Recovered & reborn
Fly ash
The fine ash captured from coal power station flues, chemically eager to react with lime: a waste stream that behaves like Roman pozzolana.
How it behaves
Replacing a share of cement with fly ash cuts a wall's embodied carbon and makes concrete denser and more durable; fly ash bricks cure without firing, sparing topsoil and kiln fuel.
Where it belongs
Wherever coal plants burn: a transitional material by definition
In a modern project
Fly ash bricks and PPC cements as the default over fired clay brick and OPC; high-volume fly ash concrete for mass elements.