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Reinforcement Bars, Recycled Steel, Concrete, Development Length, Yield Stree.

Reinforcing concrete with steel introduces a component of ductility that is impossible to attain in concrete alone due to its inherently fragile nature. This presupposes that there is such bonding between the two materials that at the moment of failure of concrete, steel holds onto the concrete and simultaneously yields to facilitate an overall ductile deformation. The tendency for steel bars to possess excessive strength makes it impossible for timely permanent deformation to occur, leading to failure in concrete long before the steel reinforcement yields. Steel bars normally have a yield stress range around which the concrete-steel composite is designed. Due to the unpredictable nature of recycled steel composition however, the resulting steel bar strength values are hard to guarantee even in the same production batch. In this paper, the tendency for steel bars to have higher than predicted yield stress levels is studied using a statistical-probabilistic approach. The batch of 72 recycled steel bars subjected to monotonic loading to failure and spark spectroscopy in this study shows a normal distribution of steel yield stresses. The cumulative distribution function P(X ≥ χ) was subsequently evaluated for 550Mpa. Over 20% of the samples were found to be above the 550Mpa design value and therefore the development length, which is directly proportional to the steel bar yield ends up with the same probability stretch. Direct proportionality between the growing yield values and the boron content has also been graphically demonstrated.