Autoactivación de cemento de escorias con polvo de vidrio de descarte

The aim of this study is to evaluate the behavior of glass powder waste as alkaline activator of slag when both are used in blended cement. The slag blended cement was prepared with 70% slag, and then the slag was replaced with 10-20% glass powder by mass. The self-activation concept is here introduced. Ground glass releases alkalis through dissolution in a slow and sustained way over time. This would activate slag. Ground glass improves fluidity of mortars and the compressive strength overcomes dilution and increases with age due to the combined pozzolanic action of slag and glass. The proposed blended cement has better mechanical properties than slag-cement. The proposed blended cement has better mechanical properties than slag-cement and due to less use of slag, it becomes more sustainable and it contributes to waste management.El objetivo del presente trabajo es evaluar el comportamiento de un residuo molido de vidrio como activador interno de la escoria cuando ambos son usados en un cemento mezcla. El cemento de escoria fue preparado con un 70% de escoria y luego la escoria se reemplazó en un 10 y 20% en masa por vidrio molido. Este trabajo introduce el concepto de auto-activación. El vidrio molido libera álcalis por disolución, en forma lenta y sostenida en el tiempo que activarían la escoria. La presencia de vidrio molido mejora la fluidez de los morteros y la resistencia a compresión supera la dilución y crece con la edad por la acción puzolánica combinada de la escoria y el vidrio. El cemento mezcla propuesto tiene mejores propiedades mecánicas que el cemento de escorias pero con menor contenido de escoria por lo que es más sustentable y contribuye al manejo de residuos

Cementos con humo de sílice y escoria granulada de alto horno: comportamiento resistente e hidratación

This paper analyses the influence of portland cement replacement by silica fume (up to 10%) and/or granulated blast furnace slag (up to 70%) on the hydration cement (XRD, heat of hydration, non evaporable water content and calcium hydroxide content) curing under sealed conditions and their effect on the mechanical strength. The obtained results indicate that binary cements containing silica fume and ternary cements there was a significant increase of hydration rate at early age. At later ages, most of studied cements have an equivalent or greater strength that those obtained in the plain portland cement.En este trabajo se analiza la influencia de la incorporación al cemento portland de humo de sílice (hasta 10%) y/o escoria granulada de alto horno (hasta 70%) sobre la hidratación (DRX, calor de hidratación, contenido de agua no evaporable y de hidróxido de calcio), bajo condiciones de curado sellado y su incidencia sobre la resistencia mecánica. Los resultados obtenidos indican que en los cementos binarios con humo de sílice y en los cementos ternarios se produce un importante aumento de la velocidad de hidratación en las primeras edades, mientras que a edades más avanzadas la mayor parte del dominio estudiado alcanza o supera la resistencia obtenida por el cemento portland sin adición

TEM and SAED Characterization of Metakaolin. Pozzolanic Activity

The present study deals with a characterization of metakaolin pozzolanic activity and its chemical character exhibited in the Ordinary Portland Cement (OPC) blends by means of Transmission Electron Microscopy (TEM) and Selected-Area Electron Diffraction (SAED) techniques principally. Metakaolin sample was prepared by calcination of kaolin rock (Guadalajara, Spain) at 780°C. Two OPC of different chemical composition from the tricalcium aluminate content point of view were chosen and Portland cement blends series elaborated and then submitted to the pozzolanic activity test (EN 196-5 or Frattini test). The main mineralogical components of the metakaolin are determined qualitatively: χ-alumina and quartz. The chemical character of the metakaolin is described because of its final composition as well as due to its Al atoms possible coordination. The crystalline order of the material is found to be of both amorphous and polycrystalline, being an intimate amorphous mixture of alumina and silica. Finally, all the alumina capable of reacting chemically is denominated and classified as reactive alumina component, Al2O3r−, of pozzolans, as well as the aluminic chemical character of metakaolin in OPC blends is once again proved and exhibited by means of Friedel's salt formation studied already at 4 h-age

Evolución de la hidratación en cementos con adiciones

In this paper, the hydration mechanism of portland cement pastes with limestone, quartz and natural pozzolan (80/20 weight) was analized. The techniques used were nonevaporable water content, pozzolanic activity and X-ray diffraction. Results show that filler effect increases initially the amount of hydration products in all pastes. For limestone pastes, the dilution effect is significant at long time, for quartz and pozzolan pastes the dilution effect was lower due to the contribution of the pozzolanic reaction.En el presente trabajo se analizó el mecanismo de hidratación de pastas de cemento portland normal con la incorporación de caliza, cuarzo y puzolana natural (proporción 80/20 en peso), por medio de la evaluación del contenido de agua no evaporable, la actividad puzolánica por vía química y la formación de productos de hidratación por DRX. Los resultados obtenidos permitieron determinar un aumento de la cantidad de productos de hidratación inicial debidos al efecto filler en todas las pastas. En las pastas con caliza se evidenció el efecto de dilución a edades avanzadas, en tanto que en las pastas con cuarzo y puzolana, este efecto fue menos predominante debido a la contribución de la reacción puzolánica

Cementos compuestos elaborados con puzolana natural y escoria granulada de alto horno

