Abstract
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.
Highlights
In Reinforced Concrete (RC) elements, the bond mechanism between steel bars and the surrounding concrete plays the key role, in order to ensure that steel reinforcement and concrete react as one material and the tensile forces are safely transferred from steel to concrete
The experimental procedure consists of four main phases: Phase I, the casting and curing of specimens with different amounts of transverse reinforcement; Phase II, the accelerated corrosion of specimens in laboratory for different exposure times in order to achieve different corrosion levels and measure the range of surface cracking on concrete; Phase III, pull-out tests, carried out in order to investigate the bond behavior; Phase IV, the breaking of specimens in order to assess the corrosion damage of reinforcement and correlate it with the pull-out results
Results and Discussion slip values corresponding to the maximum pull-out load, smax, were recorded
Summary
In Reinforced Concrete (RC) elements, the bond mechanism between steel bars and the surrounding concrete plays the key role, in order to ensure that steel reinforcement and concrete react as one material and the tensile forces are safely transferred from steel to concrete. Due to its high bearing capacity and ductility, compared to the low production costs, reinforced concrete is one of the most widely used construction materials in the existing building stock. The corrosion of steel reinforcement consists of the main durability problem of RC structures, affecting their appearance and their mechanical performance and structural integrity. Metals 2020, 10, 1327; doi:10.3390/met10101327 www.mdpi.com/journal/metals as chloride ions, are penetrated and diffused in concrete through its pores, destroying the abovementioned protection mechanisms (initiation stage of corrosion). When the chloride concentration reaches a critical value, it is considered that the passive layers of the reinforcement are demolished, and the electrochemical process of corrosion initiates (corrosion onset) [3,4].
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