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Precautions in Schmidt hammer test

Short answer

Check the hammer on a standard test anvil (rebound ~80±2). Use a smooth, clean, dry surface on a rigid member ≥100 mm thick. Hold hammer perpendicular; avoid edges, honeycombed areas, reinforcement, and wet/carbonated surfaces. Take ≥12 readings 20–50 mm apart, reject those differing >6 units from mean, and average.

Write the precautions that should be taken while performing the Schmidt hammer test of concrete.

Precautions for the rebound (Schmidt) hammer test (IS 13311 Part 2):

  1. Check the hammer on the standard test anvil (rebound number about 80 ± 2) before and after the test.
  2. Select a smooth, clean, dry surface; grind rough or plastered surfaces and remove loose scale and finishing.
  3. Test a member at least 100 mm thick that is rigidly held (a thin or loose member will vibrate and give low readings).
  4. Keep the hammer perpendicular to the surface; if it is not horizontal, apply the orientation correction.
  5. Avoid edges (at least 20 mm away), honeycombed areas, voids, and spots directly over reinforcement or aggregate pockets.
  6. Take at least 12 readings per area, 20 to 50 mm apart, never at the same point twice; reject readings that differ by more than 6 units and average the rest.
  7. Do not use on wet, frozen or carbonated surfaces without correction (carbonation raises the number), and note the age and moisture.
  8. Use the calibration curve with the same type of hammer and concrete, and handle the instrument carefully; clean the plunger regularly.

✓ Answer checked by Claude Sonnet 5.5

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