Influence of the Mixing Procedure on the Fresh State Behaviour of Recycled Mortars

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] The effect of two different mixing protocols on the fresh-state behaviour of self-compacting mortars with and without recycled sand was compared. For this purpose, the mortar mixes were designed considering three solid volume fractions, while maintaining the water to cement ratio and superplasticiser dosage constant. The results conclude that the inclusion of recycled sand harmfully affects the rheological behaviour of the mortars and this effect can be mitigated using mixing protocols with longer mixing times and delayed admixture addition times. Finally, a rheograph was developed to explain the expectable changes in a conventional mix when recycled sand is incorporated, the solid volume fraction is varied and changes are applied to the mixing procedure

Rheology, Durability, and Mechanical Performance of Sustainable Self-Compacting Concrete With Metakaolin and Limestone Filler

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] This study analyzed the performance of self-compacting concrete with a paste composition that includes limestone filler and metakaolin replacing cement to design binary (75% cement and 25% limestone filler) and ternary binders (60% cement, 25% limestone filler and 15% metakaolin). Furthermore, to analyze the effect of the solid volume fraction (volume of sand and coarse aggregate) on concrete rheology, the concretes were designed using four volumes of paste (350 l, 400 l, 450 l and 500 l). Rheological tests were performed at three resting times to measure the viscosity and yield stress over time. The results indicated that the viscosity decreased by 43.3% when the cement was replaced by limestone filler and increased by 73.1% when the cement was replaced by 15% metakaolin while maintaining the limestone filler. These values were obtained as 27.6% and 62.2%, respectively, when the yield stress was analyzed. In addition, the hardened properties (mechanical behavior and durability) were studied by measuring the strengths at 28 days, as well as the electrical resistivity and ultrasonic pulse velocity over time. In this case, at 28 days the use of binary binder reduces the strength and resistivity (about 20%) and the employment of ternary binder reduces strength (15%) while increases the resistivity up to the double (when compared to the 100 C concrete). Moreover, to measure the efficiency of the concrete, a material index was designed that considers the fresh behavior, mechanical performance, durability, cost, and environmental impact. Self-compacting concretes with ternary binders provided the highest indices. The use of alternative materials, particularly metakaolin has been proven to be a good option to enhance concrete sustainable performance.The study is part of two projects entitled: “Robust self-compacting recycled concretes: rheology in fresh state and mechanical properties (Ref: BIA2014-58063-R)” and “Sustainable High Performance Self-Compacting Concrete using low clinker cement, and integral curing and self-healing agents (HACCURACEM) (BIA2017-85657-R)” funded by MINECO. Moreover, this work was also made possible by the financial support of a pre-doctoral grant of MINECO (FPI 2015- ref BES-2015-071919) and two grants for international pre-doctoral stays: (a) FPI 2015 and (b) IACOBUS program for “Galicia–North of Portugal Euroregion

Cajas de trabajabilidad como herramienta de diseño de hormigones autocompactantes con árido reciclado

[ES] En este trabajo se diseñan siete hormigones autocompactantes convencionales y de cada uno de ellos se obtienen tres hormigones autocompactantes con árido grueso reciclado de hormigón (utilizando sustituciones del 20%, 50% y 100% en volumen). Las mezclas recicladas se fabrican utilizando el árido reciclado seco y con un 3% de humedad natural, añadiendo, en ambos casos, una cantidad de agua extra durante el amasado para compensar la elevada absorción de este tipo de árido. Todos los hormigones se ensayan en estado fresco mediante ensayos empíricos y reológicos a los 15 y 45 minutos del contacto entre cemento y agua. Los resultados indican que las relaciones entre diferentes parámetros de comportamiento en fresco en los hormigones autocompactantes reciclados (HACRs) siguen las mismas tendencias que las observadas en los hormigones autocompactantes convencionales. Para facilitar el diseño de estos HACRs, se proponen unas regiones de trabajabilidad definidas por aquellas mezclas que cumplen una serie de combinaciones de parámetros empíricos. Estas regiones permiten delimitar una caja de trabajabilidad (área en el reograma tensión de flujo estática y viscosidad plástica) en la que se garantiza que los HACRs que se sitúen en ella cumplen diferentes límites empíricos.Este estudio es parte de dos proyectos titulados: (a) “Investigación industrial sobre Hormigones para un Mercado Sostenible (InHorMeS)” financiado por la Axencia Galega de Innovación (Ref: IN852A 2013/57); (b) “Hormigones reciclados autocompactantes robustos: reología en estado fresco y propiedades mecánicas (HORREO)” financiado por el Ministerio de Economía y Competitividad (Ref: BIA2014-58063-R). Además, este trabajo fue posible gracias al apoyo de una beca predoctoral de la Xunta de Galicia (España).González Taboada, I.; González Fonteboa, B.; Martinez Abella, F.; Varela Puga, F. (2018). Cajas de trabajabilidad como herramienta de diseño de hormigones autocompactantes con árido reciclado. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 187-196. https://doi.org/10.4995/HAC2018.2018.6360OCS18719

A new primal-mixed finite element method for the linear elasticity problem

We introduced a new augmented variational formulation for the elasticity problem in the plane that involves four unknowns, namely, the displacement, the stress tensor, the strain tensor of small deformations and the pressure. We proved that this problem is well posed for appropriate values of a stabilization parameter. We also gave sufficient conditions for the well posedness of the corresponding Galerkin scheme, and detailed concrete examples of discrete spaces satisfying these conditions. We provided error estimates for these cases

Influencia de las variaciones en los materiales sobre la reología de hormigones autocompactantes reciclados

