September 2018

The Problem with Steel-Reinforced Concrete

by TRP Ready Mix on September 11, 2018

A concrete contractor works diligently along a row of rebar.

…And Why Concrete Contractors and Suppliers Prefer Alternative Reinforced Concrete Materials

A 19-century innovation, steel-reinforced concrete sought to make concrete structures more secure and stable. But as history shows, this approach to reinforced concrete hasn’t stood the test of time like its predecessors.

Concrete structures in Rome stand to this day, close to 2000 years after their creation. By comparison, many concrete highways, bridges, and buildings with steel reinforcement have already begun to crumble.

We know concrete is durable with a long lifespan. So what’s the issue?

The fact of the matter is there are several concerning disadvantages to using steel-reinforced concrete.

If you’re planning to order reinforced concrete from concrete suppliers, first consider the advantages and disadvantages of steel-reinforced concrete. You might also want to consider the alternatives that many concrete contractors prefer!

What Is Steel-Reinforced Concrete Used For?

Steel-reinforced concrete is meant to use the compressive strength of concrete with the tensile strength of steel to carry heavy loads, such as footings, foundation walls, and columns. Driveways with heavy traffic, carport floors, and large shed floors may also require reinforced concrete to support the weight.

Steel reinforcement is embedded in concrete to hold the concrete together, prevent large cracks, and add overall strength. This added strength allows for the creation of longer, thinner, cantilevered structures, and less-supported slabs that are more structurally sound due to the reinforcement.

Types of Reinforced Concrete

Reinforced concrete is often traditional cement concrete poured onto steel reinforcements. These reinforcements include:

Rebar

Rebar is short for reinforcing bar. It is a mild steel bar that comes in various thickness, such as #3 which is 10-mm thick, and #4 which is 12-mm thick. Rebar is often manufactured for better grip, such as ribbed rebar.

Welded Wire Mesh

This is steel wire welded together in a square grid pattern to form a flat sheet. The steel wire thickness is usually 4 mm. And the typical grid size is 150 mm x 150 mm.

Both types of steel reinforcement are used in masonry projects. Typically, rebar goes around the footing while the welded mesh goes into the slab, often creating a cage.

While these are cost-effective options for building with concrete, they are made of steel, so they pose a risk of rusting and causing concrete corrosion.

Advantages of Steel-Reinforced Concrete

The combination of concrete and steel gives reinforced concrete high compressive and tensile strength. As a result, reinforced concrete is considered more durable. It is also fairly fire- and weather-resistant.

Since steel reinforcement can strengthen thinner concrete slabs, so concrete contractors can use less concrete and still have a strong and supported concrete slab. By using less concrete, this saves time and labour costs for supplying, transporting, mixing, and pouring concrete.

Steel is also an affordable material and is cheaper than some of the alternative reinforcement options, such as aluminum bronze and stainless steel.

Disadvantages of Steel Reinforced Concrete

While developers can save on upfront costs with steel reinforcement, they often don’t consider the long-term costs for maintenance, repairs, and replacement.

Steel’s main component, iron, is rust-prone. As a result, corrosion remains a unique disadvantage when using steel reinforced concrete.

This corrosion is difficult to detect in concrete structures. But it destroys the durability of concrete, leading to a shorter lifespan of only 50 to 100 years, with deterioration starting in as little as 10 years. Compared to the ancient concrete structures in Rome, 50 to 100 years is not nearly enough time for modern-day structures to last.

As a result of this shorter lifespan, crumbling buildings, bridges, highways, and other infrastructure are costly to repair. The repair and rebuilding costs of steel reinforced concrete structures will only get worse over time as more structures deteriorate and lose structural integrity.

Why Steel Isn’t the Best Option

The presence of steel reinforcement in concrete makes concrete more prone to cracking. While regular concrete can handle a few tiny cracks, these cracks pave the way (pardon the pun) for a major threat to steel reinforcement—moisture.

When moisture enters concrete through these cracks, it creates an electrochemical reaction with the steel reinforcement embedded in the concrete. This reaction creates a battery, with one end of the rebar becoming an anode while the other end becomes a cathode. This battery powers corrosion, transforming the steel into rust.

Rust has the ability to expand steel up to four times its size. This expansion creates larger cracks and fractures apart concrete in a process called spalling (AKA concrete cancer).

Natural Rebar Alternatives

The concrete industry is always looking for ways to be more environmentally-friendly. One such way of doing so is with these alternatives to steel rebar:

Continuous Basalt Fiber (CBF)

Made from basalt, CBF is a dense, abrasion-resistant igneous rock. This rock fibre is more than double the strength-to-weight ratio of alloyed steel. It won’t corrode like steel and it won’t deteriorate from acids. CBF is also fire-resistant and works well with a variety of composites.

Compared to steel rebar, CBF also reduces the amount of concrete used, making for thinner, lighter concrete that allows for more insulation room. CBF is also not thermally conductive so it can connect to both inner and outer insulated wall panels without transferring heat. This means more energy-efficient buildings due to reduced heat loss.

Woven-Strand Bamboo (WSB)

WSB uses skinned bamboo stalks that are sliced lengthwise into thin strands. These strands are then carbonized, dipped into a water-based adhesive, and either hot- or cold-pressed in moulds. The result is a product that is three times the density of bamboo and is also resistant to absorbing moisture, swelling, and decaying from bacteria and fungi.

Bamboo has high tensile strength, is quickly renewable, and it sequesters carbon, making it an extremely eco-friendly reinforcement alternative to steel rebar.

Fibre-Reinforced Polymer (FRP)

FRP is another alternative to steel rebar that can build energy-efficient concrete structures and won’t corrode. FRP, especially glass FRP provides thermal and electric insulation, has a high strength-to-weight ratio, and has low maintenance costs.

By building reinforced concrete with alternatives that won’t corrode, concrete structures get a longer lifespan. They require less maintenance and fewer resources. They will be able to stand the tests of time like the ancient Roman structures, and they won’t become a costly financial burden for maintenance, repairs, or replacement.