One of the biggest and most surprising threats to modern concrete is rust.
Most concrete structures rely on steel rebar for strength, but once that steel begins to corrode, the surrounding concrete can weaken and fail long before its expected lifespan. Bridges, constantly exposed to moisture and road salt, are especially at risk.
In fact, nearly one-third of all bridges in the United States are in need of repair or replacement — a massive effort that could cost close to $400 billion over the next decade.
Engineers have long tried to slow the spread of corrosion through solutions like epoxy-coated rebar or extra layers of concrete. But these measures only delay the inevitable. The most effective — yet most expensive — option is stainless steel rebar, which is resistant to rust but costs far more than standard steel.
“It’s simply too expensive to use stainless steel in every bridge,” explained Steven Jepeal, co-founder and CEO of Allium Engineering, in an interview with News media. “That’s why cities and states only use it for their most critical infrastructure.”
Allium’s breakthrough aims to offer a middle ground. The company coats traditional steel rebar with an ultra-thin layer of stainless steel, significantly extending a bridge’s expected lifespan — from roughly 30 years to as long as 100 years.
“As long as the entire surface is covered, that thin stainless layer can resist corrosion for hundreds or even thousands of years,” said Samuel McAlpine, Allium’s co-founder and CTO.
The company’s stainless steel–layered rebar has already been deployed in several real-world projects, including a bridge deck replacement on U.S. Highway 101 in California’s Mendocino County and an upcoming Interstate 91 project in Massachusetts. Allium also supplied material for a commercial boatyard in Key West, Florida, the startup told News media.
With its innovative approach, Allium Engineering could dramatically reduce maintenance costs — and help build bridges designed to stand strong for generations.
Allium’s stainless-clad rebar aims to make stronger, greener, and more affordable bridges
For critical bridges that handle heavy traffic, engineers often specify stainless steel rebar, despite its high price tag — roughly five times more expensive than standard steel. Governments usually justify the added expense by pointing out that avoiding frequent shutdowns of major routes ultimately saves time and money.
For the majority of bridges, however, agencies turn to epoxy-coated rebar, which is around 25–50% more expensive than uncoated steel. Yet this option also comes with hidden costs: epoxy-coated rebar must be stored in covered facilities, and any scratches or weld points in the coating must be patched by hand before installation — a labor-intensive process that drives costs higher.
Allium Engineering believes it has found a better balance. The startup is pitching its stainless-clad rebar as a direct replacement for epoxy-coated steel, aiming to match or even beat its price in the near future. CEO Steven Jepeal told News Media that Allium’s rebar could actually cost less to install, since it doesn’t require the same careful handling or added concrete layers often used to protect against corrosion.
“This extra layer of concrete isn’t structural,” Jepeal explained. “It’s just there to insulate the rebar and delay the salt from reaching it.” By eliminating that additional material, cement use could drop by up to 20%, reducing both cost and carbon footprint.
CTO Samuel McAlpine added that because Allium’s rebar is more resistant to rust, transportation departments could use greener, lower-alkaline cement mixes, which are typically less compatible with conventional steel.
Allium’s production process involves cladding 7,000-pound billets of steel with a thin stainless-steel shell, effectively welding fine wires around the exterior until it’s fully coated. Each billet — typically six to eight inches square and up to 40 feet long — is then rolled repeatedly until it reaches the desired thickness, ranging from a third of an inch to a few inches in diameter.
“By cladding a smaller surface area with a thicker layer and integrating the process directly into the steel mills, we can achieve something cheaper, more scalable, and easier to control, ” Jepeal said.
As the billet is stretched — up to 150 times its original length — the stainless steel layer expands proportionally, maintaining consistent coverage. Each finished piece of rebar ends up with a 0.2 mm stainless coating, which, according to McAlpine, provides near-permanent protection:
“You’re not going to corrode through that stainless steel in concrete — basically ever,” McAlpine said.
Social Plugin