Propiedades de pastas de cementos modificados con residuos industriales

Pastas fueron elaboradas reemplazando cemento portland ordinario por caliza de bagazo de agave, ceniza volante, nano-SiO2 geotérmica y humo de sílice. Las pastas fueron curadas a 20ºC y 100% de humedad hasta 28 días. Se les evaluó la resistencia a la compresión, resistencia a la penetración de iones cloruro, porosidad y microestructura. Tras la evaluación, los resultados revelaron que las pastas reemplazadas mostraron una matriz más compacta y menos porosa, valores de resistencia a la compresión de hasta un 45% más, valores de paso de carga de hasta 57% menos, en comparación con las pastas de referencia

Concretos sustentables expuestos a altas temperaturas

Concretos fueron elaborados reemplazando cemento Portland ordinario por nano-SiO2 geotérmica y humo de sílice. Se curaron a 20ºC y 100% de humedad hasta 7 años y después fueron expuestos a altas temperaturas (350°C, 550°C y 750°C). Se les evaluó la velocidad de ultrasonidos (UPV), análisis termogravimétrico/diferencial (TG/DTA), difracción de rayos X (DRX) y microscopía electrónica de barrido (MEB). La pérdida de peso y la reducción en la UPV fue mayor para los especímenes adicionados (NSG y HS) en comparación con el espécimen de referencia (CPC 100%), además se apreció una mayor degradación en la microestructura de los especímenes con adiciones

Evaluation of Chloride Diffusion and Corrosion Resistance in Reinforced Concrete Using Internal Curing and Shrinkage Reducing Admixtures

The properties of high-performance concretes obtained by the internal curing technique were studied in the fresh and hardened states. In some of the concrete mixtures, fine normal weight aggregates were replaced with lightweight aggregates (LWA) at 20 % vol. and ordinary portland cement was replaced by pulverized class F fly ash at 20 % by mass. Additionally, some mixtures were prepared including a shrinkage-reducing admixture, either as part of the mixing water or pre-soaked into the lightweight fine aggregates. The prepared concretes were subjected to degradation tests, such as accelerated carbonation and chloride ion deterioration. In addition, the reinforced concretes were analyzed through electrochemical corrosion tests with the linear polarization resistance technique. It was found that the internally cured concretes presented a mechanical resistance similar to those reported for the reference concretes (conventional concretes), but provided a higher resistance to carbonation, rapid penetration of chloride ions, and a lower chloride ion diffusion coefficient. The reinforcing steel structure in the internally cured concretes showed lower corrosion currents (Icorr) and corrosion potentials (Ecorr) in comparison to the reference concretes. Therefore, the use of the internal curing technique in concretes with pre-soaking in either water or a solution of shrinkage-reducing admixture can be considered as a viable alternative to extend the service life of concrete structures in contact with harmful environments

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Efecto de la adición del residuo nanosílice geotérmica sobre la durabilidad de morteros y concretos base cemento portland.

Tesis (Doctor en Ingeniería de Materiales) UANL, 2011.UANLhttp://www.uanl.mx