Know the Reasons Why Threaded Steel Bar used in Concrete Reinforcement
We know that concrete is quite good in compression while steel is great in tension. Steel is also good in compression but due to its high strength, the cross section generally becomes small and the smaller the cross section more are the chances of buckling, while on the other hand concrete has low strength so we require larger cross sections and in doing so we overcome the buckling effects.
The fact which makes it possible to combine concrete and steel is that concrete contracts on setting in the air and if a threaded bar is embedded in a mass of wet concrete, it will be found that there is some amount of considerable force that is required to pull out when the concrete is set.if the steel section is in the form of a plate. When concrete is set, it will resist removal, yet it can be knocked off by sharp blows.
The concrete grips are still in first case while in the second it only adheres. The thing is, grip depends upon the strength of concrete used in the work as well as the perfection with which the concrete has been placed in a position, mixed, compacted and cured. It also depends upon the condition of the surface of the rod (whether it is smooth or rough).
Picture courtesy-Basalt rebar
Steel reinforcement bars are generally categorized into two reinforcement - primary and secondary reinforcement as given below. However there are also other minor uses.
Primary reinforcement : It refers to the steel which is employed to guarantee the resistance needed by the structure as a whole to support the design loads.
Secondary reinforcement : It also refers to distribution or thermal reinforcement and is employed for durability and aesthetic reasons, by providing enough localized resistance to limit cracking .
Threaded rebar is also employed to confer resistance to concentrated loads by providing enough localized resistance and stiffness for a load to spread through a wider area.
Steel rebars can also be used to hold other steel bars in the correct position to accommodate their loads.
Importance of concrete reinforcement in threaded bar
1) The coefficient of thermal expansion of concrete is almost similar to that of steel, due to differences in thermal expansion or contraction, large internal stresses are eliminated
2) In concrete conforms, cement sticks to the surface of steel after it gets hardened, permitting any stress to be transmitted efficiently between the two materials.Therefore, threaded steel bar are roughened or corrugated to further improve the cohesion or bond between the steel and concrete..
3) In the hardened cement paste, alkali chemical reaction forms a passivating layer on the steel surface to make it much resistant to corrosion.
For optimum results, reinforcement needs to have the following properties-
• Bond with concrete
• High relative strength
• Ductility
• Resistance against corrosion.