A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C₃A and Their Hydration Products in the Presence of Gypsum.

This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C₃A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C₃A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C₃A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C₃A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C₃A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments

Optimización de la resistencia mecánica de cementos binarios MK/GBFS activados alcalinamente por Metodología de Super?cie de Respuesta

The present article shows the compressive strength modeling and optimization for a non-conventional binder free of clinker, which was produced by the alkali activation of a binary mixture of metakaolin (MK) and a granulated blast furnace slag (GBFS). AGBFEl presente artículo muestra el modelado y la optimización de la resistencia a la compresión para un aglutinante no convencional libre de clinker, que fue producido por la activación alcalina de una mezcla binaria de metacaolín (MK) y una escoria granula

Optimización de la resistencia mecánica de cementos binarios MK/GBFS activados alcalinamente por Metodología de Superficie de Respuesta

El presente artículo muestra la modelación y optimización de la resistencia a la compresión de un conglomerante no convencional libre de cemento Portland, el cual fue producido a partir de la activación alcalina de una mezcla binaria de un metacaolín (MK) y una escoria siderúrgica de alto horno (GBFS). Como factores de estudio se consideró una relación GBFS/(GBFS/MK) entre 0,0-0,8 y una relación molar total SiO2=Al2O3 entre 2,8-4,2. La relación SiO2=Al2O3 fue ajustada a través de la contribución del precursor (MK+GBFS) y el activador alcalino. La evaluación estadística mediante la metodología de superficie de respuesta (MSR) mostró un efecto significativo entre la relación molar SiO2=Al2O3 y el contenido de GBFS sobre la resistencia a compresión. Complementariamente se desarrolló una caracterización microestructural a través de difracción de rayos X y microscopía electrónica de barrido. La incorporación de GBFS incrementó la cinética de reacción y la formación de una estructura más densa y compacta. Estos nuevos productos de reacción le otorgaron al material un mayor desempeño mecánico comparado con los constituidos con un 100% de MK. PACS: 81.05.Je; 81.05.Zx;02.70.R

Efflorescence of Alkali-Activated Cements (Geopolymers) and the Impacts on Material Structures: A Critical Analysis

Even with the rapid development of the alkali-activated cement (AAC) technology in the past few years, some phenomena still needs to be better understood, that may alter the durability of the material. In many industrial uses and laboratory researches the formation of the salts on the surface alkali-activated type cements was observed, which was identified as efflorescence. This occurs due to the presence of an alkali transported in contact with the humidity and CO2 environment. It may present externally from the formation of salts on the surface and internally with the carbonation of the alkalis in capillary pores. The effects of efflorescence on the material in use, as well as all factors that can influence its formation are not yet fully understood or reported. The search for papers was conducted using the search words efflorescence and geopolymer/alkali-activated, combined in the electronic data base. Due to the limited quantity of papers published related to efflorescence in geopolymers, the review was complemented using papers that discuss this behavior in Portland cement (PC) and based on the main properties that can influence the formation of efflorescence. In this paper, to understand the nature of efflorescence, upon which proper methods of minimizing of this issue can be based, the following aspects are discussed and re-examined: (1) the development of efflorescence's in PC concrete, (2) the role of alkalis in AACs, (3) efflorescence in AACs, and (4) effect from a physical and microstructural point of view of efflorescence's on the ACCs. This paper highlights that the nature of the pore structure and the design parameters (such as alkali concentration, presence of soluble silicates, and water content in the activator) are the two most important factors that control efflorescence rate and changes in mechanical behavior. However, the stability of the alkalis and their relationship with the formed gel, which are determining factors in the formation of efflorescence, remain not completely understood. In the same way, the effect of efflorescence in tensile strength and shrinkage needs to be evaluated

Caribbean Corals in Crisis: Record Thermal Stress, Bleaching, and Mortality in 2005

BACKGROUND The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. METHODOLOGY/PRINCIPAL FINDINGS Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. CONCLUSIONS/SIGNIFICANCE Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.This work was partially supported by salaries from the NOAA Coral Reef Conservation Program to the NOAA Coral Reef Conservation Program authors. NOAA provided funding to Caribbean ReefCheck investigators to undertake surveys of bleaching and mortality. Otherwise, no funding from outside authors' institutions was necessary for the undertaking of this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Effect of nanosilica-based activators on the performance of an alkali-activated fly ash

This paper assesses the effect of the use of an alternative activator based on nanosilica/MOH (M = K+ or Na+) blended solutions on the performance of alkali-activated fly ash binders. Binders produced with commercial silicate activators display a greater degree of reaction, associated with increased contents of geopolymer gel; however, mortars produced with the alternative nanosilica-based activators exhibited lower water demand and reduced permeability, independent of the alkali cation used. Na-based activators promote higher compressive strength compared with K-based activators, along with a refined pore structure, although K-activated samples exhibit reduced water demand. Zeolite type products are the major crystalline phases formed within these binders. A wider range of zeolites is formed when using commercial silicate solutions compared with the alternative activators. These results suggest that there are variations in the availability of Si in the system, and consequently in the alkalinity, depending on the silicate source in the activator, which is important in determining the nanostructure of the geopolymer gel.This study was sponsored by the Ministerio de Ciencia e Innovacion of Spain (Project GEORES MAT2010-19934 and research scholarship BES-2008-002440), European regional development fund (FEDER), and the Universitat Politecnica de Valencia (Spain). The participation of SAB and JLP was funded by the Australian Research Council (ARC), including partial funding through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC. A special acknowledgement is also due to the Centre of Electron Microscopy of the Universitat Politecnica de Valencia and Pedro Garces from the Universidad de Alicante for support in some experiments.Rodriguez Martinez, ED.; Bernal, SA.; Provis, JL.; Paya Bernabeu, JJ.; Monzó Balbuena, JM.; Borrachero Rosado, MV. (2013). Effect of nanosilica-based activators on the performance of an alkali-activated fly ash. Cement and Concrete Composites. 35(1):1-11. doi:10.1016/j.cemconcomp.2012.08.025S11135

