Industrial conglomerate Siam Cement PCL said Wednesday its board has approved a plan to invest THB3.2 billion in a new integrated cement plant in Cambodia.  Siam Cement will hold a 90 per cent stake in the venture, while Khaou Chuly Group, a Cambodian investor, will hold the remainder, Siam Cement said in a statement to the Stock Exchange of Thailand.  The cement plant is expected to commence operations by 2008 with an annual production capacity of 850,000t the statement said.  Published under Cement News