Why Does Concrete Need Reinforcement?

This article will answer the question “Why does concrete need reinforcement?” and will discuss topics such as the stance of concrete as a building material in terms of compressive and tensile strength. Topics about steel as a reinforcement to concrete, steel’s various forms commonly used in the construction industry, and the other concrete-reinforcing materials will also be covered in this blog post.

 Why Does Concrete Need Reinforcement?

Concrete needs additional reinforcement because plain concrete is weak in terms of tensile stress. Without reinforcements, plain concrete is vulnerable to cracks and collapse because it does not have the capacity to withstand enormous amounts of tensile loading. 

While this is often the case for most concrete projects, it is important to note that not all construction projects require reinforcements. Some projects are simply made on a smaller scale which do not require too much strength and stability for a long period of time. Hence, everything boils down to design requirements wherein questions about structural limits such as maximum allowable stresses are accurately answered.

Compressive and Tensile Strength of Concrete

The strength of building materials like concrete is often measured in terms of their resistance against stresses such as tension and compression, so it is important to understand the difference between the two.

Tensile Strength

Tension or tensile stress refers to the internal force exerted perpendicular to an object divided by its unit area. The direction of tensile stress is always away from the object, so the subject commonly results in an increase in length upon deformation.

Plain concrete is not strong enough to withstand tensile stress. In fact, its tensile strength only accounts for approximately 10-12% of its compressive strength and is low enough to consider it negligible in design perspective. Moreover, it is highly brittle and prone to crack due to the presence of internal voids even after it is completely hardened. Because of this weakness, concrete requires reinforcements from other building materials.

Compressive Strength

Unlike tensile stress, compression or compressive stress is applied towards the object and often results in a deformation by volume reduction. One of the remarkable mechanical properties of concrete is its compressive strength. Its resistance to compression is high enough to be able to withstand high amounts of impact and compaction. The compressive strength of concrete is developed during the curing process which is a chemical reaction that involves the production of calcium silicate minerals. The process generally lasts for a month, but some large-scale projects take longer time to complete. Nonetheless, the strength of all concrete mixture is logarithmically gained over time.

Steel as a Reinforcing Material to Concrete

Steel is an alloy of carbon and iron and is widely known as an effective building material in the construction industry. Besides being universal and relatively economical, steel is often utilized in construction projects because of the following remarkable mechanical properties.

  • Compressive and Tensile Strength
  • Ductility
  • Durability
  • Workability
  • Wear Resistance
  • Weldability

Because concrete is known to be brittle, the application of steel reinforcements in concrete structures provide additional strength and resistance to tensile stresses and gains ductility in its hardened form. One of the advantages of choosing steel as concrete reinforcements is its reaction to thermal stress. Concrete and steel have relatively similar thermal expansion coefficients, resulting in simultaneous expansion and contraction when exposed to thermal stress. 

As mentioned previously, using steel reinforcement is a standard in the construction industry, so it is not a surprise to know that it is available in the market in different forms.

Deformed Steel Bar

Deformed steel bar is the most widely utilized steel reinforcement for concrete. It offers remarkable flexibility and it offers additional advantage in terms of bonding strength between concrete and itself due to the deliberate rib-like deformations on its surface. Some of the common surface patterns of deformed steel bars are crescent, herringbone, and spiral shape which is consistently enveloping the entire length of the material.

Threaded Steel bar

The application of threaded steel bars is practical when dealing with projects that require longer bars while lap slicing of deformed steel bars simply does not work.  As background, lap slicing is a common technique to combine two rebars to create a single yet longer steel bar. Unlike a lap-sliced deformed steel bar, threaded steel bars use couplers to mechanically combine two separate rebar entities.

Welded Wire Fabric

Welded wire fabric reinforcement (WWF), also known as welded wire mesh or weldmesh is a form of concrete reinforcement that is commonly used in concrete slabs. This series of rectangular or square wires are meshed together by welding its intersections together in order to create a stable foundation and resistance against concrete shrinkage and thermal expansion.

