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In my 15 years of experience careers many people discuss on rust of reinforcing bars is a common question asked by both design and construction professionals, and fielded by the regional and many contractors companies. The questions usually focus on bond and development length concerns, and whether the corrosion mechanism will continue once the reinforcing bars are embedded in the concrete. In addition to rust, other common concerns are the presence of mill scale or other surface contaminants on the bars before the concrete is placed. Typical surface contaminants usually include in the form of oils, fuel spills, dirt sticking to wet bars, etc. To clear the overall doubts for these problems, I have prepared this detailed Technical case study papers concepts by considering all angle points for detailed and Technical clarification by IS/ACI/ASTM Codes and specifications. In reinforced concrete construction, bond between the concrete and reinforcing steel plays a critical role. Bond, either through adhesion/cohesion or mechanical interlock, provides for the transfer of stresses from concrete to steel, producing composite action with materials that have markedly different mechanical properties. There can be contaminants on the reinforcing bar surface, which are commonly assumed to impede the bond. If the bond becomes compromised, the ultimate behaviour and serviceability characteristics of reinforced concrete structure can be altered. Rust on reinforcing steel is not necessarily a bad condition. Present specification requirements contain very conservative language, essentially mandating cleaning of the reinforcing steel; this is not fully supported by the research evidence. In spite of these known facts, most engineers and inspectors alike take a conservative approach by requiring the removal of such materials from reinforcing bar. Rust can enhance the bond characteristics of the bar to the surrounding concrete. Obviously, loose material should be removed from the bar. Tightly adhering rust or mill scale is permissible, and will not be detrimental to bond. Generally accepted construction quality control measures require the removal of deleterious contaminants due to the concern for a reduction in bond capacity. Figure 1 illustrates a common example of rust on the reinforcing bars in a fabricated column cage. The corresponding construction activity required to clean the reinforcing bar has significant time and expense implications. This technical note explores, in-depth, a common issue of rust and mill scale on steel reinforcing bars at the time of concrete placement, and how much rust is tolerable before it becomes detrimental to the proper performance of the bar when embedded in concrete.
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