Functions of changes in the mechanical properties of reinforcing steel under corrosive conditions

Abstract

Corrosion of internal steel reinforcement is one of the main reasons causing reinforced concrete (RC) structure degradation. In order to safely use and extend the durability of the structure, it is important to understand the corrosion mechanism of steel and its influence on the RC structure. Presented research in this article covers a study on the durability of reinforcing steel in strong aggressive environments condition, induced by different concentrations of chloride ions. The main aim of the research was to determine the course of changes in the mechanical properties of reinforcing steel exposed to different environmental conditions as well as its treatments (i.e., simulate the concrete cover). A current experimental investigation was carried out for reinforcing steel with an initial yield strength of 500 MPa, as such steel is currently commonly used in RC structures. The study demonstrated that changes in steel bar parameters depended on the concentration of the aggressive agent ( Cl − ions) and the presence of concrete cover. The largest changes in yield strength (over 28 %) and reduction in tensile strength (over 32 %) were obtained in an environment with a 6 % NaCl concentration for samples without concrete cover. For the same environment, a reduction in Young’s modulus of over 10 % of the initial value was observed. Furthermore, functions representing the relationship between the concentration of chloride ions on the surface of the tested reinforcement samples and the mechanical parameters of the steel were evaluated. The presented empirical functions are an original element of this article, not published so far. Thanks to this, it is possible to estimate changes in the properties of reinforcing steel based on the reading of chloride ion concentration in RC structures. Additionally, the structure of the material subject to corrosion processes was analyzed using scanning electron microscopy (SEM) to assess the degradation and corrosion progress of tested steel bars. The obtained experimental results highlighted the corrosion influence of steel bars for RC structures.