NDT Selection Guide

This guide will help you select the appropriate Non-Destructive Testing (NDT) equipment for evaluating concrete structures without causing damage. NDT methods are essential for assessing the condition, strength, and integrity of existing concrete structures, identifying defects, and monitoring changes over time. Here’s a breakdown of common NDT methods for concrete and the equipment used:

• • • • Rebound Hammer (Schmidt Hammer):

        • Principle: Measures the rebound of a spring-loaded hammer impacting the concrete surface. The rebound number is correlated to compressive strength.
        • Equipment: Rebound Hammer (various types for different energy levels)
        • Applications: Estimating relative compressive strength, assessing uniformity of concrete, identifying areas of weakness or deterioration.
        • Considerations: Hammer type (N, L, M), calibration, surface preparation, influence of surface texture and moisture content, standards compliance (ASTM C805, EN 12504-2).

      • Ultrasonic Pulse Velocity (UPV):

        • Principle: Measures the travel time of ultrasonic pulses through concrete. Pulse velocity is related to concrete quality and can indicate the presence of voids, cracks, or other defects.
        • Equipment: Ultrasonic Pulse Velocity Tester (transmitter and receiver transducers)
        • Applications: Assessing concrete uniformity, detecting voids and cracks, estimating dynamic modulus of elasticity, monitoring changes in concrete properties over time.
        • Considerations: Transducer frequency, coupling medium, path length, standards compliance (ASTM C597, EN 12504-4).

      • Cover Meter (Rebar Locator):

        • Principle: Uses electromagnetic fields to detect and locate reinforcement bars (rebar) in concrete and measure the concrete cover thickness.
        • Equipment: Cover Meter (rebar locator)
        • Applications: Locating rebar, determining concrete cover thickness, assessing compliance with design specifications.
        • Considerations: Measurement range, accuracy, rebar diameter and spacing, standards compliance (ACI 318).

      • Chloride Ion Penetration Tests

      • Principle: To assess the resistance of concrete to chloride ion penetration, which can lead to corrosion of reinforcing steel.
      • Rapid Chloride Permeability Test (RCPT) Apparatus: Measures the electrical conductance of concrete to estimate chloride ion penetration.
      • Rapid Chloride Migration Test (RCMT): Used for non-steady-state migration tests to evaluate chloride ion penetration.
      • Considerations: Compliance with standards (e.g., ASTM C1202, AASHTO T 277), Ease of use and accuracy of results, Availability of replacement parts and consumables.