What does a half-cell potential of -450 mV against a Copper-Sulphate Electrode (CSE) indicate?

It indicates a greater than 90% probability of active reinforcement corrosion at the point of measurement (Table 1).

How is the depth of carbonation measured on-site?

By spraying a 1% phenolphthalein solution on a freshly exposed concrete surface. The uncarbonated (alkaline) concrete turns pink/purple, while the carbonated (neutralized) area remains colorless (Clause 7.2).

What does a concrete resistivity of 8 kΩ·cm suggest?

It suggests a high likelihood of reinforcement corrosion, as the low resistivity provides an easy path for the flow of corrosion currents (Table 2).

Is an Ultrasonic Pulse Velocity (UPV) test sufficient to determine concrete strength?

No, UPV is primarily for assessing the homogeneity and quality (e.g., presence of voids/cracks) of concrete. While correlations exist, it is not a direct measure of compressive strength (Clause 9).

IS 13735

: 1993

Recommendations for Assessment of Durability of Concrete - Methods of Test

CurrentSpecializedTesting MethodMaterials Science · Demolition, Renovation and Repair of Structures

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This standard provides recommendations for methods of test to assess the in-situ durability of hardened concrete. It covers procedures for visual inspection, half-cell potential measurement, resistivity, carbonation depth, permeability, and ultrasonic pulse velocity to diagnose deterioration and estimate the remaining service life of concrete structures.

Recommends methods of test for assessing the durability characteristics of concrete.

Quick Reference Values

Corrosion probability >90% (Half-cell)< -350 mV vs CSE

Corrosion probability <10% (Half-cell)> -200 mV vs CSE

Resistivity for very high corrosion likelihood< 5 kΩ·cm

Resistivity for very low corrosion likelihood> 20 kΩ·cm

Phenolphthalein indicator concentration1% solution in ethanol

UPV for Excellent Quality Concrete> 4.5 km/s

UPV for Doubtful Quality Concrete< 3.0 km/s

Practical Notes

Results from these non-destructive tests (NDT) are indicative and should be interpreted collectively, not in isolation. A conclusion on durability should be based on results from multiple tests.

Environmental conditions, especially moisture content and temperature of the concrete surface, significantly influence half-cell potential and resistivity readings. Readings on dry concrete can be misleading.

These tests are primarily used for condition assessment and forensic investigation of existing structures, not for routine quality control of new construction.