With the rise in technological advancements, the process of constructing homes and other commercial structures has been more innovated. By innovation, we mean that introduce stronger, more efficient tools and scenarios for constructing homes. We all know that steel is the primary component used for reinforcement in constructing buildings. When we look historically, different innovations of steel as reinforcement have greatly improved the overall strength and life of the building structure. The current iteration of steel reinforcement is Thermo Mechanically Treated or TMT steel rebars.
Many people have doubts about these steel bars. Most people think it is a brand of steel, Well, it is not. TMT is the name of the process by which these particular reinforced steel bars are produced. Moving on, we will how these reinforced bars are manufactured and what are the steps involved in its creation.
Why TMT bars
The thing about reinforcement is that it should provide the desired tensile strength that the concrete lacks in. The TMT steel bars are known for their excellent tensile strength and ductility. Manufactured using a unique three-stage called the Quenching & Self Tempering (QST) process, the TMT bars is the de facto standard for reinforcing concrete structures.
How is it Manufactured
The process of steelmaking and its types have been described in my previous blogs. You can check about them here. The TMT steel is manufactured, unlike any other steel until the hot rolling stage. Beyond that, the TMT steel bars undergo the QST process, which is a three-stage process that is:
Quenching: This is the 1st stage in the QST process. This stage begins right after the bar exits the mill stand. Here the hot rolled rebar undergo rapid cooling by a series of water jets at differently controlled pressures at different points. This process results in surface hardening and is converted into a “martensite” layer whereas the soft and hot inner core remains Austenitic.
Self-Tempering: The second stage in the QST process. In this stage, the residual heat is transferred from the core to the outer layer, further tempering the martensite layer i.e makes the bar harder. Since this process is done by the heat left in the core, this stage got its name.
Annealing: The bars, now at a uniform temperature, are then left to cool naturally in still air to ambient temperature At this stage, the residual austenite is transformed to a refined, tough and ductile ferrite and pearlite core which determines the ductility of the bars
All these stages are achieved without the addition of costly alloying elements which makes the TMT steel economically efficient to produce combined with the right balance of strength and ductility ratio, this makes TMT bars the most preferred bars for reinforcement. When choosing the reinforced bars always make sure to prefer the right grades as the TMT steel bars are categorized by different grades which are based on their tensile strength. They are Fe 415, Fe 500, Fe 550 and Fe 600.
The numbers denote the yield strength of the rebars. However, the higher tensile strength of the bar is achieved by compromising ductility ratio. In layman’s term, higher the tensile strength or grades, less ductile the reinforced bars become. For the construction of homes, Fe 415 grade TMT steel is the most preferred reinforced bar. Fe 415 is preferred because it is the only TMT steel bar in which has sufficient tensile strength and uncompromised ductility ratio.