We have been talking about the pros and cons of steel and concrete as a construction material. Let’s get a better understanding on why they work better together. Anyone reading about construction materials would have come across the saying – Concrete is good against compression, but weak in tension whereas steel bars are good in tension, but weak in compression. What a few had inferred from the statement is that, steel is naturally weak in the face of compressive forces, which is not the case. Steel is good in both compression and tension. Steel bars or steel reinforcement bars are weak in the face of compressive force due to their dimensional property. Steel reinforcement bars have an insignificant cross sectional area when compared to the length of the steel bars, and thus the ability to withstand compressive forces are naturally less.
Steel as a reinforcement
What makes steel the perfect reinforcement to concrete?
High Tensile strength of steel reinforcement bars
Steel is a construction material that has undergone a large phase of innovation from steel bars to mild steel to HYSD bars and each innovation contributing to the high tensile strength and higher resistance to corrosion. With the innovation of TMT (Thermo Mechanically Treated) steel bars, a revolution to the limitation presented by reinforcement bars were hence no more. With different TMT grades like Fe 415, Fe 500, Fe 550, Fe 600 & Fe 700 catering to different construction needs and each grade presenting its own unique value in construction, the life expectancy of the buildings was increased. The numbers denote the minimum yield strength of the rebar, and the lower grade reinforcement bars have higher ductile properties, which are essential for withstanding of seismic forces. A major reason why Fe 415 grade is a preffered choice in construction of homes and residential construction whereas the higher grades have been playing the roles in construction of bridges and high rise structures.
Concrete and steel makes the perfect pair
Steel is naturally prone to corrosion, a fact that remains so. A few processes like Fusion bonded epoxy coating and Anti-corrosion treatment were previously mentioned, which drives the point that steel is a naturally corrosive element. The martensite layer in TMT bars act as protection against rusting and delays the onset of rust. It will be interesting to find that concrete do delay the process of corrosion in TMT bars. They act as a protective layer covering up the TMT reinforcement bars from the external environment that accelerates the process of corrosion. Another factor to ad is the similar thermal coefficient of steel bars and concrete, which is a major factor to consider as unequal thermal expansion can cause cracks to develop faster.
Fires are one of the worst disasters for buildings. A major attraction of RCC buildings is that both steel and concrete do not catch fire. The thing about steel is that even though it has tensile strength and ductility, at higher temperatures, the high tensile strength is compromised. However, by using insulating materials,especially with concrete, steel is not directly exposed to the higher temperature of fires and concrete provides a factor of insulation to steel bars. Even in the scenarios of fire, RCC buildings can withstand temperatures as high as 500 degrees Celsius with much loss in structural integrity, which deems RCC buildings safe in scenarios of fire. Even high temperature do rob the load bearing capacity of the structure, but it is interesting to note that such high temperature exposure of TMT cannot be easily achieved in a practical RCC construct, due to the insulation provided by concrete. It also takes hours of fire, in scenarios of fire for the load bearing deterioration to take place.
The verdict shall remain so, that Reinforced Cement Concrete is better choice of construction when compared to cement concrete. Construction field is a field that is in immediate need for making sustainable choices. As per suggestions, increasing life expectancy of the buildings is the way to go, as concrete mix is non recyclable in nature and forms a major part of landfills. Another factor is depleting resources, like sand which pose a threat to construction. Sand is a resource most consumed by man after water as per UN. Sand is a resource that takes time for its formation and unlike steel which is 99% recyclable, it forms a threat of not being able to meet the rising demands. Similarly TMT reinforcement bars with its high tensile strength, has been able to reduce the amount of steel required for reinforcement, also, the TMT steel bars can be manufactured with secondary steel without bringing about any compromise in quality. Also TMT grades like Fe 415 has been a huge contributor to the safety of residential construct in a country like India. So for judicious, safe and sustainable construction, Reinforced Cement Concrete plays a major role.