Wal-Mart citing green reasons for requiring fly-ash in its concrete flooring

"Wal-Mart Stores Inc. has changed their construction specifications to require all interior steel-troweled concrete floors placed at Wal-Mart Stores, Supercenters, Neighborhood Markets, Sam's Clubs, and Distribution Centers to contain 15% to 20% fly ash by cement substitution."
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Fly ash is the residue left from incineration of various materials and can contain extremely hazardous chemicals. As methods for disposing of this toxic material at a low cost are few, many industries have looked to road building and building materials as means to dispose of this stuff cheaply. However, it remains controversial how safe these disposal methods are, because the chemicals are not permanently sealed within the concrete forever and ever.

Wal-Mart is the company that originally purchased around 300 acres of land at the N.Mesa-Executive Drive El Paso TX corner in 2005 from a realty-intermediary. Now development has begun on that site (less than one mile from the Asarco epi-center) to cluster high-density ("Smart code" i.e. "walkable" ) neighborhoods on that land, which is subjected to Asarco fugitive dusts and 100 years of chemical-deposition from the Asarco smelter emissions...

http://www.concreteconstruction.net/concrete-construction/adding-fly-ash-to-concrete-mixes-for-floor-constr.aspx