WHAT ARE THE DISADVANTAGES OF TMT BARS?

While TMT bars are generally more corrosion-resistant than mild steel due to the formation of a protective oxide layer during quenching, this resistance is not absolute. They remain vulnerable to certain aggressive environments.

• Chloride Attack: Chloride ions are able to attack the protective layer in the coastal areas, and cause pitting corrosion. This localised attack may be great and result in excessive loss of cross-sectional area which reduces structural integrity with time.
• Carbonation-Induced Corrosion: The corrosive nature of the concrete is a characteristic of forming a natural protective coat around these bars. Nonetheless, carbon dioxide in the atmosphere can seep into the concrete over decades and lower the pH of the concrete through a process known as carbonation. As this carbonation front reaches the reinforcing level, the passivating layer begins to break and corrosion then occurs with the availability of water and oxygen. The concrete cover quality is, nevertheless, outstanding, irrespective of the type of bar used.

CHALLENGES WITH WELDING AND HEAT EXPOSURE

The very thermal treatment that gives TMT bars their strength can also be a source of weakness during fabrication.

• Loss of Strength in the Heat-Affected Zone (HAZ): Welding exposes the bars to excessive heat which has the potential of altering their fine microstructure that is elaborate. The hard outer martensitic layer in the HAZ may be tempered and this leads to localised strength and hardness loss. This constitutes a potential weak spot of the reinforcement cage.
• Pre-Requirement of Specialised Techniques and Experts: To alleviate this, welding should be carefully controlled. It usually requires pre-heating, low-hydrogen electrodes, and careful heat input regulation. This requires skilled labour and it makes the welding process more complex and expensive. Welding with a wrong method may result in embrittlement and cracking of the metal which is a serious safety hazard.

QUALITY CONTROL AND COUNTERFEITING ISSUES

TMT bars performance entirely depends on the constancy and integrity of the manufacturing process. This dependency also poses serious problems in the supply chain.

• Unpredictable Production Systems: All manufacturers do not comply with the high-quality requirements that are required. The absence of uniform mechanical properties in bars such as low yield strength or bad elongation may be caused by a variation in either the temperature of the hot-rolled steel, quenching parameters or tempering.
  The bars of TMT have been in demand and consequently, the market has been flooded with imitated products and quality bars. They may be under-sized, made of scrap of bad quality or be unsuitable in terms of chemical composition. These counterfeits can only be ascertained by on site testing which cannot always be done.
• Economic and Cost consideration
  TMT bars are a great value, but their economic profile does not lack its negative aspects.
• Increased Starting Cost: TMT bars tend to be more costly than plain mild steel (MS) bars because of the complicated thermo-mechanical treatment. This initial cost is a put-off to small-scale or low-budget projects where the maximum strength does not need to be high.
• Cost of Corrosion Protection in Aggressive Environments In extremely corrosive environments such as marine or industrial ones, the natural corrosion resistance of standard TMT bars might not be very high. This will require further protective actions like epoxy coating, galvanising or using stainless-steel coating all which are very costly to the overall material of the project.

CONCLUSION

To conclude, the TMT bars are a major breakthrough in the reinforcement technology, although they are not an ideal material. Their downsides, that include not only certain corrosion susceptibilities and welding intricacies but also such severe concerns as quality management and economic considerations, need to be taken into account in any project.