HeidelbergCement AG, Heidelberg, Germany, has agreed to buy Hanson plc for about & pound; 8 billion (US$15.8 billion). The transaction forms the second largest building materials group worldwide.   ; HeidelbergCement is one of the top producers of building materials worldwide, with its core products being cement, ready-mixed concrete and concrete products, aggregates, building materials and other products. It had sales in 2006 of & euro; 9 billion (US$12.2 billion).   ; Hanson supplies heavy building materials to the construction industry, with sales of & pound; 4.1 billion (US$7.9 billion) in 2006. Its products fall into two categories: aggregates, which includes crushed rock, sand and gravel, ready-mixed concrete, asphalt and cement-related products; and building products, including concrete pipes, pre-cast products, concrete pavers, tiles and clay bricks.   ; The acquisition will be made by Lehigh, a wholly-owned direct subsidiary of HeidelbergCement.