The 'rebound hammer test' (Schmidt Hammer) gives an indication of:
Choose the correct answer
Tensile strength directly
Surface hardness — provides estimated strength correlation; useful for uniformity checks and identifying suspect areas
Depth of rebar below surface
Water-cement ratio inside concrete
Correct Answer
B. Surface hardness — provides estimated strength correlation; useful for uniformity checks and identifying suspect areas
Why is this the answer?
Rebound hammer (IS 13311 Part 2): spring-loaded hammer strikes concrete surface; rebound number R measured. Higher R = harder surface = potentially higher strength. ESTIMATE only — correlates with surface hardness (affected by carbonation, moisture, aggregate type). Not a substitute for core tests. Useful for: relative uniformity check, suspect areas, grid survey. R = 20–40 typical for structural concrete.
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