Schmidt rebound hammer Type N for non-destructive in-situ concrete strength estimation per IS 13311 (Part 2) — standard NDT tool for site quality inspection across NE India.
A rebound hammer — also called a Schmidt hammer after its inventor Ernst Schmidt — is a non-destructive testing (NDT) instrument for estimating the surface hardness and approximate compressive strength of in-situ concrete without drilling or cutting. A spring-loaded plunger is pressed against the concrete surface and released; the plunger strikes the surface and rebounds, and the rebound distance is recorded on a scale of 10–60. Higher rebound values indicate harder, stronger concrete; lower values indicate softer, potentially weaker or damaged concrete. The result is compared against a correlation chart to estimate compressive strength.
Multi Trade Combines stocks rebound hammers (Type N, the standard civil engineering type) as part of our Civil Lab Equipment range in Guwahati. We supply civil engineers, quality assurance inspectors, building condition assessment teams, and structural engineers working across Assam and Northeast India. IS 13311 Part 2 governs the use of rebound hammers in India; our instruments are supplied with calibration anvil, correlation chart, and operating instruction booklet.
Third-party quality inspection agencies working on building and infrastructure projects across Assam, Meghalaya, and Arunachal Pradesh use rebound hammers as a routine site inspection tool to assess concrete quality during and after construction. IS 456 structural concrete quality assurance requires non-destructive testing as a complementary check to cube test results when cube test failures occur — the rebound hammer is the fastest and most portable NDT method available for site use.
Structural assessment engineers in Guwahati conducting condition surveys of older buildings — reinforced concrete structures from the 1960s to 1990s that are being considered for renovation or additional loading — use rebound hammers to map concrete quality variation across columns, beams, and slabs before specifying repair or strengthening works. Areas of low rebound value are candidates for core drilling and compressive strength verification before the structural assessment is finalised.
Government agencies — PWD, NHIDCL, urban development departments — use rebound hammers for post-construction quality audits of highways, bridges, and public buildings. NDRF and disaster management teams use them for rapid structural triage assessments of buildings after earthquakes or flood damage — Assam sits in seismic zone V, and post-earthquake structural survey using NDT tools is a practised skill in the region.
Pairs with the ultrasonic pulse velocity (UPV) tester for combined NDT assessment, with cube moulds and CTM for destructive verification, and with the carbonation test kit to correct rebound readings for carbonation effect.
| Category | Civil Lab Equipment |
|---|---|
| Key specs | Concrete in-situ strength · IS 13311 (Pt 2) |
| Type | Type N (standard civil engineering) |
| Rebound scale | 10–60 (dimensionless) |
| Standard | IS 13311 (Part 2) |
| Application | In-situ concrete strength estimation |
| Availability | In stock — price on request |
The rebound hammer (Schmidt hammer) is a non-destructive testing tool that provides an estimate of concrete surface hardness, which correlates approximately with compressive strength. The correlation is not precise — it is affected by surface carbonation (which increases rebound values), surface moisture (which decreases them), aggregate type, and the age and curing history of the concrete. IS 13311 Part 2 states that the rebound hammer gives an indication of uniformity and an estimate of strength, but the result should be correlated with core drilling and compressive strength testing from the specific concrete mix being tested before being used as a structural assessment. Rebound hammer is best used for comparative scanning — identifying areas of potentially low-quality concrete for more detailed investigation — rather than as a standalone strength determination method.
Rebound values from a Type N Schmidt hammer (the most common civil engineering type) are read on a scale from approximately 10 to 60. A value of 25 on a horizontal surface indicates relatively weak concrete — using the standard correlation chart, this corresponds approximately to 15–20 N/mm² compressive strength, which is well below M25 (characteristic strength 25 N/mm²) that most structural concrete in India requires. A value of 40 corresponds to approximately 35–45 N/mm² — approaching the range of M35 grade concrete. Values must be corrected for the angle of testing (horizontal, vertical downward, vertical upward) using the correction chart supplied with the hammer. Always average at least 10 readings per test area per IS 13311 requirements.