34 research outputs found
L-Ascorbic Acid as an Efficient Green Corrosion Inhibitor of Steel Rebars in Chloride Contaminated Cement Mortar
Get PDFCorrosion of reinforcement is a major problem regarding concrete durability. In new structures the corrosion onset can be delayed if additional protection methods are provided as is the case for the addition of corrosion inhibitors in the concrete mix. The main goal of this paper is the evaluation of the effect of the ascorbic acid (AA) as a green steel corrosion inhibitor in cement mortars contaminated by chlorides. Concentration levels of ascorbic acid, ranging from 0.5 to 10−3 mol/L, were added to the mixing water. Electrochemical methods, including corrosion potential (Ecorr), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS), were employed to assess the corrosion rate of the steel embedded in the mortars. The corrosion inhibiting performance of ascorbic acid was compared with that of sodium nitrite. The interaction of the ascorbic acid with the hydrated cement matrix was also evaluated with differential thermal and thermogravimetric analysis (DTA/TG) and pH measurements. The results indicated that, depending on the ascorbic acid concentration, it can be an activator of the corrosion process or an effective corrosion inhibitor in a similar manner to sodium nitrite. A corrosion rate decrease was achieved with concentrations below 10−2 mol/L and the optimum content was 10−3 mol/L. Within this concentration range, the AA does not modify the hydration performance of the cement matrix
A novel strategy for triacylglycerides and polyhydroxyalkanoates production using waste lipids
Get PDFLipids are one of the main components of the organic matter present in the effluents of the food-processing industry. These waste streams can be biotransformed into valuable triacylglycerides (TAGs) and polyhydroxyalkanoates (PHAs), precursors of biofuels and biomaterials alternative to petroleum-based products. These compounds are yielded by mixed microbial cultures, and considering that both TAG and PHA accumulators may coexist within the community, it seems crucial to define those operational strategies that might control the selection of the dominant metabolic pathways (TAG or PHA accumulation). In this work, residual fish-canning oil was used as a carbon source in a two-stage process (culture selection and intracellular compounds accumulation) in which the substrate was simultaneously hydrolyzed in these two stages without the need for a previous fermentation unit. It was pretended to maximize preferential TAG or PHA storage in the accumulation reactor by the imposition of certain selective pressures in the enrichment one. Uncoupling C and N feedings and limiting nitrogen availability in the medium, allowed to maximize PHA production (82.3 wt% of PHAs, 0.80 CmmolPHA/CmmolS). Besides, when low pH in the famine phase was considered as additional selective pressure, it was possible to shift the ratio TAG:PHA from 4:96 obtaining 43.0 wt% of TAGs (0.67 CmmolTAG/CmmolS). Therefore, this novel and simplified process demonstrated versatility and efficiency in the storage of TAGs and PHAs from a unique residual feedstock and using an open culture proving that product selection can be harnessed if choosing the right operational conditions in the enrichment stageThis research was supported by the Spanish Government (AEI) through the TREASURE project [CTQ2017-83225-C2-1-R]. Lucía Argiz is a Xunta de Galicia fellow (2019), [ED 481A-2019/083], grant co-funded by the operative program FSE Galicia 2014-2020. Lucía Argiz, Ángeles Val del Río, and Anuska Mosquera-Corral belong to the Galician Competitive Research Group GRC ED431C 2017/29. All these programs are co-funded by the FEDER (EU)S
Evaluación de la vitamina C como inhibidor verde de corrosión y su interacción con la pasta de cemento
