Modelización del deterioro de tableros de puentes de hormigón por difusión de cloruros y corrosión de la armadura pasiva

RESUMEN La corrosión de las armaduras destaca como una de las causas más habituales en el deterioro de las estructuras de hormigón, pudiendo provocar colapsos y conllevando, en todo caso, enormes gastos de reparación y mantenimiento. La repercusión de los problemas de corrosión en las armaduras ha supuesto un acentuado crecimiento en los trabajos de investigación orientados a asegurar la durabilidad de las estructuras. Sin embargo, muchos de los factores que intervienen son todavía poco conocidos. Pese a los avances técnicos en los modelos de predicción, la estimación de la vida útil resulta aún hoy controvertida y llena de incertidumbres. Dichos modelos se refieren principalmente a la penetración de cloruros y a la carbonatación del hormigón, reconocidos agentes promotores de la despasivación de las armaduras. La presente investigación se focaliza en el análisis del ataque por cloruros, distinguiéndose las dos etapas tradicionalmente adoptadas para describir el proceso: una primera de iniciación, hasta que se alcanza una determinada concentración crítica en las inmediaciones de la barra de refuerzo; y una segunda de propagación, en la que la generación de los productos de corrosión implica la aparición de tracciones en el recubrimiento del elemento estructural. En el estudio del ingreso y transporte de iones cloruro en el hormigón, se establecen las ecuaciones diferenciales básicas que gobiernan los procesos involucrados, relativos fundamentalmente a la difusión de iones, pero también a otros fenómenos como la convección (arrastre de sustancias disueltas por movimiento del agua en los materiales porosos semisaturados) o la vinculación entre cloruros. Tres son las variables macroscópicas utilizadas: la concentración de cloruros, la humedad y la temperatura, además del tiempo equivalente de hidratación. El modelo de elementos finitos propuesto es capaz de reproducir resultados experimentales de ensayos, haciendo uso de parámetros conocidos a priori a partir de las propiedades tecnológicas del material y las condiciones medioambientales. También posibilita la reproducción de complejas geometrías bidimensionales, como es el caso de la existencia de fisuras superficiales. Sin embargo, en la predicción de los tiempos de iniciación, la definición de variables básicas como la concentración superficial de cloruros o la concentración crítica, es todavía bastante imprecisa. Respecto al periodo de propagación, los estados límites últimos se pueden referir a la pérdida de la sección de acero o de la adherencia hormigón-acero, así como al estallido del recubrimiento por la aparición de tracciones importantes. Si bien se desarrollan modelos analíticos sencillos capaces de delimitar los tiempos para la aparición de fisuración en superficie; el comportamiento en fractura del hormigón se analiza por medio de un elemento finito con fisura cohesiva embebida. Solventadas las dificultades para conseguir la localización de las fisuras, el modelo propuesto es capaz de predecir los tiempos para la aparición de fisuración en superficie; si bien es necesario hacer uso de hipótesis no suficientemente contrastadas respecto a la consideración de posibles huecos en la interfaz acero-hormigón o al relleno de las propias fisuras generadas por parte de los productos de oxidación. En cuanto a la predicción de los tiempos de propagación, las principales limitaciones se refieren a la estimación de la velocidad de corrosión y a la posible influencia de las propiedades mecánicas de la capa de óxido alrededor de la barra de refuerzo. Establecidas las herramientas de cálculo, el análisis se centra en ejemplos de aplicación relativos a losas superiores de tableros de puentes reales sometidos a la acción de sales fundentes o bien a ambientes costeros. El mallado bidimensional de elementos finitos es común a las dos fases características del proceso de corrosión, como primer paso para su integración futura. Pese a las limitaciones ya comentadas en la estimación de la vida útil, los modelos adoptados permiten comparar la influencia en la durabilidad de factores como la geometría de la sección, las características del hormigón y su puesta en obra. Como principales conclusiones, los tiempos de propagación obtenidos resultaron sensiblemente inferiores a los correspondientes de iniciación; se comprobó que unas condiciones defectuosas de ejecución pueden llegar a reducir a la mitad la estimación de la vida útil, con respecto a unas condiciones óptimas; y la repercusión del aumento de recubrimiento en la estimación de la vida útil resultó tanto mayor cuanto mejor es la calidad del hormigón, reflejada básicamente por la relación agua/cemento y la porosidad. ABSTRACT Corrosion of reinforcement bars is a primary cause in the deterioration of concrete structures, which may be led to failure and even collapse. In any case, the cost of associated repair and maintenance is enormous. Hence, investigations relating to the durability assessment of concrete structures have shown a substantial increase in the last years. However, many factors involved in the corrosion process remain poorly understood. In spite of significant progress in predicting models, the estimation of service life of reinforced concrete structures is yet to be satisfactorily defined. These models refer mainly to chloride penetration and concrete carbonation, both of them well-known causes of steel depassivation. Present work is focused on chloride attack and distinguishes the two distinct phases traditionally adopted in the literature: initiation stage, until aggressive species concentration around the reinforcement bar reaches a threshold value, necessary to trigger active corrosion; and propagation stage, in which rust generation induces tensile stresses in the concrete cover. Basically, the governing equations in modelling of chloride ingress and transport into concrete refer to ion diffusion, but also to other phenomena like convection (motion of dissolved substances caused by flow of water in pore solution of partially saturated media) or chloride binding. Three are the macroscopic variables used: chloride concentration, moisture and temperature, in addition to equivalent hydration time. The proposed finite element model reproduces results of experimental tests by means of a priori parameter estimation, according to the characteristics of materials and external environment conditions. The model can also reproduce bi-dimensional complex geometries; e.g. cracked concrete cover. However, in the initiation time prediction, basic variables like surface chloride content or threshold chloride concentration are not precisely defined yet. Regarding propagation stage, corrosion provokes the reinforcement cross-section reduction and the loss of bond between concrete and steel, as well as concrete cracking and, eventually, spalling and delaminations. Analytical models are developed to delimitate the time to the appearance of external cracks, but an embedded cohesive crack finite element is required to analyze concrete fracture. Once some conceptual difficulties concerning the localization of cracks are solved, the proposed model is capable to estimate time to surface cracking quite accurately; although it is necessary to make some assumptions about the consideration of a porous zone around the steel-concrete interface and the accommodation of corrosion products within the open cracks generated in the process. Regarding propagation time prediction, major limitations refer to the quantitative estimation of corrosion rate and the possible influence of rust mechanical properties around the steel bar. The numerical performance of the developed calculation tools was examined in some example cases concerning actual bridge deck upper slabs exposed to de-icing salts or marine environments. 2D finite elements meshes were the same in the two stages of corrosion process, as a first step towards their future integration. In spite of abovementioned limitations in the estimation of service life, adopted models assess the relative importance of factors like cross-section geometry, concrete properties and its placing and curing, in the durability of structures. As main conclusions, the corrosion propagation times were significantly lower than initiation ones; bad execution conditions may reduce service life by half; and the better of concrete quality, the impact of increasing concrete cover thickness was higher, with water to cement ratio and porosity as basic parameters

