Concrete vs Steel: What You Need to Know
In the 3rd century BCE, the combination of water with volcanic dust, aggregate, gypsum, or lime by the Romans, made the first-ever concrete mix in history. Fast forward two millenniums later, concrete is a leading construction material in the building industry.
On the other hand, steel’s use as a construction material was not until the mid-19th century. Not because of its unavailability, but mainly because it was difficult to manufacture. However, in the 1850s which was kind of a steel era, new manufacturing methods were developed causing the rise of steel as a strong and reliable building material. Over the next hundreds of years, the use of steel and concrete continued to grow, becoming the most popular construction materials.
Concrete vs Steel
It isn’t fair to say one is better than the other. However, there are similarities and differences between the two. If you find yourself at a crossroad of concrete and steel, there are several factors you need to consider. First of all, both materials are reliable. Steel costs significantly less than concrete, but concrete offers better overall performance.
To help you decide which material is better for your project, you need to know how they compare in significant properties such as strength, durability, and so on. So, without further ado, let’s dive right in.
Building materials are acted upon by various forces, one of which is the crushing force. A material’s ability to withstand this force is the compressive strength of the material. In a complete structure, the compressive strength of various building elements (slabs, beams, and foundation), gives the structure the ability to withstand vertical loads.
Another material strength property is tensile strength. This refers to a material’s ability to withstand tension forces. For example, the underside of a beam does not elongate or crack when acted upon by vertical load.
The ability of a material to resist shear in the presence of two opposite and unaligned forces is the shear strength of the material. This type of force typically occurs when a building faces lateral loads (winds and earthquakes). In other words, the shear strength of a material is its ability to resist lateral loads.
The compressive strength of concrete is excellent. Sadly, the same cannot be said for its brittleness – it fractures easily under tension. But there are measures to counter this weakness. Embedding bars made of tension resisting materials (mainly steel) into concrete, to form reinforced concrete, will do the trick.
Reinforced concrete has good shear strength. This is mainly due to the fact that, along the length of the structural members, vertical steel bars are tied with stirrups (short perpendicular bars). Stirrups are responsible for its shear strength.
You might ask, why reinforce concrete, when you can make use of steel? Well, steel’s tensile strength is its most important feature, in becoming a useful construction material. But its compressive strength is not as high as concrete. However, with the development of technology, well-designed steel structures can offer the same overall strength as reinforced concrete.
Durability is a material’s ability to stand the test of its surroundings and time. Both concrete and steel are very durable, but only if designed properly. In this case, reinforced concrete can withstand the following;
- Freeze-thaw cycles
- Solar radiation
- Vermin attacks
But despite being able to endure all these, reinforced concrete has something that can compromise its durability. You may have guessed right, the steel reinforcement that gives it tensile and shear strength. But how? Let me explain in these easy to understand steps;
- Steel is susceptible to corrosion, so the bars in the reinforced concrete can rust when exposed to moisture.
- When the bars rust, it releases itself from the bond of its surrounding concrete.
- The rusting process creates iron oxide
- This oxide could result in tensile stresses, which can eventually lead to concrete failing.
Concrete is naturally alkaline, therefore, can inhibit rebar corrosion. However, that might not just cut it, and extra measures may be necessary. Epoxy-coated, stainless steel, or composite rebar will do the trick.
Structural steel is equally prone to corrosion. To mitigate this, paint, powder coating, sacrificial layers, and corrosion inhibiting chemicals are reliable methods.
The inert nature of reinforced concrete makes it incombustible. Also, concrete has a low rate of heat transfer, preventing the spread of fire. However, when exposed to long-lasting high temperatures, both concrete, and steel, can lose their strength.
Depending on the aggregate composition of concrete, high temperatures between 800°F and 1,200°F might cause concrete to lose its strength. According to research, lightweight concrete has better fire resistance, when compared to the others. This is because of better insulating properties and a lower heat transfer rate.
On the other hand, structural steel begins to lose its strength from a temperature of 550°F. At 1,100°F, it loses 50% of its room temperature yield strength. However, there are measures that can increase the fire-resistant property of structural steel. Some of which include;
- Fire-resistive coatings
- Cooling systems
- Concrete encasement
- Active measures, such as sprinklers.
In terms of sustainability, both concrete and steel are good construction materials. The recycling process of steel is significantly easy, and that’s why 85% of the steel used in the world is recycled. This makes steel a sustainable material in the sense that recycling reduces the need for steel production. And the energy used in recycling steel is significantly lower than that needed for steel production.
Likewise, concrete has sustainable features. It can be recycled to produce materials for the following;
- Aggregate materials
- Paving materials
- Erosion control materials
Additionally, a demolished concrete can be used for landscaping, oceanic reef restoration, and much more. Also, if the concrete is not contaminated, it can be reused as new mixes for new concrete.