It is no longer a secret that superstructures like bridges (or any other concrete structures) use a component called steel rebar (short for reinforcement bar or reinforcing bar). Rebar is often referred to as reinforcing steel or steel reinforcement.
We are talking about a tension device added to concrete to form reinforced concrete and reinforced masonry structures, strengthening and aiding the concrete under tension. Concrete, although strong under compression, has low tensile strength. Rebar typically consists of steel bars, which significantly increase the tensile strength of the structure.
However, rebar has a weakness: if the metal corrodes, it can cause the concrete to fail prematurely. As bridges are exposed to water and salt, they become vulnerable to metal corrosion. About one-third of bridges in the United States need to be repaired or replaced over the next decade due to this reason, potentially costing the administration and industry players nearly USD 400 billion.
According to the American Society of Civil Engineers’ “2025 Report Card,” there are more than 623,000 bridges across the world’s largest economy, with 49.1% in “fair” condition, 44.1% in “good” condition, and 6.8% in “poor” condition.
“Unfortunately, the nation continues to see the number of fair bridges surpassing those in good condition. As bridges in fair condition continue to age—presenting the possibility of being further downgraded—they also exemplify an opportunity, as they can be preserved at a lower cost than bridges in poor condition,” the study remarked.
In this context, a start-up named Allium Engineering has emerged with a manufacturing solution in which regular rebar is covered with a thin layer of stainless steel to extend the intended life of a bridge from 30 to 100 years.
The Vision
According to the American Society of Civil Engineers (ASCE), during the Joe Biden presidency, bridges received a substantial boost through the Infrastructure Investment and Jobs Act (IIJA), including USD 27.5 billion for the Bridge Formula Programme and USD 12.5 billion for the Bridge Investment Programme. Despite this infusion of federal funding, bridge-related system rehabilitation needs are still estimated at USD 191 billion.
Therefore, strategic asset management planning and routine maintenance are crucial to preventing further decline in bridge conditions and avoiding costly repair or rehabilitation work. While extreme weather events pose threats to bridges, innovative techniques are improving their security and resilience.
When it comes to innovative techniques, engineers have several methods for coping with rust, such as coating the rebar with epoxy or pouring extra concrete to delay the seepage of water to the rebar. However, all these measures eventually fail. Allium is proposing its stainless steel-layered rebar as a potential solution.
“It’s too expensive to be used in every bridge,” Steven Jepeal, co-founder and CEO at Allium Engineering. Therefore, cities and states will only adopt it for the most critical spans.
The start-up’s stainless steel-layered rebar was recently used in a bridge deck replacement on US Highway 101 in Mendocino County, California, and another is planned for Interstate 91 in Massachusetts.
In an interview with TechCrunch, Steven Jepeal highlighted that the main challenge with the technology is its cost, which limits its application to all bridges. Currently, the solution will be utilised for maintaining the most critical components of American bridges.
“As long as we’re getting full coverage of the surface, a thin layer is enough stainless steel to resist corrosion for hundreds or thousands of years,” said Samuel McAlpine, co-founder and CTO at Allium.
When maintaining critical bridges with heavy traffic, the standard practice in the United States is to specify stainless steel rebar, which costs about five times more than regular rebar. Governments consider the added costs worthwhile if the solution ensures the bridge’s longevity.
However, for other bridges, stakeholders tend to prefer epoxy-coated rebar, which costs 25% to 50% more than uncoated rebar. Epoxy-coated rebar must be stored in covered spaces, and any welded spots or nicks in the coating need to be patched, adding additional costs.
According to Jepeal, Allium is pitching its stainless-clad rebar as a replacement for epoxy-coated rebar. The company aims to match or even undercut the price of epoxy coating in the future. Once installed, the start-up’s rebar should cost less because it doesn’t require as careful handling. Additionally, it won’t need the extra concrete added to bridges to prevent rusting.
“Eliminating that could reduce cement use by up to 20%. And because the rebar isn’t as susceptible to corrosion, it should allow transportation departments to specify the use of greener cements, which tend to be less alkaline than standard mixes,” McAlpine explained.
Allium’s process coats 7,000-pound billets of steel with a layer of stainless steel, welding wires to the exterior until it’s fully coated. The billet, typically between six to eight inches square and 40 feet long, is then passed through a series of rollers until it reaches the “desired thickness” (ranging from about a third of an inch to a couple of inches in diameter).
“By cladding a smaller surface area with a thicker layer and integrating into the mill’s process, we can do something much cheaper, more scalable, and easier to control in terms of quality,” Jepeal noted.
The Product
Allium’s innovation combats the phenomenon where exposed steel, which, due to factors like oxide (rust) buildup, exposure to water and salt, becomes “lost steel.” This occurs when the metal suffers volume loss due to corrosion, which compromises the integrity of reinforced concrete structures.
Once steel corrodes, it expands and breaks apart with the concrete it’s embedded in, exposing more steel to corrosion and restarting the cycle. Over time, this process can lead to extreme degradation and volume loss of the steel reinforcement in concrete structures, making the structure vulnerable.
Allium’s coating, called “Cladded Steel,” protects the metal from corrosion, thereby increasing the lifespan of steel. The steel core is shielded with a dual layer of thin metal coating (made of stainless steel) and a protective oxide barrier.
The cladding process integrates directly into modern steel mills, producing a durable, bendable, and robust corrosion protection for over 100 years. Allium is currently producing and selling stainless-clad rebar in collaboration with a major US steel mill.
The venture has sold and delivered over 100,000 lbs of stainless-clad rebar for bridge and boatyard construction projects in California and Florida. Besides costing a fraction of alternatives while dramatically reducing maintenance and replacement expenses, the technology is built to endure intensifying storms, freeze-thaw cycles, and coastal conditions in a changing climate.
In line with the “Buy America, Build America Materials and Technology” principle, Allium and its partners are now offering the only stainless-clad rebar product that meets the specifications for the AASHTO M 329M standard.