Gregg Granillo, vice president of fabricator ALTA Rebar, who provided a testimonial about using the product, stated, "Allium exceeded expectations ... our ironworkers found it familiar and easy to use." 

What Is Allium?

Co-founders Steven Jepeal and Sam McAlpine, who both earned doctorates at the Massachusetts Institute of Technology, describe the product as conventional ASTM A615/A706 carbon-steel rebar whose exterior has a thin layer of Type 316 stainless steel, less than 1-mm-thick. The stainless is about 5% by volume diffusion-bonded during the rolling of the steel.

“There’s the regular rebar and the stainless steel on the outside, and microstructurally they’re so well bonded that there’s a region in between where they intermix—something called ‘interdiffusion,’” Jepeal says, adding, “So what you end up with is one piece of steel—no gaps, no breaks, no hard barrier from one to the other.”

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Jepeal described the process of creating the exterior layer of stainless as similar to turning regular carbon steel into a stainless alloy.

The bar meets AASHTO M 329M, the only U.S. specification that defines stainless-bonded reinforcement, according to the company. In ASTM rapid macrocell tests simulating high-chloride conditions, Allium reports a 20-fold drop in corrosion current versus regular carbon steel rebar over 12 weeks. Those results have not yet been independently reviewed.

Allium says its price is significantly below full stainless steel rebar, which can exceed $3/lb. In the long term, Allium believes its price could be lower than epoxy coated rebar, closer to $1/lb. 

The company’s lifecycle analysis for the Caltrans deck, shared with ENR, projects an 87% reduction in deck ownership cost over 75 years—due to savings such as less maintenance cost to replace deck rebar that's worn down by traffic—using publicly available Caltrans and Federal Highway Administration data, the company said. As is standard in the industry, Allium relies on ASTM/AASHTO compliance and owner feedback rather than a specific performance warranty.

After being asked about design implications, McAlpine wrote in an email that “the weight per unit length of stainless-clad rebar is the same as conventional rebar.” 

He said cover can be reduced “in accordance with the AASHTO LRFD” compared with carbon steel or epoxy-coated rebar, and—citing a third-party test—development length "is the same as conventional rebar" because steel–concrete bond strength was within 3% to 4% of carbon steel bar. 

A March 2025 University of Nebraska–Lincoln report found an average bond ratio of 0.96—meaning the stainless‑bonded bar achieved 96% of the pull‑out strength of conventional rebar—and recommended keeping development and splice lengths identical to standard reinforcement.

"We designed it to behave exactly like conventional rebar in the field—same bends, same specs—so engineers aren’t relearning the basics, they’re just gaining corrosion resistance," McAlpine said. He said the rebar can be bent just like carbon steel rebar onsite and doesn't have its protective stainless-sheen-bonded rebar ready-to-install, as must be done with processes such as galvanizing carbon steel rebar with a zinc coating.  

McAlpine argues epoxy-coated rebar is prone to handling damage and cathodic disbondment—the Florida and Virginia departments of transportation have each stopped using it in new highway bridges—and that galvanizing is sacrificial and time-limited. 

“Polymer coatings are easy to damage and can delaminate,” he added. “Our stainless layer is metallurgically bonded, so you don’t get that cathodic disbondment problem.” 

McAlpine cites a lecture by University of California, Berkeley corrosion expert Thomas Devine on the 2008 San Francisco–Oakland Bay Bridge galvanized rod failures as a cautionary tale. According to Devine’s analysis, high‑strength seismic rods were acid‑pickled before galvanizing, trapping hydrogen in the steel and causing embrittlement when workers torqued them. The rods' fractured bolt heads could not be removed, despite the underlying steel remaining intact. 

“This failure taught us that corrosion resistance isn’t just about the coating material but also how it’s applied,” McAlpine said, noting that Allium’s process avoids acid pickling and metallurgically bonds the stainless layer in a single rolling step. 

Many corrosion problems stem from cracking, thin cover or poor detailing—not the base steel many forensic engineers have found in investigations. 

“Cracks allow direct access of oxygen, moisture and chlorides to the rebar surface, and corrosion often starts at or near crack tips,” says Kevin Yuers, vice president of product development at Kryton International, a Vancouver‑based manufacturer of integral crystalline waterproofing admixtures. His sister, Kari Yuers, the firm’s president and CEO, adds that while advanced bars have value, “cost, availability and familiarity limit widespread adoption; lowering concrete permeability can be a more economical way to protect reinforcing steel.”

As an FHWA manual notes, “Early measures included lowering the water-cement ratio and increasing concrete cover over reinforcing bars,” and a 2014 Iowa DOT study found, “No signs of corrosion were observed on the rebars collected from uncracked locations.”

Skeptics also cite century-old examples, such as San Francisco’s 1889 Alvord Lake Bridge, which has stood since 1889 with minimal maintenance. McAlpine says that structure avoided today’s dominant failure mode—chloride-driven expansion of embedded steel in reinforced concrete. 

McAlpine also pointed out that the Alvord Lake Bridge is a pedestrian bridge, rather than a highway bridge, and is not subject to the same stress and fatigue. In particular, fatigue due to vehicular loads is known to drive concrete cracks which accelerate corrosion.”

The most famous example of the longevity of a steel bridge is the Eads Bridge in St. Louis, the world's first steel-truss bridge, completed in 1874. The Eads Bridge’s steel-supported timber upper highway deck was closed in 1991 for extensive repairs after standing for 117 years. It reopened on July 4, 2003, with a new concrete deck unveiled on its 129th anniversary, according to the American Galvanizers Association and went from a railroad bridge to a vehicular traffic bridge.

Allium says it currently produces about 2,000 tons annually of its bonding billets in Massachusetts and is rolling them with U.S. mills to keep a domestic supply chain. Typical lead times are under six weeks for common sizes, Jepeal said. 

The company raised $3.25 million in March 2024 from Propeller, Aera VC. Great Wave Ventures and Anthropocene Ventures to scale production. Target markets include bridge and transit infrastructure, marine and coastal works, pavements and parking structures—places where chloride attack is common—while research and development is exploring rails, structural shapes and piles.

Caltrans has not yet released its project evaluation data. Allium’s corrosion, lifecycle and carbon-reduction numbers, from maintenance no longer required, still lack independent review; and its claim that designers can reduce cover under AASHTO LRFD awaits agency confirmation. Those answers—once they arrive—will show whether stainless-bonded rebar becomes a niche fix or a new default.