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We use reinforced concrete, concrete with steel bars inside. This allows us to built really thin and strong concrete bridges, balconies, roofs, etc. But the st
by FredPret 5y ago
We use reinforced concrete, concrete with steel bars inside. This allows us to built really thin and strong concrete bridges, balconies, roofs, etc.
But the steel rusts after a couple of decades.
Rusted steel is marginally larger than new steel.
So when the steel bars expand by rusting, it pushes against the concrete from the inside, causing cracks. Then lots of water can get in it rusts faster.
Eventually chunks of concrete fall off and structural collapse follows.
If we built like the Romans, it would be more expensive, but would last 1k+ years.
- simonebrunozzi 5y agoIs there any alternative to steel? Or, is there any promising technology that allows to use steel bars that have some space inside, so that when they rust, they don't break the concrete?
- smegger001 5y agoI wonder how long carbon fiber rebar, or plastic coated steel rebar would last.
- FredPret 5y agoInteresting idea, but carbon fiber would need to be really cheap. Would work well until a critter of some sort evolves that eats plastic
- Cerium 5y agoPlastic coated rebar is a product. In theory it can solve the rusting problem, but in practice the coating will get some nicks during installation that can concentrate corrosion leading to point weaknesses. There are additional concerns with the bonding between the concrete and the coated bar.
- tastyfreeze 5y agoBasalt rebar is chemically resistant and doesn't corrode. It does have a lower tensile strength than carbon fiber but is suitable for current designs.
- mc32 5y agoThere are stainless steel rebar and epoxy coated rebar for structures exposed to the elements. Stainless steel rebar appears to be kind of expensive so its use is limited.
- dr_orpheus 5y agoI don't know how it compares to actual rebar reinforced concrete, but we do use fiberglass reinforced concrete.
- jaclaz 5y agoBriefly (costs/duration): normal steel rebar=1 epoxy coated rebar=1.1-1.3 <- terrible in practice zinc coated rebar=1.2-1.4 <- good stainless steel rebar=3-4-5 <- very, very good carbon fiber rebar=? <- AFAIK not used in new buildings, as it has a series of issues in practice, used in some rare cases of consolidation/repair of old buildings, mostly not as rebar but rather as mesh/net. What is used, not as "main" reinforcement but to have a (much better) mass strength are fibers, they can be either steel or plastic.
- Sankozi 5y agoI think I do not understand the numbers. You wrote "costs/duration" so higher the number the worse solution (bigger costs or worse durability), yet the descriptions suggests otherwise.
- jaclaz 5y agoSorry, numbers are cost only (1 is "normal" rebar steel) order and text are duration ("normal" steel no text, base duration, the terrible in practice means that it doesn't offer longer duration, and may have issues in adherence to concrete). Not so surprisingly the higher the cost the longer the duration.
- bluGill 5y agoSteel and concrete have similar coefficients of expansion. Most other choices don't and so as temperature changes something has to bend or give which reduces life.
- WalterBright 5y agoIt's critical to protect the concrete from water.