Influence of accidental over-polarisation on the mechanical properties of cathodically protected pre-tensioned tendons

摘要

This paper investigates the performance of pre-tensioned tendons deliberately exposed to higher than normal impressed current cathodic protection (ICCP) to replicate accidental over-polarisation. Plain ungalvanised tendons, 5.4 mm o, were pre-stressed in moulds and cast in mortar. Two levels of pre-tensioning were investigated, low (similar to 30% ultimate tensile strength [UTS]) and high level (similar to 80% UTS). Three different degrees of corrosion with target losses of cross-sectional area of 0%-1%, 2%-4% and 4%-7%, respectively, were employed to replicate in situ conditions. ICCP was applied to the tendons at two levels of polarisation, normal protection (ICCP-N) in the range of -650 to -750 mV and overprotection (ICCP-O) ranging between -850 and -1300 mV, both versus Ag/AgCI/0.5-M KCI for an extended period. After ICCP, the tendons were removed from the mortar and slow strain tensile tests were conducted. The results show that ICCP at both normal and overprotection had no significant influence on the elastic modulus, yield, 0.2% proof stress and ultimate strength of the tested tendons. Although ductility was reduced, fracture occurred after reaching the ultimate strength.