Swiss specialty chemicals company Sika AG will buy the concrete additives business of Swedish Cementa AB for an undisclosed sum, Sika said on October 1, 2004.  The unit generates 18 mln Swedish crowns (Euro2.0m) annual sales, Sika added.  Cementa AB is owned by German building materials producer HeidelbergCement, which is focusing on core businesses and has been seeking to sell off the unit for several months.