Issue 50

Ch. Apostolopoulos et alii, Frattura ed Integrità Strutturale, 50 (2019) 548-559; DOI: 10.3221/IGF-ESIS.50.46 549 and the reliability, not only of the material, but also of the whole structure [1]. Corrosion of steel reinforcement constitutes a major problem for reinforced concrete structures, as far as their durability is concerned, as it has also been mentioned by Almusallam [2]. Corrosion degradation is responsible for several issues, such as deterioration of both durability and service life of structures, resulting in premature failure. Ιn recent years, the problem of the actual residual strength degradation of ageing reinforced concrete structures has attracted considerable attention, however it is far from being fully understood and even less resolved. According to Apostolopoulos et al. [3], Papadakis [4], Capazucca[5], Diamond [6] and Alvarez et al. [7], this scenario becomes even worse when coastal environment, which is rich in chlorides, is combined with seismic phenomena. Cyclic loading, which is due to seismic activity, in conjunction with the pre-existing downgrade, which results from corrosion effect, leads to prompt deterioration of useful lifespan of structures, that face durability issues. Furthermore, cyclic loading, leads to a non- linear response of the structures that face durability issues. Therefore, to predict the time dependent damage of corroded reinforced concrete structures under seismic loading it is necessary to consider the effects of material degradation, due to corrosion [8]. In the present work, the effects of chloride-induced corrosion on two different steel bar categories, B400c and B450c are evaluated, in terms of corrosion resistance and mechanical characteristics, before and after the corrosion process. The method that was used for the accelerated corrosion tests, was salt spray chamber and the mechanical tests performed for both steel bar categories were tensile tests and Low Cycle Fatigue Tests. The goal of the study was to highlight the differ- ences among the two steel categories, as far as their mechanical performance and their resistance to corrosion is concerned. Given that both steel grades have been used in existing civil engineering structures, it is important to gain knowledge of their mechanical behavior and their vulnerability to corrosion factor, so as to be able to estimate their life expectancy. M ATERIALS AND METHODS or the goals of the present study, material of two different steel reinforcement categories B400c and B450c was used. The material, for both categories, was received from European factories and were produced by the same steel manufacturer using the “tempcore” method. The chemical composition, which is approximately the same for the two different steel bar categories. Specifically, both steel categories contain 0.22% C, 0.05% P, 0.05% S, 0.8% Cu and 0.012% N, while B450c has an additional 0.5% Ceq. Two series of specimens, 500mm and 250mm long, of 16mm nominal diameter, were organized for each steel grade. For comparison reasons, one more set of specimens of nominal diameter 12mm and 500mm long was prepared for B450c. Given that the goal of the present study is to evaluate the mechanical performance of both steel categories, before and after corrosion, salt spray chamber method was used for the performance of the corrosion tests. Exposure periods equal to 0 days, 45 days and 90 days were scheduled for each set of specimens. Consequently, each set was separated into three smaller groups, the first of which was only mechanically tested (Reference Specimens) while for the rest two groups corrosion took place prior to the mechanical tests. Before the corrosion process, specimens were properly prepared. They were primarily cleaned in order to remove all the unwanted impurities from their surface. The configuration of equal surface areas, that would be exposed to the corrosive media, was necessary for comparison reasons. The exposed length for each specimen was equal to 20mm, while the rest part of the metal was covered with wax, to prevent corrosion (Fig.1). The samples were exposed to the corrosion process and they were mechanically tested in Tensile and Low Cycle Fatigue (LCF) tests. Artificial corrosion tests were executed with the use of salt spray fog chamber – according to ASTM B117 [9]. Figure 1: Preparation of the “short” specimens. F