The deal, which will transform the Irish company into the world’s third-biggest building materials supplier, was announced in February and will allow CRH to significantly expand its business in the UK and globally.
Lafarge and Holcim must offload a chunk of assets to meet competition authority requirements ahead of their planned £30bn mega-merger.
As well as the Lafarge Tarmac business, CRH will acquire production facilities in the Philippines, Canada, Brazil and several countries in Europe.
Lafarge Tarmac was put up for sale last summer, with the exception of its Cauldon cement works in Staffordshire, which is being kept, with a price tag of around £1.4bn.
The acquisition is expected to complete in the second half of this year.