Nice article, and this is certainly a topic that everyone should know a little about seeing how fundamental cement is to our civilization. But it left out something very important at the end there... steel reinforced concrete is fantastic stuff of course, but it also comes with a drawback that is about to cost us very dearly; it doesn't last very long. All of our magnificent bridges and fantastic architecture come with a built-in expiration date because the steel inside them is rusting. That expiration date is somewhere between 50 and 150 years, and for a lot of our infrastructure it's coming due.
Concrete made from portland cement is waterproof but it isn't moisture proof, nor airtight. It breathes just enough that the oxidation of steel isn't completely stopped. And when the rebar rusts it expands, which causes the concrete to crack, letting more moisture and air in, causting the rebar to rust faster.
There are solutions to this problem, such as using rebars made from materials less susceptible to rust (stainless steel or even carbon fiber), but for the most part they are either a lot more expensive or nowhere nearly as strong. And there is susprisingly little research into this considering how important it seems... our civilization isn't very good at committing resources to things that have payoffs longer than 50 years, so everyone continues to use plain old steel as rebar in their constructions.
Meanwhile, the Roman pantheon remains standing, perhaps another couple of thousand years?
Basalt fibre reinforced concrete looks promising. The tensile strength is greater than steel rebar, and inexpensive when compared to carbon fibre. The environmental impact is much lower, as it's a melting process similar to fibreglass production, rather than smelting.
I get the impression that the continued use of steel rebar is less because there aren't superior technical solutions, but because there are significant regulatory, training and qualification hurdles. Use of non-steel rebars seems to complicate projects, and is only justifiable in special situations. Steel is usually adequate when appropriate anti-corrosion measures are taken (such as coating the rebar in epoxy).
Actually epoxy coated rebar has pretty major debonding issues in practice. If the epoxy coating was continuous then sure, but realistically during bending, cutting, tying, etc you're basically guaranteed to introduce scratches through that thin epoxy layer and once that steel starts rusting it'll tend to spread under the surface causing more cracks in the epoxy and allowing more corrosion.
>Adhesion loss of the epoxy coating to the steel surface was detected in all but one deck
that was 4 years old and older. The epoxy coatings were debonding from the reinforcing bars.
Whereas a bonded coating can be expected to protect the steel, a debonded coating allows
chlorides, moisture, and oxygen to reach the steel and initiate a rapid corrosion mechanism.
Reinforcing bars in various stages of adhesion loss showed visible signs of a corrosion process
underneath the coating, suggesting that ECR will provide little or no additional service life for
concrete bridge decks in comparison to bare steel. Other systems that will provide longer
protection against chloride-induced corrosion of the reinforcing steel with a higher degree of
reliability should be considered.
Counterpoint: Why do we need or even want anything to last a thousand years? In a hundred years we'll probably have much better technologies than today, and hopefully we'll be much richer. Why not rebuild stuff?
(I don't 100% buy this myself, just challenging the premise)
I actually think this is a good question and there are arguments on both sides:
pro-lasting: there are plenty of places with buildings that are hundreds of years old that are perfectly fine and useful buildings and there's no really compelling reason to tear them down and rebuild them.
Another argument is that the longer stuff lasts the less you may need to maintain it. Given that maintenance costs are hard to figure out and it's hard to get dedicated budget to keep things going (the present problem in the U.S. w/r to infrastructure for example), it's unlikely that things will be well maintained throughout their potentially useful life. If the stuff just lasts better, it's more likely to have a longer useful life...which is simply cheaper.
pro-replacing: An awful lot of national GDP in many countries comes from construction projects. Keeping a constant turnover in infrastructure and housing keeps huge populations employed with decent paying jobs.
Cities don't always have an infinite utility. The U.S. Rust Belt is an example of many cities that may have outlived their intended utility. This means that populations will migrate to cities with more current utility and the need to rearrange those areas to suit the change in population is important. A fixed or stagnate inner core, that could be replaced with higher density housing, is preferable than simply sprawling out elsewhere.
Concrete made from portland cement is waterproof but it isn't moisture proof, nor airtight. It breathes just enough that the oxidation of steel isn't completely stopped. And when the rebar rusts it expands, which causes the concrete to crack, letting more moisture and air in, causting the rebar to rust faster.
There are solutions to this problem, such as using rebars made from materials less susceptible to rust (stainless steel or even carbon fiber), but for the most part they are either a lot more expensive or nowhere nearly as strong. And there is susprisingly little research into this considering how important it seems... our civilization isn't very good at committing resources to things that have payoffs longer than 50 years, so everyone continues to use plain old steel as rebar in their constructions. Meanwhile, the Roman pantheon remains standing, perhaps another couple of thousand years?