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 Join 10k+ tech and VC leaders for growth and connections at Disrupt 2025 Netflix, Box, a16z, ElevenLabs, Wayve, Hugging Face, Elad Gil, Vinod Khosla — just some of the 250+ heavy hitters leading 200+ sessions designed to deliver the insights that fuel startup growth and sharpen your edge. Don’t miss the 20th anniversary of TechCrunch, and a chance to learn from the top voices in tech. Grab your ticket before doors open to save up to $444. Join 10k+ tech and VC leaders for growth and connections at Disrupt 2025 Netflix, Box, a16z, ElevenLabs, Wayve, Hugging Face, Elad Gil, Vinod Khosla — just some of the 250+ heavy hitters leading 200+ sessions designed to deliver the insights that fuel startup growth and sharpen your edge. Don’t miss a chance to learn from the top voices in tech. Grab your ticket before doors open to save up to $444. San Francisco | REGISTER NOW
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 rebar, which is only about 25% to 50% more than uncoated rebar. Epoxy-coated rebar needs to be housed in covered storage, and any welded spots or nicks in the coating need to be patched, both of which add additional indirect costs.
... continue reading