TMT bars and Rust Part 1

Fe415-TMT-grade-rebar-rust-corrosion-proof

Steel has been used for many decades by many civilizations for building structural and engineering purposes, they have continued prove very effective in both land and marine environments due their unique combination of mechanical properties which gives them natural protection against natural variables. Where steel stumbles as the ultimate building block is with its corrosion by various environmental actions. When it comes to modern construction, generally, the concrete mix is reinforced by steel bars in the case of the common RCC structures.

Before the advent of TMT bars, conventional hot rolled and normalized mild steel bars have been used for reinforcing concrete structures which came with more downsides than upsides other than the fact it was cheap, but ultimately proved costly in the long run. In the case of India, corrosion is due many reasons such as higher level of residual stress, environment which actually aids corrosion such as high humidity, this responsible for higher
corrosion rate in India. The effect of rust goes beyond the brown eye sore which we have grown accustomed to, India spends more money on fighting rust than on education.

How Corrosion happens on Steel Bars

It is clear that sea water caused higher corrosion rate for all steel bars. Many investigators
mentioned chloride ion to be a very powerful agent for corrosion of iron based alloys. In the case of sea water the higher corrosion rate was arguably due to the availability of chloride ions in it. Concerning corrosion rate, the most important observation is that high strength steel bars for both groups corroded in a significantly slower rates than that of the corresponding low strength conventional steel bars. Some practicing designers show reluctant in using HS TMT steel bars as they believe these steel bars to be more corrosion sensitive in RCC structures. From this study, it has been clearly revealed that high strength is not the only parameter to control the corrosion sensitivity of steel bars. There are many other important parameters; the grain size of the steel bars as well as alloying elements that also influence the corrosion rate significantly. it is very clear that the surface microstructures of TMT steel bars are significantly finer than that of the corresponding LS HR grade steel

TMT Bars and Corrosion

Although, it is thought by many users as well as designers that the corrosion rate of high strength thermo mechanically treated (TMT) steel bars are much higher than that of low strength conventional hot rolled (HR) steel bars of similar chemical compositions, no such evidence has been found in this research work. Finer tempered martensites or ferrite-pearlite grain sizes and presence of small amount of alloying elements rather, than the strength levels of the steel bars, have been found to be more effective to reduce the corrosion rates either in normal water or sea water medium. So, TMT steel bars containing sufficient amount of corrosion reducing as well as grain refining alloying elements such as copper, chromium and nickel are more suitable for uses in the coastal as well as industrial areas where corrosion of steel bars in RCC is a great concern.

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3 Comments

  1. Thanks for sharing this article.You have very nicely explained it in a detailed manner.Keep posting such article.

  2. Some quantity of 10mm tmt500 steel is lying for almost a year and it has got rusted to a minor extent. Can we use it or should this be rejected. It has been lying in open in the rainy season. Please let me know whether it can be used or not.

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