When that happens, and a sinkhole threat has been established, crews can pump a thick grout a mixture of sand and cement into the ground to fill the holes.

NPR: Work Continues, Future Uncertain For Sinkhole Site

This process of combining of water, cement paste, sand and rock creates an awful lot of CO2 gases - which are linked by some scientists to global warming - about five to 10% of the world's total emissions.

BBC: By Ian Hardy

That includes aggregates, sand, concrete, asphalt and cement.

BBC: UK economy: Two views of the recession

According to his company's website, Mr Dini's industrial sized 3D printer uses sand and a special binding agent to create a "marble like material" stronger than cement.

BBC: Landscape House