One startup’s paper-thin stainless steel could change how bridges are built

Summary

The scourge of modern concrete is, perhaps surprisingly, rust. Most concrete structures are laced with steel rebar to add strength, but if the metal corrodes, it can cause the concrete to fail prematurely. Bridges, which are exposed to water and salt, are some of the most vulnerable. About one third of bridges in the United States need to be repaired or replaced, which could cost nearly $400 billion over the next decade. There are plenty of ways engineers cope with rust, from coating the rebar with epoxy to pouring extra concrete to buy some time before seeping water reaches the rebar. Eventually these measures fail, too. The only way to truly prevent problematic rust is to use stainless steel rebar, which isn’t cheap. “It’s too expensive to be used in every bridge,” Steven Jepeal, co-founder and CEO at Allium Engineering, told TechCrunch. So cities and states will only turn to it for the most critical spans. But Allium is proposing a compromise, of sorts, by covering regular rebar with a thin layer of stainless steel to prolong the intended life of a bridge from 30 to 100 years. “As long as we’re getting full coverage of the surface, a thin layer is enough stainless steel to where it’s going to resist corrosion for hundreds or thousands of years,” said Samuel McAlpine, co-founder and CTO at Allium. The startup’s stainless steel-layered rebar was recently used in several bridge deck replacements, including one on Interstate 91 in Massachusetts and another on U.S. Highway 101 in Mendocino County, California. It also contributed to a commercial boat yard in Key West, Florida, Allium exclusively told TechCrunch. Techcrunch event San Francisco | October 27-29, 2025 For critical bridges that carry lots of traffic, engineers sometimes specify stainless steel, which costs around five times more than regular rebar. Governments consider the added costs are worth it if they don’t have to shut down a major artery. But for most other bridges, they tend to specify epoxy-coated r...