For reasons of market demand and Portland cement production,the manufacture of cements with two or more separately ground additions to produce customized cements is becoming common practice.When pozzolan or slag content in this type of cements is high, however, the initial strength of the resulting product may be adversely impacted. This problem can be minimized by activating one or both of the replacement materials. The present study analyzes the effect of Portland cement additions such as physically activated natural pozzolan(up to 20%) and/or granulated blast furnace slag (up to 35%) on mortar flexural and compressive strength. The results show that higher strength is attained in ternary than binary cements. Initially (2 and 7 days), the highest compressive strengths are reached by mortars with up to 13% natural pozzolan and 5% slag, whereas at later ages mortars with larger proportions of additions are found to perform best.Debido a las exigencias del mercado y de la producción de cemento Portland, es cada vez más frecuente la elaboración de cementos con dos o más adiciones a partir de la molienda separada de sus constituyentes, dando origen a la formulación de los cementos a medida.Cuando el contenido de adiciones es alto, la utilización de puzolana y escoria en este tipo de cementos presenta la peculiaridad de disminuir la resistencia inicial del cemento resultante. Sin embargo, si algunas o ambas adiciones se activan, este problema puede minimizarse. En este trabajo se analiza la influencia de la incorporación al cemento Portland de puzolana natural (hasta 20%) activada físicamente y/o escoria granulada de alto horno (hasta 35%) sobre la resistencia a flexión y a compresión de morteros. Los resultados indican que los cementos ternarios presentan un mejor comportamiento resistente que los cementos binarios. Las máximas resistencias a compresión en las primeras edades (2 y 7 días)se alcanzan con hasta 13% de puzolana natural y 5% de escoria, mientras que a edades más avanzadas se trasladan a mayores contenidos de puzolana y escoria

Vitamin d status predicts 30 day mortality in hospitalised cats

Vitamin D insufficiency, defined as low serum concentrations of the major circulating form of vitamin D, 25 hydroxyvitamin D (25(OH)D), has been associated with the development of numerous infectious, inflammatory, and neoplastic disorders in humans. In addition, vitamin D insufficiency has been found to be predictive of mortality for many disorders. However, interpretation of human studies is difficult since vitamin D status is influenced by many factors, including diet, season, latitude, and exposure to UV radiation. In contrast, domesticated cats do not produce vitamin D cutaneously, and most cats are fed a commercial diet containing a relatively standard amount of vitamin D. Consequently, domesticated cats are an attractive model system in which to examine the relationship between serum 25(OH)D and health outcomes. The hypothesis of this study was that vitamin D status would predict short term, all-cause mortality in domesticated cats. Serum concentrations of 25(OH)D, together with a wide range of other clinical, hematological, and biochemical parameters, were measured in 99 consecutively hospitalised cats. Cats which died within 30 days of initial assessment had significantly lower serum 25(OH)D concentrations than cats which survived. In a linear regression model including 12 clinical variables, serum 25(OH)D concentration in the lower tertile was significantly predictive of mortality. The odds ratio of mortality within 30 days was 8.27 (95% confidence interval 2.54-31.52) for cats with a serum 25(OH)D concentration in the lower tertile. In conclusion, this study demonstrates that low serum 25(OH)D concentration status is an independent predictor of short term mortality in cats

Recycled Construction and Demolition Waste as Supplementary Cementing Materials in Eco-Friendly Concrete

Growing environmental awareness and scarcity of natural resources are forcing the world to migrate from linear to circular economies. The possibility of partially replacing cement with ceramic-based waste from construction and demolition waste (C&DW) is a government and industry focus. The present study analyzes the effects of including finely ground complete walls of ceramic blocks (including masonry mortars) as supplementary cementing materials (SCM) on the physical, mechanical, and transport properties (water absorption and permeability) of concrete. The replacement ratio employed was 25% by weight of cement. Studies of the hydration evolution of cement pastes support the described properties of concretes. The findings reveal that the ground ceramic-based waste from C&DW stimulates hydration at all ages. Initially, this stimulation is predominantly physical (filler effect), but in later stages, it becomes chemical (pozzolanic reaction). Based on the results obtained in this study, it is possible to produce concrete with mechanical properties comparable to those of conventional concrete at 28 days

Does the colour of the waste glass affect their efficiency as supplementary cementitious material?

Glass from the solid urban waste is presented mainly in amber, green and transparent colour. Regarding their reactivity, several studies argue that there are differences among each colour when they are used as supplementary cementitious material. Nevertheless, the current literature lacks of an assessment of the significance of these differences from a practical perspective. On top of that, one of the problems for effective glass recycling is that they are mixed at the waste collection centres and the separation cost would be too expensive or even impossible. Considering the technological and the economical benefits of using the waste glass with no separation, the hypothesis assessed in this paper was that the colour of the glass is not statistically significant (ANOVA test). Blended cements replaced up to 30% shown stimulation of the hydration at 2 days (isothermal calorimetry) and the pozzolanic activity at 7 days (Frattini test). At 28 days, the development of the compressive strength with the pozzolanic supply of the glass powders, lead to equal or higher values than the control. The ANOVA and Tukey tests have shown that at 28 days neither each glass colour powder per se nor a mix of them are a significative variable for the development of the compressive strength performance of the mortars up to 30% of replacement