Concrete can be recycled by grinding it up, then using screens to separate fine and coarse materials, magnets to remove steel, and water floatation to remove other unwanted materials. It can then be used to form hardcore sub-bases underneath new structures, gravel for paths or driveways, or even act as the aggregate for new concrete.
It’s harder to recycle concrete if it contains lots of contaminants, but it’s really worth trying: recycling means less gravel mining and less landfill, so recycling one tonne of concrete could save 6,182 litres of water and 900kg of CO2.
Sometimes only about 30 per cent of the materials in new concrete is recycled, because its performance may otherwise be reduced. But new processes using chemical additives can help break down old concrete into sand, gravel and limestone, sequestering 60kg CO2 per tonne and enabling much higher quality new concrete to be made from recycled materials.
Researchers at Tokyo University have also suggested a new kind of concrete that is inspired by the way some aquatic organisms harden into fossils over time. They extract calcium from discarded concrete and combine it with carbon dioxide from industrial exhaust or even from the air, making new ‘calcium carbonate concrete’.
Read more:
- Why is black plastic so difficult to recycle?
- How much of a cereal box gets reused when it is recycled?
- How do recycled plastic building bricks work?
- Why can’t I recycle takeaway pizza cartons?
Asked by: Neil Crimmings, Swansea
Every week on BBC World Service,CrowdScienceanswers listeners’ questions on life, Earth and the Universe. Tune in every Friday evening on BBC World Service, or catch up online atbbcworldservice.com/crowdscience
- This article first appeared inissue 373ofBBC Science Focus Magazine–find out how to subscribe here
