Standard Type N Original Schmidt Rebound Hammer
Mechanical impact hammer (2.207 N·m impact energy) with hardened spherical plunger tip and sliding rider scale.
Civil Engineering / Schmidt Rebound Hammer
FREE TO EXPLORELABORATORY 50 · CIVIL ENGINEERING
Non-Destructive In-Situ Concrete Compressive Strength Estimation via Schmidt Rebound Hammer
Estimate surface hardness and uniform compressive strength of in-situ structural concrete elements using the spring-loaded Type N Schmidt rebound hammer according to ASTM C805 / BS EN 12504-2. Explore interactive structural mechanics, materials simulation, and civil engineering telemetry.
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Your virtual civil engineering laboratory.
ESTIMATED COMPRESSIVE STRENGTH F_C—
CIVIL INFRASTRUCTURE TELEMETRY
Ready to sample with Rebound Number R = 32.0 R-units.
Adjust Rebound Number R, then execute civil engineering measurement.
Civil engineering telemetry is evaluated rigorously using 64-bit IEEE 754 precision. Residuals reflect ordinary least-squares regression across successive observations. Continuous data structures support high-fidelity structural mechanics and geotechnical continuum modeling.
Civil engineering assumptions and boundary condition limits
The civil engineering physical models apply within the specified calibrated operational window (20.0 to 50.0 R-units). Tested on horizontal impact faces of matured concrete specimens. Linearized calibration correlates estimated compressive strength f_c directly to rebound number R with slope 0.8500 MPa/R and intercept 12.00 MPa.
Laboratory apparatus & testing equipment.
Heavy Steel Calibration Anvil
Hardened cylindrical steel test anvil (mass ≥ 16 kg) verifying hammer calibration (reads R = 80 ± 2).
Medium-Grit Silicon Carbide Abrasive Grinding Stone
Prepares test surface by rubbing off soft laitance, carbonated crusts, and formwork oils.
Rigid In-Situ Structural Concrete Test Blocks
Cured C20 to C50 structural concrete elements mounted rigidly in laboratory reaction frame.
Phenolphthalein Chemical Indicator Spray Solution
Tests surface carbonation depth by spraying freshly exposed concrete (turns pink on uncarbonated concrete).
Measuring Grid Template (100 mm × 100 mm)
Ensures 10 individual impact test points are spaced strictly ≥ 25 mm apart.
FOLLOW THE METHOD
A reason behind every step.
Estimate surface hardness and uniform compressive strength of in-situ structural concrete elements using the spring-loaded Type N Schmidt rebound hammer according to ASTM C805 / BS EN 12504-2. Standardized parameter settings: 20.0, 26.0, 32.0, 38.0, 44.0, 50.0 R-units.
01
Calibration Anvil Verification
Position Type N hammer vertically downward onto 16 kg steel test anvil; execute three test impacts; verify scale reading is R = 80 ± 2; clean hammer plunger if required.
02
Concrete Surface Preparation & Grinding
Select smooth structural concrete area; grind surface in circular motions using silicon carbide stone to remove weak surface laitance; blow away fine dust.
03
Test Point Grid Layout (10 Impact Points)
Draw a 10-point test grid using marker template, ensuring impact points are spaced at least 25 mm apart and at least 50 mm from structural edges.
04
Perpendicular Impact Execution
Hold hammer firmly perpendicular (90°) to the concrete surface; push instrument smoothly toward surface until the internal spring releases and the hammer strikes; lock pointer rider with push-button.
05
Ten-Point Reading & Outlier Rejection
Record rebound number R for each of the 10 grid points; calculate mean; discard any individual reading deviating by more than 6 units from the mean; re-average remaining readings.
06
Compressive Strength Conversion & Impact Angle Correction
Apply orientation correction if impacting vertically downward or upward; use calibration equation f_c = 0.8500 · R + 12.00 to calculate estimated compressive strength in MPa.
YOUR NOTEBOOK · 0 OBSERVATIONS
Turn measurements into civil engineering insight.
Points are your recorded observations. The solid regression line validates Schmidt Rebound Hammer mathematical scaling.
LINEAR REGRESSION FIT · y = mx + b
f_c = 0.8500 · R + 12.00
| # | Schmidt Rebound Hammer Number R (R-units) | Estimated Compressive Strength f_c (MPa) | Schmidt rebound hammer index R (dimensionless units) | Estimated in-situ concrete compressive strength f_c (MPa) | Remove |
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CHECK YOUR UNDERSTANDING
Explain what the civil engineering metrics mean.
The standard impact energy of the Type N original Schmidt rebound hammer is:
The minimum distance between adjacent impact test points on a concrete surface must be at least:
Surface carbonation of an outdoor concrete structure causes rebound hammer readings to be:
Under ASTM C805 outlier rejection criteria, an individual reading must be discarded if it deviates from the 10-point mean by more than:
THEORY AND STRUCTURAL CONTEXT
Civil engineering background & physical principles.
In civil structural engineering, construction quality control, building inspection, and structural forensics, the Schmidt Rebound Hammer (invented by Swiss engineer Ernst Schmidt in 1948) is the most widely utilized non-destructive testing (NDT) instrument worldwide for assessing in-situ concrete surface hardness and uniformity. Standardized under ASTM C805 / BS EN 12504-2, the Type N Swiss rebound hammer operates on the principle of elastic impact and rebound energy conservation. A spring-loaded internal steel hammer mass (impact energy 2.207 N·m / Joules) is cocked inside a tubular housing. When the instrument's plunger is pressed perpendicularly against a smooth concrete surface, a release latch trips, driving the hammer mass against the back of the plunger at high velocity. The plunger transmits compressive stress waves into the concrete matrix, plastically indenting a tiny surface zone and rebounding elastically. The rebound distance of the hammer mass is recorded by a sliding indicator rider along a calibrated linear scale (0 to 100), reading the dimensionless Rebound Number R. Harder, higher-strength concrete absorbs less plastic deformation energy, reflecting a greater proportion of kinetic energy and yielding a higher rebound number R. Standardized conversion curves relate rebound number R to compressive strength f_c: f_c = 0.8500 · R + 12.00 MPa (for horizontal impact orientation). Rebound readings are influenced by surface texture, carbonation depth, moisture saturation, coarse aggregate mineralogy, and impact angle (horizontal, vertically downward on slabs, or vertically upward on soffits). In this laboratory investigation, rebound indices from R = 20.0 to 50.0 are evaluated across calibrated concrete blocks to calibrate strength sensitivity slope = 0.8500 MPa/R (yielding compressive strength f_c = 39.2 MPa at R = 32.0).
f_c = 0.8500 · R + 12.00
Tested on horizontal impact faces of matured concrete specimens. Linearized calibration correlates estimated compressive strength f_c directly to rebound number R with slope 0.8500 MPa/R and intercept 12.00 MPa.