The primary link doesn't explain the other 60% of the formulation, but IIRC (from watching the video linked in my top-level comment) the other component is wast

The primary link doesn't explain the other 60% of the formulation, but IIRC (from watching the video linked in my top-level comment) the other component is waste dirt from construction projects. I'd expect it to be less strong than concrete, so I guess more fair comparisons might be mud bricks, other mud-brick + X formulations, and traditional clay bricks? edit: but worth noting that the paper you linked does mention that someone else is making "sargacreto" that is 40% sargassum and 60% concrete, though it says there aren't numbers to cite for its strength yet.