Cover cracking of the reinforced concrete due to rebar corrosion induced by chloride penetration

This paper is focused on the problem of the chloride-induced corrosion of the rebar in reinforced concrete, with special application to the slabs and decks of the bridges. High superficial concentrations may be usual in these structures (marine environments or de-icing salts in roadway bridges, e.g.). Like any aggressive agent such as water, gases or other dissolved ions, chloride induced deterioration is very conditioned by possibilities of transport through concrete mass

Cover cracking of reinforced concrete due to rebar corrosión induced by chloride penetration

Este artículo estudia el proceso de fisuración del hormigón por corrosión de la armadura. Se presenta un modelo de transporte de cloruros en el hormigón, que contempla la no-linealidad de los coeficientes de difusión, las isotermas de absorción y el fenómeno de convección. A partir de los resultados de penetración de cloruros, se establece la corrosión de la armadura con la consiguiente expansión radial. La fisuración del hormigón se estudia con un modelo de fisura embebida. Los dos modelos (iniciación y propagación) se incorporan en un programa de elementos finitos. El modelo se contrasta con resultados experimentales, obteniéndose un buen ajuste. Una de las dificultades es establecer el umbral de concentración de cloruros que da lugar al inicio de la corrosión de la armadura.This paper is focused on the chloride-induced corrosion of the rebar in RC. A comprehensive model for the chloride ingress into concrete is presented, with special attention to non-linear diffusion coefficients, chloride binding isotherms and convection phenomena. Based on the results of chloride diffusion, subsequent active corrosion is assumed and the radial expansion of the corroded reinforcement reproduced. For cracking simulation, the Strong Discontinuity Approach is applied. Both models (initiation and propagation corrosion stages) are incorporated in the same finite element program and chained. Comparisons with experimental results are carried out, with reasonably good agreements being obtained, especially for cracking patterns. Major limitations refer to difficulties to establish precise levels of basic data such as the chloride ion content at concrete surface, the chloride threshold concentration that triggers active corrosion, the rate of oxide production or the rust mechanical properties

