Thanks friend!

Concrete being the inert material, and mushrooms being the organic/active material, since its dark inside the concrete, and rain would make the spores/tissue come alive. It could even be the insulating concrete you wrote about, mixed in with dried yet live mushroom tissue. The mushrooms would grow/expand in whatever concrete mix, breaking it and collapsing it at a certain point. Mushrooms love eating through gypsum and using it for energy.

For fiction, anything is possible.