[ES] Este trabajo se centra en el análisis de la influencia de las variaciones de materiales sobre el comportamiento reológico de los hormigones autocompactantes fabricados con árido grueso reciclado. Se diseña un hormigón autocompactante patrón y tres reciclados con porcentajes de sustitución del 20%, 50% y 100% en volumen. Asimismo, en cada una de estas mezclas se aplican variaciones en el contenido de agua, superplastificante y cemento para simular los errores que se producen en las plantas de fabricación: ± 3% en el agua, ± 5% en el superplastificante y ± 3% en el cemento. Todos los hormigones se estudian en estado fresco mediante los ensayos reológicos stress growth test y flow curve test. Mediante reógrafos se evalúan los cambios reológicos que los incrementos o decrementos de agua, superplastificante o cemento pueden ocasionar. Los resultados permiten estudiar a qué variación de material es más sensible un hormigón autocompactante reciclado (HACR) y qué porcentajes de árido reciclado sería más recomendable utilizar para obtener un hormigón robusto.Este estudio es parte de los proyectos (a) “Investigación industrial sobre Hormigones para un Mercado Sostenible (InHorMeS)” financiado por la Axencia Galega de Innovación (Ref: IN852A 2013/57); y (b) “Hormigones reciclados autocompactantes robustos: reología en estado fresco y propiedades mecánicas (HORREO)” financiado por el Ministerio de Economía y Competitividad (Ref: BIA2014-58063-R). Además, este trabajo fue posible gracias al apoyo de una beca predoctoral de la Xunta de Galicia (España).González Taboada, I.; González Fonteboa, B.; Martinez Abella, F.; Rojo López, G. (2018). Influencia de las variaciones en los materiales sobre la reología de hormigones autocompactantes reciclados. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 65-74. https://doi.org/10.4995/HAC2018.2018.6361OCS657

Alongshore upwelling modulates the intensity of marine heatwaves in a temperate coastal sea

Analyses of long-term temperature records based on satellite data have revealed an increase in the frequency and intensity of marine heatwaves (MHWs) in the world oceans, a trend directly associated with global change according to climate model simulations. However, these analyses often target open ocean pelagic systems and rarely include local scale, field temperature records that are more adequate to assess the impact of MHWs close to the land-sea interface. Here, we compared the incidence and characteristics of open ocean MHWs detected by satellites with those observed in the field over two decades (1998-2019) at two temperate intertidal locations in the central Cantabrian Sea, southern Bay of Biscay. Satellite retrievals tended to smooth out cooling events associated with intermittent, alongshore upwelling, especially during summer. These biases propagated to the characterization of MHWs and resulted in an overestimation of their incidence and duration close to the coast. To reconcile satellite and field records, we developed a downscaling approach based on regression modeling that enabled the reconstruction of past temperatures and analyze MHW trends. Despite the cooling effect due to upwelling, the temperature reconstructions revealed a six-fold increase in the incidence of MHWs in the Cantabrian Sea over the last four decades. A comparison between static (no trend) vs. dynamic (featuring a linear warming trend) MHW detection thresholds allowed us to attribute over half of the increase in MHW incidence to the ocean warming trend. Our results highlight the importance of local processes to fully characterize the complexity and impacts of MHWs on marine coastal ecosystems and call for the conservation of climate refugia associated with coastal upwelling to counter the impacts of climate warming. [Abstract copyright: Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.

Stress compensation by gap monolayers for stacked InAs/GaAs quantum dots solar cells

In this work we report the stacking of 10 and 50 InAs quantum dots layers using 2 monolayers of GaP for stress compensation and a stack period of 18 nm on GaAs (001) substrates. Very good structural and optical quality is found in both samples. Vertical alignment of the dots is observed by transmission electron microscopy suggesting the existence of residual stress around them. Photocurrent measurements show light absorption up to 1.2 μm in the nanostructures together with a reduction in the blue response of the device. As a result of the phosphorus incorporation in the barriers, a very high thermal activation energy (431 meV) has also been obtained for the quantum dot emission

Winter-mixing preconditioning of the spring phytoplankton bloom in the Bay of Biscay

The spring phytoplankton bloom plays a key role in the dynamics of temperate and polar seas. Nevertheless, the mechanisms and processes behind these blooms remain a subject of considerable debate. We analyzed the influence of deep mixing during winter on the spring phytoplankton bloom in the Cantabrian Sea (southern Bay of Biscay). To this end, we combined long-term physical and biogeochemical in situ data (1993–2012) and satellite observations (1997–2012). Deeper winter mixing led to higher nitrate and chlorophyll concentrations through the water column during the spring bloom. However, this effect was modified by short-term variability in near-surface stratification in spring. Winter-mixing preconditioning also influenced different spring bloom metrics: deeper and later mixing in winter was followed by later blooms with a larger peak. In these enhanced blooms, nitrate was taken up at faster rates, indicating higher rates of phytoplankton production. Winters with weaker mixing (that led to weaker spring blooms) were associated with warmer surface temperatures. This relationship suggests that the multi-decadal trend toward warmer surface temperatures in the Bay of Biscay may promote a decrease in the magnitude of the spring bloom, which could impact upper trophic levels and also deep carbon export in the future

Differentiating between fatal and non-fatal mining accidents using artificial intelligence techniques

Using statistical methods for categorical data analysis, namely multiple correspondence analysis and Artificial Intelligence through Bayesian networks, we analysed a database of occupational mining accidents for Spain for the period 2004–2017 to identify the factors most associated with the occurrence of fatal and non-fatal accidents. The results obtained allow to shed light on the hidden patterns present in different work situations where accidents can have fatal consequences. In addition, this study exemplifies the application of statistical techniques suitable for Big Data and data-driven decision making in the mining sector.Xunta de Galicia | Ref. ED431C 2018/4