(Adds details on deal, divestiture)
WASHINGTON, June 14 (Reuters) - Construction company CRH Plc agreed to divest facilities in three states in order to win U.S. antitrust approval to buy Ash Grove Cement Co, the Federal Trade Commission said on Thursday.
Already North America's biggest maker of concrete products and second largest supplier of aggregate materials for construction, CRH said in September it would buy Ash Grove for $3.5 billion.
To win antitrust approval for the deal, CRH agreed to sell a cement plant and quarry in Montana, sand and gravel pits in Nebraska and four facilities in Kansas - two limestone quarries and two asphalt plants.
(Reporting by Diane Bartz; Editing by Leslie Adler)