Stainless Steel Bridges: A Startup's Innovative Solution

The Unexpected Threat to Concrete Infrastructure: Corrosion

A surprising factor contributing to the deterioration of modern concrete structures is the presence of rust.

Steel rebar is commonly embedded within concrete to enhance its strength. However, when this metal undergoes corrosion, it can lead to premature structural failure. Bridges, particularly those exposed to water and de-icing salts, are especially vulnerable to this issue.

The Scale of the Problem

Approximately one-third of bridges in the United States require repair or replacement, representing a potential cost of nearly $400 billion over the coming decade.

Engineers currently employ various methods to combat rust, including applying epoxy coatings to the rebar and increasing the concrete cover. However, these solutions are ultimately temporary.

The Stainless Steel Solution – And Its Limitations

The most effective way to prevent problematic rust is to utilize stainless steel rebar. Unfortunately, its high cost restricts its use to only the most critical infrastructure projects.

Steven Jepeal, CEO of Allium Engineering, explained to TechCrunch that widespread implementation is financially prohibitive.

Allium Engineering’s Innovative Approach

Allium Engineering proposes a novel solution: coating conventional rebar with a thin layer of stainless steel. This aims to extend a bridge’s lifespan from the typical 30 years to a century or more.

According to Samuel McAlpine, CTO of Allium, complete surface coverage with even a thin stainless steel layer provides sufficient corrosion resistance for hundreds, even thousands, of years.

Real-World Applications

Allium’s stainless steel-layered rebar has recently been implemented in a bridge deck replacement project on U.S. Highway 101 in Mendocino County, California.

Another project is planned for Interstate 91 in Massachusetts, and the technology was also utilized in a commercial boat yard in Key West, Florida, as exclusively reported to TechCrunch.

Cost Considerations

Stainless steel rebar, while effective, costs roughly five times more than standard rebar. This expense is often justified for critical bridges where closures would severely disrupt traffic flow.

Epoxy-coated rebar, a more common alternative, adds only 25% to 50% to the cost of uncoated rebar. However, it requires careful storage and meticulous patching of any coating damage, adding indirect expenses.

Allium’s Competitive Advantage

Allium aims to position its stainless-clad rebar as a direct substitute for epoxy-coated rebar, potentially even undercutting its price.

Jepeal notes that Allium’s rebar requires less careful handling during installation, leading to lower overall costs. Furthermore, it eliminates the need for additional concrete often used to delay rust formation.

Reducing Concrete Usage and Promoting Sustainability

This additional concrete is not structurally necessary; it merely serves as insulation against salt penetration. Eliminating it could reduce cement usage by up to 20%.

Moreover, the increased corrosion resistance allows transportation departments to utilize greener cement formulations, which tend to be less alkaline than conventional mixes, as McAlpine points out.

The Manufacturing Process

Allium’s process involves cladding 7,000-pound steel billets with stainless steel. This is achieved by welding wires to the exterior until fully coated.

The billet, typically six to eight inches square and 40 feet long, is then passed through rollers to achieve the desired thickness, ranging from approximately a third of an inch to a couple of inches in diameter.

Scalability and Cost-Effectiveness

“By cladding a smaller surface area with a thicker layer and integrating into the mills process, we can do something that’s a lot cheaper, a lot more scalable, a lot easier to control the quality of,” Jepeal stated.

As the billet is thinned, it expands in length up to 150 times, and the stainless steel layer grows proportionally.