Effect of exposure conditions and concrete quality on pyrrhotite oxidation and internal sulfate attack

Thousands of homes in County Donegal, Ireland, are damaged by cracks formed a few years after construction. The authorities have erroneously attributed the damages to the presence of muscovite mica in the concrete blocks used to build the homes. Only recently, research has shown that pyrrhotite oxidation triggering internal sulfate attack (ISA) is the cause. In this study, the strip foundation, the rising blocks elevating the structure to ground level and the inner and outer leaf of one affected home are investigated. As these four types of structural components differ by concrete quality, exposure condition or both, their effect on pyrrhotite oxidation and ISA is investigated. Sulfur analysis, X-ray diffraction and scanning electron microscopy are used to characterize the concrete

ASR expansions at the level of a single glass-cement paste interface: experimental results and proposal of a reaction-expansion mechanism

A new experimental methodology for studying ASR expansions at the level of a single aggregate-cementitious matrix interface is proposed. For this methodology, small sandwich-like specimens, with cement paste or mortar on top and bottom of a disc of soda-lime (SL) glass in the middle, are used. These specimens are placed in airtight containers with an alkaline solution and heated in an oven at 60 °C. In these conditions, ASR products are formed rapidly at the interface of the disc and the cementitious matrix, inducing length changes in the specimen which are measured regularly. The morphology and composition of the ASR products are studied by means of SEM/EDS analyses. This inexpensive and very easy to replicate methodology may provide valuable information about the ASR expansion mechanisms. The specimens developed expansions of about 30 µm before the SL glass got detached from the cement paste matrix. SEM/EDS analyses of the reaction products formed in between the SL glass and the cement paste matrix indicate calcium-to-silica molar ratios ranging between 1.0 and 1.5. Finally, based on the experimental results presented in this paper, as well as on other experimental and theoretical results found in the literature, a reaction-expansion mechanism for ASR in SL glass concrete is proposed.Peer ReviewedPostprint (author's final draft

Zum Zusammenhang von Geschlechterungleichheiten in Bildung, Beruf und Karriere : ein Ausblick

Ziel der folgenden Ausführungen im abschliessenden Teil dieses Sammelbands zur Entwicklung und Genese von geschlechtsspezifischen Bildungsungleichheiten ist es, den Blick zu öffnen in Richtung Berufsleben. Wie sind die verbesserten Bildungsmöglichkeiten von Frauen zu interpretieren? Ist es in den letzten Jahrzehnten gelungen, eines der grundlegendsten gesellschaftlichen Ungleichheitsverhältnisse zu beseitigen? Oder beginnt sich dieses sogar zu verkehren in eine gesellschaftliche Benachteiligung der Männer? Wir gehen bei unseren Überlegungen von der These aus, dass ein Abbau von Benachteiligungen der Frauen im Bildungssystem für sich genommen noch wenig aussagekräftig ist, wenn wir uns mit der klassischen soziologischen Frage der Persistenz bzw. des Wandels von gesellschaftlichen Ungleichheiten befassen wollen. Erst wenn die ganze Verknüpfung von Bildung und gesellschaftlicher Ungleichheit in den Blick genommen wird und sich dabei zeigt, dass Frauen ihre Bildungsgewinne auch in entsprechende Chancen im Beschäftigungssystem umsetzen können, sind ihre verbesserten Bildungschancen ein Gewinn für die Individuen und ein Fortschritt für die Gesellschaft – und erst dann könnten mögliche Bildungsvorteile von Frauen, wie sie in den vorliegenden Aufsätzen z.T. diagnostiziert werden, gar als neue gesellschaftliche Benachteiligungen von Männern skandalisiert werden

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Characterization of amorphous and crystalline ASR products formed in concrete aggregates

Amorphous and crystalline alkali silica reaction (ASR) products formed in aggregates of two different concrete mixtures exposed to the concrete prim test both at 38 °C and 60 °C have been analysed by scanning electron microscope with energy dispersive X-ray spectroscopy and by Raman microscopy. Additionally, amorphous ASR products were synthesized and analysed with Raman microscopy and 29Si nuclear magnetic resonance. Amorphous ASR products display a higher Na/K-ratio than crystalline ones. Both types of products display a structure dominated by Q3-sites (Si-tetrahedra with three bridging oxygen atoms typical for a layer structure) with a secondary amount of Q2-sites (Si-tetrahedra with two bridging oxygen atoms typical for a chain structure). Temperature in the CPT alters the structure of the crystalline ASR. While the Raman spectra of the product formed at 38 °C is identical to the one formed in concrete structures, the one of the 60 °C product corresponds to K-shlykovite.publishedVersio

Characterization of ASR products formed in concrete aggregates

ASR products formed in various aggregates of two different concrete mixtures tested both at 38 °C and 60 °C with the concrete prism test have been analysed by scanning electron microscope with energy dispersive X-ray spectroscopy. Additionally, Raman spectra of ASR products have been acquired. The variations in the chemical composition of ASR products formed in individual aggregates is relatively small. This applies as well to the average composition of ASR products formed in the concrete tested at 38 and 60 °C. However, the Raman spectra of crystalline ASR products formed at 38 °C differ from the ones formed at 60 °C. The first correspond to ones obtained in aggregates of concrete structures, while the later is identical to synthesized shlykovite

Assessment of Damage and Expansion

An indication about the expansion of the concrete can be derived from the crack-index [1]. The crack-index is determined by measuring the crack width along pre-drawn lines, Fig. 2.1 and is expressed as crack-width per measured length. However, it has to be kept in mind that the formation of the cracks may not be attributable solely to AAR. Still, the crack index indicates a concrete expansion at the studied location in mm/m.Peer reviewe