Geopolymers based on spent catalyst residue from a fluid catalytic cracking (FCC) process

This paper assesses the use of alkali activation technology in the valorization of a spent fluid catalytic cracking (FCC) catalyst, which is a residue derived from the oil-cracking process, to produce geopolymer binders. In particular, the effects of activation conditions on the structural characteristics of the spent catalyst- based geopolymers are determined. The zeolitic phases present in the spent catalyst are the main phases participating in the geopolymerization reaction, which is driven by the conversion of the zeolitic material to a highly Al-substituted aluminosilicate binder gel. Higher alkali content and SiO2/Na2O ratio lead to a denser structure with a higher degree of geopolymer gel formation and increased degree of crosslinking, as identified through 29Si MAS NMR. These results highlight the feasibility of using spent FCC catalyst as a precursor for geopolymer production.This study was sponsored by research scholarship BES-2008-002440 and EEBB-2011-43847 from the Ministerio de Ciencia y Tecnologia of Spain, the European regional development fund (FEDER), and the Universitat Politecnica de Valencia (Spain). The participation of SAB and JLP was funded by the Australian Research Council through the Discovery Projects program, and also including partial funding through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC. The authors wish to acknowledge the Advanced Microscopy Facility at The University of Melbourne for assistance with the electron microscopy experiments conducted in this study.Rodriguez Martinez, ED.; Bernal, SA.; Provis, JL.; Gehman, JD.; Monzó Balbuena, JM.; Paya Bernabeu, JJ.; Borrachero Rosado, MV. (2013). Geopolymers based on spent catalyst residue from a fluid catalytic cracking (FCC) process. Fuel. 109:493-502. https://doi.org/10.1016/j.fuel.2013.02.053S49350210

Higher COVID-19 pneumonia risk associated with anti-IFN-α than with anti-IFN-ω auto-Abs in children

We found that 19 (10.4%) of 183 unvaccinated children hospitalized for COVID-19 pneumonia had autoantibodies (auto-Abs) neutralizing type I IFNs (IFN-alpha 2 in 10 patients: IFN-alpha 2 only in three, IFN-alpha 2 plus IFN-omega in five, and IFN-alpha 2, IFN-omega plus IFN-beta in two; IFN-omega only in nine patients). Seven children (3.8%) had Abs neutralizing at least 10 ng/ml of one IFN, whereas the other 12 (6.6%) had Abs neutralizing only 100 pg/ml. The auto-Abs neutralized both unglycosylated and glycosylated IFNs. We also detected auto-Abs neutralizing 100 pg/ml IFN-alpha 2 in 4 of 2,267 uninfected children (0.2%) and auto-Abs neutralizing IFN-omega in 45 children (2%). The odds ratios (ORs) for life-threatening COVID-19 pneumonia were, therefore, higher for auto-Abs neutralizing IFN-alpha 2 only (OR [95% CI] = 67.6 [5.7-9,196.6]) than for auto-Abs neutralizing IFN-. only (OR [95% CI] = 2.6 [1.2-5.3]). ORs were also higher for auto-Abs neutralizing high concentrations (OR [95% CI] = 12.9 [4.6-35.9]) than for those neutralizing low concentrations (OR [95% CI] = 5.5 [3.1-9.6]) of IFN-omega and/or IFN-alpha 2

Autoantibodies against type I IFNs in patients with critical influenza pneumonia

In an international cohort of 279 patients with hypoxemic influenza pneumonia, we identified 13 patients (4.6%) with autoantibodies neutralizing IFN-alpha and/or -omega, which were previously reported to underlie 15% cases of life-threatening COVID-19 pneumonia and one third of severe adverse reactions to live-attenuated yellow fever vaccine. Autoantibodies neutralizing type I interferons (IFNs) can underlie critical COVID-19 pneumonia and yellow fever vaccine disease. We report here on 13 patients harboring autoantibodies neutralizing IFN-alpha 2 alone (five patients) or with IFN-omega (eight patients) from a cohort of 279 patients (4.7%) aged 6-73 yr with critical influenza pneumonia. Nine and four patients had antibodies neutralizing high and low concentrations, respectively, of IFN-alpha 2, and six and two patients had antibodies neutralizing high and low concentrations, respectively, of IFN-omega. The patients' autoantibodies increased influenza A virus replication in both A549 cells and reconstituted human airway epithelia. The prevalence of these antibodies was significantly higher than that in the general population for patients 70 yr of age (3.1 vs. 4.4%, P = 0.68). The risk of critical influenza was highest in patients with antibodies neutralizing high concentrations of both IFN-alpha 2 and IFN-omega (OR = 11.7, P = 1.3 x 10(-5)), especially those <70 yr old (OR = 139.9, P = 3.1 x 10(-10)). We also identified 10 patients in additional influenza patient cohorts. Autoantibodies neutralizing type I IFNs account for similar to 5% of cases of life-threatening influenza pneumonia in patients <70 yr old