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The scarcity of high-purity limestone subjects the cement industry to consider alternative supplementary cementitious materials for cement production. This research aimed to investigate the mechanical properties and the hydration kinetics of cement pastes in the presence of high levels and different fineness of dolomite, especially the formation of thaumasite. A dolomite filler with 20% magnesium oxide, with average diameters of 10 µm, 6 µm and 4 µm was used as a partial replacement for Portland cement at 0%, 15% and 35% in cement pastes cured at 5 ºC and 20 ºC. The results of compressive strength showed similarities in all pastes analyzed, but the fineness of the dolomite showed a significant difference between the strengths obtained. The isothermal calorimetry indicated that the presence of dolomite had a nucleation and dilution effect. The thermogravimetry revealed that dependent of the substitution levels, the pastes with dolomite presented significant differences in the amount of ettringite and carbonate phases. The mineralogical analysis detected the presence of thaumasite only at the temperature of 20 ºC, which this mineral can also form at higher temperatures than those reported in the literature. Finally, we conclude positively about the possibility of using dolomite in cementitious matrices at levels up to 35%, regardless of fineness and curing temperature. Resumo A escassez de calcário de alta pureza sujeita a indústria cimenteira a considerar materiais cimentícios suplementares alternativos para a produção de cimentos. Esta pesquisa buscou investigar a cinética de hidratação e as propriedades de pastas cimentícias na presença de elevados teores e diferentes finuras de dolomita, em especial à formação de taumasita. Adotou-se um fíler dolomítico com 20% de óxido de magnésio, de diâmetros médios de 10 µm, 6 µm e 4 µm como substituto parcial do cimento Portland nos teores 0%, 15% e 35% em pastas cimentícias curadas a 5 ºC e 20 ºC. Os resultados de resistência à compressão apresentaram semelhanças em todas as pastas analisadas, mas a finura da dolomita mostrou uma diferença significativa entre as médias de resistências obtidas. A calorimetria isotérmica apontou que a presença de dolomita apresentou efeito de nucleação e diluição. A termogravimetria revelou que dependente dos teores de substituição, as pastas com dolomita apresentaram diferenças significativas na quantidade de fases de etringita e carbonatos. A análise mineralógica detectou a presença de taumasita apenas na temperatura de 20 ºC, em que esse mineral também pode se formar em temperaturas mais elevadas do que as temperaturas relatadas na literatura. Por fim, conclui-se positivamente sobre a possibilidade de utilização de dolomita em matrizes cimentícias em teores de até 35%, independente da finura e da temperatura de cura.

BACKGROUND: Patients hospitalized with COVID-19 suffer thrombotic complications. Risk factors for poor outcomes are shared with coronary artery disease.OBJECTIVES: To investigate the efficacy of an acute coronary syndrome regimen in patients hospitalized with COVID-19 and coronary disease risk factors.METHODS: A randomized controlled, open-label trial across acute hospitals (United Kingdom and Brazil) added aspirin, clopidogrel, low-dose rivaroxaban, atorvastatin, and omeprazole to standard care for 28 days. Primary efficacy and safety outcomes were 30-day mortality and bleeding. The key secondary outcome was a daily clinical status (at home, in hospital, on intensive therapy unit admission, or death).RESULTS: Three hundred twenty patients from 9 centers were randomized. The trial terminated early due to low recruitment. At 30 days, there was no significant difference in mortality (intervention vs control, 11.5% vs 15%; unadjusted odds ratio [OR], 0.73; 95% CI, 0.38-1.41; p = .355). Significant bleeds were infrequent and were not significantly different between the arms (intervention vs control, 1.9% vs 1.9%; p > .999). Using a Bayesian Markov longitudinal ordinal model, it was 93% probable that intervention arm participants were more likely to transition to a better clinical state each day (OR, 1.46; 95% credible interval [CrI], 0.88-2.37; Pr [beta > 0], 93%; adjusted OR, 1.50; 95% CrI, 0.91-2.45; Pr [beta > 0], 95%) and median time to discharge to home was 2 days shorter (95% CrI, -4 to 0; 2% probability that it was worse).CONCLUSION: Acute coronary syndrome treatment regimen was associated with a reduction in the length of hospital stay without an excess in major bleeding. A larger trial is needed to evaluate mortality.

