Ryan Ferguson I think this is a great way to use recycled plastic as it provides the flexibility to mold as needed. If this material can be used for 3D printing, it will also help reduce transportation costs by building them locally simply by sharing the design to the local printer or making it open source for people to play with it to meet their particular needs.
Can the grind materials be made to have the rigidity to handle this type of application?
I also think that you might get some ideas from the recycling system used in South Korea: https://www.pbs.org/newshour/show/policies-helped-south-koreas-capital-decrease-food-waste

There will surely be some push back, as with everything related with plastic. I cannot say the validity of this concern until bench tests are performed to understand their resistance to marine environments

Thanks, that is a challenge that needs to be tested at bench scale. I would hope that these structures work as foundation for new coral and marine life to latch onto and grow so the rubber and the concrete would be affixed this way.

I appreciate you taking the time to provide your perspective and suggestions!