CRH, which said it will fund the acquisition with cash, new debt and a 9.99 percent equity placing, beat a consortium led by Blackstone, whom several people familiar with the matter told Reuters were also in the running.
CRH, already the United States' leading producer of asphalt for highway construction, said in a statement that a stock market announcement setting out the full details of the acquisition would be released as soon as possible.
France's Lafarge and Swiss peer Holcim announced merger plans last year, hoping to cut costs and tackle overcapacity and weak demand. The new company will be the world's biggest cement maker with $44 billion in annual sales.
One source told Reuters last month CRH was seen as the front runner having put forward the highest offer. The Blackstone consortium, which also includes Cinven and Canadian pension fund CPP, bid 5.5 billion euros, a second source said.
A person familiar with the process had said that CRH had a better opportunity to benefit than buyout groups because it can integrate the assets into its own business, and could therefore offer a higher price.
The companies initially received more than 60 tentative bids from industry and private equity firms for some or all of the assets, which they must sell before completing the merger.
CRH, whose cement operations represent about 15 percent of earnings, embarked on its own disposal plan last year, one of the first steps Albert Maniford took as the new chief executive.
It plans to sell 1.5 to 2 billion euros worth of net assets and generated 350 million euros from its first set of disposals last year with another 295 million due in the coming months as another deal closes.The Dublin-based group, which in recent years has followed a strategy of making smaller bolt-on acquisitions - said last year that it also had the capacity to spend some 1.5 billion euros on deals going forward with the cash on its balance sheet.