How are structures that are constantly in contact with water repaired or maintained? I imagine there has to be some sort of preparation or specific process for this?
In: Engineering
Concrete 100% submerged is significantly less susceptible to deterioration than concrete that goes through wet/dry cycles which would be in shallower depths. For shallow depth repair work, you can install temporary cofferdams around the work area to dewater the immediate area to complete the required work. Also divers can do many repairs, albeit slower/costlier in general.
Modern day dams have sensors and a team of people who ensure everything is working correctly.
Smaller dams are checked and maintained by third party companies like “Damwatch” who specialise in this very task.
There is lots of work that can be done under water. For more serious work you’d set up a barrier around the work area, then pump out the water, perform the work, then fill it back up and remove the barrier.
For something like a dam you can drain the water if needed.
What about dams and other structures that aren’t made of concrete, i.e. earth?
There are hydrophobic, crystalline additives that can be added to the concrete mix that fills the voids and strengths the concrete. There are also coatings and cementitious grouts that can be applied underwater for spot repairs.
The intakes are covered by a mesh which gets covered in debris. When there is enough, they will use diggers but where instead of a shovel, it’s a trash rack with long “fingers” to scrape the trash off and bring it up to be collected.
Generally, you can instal temporary containment barriers in a small area to divert the water. Then you drain the area so you can do the work, then allow it to flood again when finished
Some common, but incorrect/misleading ideas about concrete here.
1. Concrete needs water to cure. The water is already in the concrete when it’s poured. This is all the water the concrete needs. When you cure concrete you mostly need to make sure none of the water already in it evaporates from the surface during curing or you’ll get cracking. There are several ways of accomplishing this – some involve keeping the concrete wet, others involve putting a waterproof membrane over it to stop evaporation.
2. More water in the mix =/= stronger concrete. The exact opposite. When you look at concrete mix designs there is typically a straight line of strength loss as you add more water to any given mix. If you want strong concrete you (simplified somewhat) put as little water in as possible while maintaining workability (more water = more flowable concrete = easier to pump, place and compact, but weaker compared to an otherwise equal mix)
3. U/timster1 is correct about the crystalline waterproofing admixture. This works pretty much as they describe. There are some other admixtures they can use also when there’s reinforcement in the concrete. They can also work with other aspects of the mix design – cement content, air entrainment (tiny microscopic air bubbles that allow stress relief to prevent damage from freeze thaw cycles)
The dam by me has a bypass gate they can dump water below the dams spill level if needed. But more interestingly is the top 3 feet of the dam are like.. Railroad ties secured with steel cables and rods. Likely due to ice (Minnesota) they’re easier to replace and more flexible when struck by chunks of ice.
Concrete sets harder if under water. It can be poured down a submerged chute into a form. The form can be built on land.
Concrete is not something that can be done in layers, because the layers won’t stick to one another. Any repairs are more like a bandaid. The engineering has to be done correctly the first time by using extensively reinforced concrete, and a cement mixture designed for that specific use.
If the structure is in sea water then extra steps and processes are involved because of how corrosive the water and mist is. Metal needs to be painted regularly, and concrete needs to be encased.
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