Linear Polarisation Resistance

Linear polarisation resistance (LPR) is the standard electrochemical technique for measuring the actual corrosion rate of reinforcement embedded in concrete. While half-cell potential mapping indicates the probability that corrosion is occurring, LPR quantifies how fast it is occurring, the corrosion current density (icorr) expressed in µA/cm². This measurement directly feeds into service life predictions and intervention urgency assessments.

The technique applies a small electrical perturbation (±10–20 mV) to the embedded reinforcement and measures the resulting current response. The polarisation resistance, the ratio of applied voltage to measured current, is inversely proportional to the corrosion rate. Higher polarisation resistance indicates slower corrosion; lower polarisation resistance indicates faster corrosion. The measurement is non-destructive and does not alter the corrosion state of the reinforcement.

Corrosion rate data converts the half-cell potential corrosion probability map into a quantified time-to-damage prediction. If corrosion is active at a rate of 1 µA/cm² (low), section loss of approximately 0.012mm per year is expected, potentially decades before structural consequences emerge. At 10 µA/cm² (high), the same section loss occurs in years rather than decades. This distinction directly affects intervention urgency and monitoring frequency.

TRSC uses LPR where the engineering question requires quantified corrosion rate data, typically for durability modelling, remaining service life estimation, and evaluating whether monitored deferral of intervention is justified. The technique complements half-cell potential mapping (which answers "where is corrosion occurring?") and concrete resistivity (which answers "how conductive is the environment?") to provide a complete corrosion assessment.