Tam Diep Cement Co. under Vietnam Cement Corp. has recently put its factory into operation in the northern province of Ninh Binh to produce high quality cement, PCB-40.    The factory, costing VND4 trillion (US$254.8m), uses rotary kiln technology supplied by FLS Denmark and has a designed capacity of 1.4Mta. It will provide cement for Ninh Binh province and other provinces in central Vietnam.    "The factory will help stabilize the local cement market in late 2004 and provide cement for the market in the following years," said Deputy Minister of Construction Tong Van Nga at the opening ceremony of the factory on Sunday.