Here, we examine imidazoles featuring oligo­(ethylene glycol) substituents (“PEG_<i>n</i>-imidazoles”) as an opportunity to improve upon the separation performance of this class of molecules. In the current work, we have characterized the density and the viscosity of PEG_<i>n</i>-imidazoles over the temperature range 20–80 °C. PEG_<i>n</i>-imidazoles are slightly more viscous than 1-<i>n</i>-alkylimidazoles but still fall below 20 cP. Ideal gas solubilities of CO₂ and CH₄ were measured in PEG_<i>n</i>-imidazoles at gas partial pressures of ∼5 bar and temperatures of 25–70 °C. Solubilities of CO₂ and CH₄ were both found to decrease with increasing temperature, with a stronger dependence for CO₂. However, better CO₂/CH₄ selectivity was achieved in PEG_<i>n</i>-imidazoles at lower operating temperatures than was observed for 1-<i>n</i>-alkylimidazoles. Physical properties and gas separation performances were correlated with fractional free volume calculated via COSMOtherm, as well as solubility parameters. The results show trends of decreased FFV when polar ether groups comprise the substituent, and that CO₂ solubility and solubility selectivity for CO₂/CH₄ are improved compared to their nonpolar, hydrocarbon-based analogues

Building Blocks for Ionic Liquids: Vapor Pressures and Vaporization Enthalpies of Alkoxy Derivatives of Imidazole and Benzimidazole

The design of physical solvents for applications such as CO₂ capture has been an important research area as great emphasis is being placed on reducing greenhouse gas emissions. In gas treating with physical solvents, one of the most important solvent properties needed for efficient process operation is a low vapor pressure (≪100 Pa) at ambient temperature. We have identified alkoxy-functionalized imidazoles and benzimidazoles as candidates that can meet this criterion. Vapor pressures of alkoxy derivates of imidazole and benzimidazole have been determined as a function of temperature by the transpiration method. From these data, the molar enthalpies of vaporization (Δ_l^g<i>H</i>_m) were calculated. The measured data sets were successfully checked for internal consistency by comparison with vaporization enthalpies of the parent speciesdimethyl ethers of ethylene glycol, diethylene glycol, and triethylene glycol. We observe that for species with the same number of atoms in the side chain [e.g., 1-butylimidazole and 1-(2-methoxyethyl)-imidazole], replacing every third methylene group with an ether oxygen reduces vapor pressure by 50–75%

Mixed Conductive Soft Solids by Electrostatically Driven Network Formation of a Conjugated Polyelectrolyte

A conjugated polyelectrolyte (poly­[2,6-(4,4-bis-potassium butanylsulfonate-4<i>H</i>-cyclopenta-[2,1-b;3,4-b’]-dithiophene)-<i>alt</i>-4,7-(2,1,3-benzothiadiazole)], PCPDTBT-SO₃K) assembles into a novel, hierarchical hydrogel structure with all structural evidence indicating dominant electrostatic rather than aromatic or mesogen interactions. PCPDTBT-SO₃K forms an entangled polymer mesh, where polymer chains are tied together by ionic cross-links, comprising microgel clusters that percolate to form a macroscopic three-dimensional network. With increasing temperature, ions gain mobility to move toward the exterior of the microgel clusters, dissolving the ionic cross-links and inhibiting network percolation through electrostatic repulsion. While π–π stacking interactions may be present in a disorganized fashion, no long-range π–π stacking is evident in X-ray scattering. Soft materials based on PCPDTBT-SO₃K remain semiconducting and exhibit elevated ionic conductivity at the structural reorganization temperature