Romans invented the world’s first concrete mix in the 3rd century BCE by combining water, volcanic dust, aggregate, and gypsum or lime. Two millennia later, concrete has earned its rightful place as a trustworthy structural building material.
On the other hand, Steel’s discovery as a building material isn’t quite as old-it wasn’t widely used in construction until the mid-19th century due to its challenging manufacturing process. In the 1850s, new methods sped up steel production and it quickly gained fame as a strong and durable building material. Over the next 150 years, steel’s popularity has continued to grow, and now, along with concrete, it’s one of the most widely used structural materials.
So, which of these materials is more suitable for your project?
If you are contemplating whether to use concrete or steel as your project’s primary building material, you have several factors to consider. Both are equally worthy structural materials. Concrete costs more, but arguably offers better overall performance. To understand which material suits your project better, you must know how they compare in strength, durability, fire resistance, sustainability, and, of course, cost.
Compressive strength is a material’s capacity to withstand a crushing force. In a building, the compressive strength of slabs, beams, columns and the foundation allows these elements to resist the building’s vertical loads without sustaining damage.
Tensile strength is a material’s resistance to failure when stretched. A beam’s ability to resist vertical loads is an example of tensile strength, as it stops its underside from elongating and cracking when a load is applied on top.
Shear failure is caused by two unaligned forces acting on a building in different directions and typically occurs during an earthquake or due to strong winds. Shear strength is a material’s capacity to resist this type of failure.
Concrete has excellent compressive strength, but is very brittle, and fractures easily under tension. To counter this weakness, reinforcing bars made of a tension-resisting material are embedded into it. These bars are typically steel, although composite options are also available.
In reinforced concrete, the overall strength comes from the concrete’s compressive strength and the tensile strength of steel rebars. Vertical bars running along the length of the structural member are tied with shorter, perpendicular bars called stirrups, these stirrups provide the shear strength.
Steel’s tensile strength is one of its best-selling features, but skillfully designed steel buildings offer equal overall strength to that of their reinforced concrete counterparts. Sound structural design is key to achieving sufficient compressive, tensile, and shear strength in a steel structure.
Durability is the degree to which a material can weather its surroundings. Both reinforced concrete and steel can last a long time without deteriorating if they’re fine-tuned to their settings.
Properly adapted, reinforced concrete endures freeze-thaw cycles, chemicals, seawater, moisture, solar radiation, and abrasion. Because it’s inorganic, concrete doesn’t suffer from vermin attacks. More importantly, it doesn’t burn or melt.
But despite its high durability, reinforced concrete hides a potential flaw - the same corrosion-prone steel reinforcement that makes it stronger. Rusting rebar loses its bond with the surrounding concrete and creates iron oxide, which expands, resulting in tensile stresses and eventual deterioration. Although concrete’s natural alkalinity reduces rebar corrosion, further protection may be needed for reinforced concrete exposed to seawater or large quantities of deicing salt. Epoxy-coated, stainless steel, or composite rebar work well for this purpose.
Structural steel is as susceptible to corrosion as rebar and also requires protection. Paint, powder coating, sacrificial layers, and corrosion inhibiting chemicals are all methods that can eliminate or limit corrosive damage to structural steel.
3. Fire Resistance
Reinforced concrete’s composition makes it essentially inert and thus noncombustible, while its low rate of heat transfer prevents fire from spreading between spaces.
That said, both the concrete and the steel reinforcement can lose their strength once exposed to high temperatures for a long time. Depending on the type of aggregate used, concrete may start to lose its compressive strength at temperatures between 800°F and 1,200°F. Studies show that lightweight concrete has the best resistance to fires thanks to its insulating properties and a poorer rate of heat transfer.
Structural steel is less resistant to fire than reinforced concrete. It begins to lose its strength at temperatures over 550°F and retains only 50% of its room temperature yield strength at 1,100°F. A variety of methods can slow the rate of temperature rise in the structural steel elements of a building. These may include fire-resistive coatings, barriers, cooling systems, concrete encasement, and active measures, such as sprinklers.
Both concrete and steel offer environmental benefits when used in construction. About 85% of all steel used in the world eventually gets recycled. It only makes sense, given the abundance of scrap metal and the easy recycling process. Besides reducing the demand for newly mined resources, steel recycling consumes only a third of the energy to that consumed during steel production.
Concrete also boasts several sustainable features. Most of it originates in relative proximity to the construction site, curtailing the amount of energy needed for shipping. After demolition, it can be recycled to produce gravel, aggregate or paving materials for roadway construction, erosion control, landscaping, oceanic reef restoration, and other tasks. Uncontaminated concrete may be turned into aggregate for new mixes.
Recycling concrete has many environmental benefits. It keeps rubble out of landfills, cuts down construction waste, and replaces gravel and aggregates that would otherwise be mined and shipped.
Reinforced concrete tends to be a costlier alternative to structural steel. The labor and materials involved in placing formwork and rebar, pouring concrete, and ensuring that it cures properly, can comprise a significant chunk of the total costs.
That said, concrete prices are relatively stable. Since 2000, prices for various concrete products have grown steadily with the rate of inflation, and this is an important factor to keep in mind when pricing projects planned for the distant future.
Despite the higher cost, concrete’s strength, durability, and fire resistance don’t go unnoticed by insurance underwriters. Typically, insurance companies give concrete structures higher safety rankings and lower premiums on their policies.
Steel is cheaper than concrete and faster to erect, but comes with a longer lead time. Due to its lower fire resistance, insurance premiums for steel structures tend to be higher.
Steel prices are notoriously volatile, and the last two decades paint a chaotic picture. After peaking in the early months of 2008, they entered a downward spiral with the Great Recession. Ten more years of ups and downs, and steel spiked once more in 2018. Now in a buyer’s market, they are falling but some experts expect them to recover later in the year. Such price fluctuations present a major budgeting challenge and this is likely to continue given the current global economic instability.
Design Everest Can Help
If you’re not sure whether steel or concrete is more suitable for your building, we can help. Our engineers will assess the variables that impact your project and propose a cost-effective solution that’s customized to your design intent. Call us at (877) 892-0292 for a FREE consultation and quote.
- http://by.genie.uottawa.ca/~murat/Chapter 2 - SHEAR DESIGN SP 17 - 09-07.pdf
*Note: The content published above was made in collaboration with members of Design Everest.
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