University of New Mexico

Civil Engineering Department

Civil Engineering Materials Laboratory, CE 305L

REBOUND NUMBER OF HARDENED CONCRETE

ASTM C805

Scope

This ASTM test method covers the determination of the rebound number of hardened concrete using a spring-driven steel hammer.

Summary

A steel hammer impacts, with a predetermined amount of energy, a steel plunger in contact with a surface of concrete, and the distance that the hammer rebounds is measured.

This test method may be used to assess the in-place uniformity of concrete, to delineate regions in a structure of poor quality or deteriorated concrete, and to estimate in-place strength development. To use this method to estimate strength development requires establishment of a relationship between strength and rebound number for a given concrete mixture.

Apparatus

Rebound Hammer – a spring-loaded steel hammer which when released strikes a steel plunger in contact with the concrete surface.

Test anvil – a 6 inch diameter by 6 inch long high-carbon steel cylinder hardened to Rockwell 65-67 C.

Abrasive stone – silicon carbide of medium grain texture.

Procedure

Download Procedure for Rebound Number

•  Firmly hold the instrument in a position that allows the plunger to strike vertically downwa rd against the test anvil and verify that the rebound hammer provides the rebound number specified. Be sure to follow the same procedure as for testing the subsequent concrete test surface. Note that the test anvil shall be placed on a solid surface, e.g., concrete floor.

2) Grind and clean the concrete surface using the abrasive stone.

•  Firmly hold the instrument in a position that allows the plunger to strike perpendicularly to the concrete test surface.

•  Gradually increase the pressure on the plunger until the hammer impacts.

5) Examine the impression; if the impact crushes or breaks through a near surface void, discard the reading.

6) After impact, record the rebound number to the nearest whole number.

View a Quicktime Movie of a rebound hammer test

Report

1) Report the test date, type of concrete, and estimated unconfined compressive strength.

•  Hammer orientation, i.e., downward, upward, horizontal, or at a specific angle.

3) Average rebound number to the nearest whole number.