No full textEl hormigón es uno de los materiales más utilizados en el sector de la construcción debido a sus buenas características mecánicas y a su elevada durabilidad. Pese a los grandes avances con los que hoy en día contamos, los problemas de corrosión se siguen dando en numerosas estructuras. Esta corrosión generalmente es debida a los ambientes agresivos a los que se expone el hormigón, como puede ser la presencia de cloruros, que en la mayoría ocasiones no se pueden evitar. Es por eso por lo que aparece el concepto de los inhibidores. En la actualidad, el más usado tanto a nivel industrial como en estudios es el nitrito de calcio, debido a que tiene un mecanismo de protección bien definido, además de comprobarse que su adición aumenta la resistencia a compresión y no han sido observados riegos de reacción árido-álcali. Pese a que este inhibidor sintético brinda una excelente eficacia anticorrosiva, es altamente tóxico y pueden causar riesgos perjudiciales tanto en los seres humanos como en el medio ambiente. Es ahí donde surge la necesidad de encontrar inhibidores que no generen problemas ambientales, los llamados “inhibidores verdes”. El objetivo principal del presente trabajo es evaluar el efecto que tiene un producto natural como la vitamina C como “inhibidor verde” en el escenario de una corrosión inducida por cloruro, con el fin de encontrar una alternativa ecológica y eficaz frente a los inhibidores de corrosión inorgánicos. Para obtener resultados comparativos se empleará como referencia un inhibidor basado en nitrito, cuya efectividad está ampliamente establecida. Para evaluar el comportamiento del acero en las diferentes etapas del proceso de corrosión e inhibición se utilizarán técnicas electroquímicas tales como el potencial de corrosión, la Resistencia a la Polarización y la Espectroscopía de Impedancia Electroquímica y técnicas de caracterización como análisis termogravimétrico (ATD) y análisis químicos como el pH. Las pruebas se realizarán con dos tipos de probetas, unas que contienen un 2% de iones cloruros en peso de cemento y otras con un 2.5% de iones cloruro en peso de cemento. Los inhibidores y los iones cloruro se agregarán en el agua de amasado del mortero y la pasta de cemento. Las dosis de los dos inhibidores y de los iones cloruro utilizadas han sido seleccionadas de acuerdo con la literatura.
ABSTRACT
Concrete is one of the most used materials in the construction sector due to its good mechanical properties and high durability. Despite the great advances that we have today, corrosion problems continue to occur in many structures. This corrosion is generally caused by the aggressiveness of the environments which is exposed too, such as the presence of chlorides, which on many occasions cannot be avoided. That is why the concept of inhibitors appears. Actually, the most used is calcium nitrite, because it has a well-defined protection mechanism, in addition to verifying that its addition increases compressive strength and no arid alkali reaction risks have been observed. Although this synthetic inhibitor provides excellent anticorrosive efficacy, it is highly toxic and can cause harmful risks to both humans and the environment. This is where the need arises to find inhibitors that do not generate environmental problems, the so-called “green inhibitors”. The main objective of this work is to evaluate the effect of vitamin C as a “green inhibitor” in the scenario of chloride-induced corrosion, in order to find an ecological and effective alternative to toxic corrosion inhibitors. To obtain comparative results, an uninhibited reference and a nitrite-based inhibitor, whose effectiveness is widely established, will be used. To evaluate the behavior of steel in the different stages of the corrosion and inhibition process, electrochemical techniques such as Polarization Resistance and Electrochemical Impedance Spectroscopy will be used. The tests were carried out with two types of test pieces, some containing 2% chloride ions by weight of cement and others with 2.5% chloride ions by weight of cement. Inhibitors will be added as additives in the mortar mix. The doses of inhibitors used have been selected according to the literature
Effect of the aggregate grading on the concrete air permeability
Get PDFGreat durability problems are being found in concrete structures related to the penetrability of aggressive agents through the concrete (ie. chloride penetration, sulphate attack, carbonation, freezing and thawing, and so on). Air permeability coefficient is used as an effective tool to estimate the potential durability of concrete structures due to its direct relation with the microstructure and the moisture content.
