Néstor F. Ortega

Assessment of Residual Life of concrete structures affected by reinforcement corrosion

Abstract The corrosion process in reinforced concrete structures, exposed to marine or industrial environments, causes the appearance and growth of cracks. As a consequence, this produces a slow degradation of the material physical properties, steel fragilization and a decrease of the bond strength and steel reinforcements, cross section, affecting its static and dynamic behavior. In the second half of the twentieth century, the importance of constructions’ service life was noticed, so different techniques have been developed to predict the Residual Life of existing structures, in order to increase it. This situation has a significant economic impact on society. This paper presents a non-destructive technique to predict the Residual Life of reinforced concrete beams having different cracking levels, as results of steel reinforcement corrosion, considering the variation produced in the dynamic behavior, through the variation of the first natural vibration frequency. The reinforcement corrosion is an electrochemical process that can be quantified by measuring the intensity of the current on the concrete surface. In this paper, to simulate the corrosion process, a current is externally applied to the studied structure reinforcement and then crack widths and vibration natural frequencies are measured. Based on these measurements a mathematical model is proposed to predict structure remaining life.

Damage Identification in 2D Structures Through Static Response

The local stiffness reduction produced by cracks change the static and dynamic behavior of the structural ele- ments and, by examining this change, crack position and magnitude can be identified. This paper presents a methodology which aim is the detection, location and quantification of the damage through the values of vertical displacements, pro- duced by static loads. With the purpose of establishing the precision of the results obtained in planar structures, numerical simulations were made, analyzing them with the Finite Element Method. Furthermore, two techniques for the detection and damage location are presented. The first one is related to the displacement variation in a damaged structure in relation to the same structure without damage. The second technique is based on the elastic curvature which is computed by means of the Finite Differences Method. The techniques presented are versatile tools, of easy application at work, for structural damage identification.

Corrosion in Concrete Structures with Permanent Deformation in Marine Environment

Concrete is usually highly alkaline (pH around 12), thus protecting reinforcement against corrosion. The occurrence of oxides is favored when the medium pH surrounding the bar is in values near to 9 or lower. Aggressive substances for reinforcements generally enter concrete through its pore structure, and cracks tend to decrease pH, stimulating corrosion process. There are several causes for cracks, including structure bending caused by loads. This research established the influence of concrete coating cracks, caused by permanent deflection, on the durability of reinforced concrete beams in contact with chloride-containing water (at a similar ratio as seawater), over a five-year period. It analyzes the influence of deflections suffered by the specimens on corrosion potentials and concrete coating cracking. It was established that, from the durability point of view and for structures exposed to marine environment, it would be advisable to set stricter admissible deflection and/or concrete cracking limits than those set by the analyzed standards.

Briefing: Non-destructive evaluation and contrasts of concrete overheated and abruptly cooled

Concrete structures can suffer different pathologies, one of which may be due to exposure to high temperatures. In this briefing paper, different concrete types were exposed to high temperatures. T...

Damage Evaluation in Shells from Changes in Its Static Parameters

Displacements of a structure depend on its geometry, properties of the material and acting loads. The presence of cracks in the structures originates local rigidity changes affecting its static and dynamic behavior. In this paper different methodologies for damage identification, based on the static response of reinforced concrete shells are formulated. The first three damage analysis stages, namely, detection, location and quantification are analysed using as study parameters the vertical displacement, elastic curvature, elastic curvature variation and volumetric displacements. Numerical simulations were carried out, with models analyzed by the Finite Element Method. In order to validate the damage identification capability of the proposed methodologies the sensitivities of the various parameters proposed for damage identification were investigated.

Generación de desechos de hormigón y su utilización como agregado grueso en nuevos hormigones

En este trabajo se presenta un estudio realizado en la ciudad de Bahia Blanca, sobre las posibilidades de reciclado de hormigones provenientes de demoliciones, para ser usados como agregado grueso de hormigones nuevos. Se estudiaron diversos lugares de vertido de residuos de la construccion (vertederos oficiales y clandestinos) determinandose los porcentajes aproximados existentes de los distintos tipos de residuos. Por otro lado, con el fin de analizar las posibilidades tecnologicas, se moldearon probetas de hormigon, reemplazando un 75% de su agregado grueso, por agregado grueso reciclado, para analizar las propiedades relacionadas con la resistencia mecanica (compresion y traccion indirecta) y con la estructura de poros (absorcion capilar). Se emplearon distintas relaciones agua/cemento del hormigon (a/c=0.45 y a/c=0.60), con la incorporacion de dos diferentes tipos de aditivos: Incorporador de Aire y Superfluidificante. El hormigon reciclado empleado, fue producto de la trituracion de hormigones realizados con canto rodado patagonico. Como resultado de estos ensayos se pudo observar que la incorporacion de estos aditivos genera variaciones en el comportamiento mecanico y en la estructura de poros del hormigon en estudio, y dichas variaciones son diferentes para cada relacion agua/cemento analizada.

Una Fuente Alternativa de Agregados Finos para el Hormigón

El hormigon es uno de los materiales mas utilizado en las obras civiles, y requiere de grandes volumenes de recursos no renovables para su fabricacion. En la actualidad, existe una gran cantidad de agregados finos naturales cuyos yacimientos proveedores se encuentran en vias de extincion o su explotacion resulta problematica por razones ambientales. Por otra parte, durante la produccion de agregados petreos, aproximadamente el 40-50 % de la roca se transforma en arena cuyo uso en el hormigon esta muy limitado, sin embargo se puede obtener hormigones de adecuada calidad utilizando las tecnologias disponibles.