His new idea? Legos, sort of. To be precise, large, stone Lego-like building blocks.
See, it sounds bananas at first, then you really get what he's saying and it's pretty clever. As The Verge reports, this isn't even that new. The Boring Company, which Musk founded to facilitate actually boring tunnels for his super-futuristic Hyperloop, planned some practical use for displaced rocks from the tunnels long ago:
The Boring Company is investigating technologies that will recycle the earth into useful bricks to be used to build structures. This is not a new concept, as buildings have been constructed from Earth for thousands of years including, according to recent evidence, the Pyramids.
These bricks can potentially be used as a portion of the tunnel lining itself, which is typically built from concrete. Since concrete production accounts for 4.5% of the world’s greenhouse gas emissions, earth bricks would reduce both environmental impact and tunneling costs.
The Hyperloop, an extraordinarily ambitious project that aims to provide underground travel from New York to DC in half an hour, isn't the kind of thing that will be done overnight. Still, Musk seems to be moving forward, so these big-ass "lego" bricks might be available sooner than you think.
Now go torch something with your flamethrower while you wait.