PSI - Issue 13

Myroslava Hredil / Procedia Structural Integrity 13 (2018) 1657–1662 Author name / Structural Integrity Procedia 00 (2018) 000–000

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2.2. Test procedure. For the accelerated corrosion test the specimen with the reinforcement 1 (anode) was fixed in a framework made of stainless steel, and containing plates 2 and rods 3 serving as cathodes (Fig. 2). The reinforcing rod contacted with a corrosive environment 4 only through concrete layer (lateral surface of the specimen). In order to prevent the direct contact of the solution with reinforcement, rubber spacers 5 were used. At the beginning, a specimen was kept in 3% NaCl solution for 1 h to stabilize the conditions of the environment penetration to the metal–concrete interface from the specimen lateral surface. Then the specimen was subjected to polarization. For polarization a constant voltage was applied to the electrodes using the power supply 6 , and the changes of current with time were recorded.

Fig. 1. Fig. 2. Fig. 1. Specimens R1( left ) for the accelerated corrosion and R2 ( right ) for pull-out tests. 1 , 1’ – steel rod; 2 – concrete; 3 – spacer; 4 – isolation. Fig. 2. Scheme of the installation for the accelerated corrosion test : 1 – steel rod, 2 – stainless steel plates, 3 – stainless steel rods (auxiliary electrodes), 4 – aggressive environment (3% NaCl), 5 – rubber gasket, 6 – power supply. In the case of cathodic polarization (hydrogen charging) the longer rod which served as a cathode was connected to the power supply while the protruding part of the shorter one was isolated. A thin-walled hollow cylinder made of stainless steel was used as an auxiliary electrode in this case to enlarge its effective surface, and it was placed around the specimen. Impressed current (2.6 mA/cm 2 ) was applied to the specimen for 7 days. It should be emphasized that the only one of two rods in the specimen is subjected to polarization. It is suggested that another one did not undergo any essential harmful influences; its corrosion is negligible since time of the experiment is short enough. Control specimens were also kept in the same environment during the experiment. After that the pullout test was performed using 100 kN testing machine UME-10T with a constant displacement rate of 0.5 mm/min. Under these conditions, the rod will be pulled out of the specimen, which requires less force. The procedure used by Hredil (2013) was expanded to three polarization modes with a constant voltage in the range of 10 … 40 V. Under the most intensive one, the first crack appeared on the surface of the specimen after a small period of 18 h (Fig. 3), whereas for the lowest voltage, a similar picture was observed only after 36 days, which is explained by the lower intensity of the reinforcement corrosion. This is also indicated by accelerated-corrosion current changes in the course of the tests: the current density in the specimen for the higher voltage is also much higher. The amount m of dissolved iron was calculated according to the Faraday law (Table 1). It should be pointed out that, under the conditions of the most intensive corrosion, the smallest amount of corrosion products is required to create a wedging pressure on the steel–concrete interface promoting the initiation of cracks in concrete. Evidently, macrockracking of concrete is a nonspontaneous process; it follows after subcritical crack growth from the concrete–rebar interface towards the specimen surface. Corrosion products fill up the formed cracks, as illustrated in Fig. 4, attenuating an expanding pressure of newly formed rust. Thereby, not all corrosion products exert expanding pressure at the steel–concrete interface. A part of these products fill cavities and pores near the reinforcement. Moreover, Wong et al. (2010) stated that some products migrate into the bulk of concrete through pores. Therefore prediction of the corrosion products role in a formation of a stress state in concrete in this case is complicated by their ability to fill not 3. Results and discussion 3.1. Accelerated corrosion