Corrosion Rate Measurement Resistivity Test developed for insitu testing empirical criteria developed relating resistivity to corrosion rate extensive field data available Polarization Resistance Relatively new test Relationship to corrosion poor The flow of current between the anode and cathodic can be controlled by the electrical resistance between them. This is a function of the distance between them and resistivity of the concrete or electrolyte. There are other factors that can control the current flow like anode to cathodic area but the influence of resistivity is high then corrosion will be insignificant regardless of all other factors. If its low then other factors may be limiting but with the exception of oxygen supply are unlikely be sufficiently controllable to cast in designing corrosion rate control. Resistivity is relatively simple to measure but as the concrete’s resistivity is strongly influenced by its moisture and chloride content testing conditions have to be given. The lowest resistivity is obtained in a saturated chloride state and as we are interested in marine performance, a suitable performance limit might be the resistivity of seawater saturated concrete. Resistivity testing originally developed in soils testing and has been used as a tool for assessing concrete structures for over 15 years. Extensive field and laboratory data is available. Research at Taywood Engineer and TRRL has shown that at over 20,000 ohm on the corrosion rate is insignificant. There has been alot of work done with polarisation resistancebut to date reliable test methods and assessment criteria have not been developed and the technique remains a specialised research tool.

Liner Polarisation

Corrosion Rate (m/year) 1/12/98 1/6/99 1/12/99 31/5/00 30/11/00 1/6/01 30/11/01 1/6/02 5 Corrosion Rate (m/year) 10 Contaminated Uncontaminated -100 Contaminated Uncontaminated -200 -100 -300 Ecorr (mV Ag/AgCl) Ecorr (mV Cu/CuSO4) -200 -400 -300 -500 1/12/98 1/6/99 1/12/99 31/5/00 30/11/00 1/6/01 30/11/01 1/6/02