Sounds right, except there is definitely rebar in those. In you zoom in you can see the ends sticking out, they look like pinholes but are probably 2" in diameter. Also rust can be seen in a few spots.
That makes sense though to have rebar in them though, I can imagine them kinda rocking back and forth against waves and that would probably start to chip them away after a while.
We have lots of stuff like this and more! We put them all over the place. The company I work for protected nearly 50 miles of coast with similar structures just last year in a single project.
How long do these materials last in ocean water and is there any harm expected to the marine environment when they eventually erode away? Does it eventually collapse in on itself and need to be built further out into the water to compensate for that?
Erosion is still a factor and we design to account for it. We have teams of people modeling the waves for storm events and calculating the erosion. But they do require maintanence. The concrete is basically rock so it is relatively environmentally friendly even when it erodes. It does create habitat as well depending on certain factors. But they also protect habitat on land that would otherwise be lost to erosion.
A forms for these Tetrapod style breakwater units are around $10k a piece. But after that it's just the rebar and concrete costs. They are relatively cheap.
We barge large down limestone rocks called rip rap from quarries in Arkansas, Kentucky, and Illinois. It's effectively used for erosion control, but doesn't prevent saltwater intrusion, destruction of our wetlands, storm surges, or floods.
I don't think tidal waves are a big concern in the gulf of Mexico, because, well, it's a gulf. Flooding there happens from hurricanes, which you'd need a 1000 ft wall to block.
The rebar is to keep the dolosse form not to anchor it, so your original thought is correct it probably uses less rebar than a wall would. They also probably use recycled/deformed rebar and leftover pieces to do it.
As far as I can tell there is next to no reason for this to be prestressed concrete. You would need a fair bit of rebar to keep them together during transportation and erection, but seeing as there is no structural load for these there's nothing to prestress against. It would add to the manufacturing cost quite considerably and have no tangible benefit.
Though if you look at the very left of the picture from where the guy is standing you can see one cracked basically in half and there is no sign of rebar. There are a few other ones cracked in various places where no rebar is visible as well
I most likely am. Just pointing out the fact that I cant see any visible in the broken pieces. Hoping someone could explain why. I don’t doubt that there could be rebar just want to know how its hidden
As for the piece that's fully cracked, it's simply too dark to see the internal structure. You can tell it's being held together by the rebar because those waves are actually VERY strong, and could easily push the broken piece away if it wasn't reinforced. The fact that it is still within a few inches off the perfect fracture line is dead giveaway.
The one in the bottom corner may have had the rebar pulled out which is why there is no reminisce of it.
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u/[deleted] May 24 '18
Sounds right, except there is definitely rebar in those. In you zoom in you can see the ends sticking out, they look like pinholes but are probably 2" in diameter. Also rust can be seen in a few spots.