Colonization of Vitis vinifera L. by the Endophyte Trichoderma sp. Strain T154: Biocontrol Activity Against Phaeoacremonium minimum

[EN] Trichoderma strains used in biological control products usually exhibit high efficiency in the control of plant diseases. However, their behavior under field conditions is difficult to predict. In addition, the potential of indigenous strains has been poorly assayed as well as their possible behavior as endophytes. Hence, niche colonization is a key feature for an effective protection. In this study, we aimed to: (i) explore the possibility of using a new Trichoderma strain isolated from vine to control pathogens, (ii) study the in planta interaction with the pathogen Phaeoacremonium minimum W. Gams, Crous, M.J. Wingf. & L. Mugnai (formerly Phaeoacremonium aleophilum), a pioneer fungus involved in Grapevine Trunk Diseases (GTDs) such as esca. For this purpose, fluorescently tagged Trichoderma sp. T154 and a P. minimum strain were used for scanning electron microscopy and confocal scanning laser microscopy analyses. Data showed that the Trichoderma strain is able to colonize plants up to 12 weeks post inoculation and is located in xylem, fibers, as well as in parenchymatic tissues inside the wood. The beneficial fungus reduced colonization of the esca-related pathogen colonizing the same niches. The main observed mechanism involved in biocontrol of Trichoderma against the esca pathogen was spore adhesion, niche exclusion and only few typical hypha coiling was found between Trichoderma and the pathogen. These results suggest that the Trichoderma strain has potential for reducing the colonization of Phaeoacremonium minimum and thus, an inoculation of this biological control agent can protect the plant by limiting the development of GTD, and the strain can behave as an endophyte.SIThe grant awarded to GC-H (FPU15/04681) comes from the Ministry of Education, Culture, and Sport (Spain). We thank Pago de Carraovejas winery for the project “GLOBALVITI IDI- 20120746” “Solució n global para mejorar la producció n vitivinı́ cola frente al cambio climá tico basada en robó tica, tecnologı́ a IT y en estrategias biotecnoló gicas y de manejo del viñedo” (Global solution for enhancing viticulture production against: climatic change based on: robotics, IT technology, biotechnological strategies, and vineyard management) that was granted by the Centro para el Desarrollo Tecnoló gico Industrial –CDTI-. SC and MG received funding via DaFNE Project Nr. 101384 from the Austrian Federal Ministry for Sustainability and Tourism (BMNT)

The Influence of Temperature on the Growth, Sporulation, Colonization, and Survival of Trichoderma spp. in Grapevine Pruning Wounds

[EN] Trichoderma is a genus of fungi used for the biological control of plant diseases and a large number of its bio-formulates are available in the market. However, its efficacy under field conditions remains unclear, especially for the protection of grapevine plants against Grapevine Trunk Diseases (GTDs). These diseases are caused by a complex of fungal pathogens whose main point of entrance into the affected plants is through pruning wounds. In this research, different Trichoderma native strains have been evaluated according to their ability to grow at different temperatures and their capacity to colonize pruning wounds in adverse climatic conditions. Strains from section Trichoderma have adapted to cooler conditions. On the other hand, strains from clade Harzianum/Virens grow at higher temperatures. However, differences can also be found between strains inside the same clade/section. Native strains were able to colonize more than 70% of vine pruning wounds in winter conditions. The Trichoderma strain T154 showed a significantly higher re-isolation degree from vine plants and its concentration was optimized for spraying onto vine plants. In conclusion, Trichoderma native strains are better adapted to survive in a changing environment, and they could give better protection to grapevine plants in co-evolution with each specific vineyardSIThis research was supported by project GLOBALVITI ‘Solución global para mejorar la This research was funded by the Centro para el Desarrollo Tecnológico Industrial–CDTI—(Madrid, Spain) for the project GLOBALVITI project (CIEN Program) IDI-20160746, and the project LowpHwine (CIEN Program) IDI ‘Estudio de nuevos factores relacionados con el suelo, la planta y la microbiota enológica que influyen en el equilibrio de la acidez de los vinos y en su garantía de calidad y estabilidad en climas cálidos’—and the grant awarded to GC-H comes from the Ministry of Education, Culture, and Sport (SPAIN), grant number (FPU15/04681) and Bodega Pago de Carraovejas S.L.U. We thank technical assistance of Javier Saiz Gade