Fiber-reinforced Polymer Bars

Fiber-reinforced polymer bars or FRP is one of the alternatives to deformed steel bar reinforcements especially when the structural design requires minimal allowance against corrosion attacks as well as additional protection to state-of-the-art machines and equipment that are directly affected by the presence of metals.

Like steel, FRP is available in various forms such as bars, cables, sheets, and plates which have niche applications in the construction industry. Moreover, FRP has several remarkable properties that qualify and level its stance against other building materials. Like steel, FRP has a comparable thermal expansion coefficient with concrete, is noncorrosive, and nonmagnetic. This implies FRP’s remarkable resistance against thermal and corrosive attacks. Furthermore, its nonmagnetic property paves its way to projects that involve specialized medical equipment like MRI.

However, the downside of using FRP includes its inability to be stretched without breaking due to brittleness and its vulnerability to irreversible damages due to UV radiation.

Fiber-reinforced Concrete

Fiber-reinforced concrete (FRC) is a type of concrete reinforcement that uses heterogenous fiber mixture made of various materials such glass, steel, and both artificial and natural fibers. This reinforcement increases the resistance of concrete against cracks due to shrinkage by improving concrete’s durability.

Among the list of tested applications of fiber-reinforced concrete, its use in the construction of slabs for airport runways, industrial structural, and commercial establishments are most remarkable.

Conclusion

The blog post answered the question “Why does concrete need reinforcement?” It was clearly pointed out that concrete requires additional material for reinforcement to improve its low tensile strength. Steel happens to have a remarkable resistance to tensile stress, so it is highly sought as a reinforcing material to concrete. There are various forms of steel that are used in the construction industry some of which are deformed steel bar, welded wire fabric reinforcement, and threaded steel bar. Deformed steel bar is most utilized in building projects and is capable of offering mechanical bonds between concrete and steel. Other concrete reinforcements tackled in this article include  fiber reinforced polymer bars, and fiber reinforcements.

For any questions and suggestions about this article, please feel free to submit your thoughts in the comment section below.

Frequently Asked Questions (FAQs): Why Does Concrete Need Reinforcement?

Does concrete need reinforcement?

Not all the time. While concrete reinforcements using steel is a standard to large-scale projects such as buildings, walls, and driveway that carry enormous loading, it is definitely not practical to spend for additional building materials for small-scale projects that simply do not require additional protection that steel-reinforcements guarantee.

Will concrete crack without rebar?

 Believe it or not, but concrete does crack with or without reinforcement. But this doesn’t mean that cracks are safe all the time and that rebars are useless anyway. The truth is cracks are manageable to some extent. Having steel reinforcements prevent these cracks from aggravating by increasing the tensile strength of the structure.

What’s the best mix for concrete?

Unfortunately, there’s no “one” best mix for all kinds of structural projects that use concrete as main building material. It really depends on the purpose of the structure. IF it requires higher strength to support enormous loading, the concrete mixture needs to be designed accordingly to support the requirement. Generally, the standard concrete mixture would be on the ratio of 1:2:4 (cement to sand to rock aggregates) while foundational structures require a ratio of 1:3:6 (cement to sand to rock aggregates).

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Can I pour concrete in a hole full of water?

Yes, can may pour a fresh concrete mixture in a hole full of water. It will harden and attain structural integrity over a period of time just like how underwater concrete structures are made. Just be mindful of the movement of water in the hole. When there is active water movement, chances are the cement that binds the materials together will disintegrate from the matrix.

Does adding more cement make concrete stronger?

Adding cement to your concrete mixture could increase the strength of the final structure but only to some extent. You do not add an enormous amount of cement to simply make your concrete stronger, in fact it could compromise the integrity when very large amounts of cement are introduced. The strength of concrete generally depends on the water-to-cement ratio. While large values of water to this ratio implies weaker strength, very small values do not guarantee stronger structure. In simple terms, you have to design your mixture on a right proportion to avoid a very high and very low water-to-cement ratio.

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