There are lots of uses for free chunks of broken concrete, also known as urbanite or urbancrete. This particular project by Danielle at Earthen Acres caught my eye. A series of photos on her site shows how they built it. She and her friends also built their foundation out of urbanite.
You might also be interested in her workshop in June in Durham, North Carolina, where they’re going to build a strawbale garden wall and cob meditation studio. Maybe you’re planning on using different materials on your house. That’s okay because there’s lots of overlap between various natural building methods and so you’re sure to gain numerous useful skills as well as make some new friends.