Vineyard Management and Physicochemical Parameters of Soil Affect Native Trichoderma Populations, Sources of Biocontrol Agents against Phaeoacremonium minimum

[EN] Native strains of Trichoderma in vineyard soil represent an opportunity for reducing the incidence of grapevine trunk diseases (GTDs) in vineyards. Moreover, its relationship with the environment (physicochemical soil characteristics and farming management practices) remains unclear. In the current study, a survey was carried out on farming management used by viticulturists, and soil samples were studied to analyze their physicochemical properties and to isolate Trichoderma strains. Later, statistical analyses were performed to identify possible correlations between Trichoderma populations, soil management and soil characteristics. In addition, in vitro tests, including antibiosis and mycoparasitism, were performed to select those Trichoderma strains able to antagonize Phaeoacremonium minimum. In this study a positive correlation was found between the iron content and pH in the soil, and a lower pH increases Trichoderma populations in soils. Vineyard management also affects Trichoderma populations in the soil, negatively in the case of fertilization and tillage and positively in the case of herbicide spraying. Two Trichoderma native strains were selected as potential biocontrol agents (Trichoderma gamsii T065 and Trichoderma harzianum T087) using antibiosis and mycoparasitism as mechanisms of action. These results led to the conclusion that native Trichoderma strains hold great potential as biological control agents and as producers of secondary metabolites.SIThis research was funded by project GLOBALVITI ‘Solución global para mejorar la’ Centro para el Desarrollo Tecnológico Industrial–CDTI—(Madrid, Spain) Project, GLOBALVITI project (CIEN Program) IDI-20160746, the project LowpHwine (CIEN Program) IDI ‘Estudio de nuevos factores relacionados con el suelo, la planta y la microbiota enológica que influyen en el equilibrio de la acidez de los vinos y en su garantía de calidad y estabilidad en climas cálidos’ and Bodega Pago de Carraovejas S.L.U. Thanks to all the wineries and viticulturists who kindly let us sample their vineyards. Thanks also to the research staff of the GUIIAS group for their technical support

Experimental and theoretical characterization of the Zn - Zn bond in [Zn2(η5-C5Me5)2]

The existence and characterization of a bond between the Zn atoms in the recently synthesized complex [Zn2(5-C5Me5)2], as well as between Zn and ligand C atoms is firmly based on neutron diffraction and low-temperature X-ray synchrotron diffraction experiments. The multipolar analysis of the experimental electron density and its topological analysis by means of the Atoms in Molecules (AIM) approach reveals details of the Zn - Zn bond, such as its open-shell intermediate character (the results are consistent with a typical metal-metal single bond), as well as many other topological properties of the compound. Experimental results are also compared with theoretical ab initio calculations of the DFT (density functional theory) and MP2 (Mller-Plesset perturbation theory) electron densities, giving a coherent view of the bonding in the complex. For instance, charges calculated from the AIM approach applied to the atomic basin of each Zn atom are, on average, +0.72 e from both the experimental and the theoretical electron density, showing a moderate charge transfer from the metal, confirmed by the calculated topological indexes.Ministerio de Educación y Ciencia MAT2006-0199

Influence of Physicochemical Characteristics of Bean Crop Soil in Trichoderma spp. Development

[EN] Spain has ranked 6th on the harvested bean area and 8th in bean production in the European Union (EU). The soils of this area have mixed silt loam and sandy loam texture, with moderate clay content, neutral or acidic pH, rich in organic matter and low carbonate levels, providing beans with high water absorption capacity and better organoleptic qualities after cooking. Similar to other crops, it is attacked by some phytopathogens. Hitherto, chemical methods have been used to control these organisms. However, with the Reform of the Community Agrarian Policy in the EU, the number of authorized plant protection products has been reduced to prevail food security, as well as to be sustainable in the long term, giving priority to the non-chemical methods that use biological agents, such as Trichoderma. This study aimed to investigate the relative importance of various crop soil parameters in the adaptation of Trichoderma spp. autoclaved soils (AS) and natural soils (NS) from the Protected Geographical Indication (PGI) “Alubia La Bañeza—León” that were inoculated with Trichoderma velutinum T029 and T. harzianum T059 and incubated in a culture chamber at 25◦C for 15 days. Their development was determined by quantitative PCR. Twelve soil samples were selected and analyzed from the productive zones of Astorga, La Bañeza, La Cabrera, Esla-Campos and Páramo. Their physicochemical characteristics were different by zone, as the texture of soils ranged between sandy loam and silt loam and the pH between strongly acid and slightly alkaline, as well as the organic matter (OM) concentration between low and remarkably high. Total C and N concentrations and their ratio were between medium and high in most of the soils and the rest of the micronutrients had an acceptable concentration except for Paramo’s soil. Both Trichoderma species developed better in AS than in NS, T. velutinum T029 grew better with high levels of OM, total C, ratio C:N, P, K, Fe, and Zn than T. harzianum T059 in clay soils, with the highest values of cation exchange capacity (CEC), pH, Ca, Mg and Mn. These effects were validated by Canonical Correlation Analysis (CCA), texture, particularly clay concentration, OM, electrical conductivity (EC), and pH (physical parameters) and B and Cu (soil elements) are the main factors explaining the influence in the Trichoderma development. OM, EC, C:N ratio and Cu are the main soil characteristics that influence in T. velutinum T029 development and pH in the development of T. harzianum T059.SIThis research was funded by Junta de Castilla y León, Consejería de Educación for the project “Application of Trichoderma strains in sustainable quality bean production” (LE251P18

