The current experimental study presents the results of bond strength loss (steel bar concrete) due to the corrosion damage of steel bar specimens, semiembedded in concrete, at various times of exposure to corrosive environment. In this case, a correlation was made between the width of the surface cracks of concrete caused by reinforcing steel corrosion and bond strength for different distances between stirrups and different cover thickness of concrete. The study indicates close relationship between the width of surface cracking, the percentage mass loss of embedded reinforcing bar, the distance between stirrups, and the cover thickness. In addition, mathematical predictive models of bond strength loss of corroded specimens were proposed. The model outcomes showed that the cracking development on concrete surface up to a width of 1.6 mm is accompanied by an exponential reduction of bond strength loss between steel reinforcement and concrete. Furthermore, the investigation has shown that the increase of transverse reinforcement (stirrups) percentage and the cover thickness play a significant role in durability of reinforced concrete elements and in bond strength maintenance between rebar and concrete.

The current experimental study consists of part of an extensive and ongoing research on bond behavior of RC elements damaged by corrosion, focusing on stirrups spacing effect on bonding. For this, RC specimens with different cases of stirrups spacing were casted. Accelerated corrosion was induced in order to simulate the slow process of nature corrosion on RC specimens and the corrosion damage was estimated in terms of mass loss of steel bars and average width of surface concrete cracking. Subsequently, pull-out tests were carried out to examine the bonding resistance between steel and concrete. The study indicates the great influence of density of stirrups on the percentage mass loss of the embedded reinforcing bar, accompanied by width of surface concrete cracking, as well as on bond strength between steel and concrete. The results of bond stress–slip curves show that the densification of stirrups plays a significant role in bonding, leading to higher bond strength values and delaying the degradation of bond loss as corrosion damage increases. However, it becomes apparent that, although the densification of stirrups (Φ8/60 mm) result in the full anchorage of steel-reinforcing bars, it may be inappropriate, since it can lead to a substantial increase in costs and a rapid rise in corrosion rate, due to potential increase. Furthermore, the recorded values of relative slip at bond strength are between 1 and 3 mm, regardless of corrosion damage or concrete cracking, which depends on the ribs geometry and crushing of concrete in front of them. To conclude, the results of the present manuscript indicate that the increase in transverse reinforcement (stirrups) percentage plays a key role in the durability of reinforced concrete elements and in bond strength maintenance between rebar and concrete.

Purpose Structures in seismic areas, during their service lifetime, are subjected to numerous seismic loads that certainly affect their structural integrity. The degradation of these structures, to a great extent, depends on the scale of seismic events, the steel mechanical performance on reversal loads and its resistance to corrosion phenomena. The paper aims to discuss these issues. Design/methodology/approach Based on the experimental results of seismic steel behavior S400 (BSt III), which was widely used in the past years, a prediction study of seismic steel behavior was conducted in the current study. This prediction on behavior of both reference and corroded steel was succeeded through a simulation of experimental low cycle fatigue conditions (LCF – strain controlled). Findings At the same time, the present study analyses fatigue factors (ef, a, fSR, ed, ep, R, b) that define their inelastic relation between tension – strain and a prediction model on behavior of both reference and corroded steel rebar, in seismic loads conditions (LCF), is proposed. Originality/value Moreover, this study dealt with the synergy of corrosion factor and the existence of superficial ribs (ribbed and smoothed) in seismic behavior of steel bar S400 (BSt420). The S-N curves that are exported can be resulted in a first attempt of prediction of anti-seismic behavior on reinforced concrete structures with this the same steel class.

As is well known, corrosion of steel reinforcement deteriorates the steel–concrete interface and causes concrete cracking, degrading significantly the bond strength. Several experimental studies have investigated the magnitude of residual bond strength due to corrosion, which affects either the function of corrosion-damaged steel bars or the surface crack width in concrete. As a result, linear and exponential correlation relationships have been proposed in order to predict the bond loss due to corrosion. Based on the results of an ongoing experimental campaign on the degradation of bond strength of RC specimens, combined with comparable outcomes from existing literature, this manuscript summarizes a database, comparing with the recommendations of Model Code 2010, to analyze and interpret the corrosion effect on the bond loss and highlights some points that need improvement in the current regulations. As indicated, the density of transverse reinforcement (stirrups spacing) has intense impact on the resulting bond loss due to corrosion. Hence, in order to quantify this aspect, the present manuscript introduces a discretization of confinement levels of RC elements, depending on the stirrups spacing. Based on this, regression analyses of data were conducted to extract fitting curves of bond loss, taking into account the amount of transverse reinforcement and predictive zones of residual bond strength in relationship to either corrosion penetration or surface crack width. Furthermore, the outcomes demonstrate that the corrosion penetration depth is an appropriate assessment tool to correlate the residual bond strength with the corrosion level, whereas the surface crack width on concrete is not yet an effective index, since there is a plethora of factors affecting the crack width. Due to this, more research is needed to improve the current level of knowledge on the surface crack width and link it with the corrosion damage of the steel bar and the residual bond strength due to corrosion.

In this work, the effects of chloride-induced corrosion on tempcore B400c and B450c steel grades are evaluated, in terms of corrosion resistance and mechanical characteristics, after the performance of Tensile and Low Cycle Fatigue Tests. Both steel categories, characterized by high strength and high ductility, have been used in existing structures, indicating that they demonstrate different performance against the ascribed corrosion environments. B450c steel grade seems to preserve higher energy reserves, ensuring higher expectancy to the corresponding reinforced concrete structures. Additionally, due to buckling and buckling reversal, both steel grades demonstrate limited ductility at 4%. Finally, when cyclically stresses occur, crack nucleation is taking place, at the areas where sulphides, FeS and MnS can be found, leading to sub-surface crack propagation, interacting with external pits.