ISO 1920-7:2004

Overview

ISO 1920-7:2004 - Testing of concrete - Part 7: Non-destructive tests on hardened concrete - specifies standard procedures for three common non‑destructive testing (NDT) methods used on hardened concrete: rebound number (rebound hammer), ultrasonic pulse velocity (UPV), and pull‑out force. These methods are intended for quality assessment and in‑situ estimation of concrete properties, not as direct replacements for compressive strength tests; however, with suitable correlations they can provide useful strength estimates.

Key topics and technical requirements

• Scope and terms: Defines key terms (rebound number, transit time, onset, rise time) and limits of application.
• Rebound number (rebound hammer):
  • Principle: measures energy returned by a spring‑propelled mass striking the surface.
  • Apparatus: spring‑loaded rebound hammer, steel reference anvil (≈52 HRC, ~16 kg), abrasive stone.
  • Procedure highlights: preconditioning the hammer, minimum 9 readings per test area, impact point spacing ≥ 25 mm, ≥ 50 mm from edges; discard sets if >20% of readings deviate >6 units from the mean.
  • Calibration: hammer verification on reference anvil; calibration at least twice a year.
• Ultrasonic pulse velocity (UPV):
  • Principle: measure transit time of longitudinal pulses between transducers to calculate pulse velocity.
  • Apparatus: pulse generator, transducer pair (typical natural frequency 20–150 kHz; guidance for lower/higher frequencies), amplifier, oscilloscope or interval timer.
  • Performance: transit time accuracy to ±0.1 µs, controlled excitation rise time, calibration on standard bar.
• Pull‑out force:
  • Principle and apparatus defined for measuring localized pull‑out resistance; procedures and reporting requirements included.
• Reporting and annexes: Standard specifies required contents of test reports and includes informative annexes on correlations (strength vs. rebound/UPV), factors influencing measurements, example reports, and indirect UPV transmission.

Practical applications

• Quality control on new concrete and verification of uniformity across elements.
• Condition assessment for bridges, slabs, columns and other structural elements where cores are impractical.
• Site troubleshooting (detecting weak zones, workmanship issues, or changes in material properties).
• Estimating in‑situ strength through calibrated correlations when cores or standard compressive tests are not feasible.

Who should use this standard

• Structural and civil engineers, concrete technologists, laboratory technicians, construction QA/QC personnel, and inspection agencies performing concrete NDT and field assessments.

Related standards

• ISO 1920 series (other parts cover sampling, fresh concrete properties, specimen making/curing, compressive strength, core testing). Use ISO 1920-7 together with the relevant parts of ISO 1920 for comprehensive concrete testing practice.

Keywords: ISO 1920-7:2004, non‑destructive tests, hardened concrete, rebound number, ultrasonic pulse velocity, pull‑out force, concrete testing, NDT, in‑situ strength.