Workers at a Waurn Ponds cement plant are set to lose their jobs today, just 10 days before Christmas.   The workers were employed by contractor Lucon on a $50m upgrade of Blue Circle Southern Cement’s Waurn Ponds plant.   Victorian State Official with the metals division of the Australian Manufacturing Workers Union Gary Robb said the site’s principal contractor Humboldt had terminated Lucon’s contract.  "They’re not happy with Lucon’s performance," Mr Robb said.   He said most of Lucon’s 48 workers would be told they had lost their jobs today.   A small crew would remain to demobilise the site.