This paper discusses the effect of the aggregate grading and water/cement ratio on the air permeability coefficient. An aggregate grading with more sand than coarse aggregates has resulted more beneficial from the point of view of concrete air permeability. This fact can be attributed to a denser skeleton formed by the finer aggregates. With fine aggregates, the higher water/cement ratio, the lower air permeability. However, the contrary was found with coarse aggregates. Overall, a temperature increase from 20 °C to 60 °C during preconditioning led to a Dair increase of 40–80%.Se han encontrado una gran cantidad de problemas de durabilidad de estructuras de hormigón relacionados con la penetración de agentes agresivos externos (es decir, penetración de cloruros, ataque por sulfatos, carbonatación, hielo-deshielo, etc.). El coeficiente de permeabilidad al aire se utiliza como una herramienta eficaz para estimar la durabilidad potencial de las estructuras de hormigón debido a su relación directa con su microestructura y contenido de humedad.
Se discute el efecto de la gradación de los áridos y relación agua/cemento en el coeficiente de permeabilidad al aire. Con áridos más finos que gruesos, el resultado es más beneficioso, lo que se atribuye a que la arena forma un esqueleto más denso. Con áridos más finos, al aumentar la relación agua/cemento, disminuye la permeabilidad al aire; pero con áridos más gruesos se ha observado lo contrario. Cuando se pre-acondiciona de 20 °C a 60 °C, se produce un aumento del Dair del 40–80%
La nueva norma europea de especificaciones de cementos comunes UNE-EN 197-1:2011
Get PDFIn this paper, the novelties of European standard EN 197-1:2011 which has been aprobed on 6th August, 2011 are presented. The european standard EN 197-1:2011 has been published in the Official Journal of the European Union on 19th June, 2012 (C 176/1). The UNEEN 197-1:2011 will be published in Spain in the Official Journal of Spain (B.O.E.). The date of applicability (DAV) of the standard as a harmonised European standard is on 1st of July, 2012 and the date of the end of the coexistence period is on 1st of July, 2013.
The former EN 197-1:2000 has been the first European standard in the field of the Construction Products Directive (CPD) and this first revision include the requirements needed for a common cement to be, in addition, sulphate resisting cement. Therefore, the mandate given by the European Commission to CEN to prepare harmonised standards in the cement field (mandate M114) has been fulfilled.En este artículo se presentan las novedades de la nueva norma europea de especificaciones de cementos comunes UNE-EN 197-1:2011 aprobada el 6 de agosto de 2011 como EN 197-1:2011 y publicada el 19 de junio de 2012 en el Diario Oficial de la Unión Europea (DOUE). Esta norma se publicará en el Boletín Oficial del Estado (BOE) antes de final de año. La fecha de disponibilidad (date of applicability, DAV) es el 1 de julio de 2012 y el periodo de coexistencia finalizará el 1 de julio de 2013.
La UNE-EN 197-1:2000 fue la primera norma armonizada dentro del campo de la Directiva de Productos de la Construcción (DPC) europea y esta primera revisión incorpora unos nuevos requisitos para establecer cuándo un cemento común, además, es resistente a la acción de los sulfatos. De esta forma, se completa el mandato dado por la Comisión Europea a CEN para la elaboración de normas armonizadas de cementos (mandato M114)
Valorization of lipid-rich wastewaters: A theoretical analysis to tackle the competition between polyhydroxyalkanoate and triacylglyceride-storing populations
No full textThe lipid fraction of the effluents generated in several food-processing activities can be transformed into polyhydroxyalkanoates (PHAs) and triacylglycerides (TAGs), through open culture biotechnologies. Although competition between storing and non-storing populations in mixed microbial cultures (MMCs) has been widely studied, the right selective environment allowing for the robust enrichment of a community when different types of accumulators coexist is still not clear. In this research, comprehensive metabolic analyses of PHA and TAG synthesis and degradation, and concomitant respiration of external carbon, were used to understand and explain the changes observed in a laboratory-scale bioreactor fed with the lipid-rich fraction (mainly oleic acid) of a wastewater stream produced in the fish-canning industry. It was concluded that the mode of oxygen, carbon, and nitrogen supply determines the enrichment of the culture in specific populations, and hence the type of intracellular compounds preferentially accumulated. Coupled carbon and nitrogen feeding regime mainly selects for TAG producers whereas uncoupled feeding leads to PHA or TAG production function of the rate of carbon supply under specific aeration rates and feast and famine phases lengths.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.BT/Environmental Biotechnolog
