Cemex  is negotiating a US$800m three-year syndicated loan to refinance other debt, Loan Pricing Corp. said, citing unnamed market sources.  According to LPC, a unit of global news and information company Reuters Group Plc, Cemex has bumped up the size of the loan from an original $500m.  Cemex, which has promised to pay down debt this year in the absence of attractive acquisitions, declined to comment. Its net debt at the end of March stood at $5.352bn.  Cemex said in mid-June that its second-quarter EBITDA will rise 11 per cent to exceed US$610m.