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Comment by dustfinger | Hacker News Reader

I wonder if it would be feasible to replace the steel reinforcement rods with ceramic? No iron no rust.

I also wonder if concrete might bond better with ceramic. My understanding is that concrete does not bond well with steel.

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It'd be a material engineering feat to get the required plasticity and tensile strength out of ceramics. The plasticity is probably more worrying in practice - the failure mode of rebar rusting is usually visible to inspection and slow enough that action can be taken to ensure that the structure remains safe. The failure mode of a brittle reinforcing member suddenly failing is much more worrying from a safety perspective.

In structural engineering we call this plasticity "ductility", but you're exactly right. We want ductile failures not sudden brittle ones, and that can only be achieved with yielding reinforcing. Ceramics generally will fail brittly, or cause the concrete to crush if the member is over-reinforced.

> the failure mode of rebar rusting is usually visible to inspection and slow enough that action can be taken to ensure that the structure remains safe. The failure mode of a brittle reinforcing member suddenly failing is much more worrying from a safety perspective.

That is an excellent point!

Basalt rebar, which is basically like epoxy fiberglass as used in boats, wind generator blades, etc. except basalt fibers and just really long. However, it can't be bent so you have to make joins at every corner and have to order all bent pieces ahead of time.

Lots of different materials and techniques have been tried, but nothing so far seems to have really stuck. As an observer I think there are two main factors:

1) The types of steel used coincidentally have nearly identical coefficients of thermal expansion as the concrete used.

2) Everybody in the construction industry and the entire supply chain is familiar with and habituated to steel rebar. The inertia is tremendous.

That's a very high bar to meet to gain a foothold with new materials or new techniques as the entire system has evolved to fit the pros and cons of steel rebar. Anything that departs from standard practice becomes very costly, very quickly, for a gazillion reasons.

I never considered the potential social side to this problem. Thank you for commenting.

I think concrete bonds with steel just fine. Problem is when it rusts or is exposed to chloride the steel corrodes which expands and cracks the concrete.

I think massive reinforced concrete sections that are kept dry are stable long term.

Some work is being done to find alternatives. Difficult because you need high tensile strength and toughness. And the alkaline environment will wreck other materials. I think ordinary fiber glass turns to gel over time.

A lot of reinforcing bar is coated with epoxy. But I think that's not working out very well in practice. Any nick in the coating directs the corrosion to that point.

Whole thing is an open problem

Stainless steel seems to be working well, though much too expensive for most projects. Maybe part of the problem is that because stainless steel is a proven alternative where it matters, it's hard for other alternatives to break into the market, either at the low-end where there's zero chance your crews are going to apply the new procedures properly, or at the high-end where conservatism and greater access to cash make stainless viable.

If corrosion of rebar is limiting the lifespan of concrete structures then using a resistant rebar could increase the lifespan of a building enormously. Modern buildings could last multiple centuries instead of starting to crumble at 80 years.

It looks like some effort was made in 2010 to coat the reinforcing steel with a porcelain enamel [1]. I believe the enamel's primary function was to provide a bond with the encasing concrete. Naturally, it would also help to protect the steel from water and oxygen.

There must be a reason why ceramic cannot fully replace steel. Cost perhaps.

Maybe these technologies would be better combined.

[1] https://www.ceramicindustry.com/articles/90943-improving-ste...

A big part of the problem with coated steel rebar is that rebar is treated very roughly on construction sites, and any nick or failure of the coating is really bad news when the chemical isolation provided by the concrete fails. Instead of the corrosion happening relatively uniformly at a slow rate across the entire length of the reinforcing bar, it'll happen at a few select sites at a significantly higher rate.

What about using plastic or some flexibly epoxy. Would it have some adverse effect or is there a cost issue?

Epoxy-coated steel rebar has the problem I mentioned, as well as being more expensive than standard rebar. You can remove the steel and use non-corroding materials, but these tend to have significantly less stiffness than steel (and reinforcing stiffness determines the load-to-crack-size ratio)

That is really interesting. I didn't realize that corrosive oxidation would become concentrated and react at a higher rate if the point of exposure was limited.

Why isn't it galvanized like a nail or a porsche?

It can be, but it adds cost to the project, and any galvanized rebar has to be bent before it gets galvanized rather than on-site.

What about wood?

Wood absorbs water causing it to warp, swell and decay. Having said that, steel rebar is expensive which has motivated some organizations to use wood, as well as other plant materials, as a reinforcement material in concrete with some success [1].

[1] https://www.quora.com/Was-wood-used-as-a-reinforcement-mater...

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