Full factorial design to assess the concrete gas permeability
No full textNovel composite material durability is mainly affectedby the transport of fluids and ions through thepore system which are potentially able to producedamage. Then, a key indicator of long-term durabilityof the structures can be the ease with which aggressiveagents are transported through the pore system,i.e. composite material permeability. The purpose ofthis paper is to broaden our knowledge of air permeabilitytesting conditions and, in particular, how it isaffected by the preconditioning temperature and testingpressure. Optimization of variables to determinatethe air permeability coefficient was done by using a 23full factorial design. Air permeability results are recordedin ∅150x70 mm3 concrete specimens. The airpermeability determination procedure gives reliableinformation about the quality of concrete with regardto its durability
Prestaciones del cemento portland ultrafino
Get PDFBy mixing several binder materials and additions with different degrees of fineness, the packing density of the final product may be improved. In this work, ultrafine cement and silica fume mixes were studied to optimize the properties of cement-based materials. This research was performed in mortars made of two types of cement (ultrafine Portland cement and common Portland cement) and two types of silica fume with different particle-size distributions. Two Portland cement replacement ratios of 4% and 10% of silica fume were selected and added by means of a mechanical blending method. The results revealed that the effect of the finer silica fume mixed with the coarse cement enhances the mechanical properties and pore structure refinement at a later age. This improvement is somewhat lower in the case of ultrafine cement with silica fume.La densidad de empaquetamiento del producto final se puede mejorar cuando se mezclan varios conglomerantes y adiciones de diferente finura. En este trabajo se estudiaron varias mezclas de cemento ultrafino y humo de sílice para optimizar las propiedades de los materiales de base cemento. Esta investigación se realizó con morteros fabricados con dos tipos de cemento (cemento Portland ultrafino y cemento Portland común) y dos tipos de humo de sílice con diferentes tamaños de partícula. Se seleccionaron dos porcentajes de sustitución de cemento Portland por humo de sílice (4% y 10%) que se mezclaron mecánicamente. Los resultados revelaron que la mezcla del humo de sílice más fino con el cemento grueso mejora las propiedades mecánicas y el refinamiento de la distribución del tamaño de poro a edades avanzadas. Esta mejora de resistencias y reducción del tamaño de poro era menor en el caso del cemento ultrafino con el humo de sílice
Combined effect of nano-SiO<sub>2</sub> and nano-Fe<sub>2</sub>O<sub>3</sub> on compressive strength, flexural strength, porosity and electrical resistivity in cement mortars
Get PDFThe compressive strength, flexural strength, porosity and electrical resistivity properties of cement mortars with nano-Fe2O3 and nano-SiO2 are studied. Amorphous silica is the main component of pozzolanic materials due to its reaction with calcium hydroxide formed from calcium silicate (C3S and C2S) hydration. The pozzolanic reaction rate is not only proportional to the amount of amorphous silica but also to the surface area available for reaction. Subsequently, fine nano-Fe2O3 and nano-SiO2 particles in mortars are expected to improve mortar performance. The experimental results showed that the compressive strength of mortars with nano-Fe2O3 and nano-SiO2 particles were lower than those obtained with the reference mortar at seven and 28 days. It was shown that the nano-particles were not able to enhance mechanical strength on every occasion. The continuous microstructural progress monitored by mercury intrusion porosimetry (MIP) measurements, pore-size distribution (PSD), total porosity and critical pore diameter also confirmed such results.</jats:p
