reliably measure compressive strength?
Rebound hammers test the surface hardness of concrete, which cannot be converted directly to compressive strength. ASTM C 805-97, Standard Test Method for Rebound Number of Hardened Concrete, states, “because of the inherent uncertainty of estimating strength with a rebound number, the test is not intended as the basis for acceptance or rejection of concrete.” There are many factors other than concrete strength that influence rebound hammer test results, including surface smoothness, finish, moisture content, coarse aggregate type and the presence of carbonation. Although rebound hammers can be used to estimate concrete strength, the rebound numbers must be correlated with the compressive strength of moulded specimens or cores taken from the structure. The procedure used to develop this relationship is described in ACI 228.1R-03, In-Place Methods to Estimate Concrete Strength, American Concrete Institute.