Effect of Social Rank upon Estrus Induction and Some Reproductive Outcomes in Anestrus Goats Treated With Progesterone + eCG

We evaluated the possible role of the social rank [R] (i.e., low—LSR, middle—MSR, or high—HSR) in anestrus goats exposed to a P4 + eCG [D] (i.e., 100 or 350 IU) estrus induction protocol (EIP). Adult, multiparous (two to three lactations), multiracial, dairy-type goats (Alpine–Saanen–Nubian x Criollo goats (n = 70; 25°51′ North) managed under stall-fed conditions were all ultrasound evaluated to confirm anestrus status while the R was determined 30 d prior to the EIP. The variables of estrus induction (EI, %), estrus latency (LAT, h), estrus duration (DUR, h), ovulation (OVU, %), ovulation rate (OR, n), corpus luteum size (CLS, cm), pregnancy (PREG, %), kidding (KIDD, %), and litter size (LS, n) as affected by R, D, and the R × D interaction, were evaluated. While OVU and CLS favored (p 0.05; 38.5%) KIDD. However, EI, LAT, DUR, OR, and PREG were affected by the R × D interaction. The HSR group had the largest (p < 0.05) EI % and DUR h, irrespective of D. The shortest (p < 0.05) LAT occurred in D350, irrespective of R. While the largest (p < 0.05) OR occurred in HSR and MSR within D350, the HSR + D350 group had the largest PREG (p < 0.05). These research outcomes are central to defining out-of-season reproductive strategies designed to attenuate seasonal reproduction in goats

Effect of Farnesol in Trichoderma Physiology and in Fungal–Plant Interaction

[EN] Farnesol is an isoprenoid intermediate in the mevalonate (MVA) pathway and is produced by the dephosphorylation of farnesyl diphosphate. Farnesol plays a central role in cell growth and differentiation, controls production of ubiquinone and ergosterol, and participates in the regulation of filamentation and biofilm formation. Despite these important functions, studies of farnesol in filamentous fungi are limited, and information on its effects on antifungal and/or biocontrol activity is scarce. In the present article, we identified the Trichoderma harzianum gene dpp1, encoding a diacylglycerol pyrophosphatase that catalyzes production of farnesol from farnesol diphosphate. We analyzed the function of dpp1 to address the importance of farnesol in Trichoderma physiology and ecology. Overexpression of dpp1 in T. harzianum caused an expected increase in farnesol production as well as a marked change in squalene and ergosterol levels, but overexpression did not affect antifungal activity. In interaction with plants, a dpp1-overexpressing transformant acted as a sensitizing agent in that it up-regulated expression of plant defense salicylate-related genes in the presence of a fungal plant pathogen. In addition, toxicity of farnesol on Trichoderma and plants was examined. Finally, a phylogenetic study of dpp1 was performed to understand its evolutionary history as a primary metabolite gene. This article represents a step forward in the acquisition of knowledge on the role of farnesol in fungal physiology and in fungus-environment interactionsSIThis research was funded by the Spanish I+D+i Grants AGL2012-40041-C02-02, AGL2015-70671-C2-2-R, RTI2018-099600-B-I00 and PID2021-123874OB-I00, financed by the MCIN/ AEI/10.13039/501100011033. GC-H was awarded with a Grant from the Ministry of Education, Culture, and Sport (Spain) (Grant number FPU15/04681). NM-R was awarded with a Grant from the Junta de Castilla y León (Spain) (ORDEN EDU/875/2021, 13 July 2021