Building materials supplier Boral says its $US2.6 billion ($A3.5 billion) acquisition of US firm Headwaters Incorporated will more than double Boral's US business and transform the whole group.

Headwaters, with revenue of $US1.1 billion and earnings of $US218 million, is a manufacturer of building products and one of the largest marketers of fly ash in the United States. Fly ash, a by-product of coal combustion in power stations, is added in manufacturing of concrete as a cement substitute…