Submitted by Anna Barbara Alves Beraldine (annabarbara@unisinos.br) on 2022-03-16T17:35:41Z No. of bitstreams: 1 David Brandão Nunes_.pdf: 5973993 bytes, checksum: fddb614a99866111b1b5eb77914199c9 (MD5) Made available in DSpace on 2022-03-16T17:35:41Z (GMT). No. of bitstreams: 1 David Brandão Nunes_.pdf: 5973993 bytes, checksum: fddb614a99866111b1b5eb77914199c9 (MD5) Previous issue date: 2021-12-20 Nenhuma As pozolanas são materiais que reagem com hidróxido de cálcio na presença de água formando produtos hidratados secundários e promovendo ganho de resistência e durabilidade em produtos cimentícios. Estes materiais devem ser compostos principalmente por óxidos de silício, alumínio e ferro, que, em fases amorfas, proporcionarão a reação pozolânica. O objetivo deste trabalho foi estudar a reatividade do óxido de ferro e sua influência na reação pozolânica da metacaulinita. Foi realizada calcinação de caulim com elevada pureza para obtenção de um metacaulim com desidroxilação de 97,17%. O estudo foi conduzido em pasta de cimento branco, por ser isento de ferro, com substituições de 25% da massa de cimento por composições dos materiais testados. Os teores de óxido de ferro empregados em relação à massa total foram de 1,5%, 3%, 4,5%, 6%, 9% e 25%. A fim de comparar com pastas com metacaulim e sem óxido de ferro, mas que tivessem o mesmo consumo de cimento, foram produzidas amostras com composições de metacaulim e pó de quartzo (considerado inerte nesta pesquisa) para avaliação da hidratação aos 3, 7, 28 e 63 dias. As amostras produzidas com 25% de metacaulim obtiveram índice de desempenho mecânico aos 63 dias de 141,17% em relação à amostra padrão com 100% de cimento, enquanto as amostras com 25% de óxido de ferro e 25% de pó de quartzo obtiveram índices de 82,11 e 83,86 % respectivamente; enquanto as amostras com composições de metacaulim com pó de quartzo ou óxido de ferro apresentaram elevação nos índices à medida que o teor de metacaulim aumentou, não sendo observada diferença significativa quando compara-se pastas com mesmo teor de óxido de ferro e pó de quartzo. Houve redução do teor de portlandita e crescimento na formação dos demais produtos hidratados com o aumento do teor de metacaulim nas composições, verificados pelas áreas de curvas de DTG e pelo aumento da água combinada; sendo proposto ainda um método de cálculo de água combinada efetiva (sem portlandita). Destaca-se que nos difratogramas de DRX não foi possível identificar a formação de produtos hidratados contendo ferro, inferindo-se que o óxido permaneceu inerte durante o processo de hidratação do cimento e durante a reação pozolânica da metacaulinita. Diante do estudo realizado, compreende-se que o único óxido de ferro presente em argilas calcinadas é a hematita, observada em análise de DRX, que não possui atividade pozolânica e não participa da hidratação do cimento, não podendo ser classificado como óxido pozolânico. Pozzolans are materials that react with calcium hydroxide in the presence of water, forming secondary hydrated products and promoting gains in strength and durability in cementitious products. These materials must be composed mainly of silicon, aluminum and iron oxides, which, in amorphous phases, will provide the pozzolanic reaction. The objective of this work was to study the reactivity of iron oxide and its influence on the pozzolanic reaction of metakaolinite. Kaolin, with high purity, was calcined to obtain metakaolin with 97,17% dehydroxylation. The study was conducted in white cement paste, as it is Fe-free, with 25% replacement of the cement mass by compositions of the materials tested. The iron oxide contents used in relation to the total mass were 1,5%, 3%, 4,5%, 6%, 9% and 25%. To compare pastes with metakaolin and without iron oxide, but which had the same cement consumption, samples were produced with compositions of metakaolin and quartz powder (considered inert in this research) to evaluate hydration at 3, 7, 28 and 63 days. The samples produced with 25% metakaolin had a mechanical performance index at 63 days of 141,17% compared to the standard sample with 100% cement, while the samples with 25% iron oxide and 25% quartz powder obtained indexes of 82,11 and 83,86% respectively; while the samples with compositions of metakaolin with quartz powder or iron oxide showed an increase in the indexes as the metakaolin content increased, with no significant difference being observed when comparing pastes with the same iron oxide content and quartz powder. There was a reduction in the content of portlandite and growth in the formation of other hydrated products with the increase in the content of metakaolin in the compositions, verified by the areas of DTG curves and by the increase in the combined water; a method for calculating effective combined water (without portlandite) is also proposed. It is noteworthy that in XRD diffractograms it was not possible to identify the formation of hydrated products containing iron, implying that the oxide remained inert during the cement hydration process and during the pozzolanic reaction of metakaolinite. In view of the study carried out, it is understood that the only iron oxide present in calcined clays is hematite, observed in XRD analysis, which does not have pozzolanic activity and does not participate in the hydration of cement, and cannot be classified as pozzolanic oxide.