4 ms·
"The rebar can rust, and the rust can cause the concrete to fracture." The rebar will only rust if the concrete PH is neutralized. (Cement is pretty strong bas
by vlehto 11y ago
"The rebar can rust, and the rust can cause the concrete to fracture."
The rebar will only rust if the concrete PH is neutralized. (Cement is pretty strong base.) This neutralization happens when the concrete slowly reacts with oxygen. Typically reinforced concrete has safe lifespan of about 70 years, while unreinforced concrete only reaches its max strength around 90 years. Typically lifespan and hardening are both slowed down if the concrete is sealed from water. (By paint or preferably with some external cladding and some passive ventilation between cladding and concrete.)
Reinforced concrete is shit if you consider only strenght/weight. It's kinda OK if you take into account price. But if you need good fire safety, it's bloody brilliant stuff. So for big buildings, staircases, elevator shafts and underground spaces it's good choice.
- wycx 11y agoSomething I recently learned of is basalt fiber rebar. It won't rust, but I guess on a long enough time frame it will devitrify. https://en.wikipedia.org/wiki/Basalt_fiber https://en.wikipedia.org/wiki/Basalt_fiber
- vlehto 11y agoThanks for the info, I learned something. The trick usually in reinforcing is that you need to find two materials that have relatively equal heat expansion coefficient, while the fiber needs to be lot stiffer than the matrix. Luckily concrete is quite "springy" compared to most metals and ceramics. In composite structures the ultimate strength of the fiber is often not the limiting factor. The limit is how large share of the load is carried by the reinforcement, which is proportionate to the ratio of Young's moduli of the matrix and the fiber (+ fiber length, average direction and volumetric proportion). Steel has almost same expansion coefficient as concrete. Basalt is significantly lower. So it would probably best suit reinforcing in stable climates or used as relatively short fibers. You would not want hundreds of meters long basalt fiber rope to be pretensioned inside concrete bridge, as the rope might crumble the surrounding concrete at hot weather.