Reinforcing steel rods, bars or meshes are essential components of a concrete structure, as they absorb tensile, shear, and sometimes compressive stresses. Smooth concrete is not suitable for most structural applications as it does not easily withstand the tensile and shear forces caused by wind, earthquakes, vibrations and other external forces. To demonstrate this, two concrete cylinders were cast from the same batch and tested to see how much load they could take before failing. Under compression, the cylinder broke with a load of approximately 1000 lbs (450 kilos).The low strength of the cylinder was due to the high water content in the mix.
To test its tensile strength, eye bolts were attached to the sample and it was hung from the joists of the store. A bucket filled with gravel was not heavy enough to fail the sample, so a dumbbell was added to push it over the edge. The weight of this cube was only 80 pounds or 36 kilos, that is, less than 10% of the compressive strength. Concrete needs reinforcement because it is weak in terms of tensile stress. Without reinforcements, smooth concrete is vulnerable to cracking and collapse due to its inability to withstand enormous amounts of tensile loads.
Concrete is only strong against compressive forces and has low tensile strength and ductility. Steel is used as reinforcement material because it adheres well to concrete and expands and contracts due to temperature at similar speeds. In many cases, larger concrete jobs that require reinforcing steel also require a building permit of some kind, in which case reinforcing steel requirements will be documented in the plans. Concrete that withstands heavy loads (such as footings, foundation walls and columns) almost always requires reinforcing steel. Rebar is added to concrete, which is known as reinforced concrete. Rebar is very good at withstanding tensile stress and this is why it is used to make reinforced concrete.
Adding rebar to concrete makes its strength more general and decreases the rate at which failure occurs. This gives engineers time to spot a problem before it gets out of hand. A single steel bar offers crucial new ways to cope with stress. It is tempting to think of force as a simple variable and that various materials fall somewhere in a spectrum from strong to weak. The reality, of course, is much more complex. Different materials are strong in specific situations, but weak in others.
To get a really robust material, you have to start mixing and matching. Reinforced concrete is a perfect example. Brutalism, an architectural style that emphasized exposed concrete, was popular from the 1950s to the 1970s. Steel reinforcing bars are often treated before pouring cement to protect it from the elements, although they will soon be enclosed in concrete. When water infiltrates reinforced concrete, it can alter the pH balance of the environment and cause chemical reactions within the concrete. The deformed steel bar is used more in construction projects and is capable of offering mechanical bonds between concrete and steel.
It can withstand compression but stretching movements and side-to-side movements quickly break unsupported concrete. Reinforced concrete is made to last for many years, making it an excellent building material for structures that must last for a long time. These alkalines in water can react with silica in concrete aggregates to form new crystals. Concrete projects such as roads, some driveways, and small shed floors or playhouses generally don't require any steel reinforcement at all. Reinforced concrete did not become a widely used building material until twisted rebar and prestressed concrete were developed in the 1880s. However, when you look at the internal stresses inside the concrete, you will see that when there is compression there is often tension as well. Because reinforced concrete is used in many different situations it is often necessary to build fairly elaborate internal structures from steel reinforcing bars before pouring cement. In an extremely fortuitous coincidence steel and concrete have very similar coefficients of thermal expansion.
It will harden and achieve structural integrity over a period of time as will underwater structures manufactured with this material. Steel is particularly suitable as reinforcement because it adheres well to concrete and expands at the same speed. Concrete always experiences both types of stress in construction and if you place weight on the top of a concrete beam it will hold but deform when it experiences tensile stress. As we have learned flat concrete is only useful in very limited applications because it is strong against compressive forces but weak against stress and shear forces.