Estudio de la vida útil de estructuras de hormigón pretensado frente a corrosión por cloruros

Abstract

The primary structure function is to resist the loads acting on it. The structure capacity should be understood in an extensive sense and not to be restricted only to the mechanical resistance. In particularly, the resistance to the environmental actions and the adequate durability during the service life period estimated in the project of the structure are essential aspects. In order to improve the durability of the prestressed concrete structures, this research focuses in the study of the chloride diffusion in the concrete, the grout and the prestressing steel. Then a service model is developed that can be used for the design of new structures or for the evaluation of existing ones. This model represents what occurs in the reality. Extensive experimental campaigns and theoretical developments were carried out: A quite simple mechanism was designed to obtain the tension of the test attacked steel specimen in a reduced space, using concrete creep frames. A framework was designed to transform the compression load applied by the frames in a tension to prestress the wires with a constant load. An automatic machine was designed to control the cycles attacks (humid-dry), which work with a specific software. All this attack system was placed inside a climatic room where a 50% relative humidity and 20ºC temperature was maintained. Results regarding the ions chloride diffusion in the concrete mass and in the grout were obtained experimentally. The diffusion coefficients were obtained and the chlorides superficial concentration in the concrete and in the grout was considered constant. A coefficient that evaluates the influence of the crack geometry carried out mechanically in the wires was calculated. Degradation coefficients for ultimate tensile and for the chemically attacked steel residual mass were obtained. The chemical attack was produced with a sodium chloride solution. The influence of the tension in the wires was obtained experimentally. Corroded wires without tension were compared with corroded wires prestressed in a frame. A service life model for reinforced/prestressed concrete with a corrosion attack by chloride was proposed. This model could be applied in new structures design, and in the evaluation structures in service, too. This model is based on the Tuutti durability model (1982), but it is more extensive because this work not only studies the contribution of the degradation of the concrete, it studies the degradations of other materials that compose the reinforced concrete and prestressed (grout, steel). Good correlation with experimental results was found.