Technical Questions

ACI Committees, Membership, and Staff have answered common questions on a variety of concrete related topics.

Rebound hammer and in-place strength testing

Q. According to Provision of ACI 301-20, a rebound hammer cannot be used for in-place strength testing. Does ACI recommend any other nondestructive testing (NDT) method for in-place strength evaluation?


A. You are correct, Provision of ACI 301-20 allows use of a rebound hammer in accordance with ASTM C805/C805M, if specified by the Architect/Engineer, only “to evaluate uniformity of in-place concrete or to select areas to be cored.” The same restriction applies to the pulse velocity method per ASTM C597. At the same time, Provision states: “Results of in-place strength tests will be evaluated by Architect/Engineer and are valid only if tests are conducted using properly calibrated equipment in accordance with recognized standard procedures and an acceptable correlation between test results and concrete compressive strength is established and submitted.” However, no specific NDT methods or equipment for in-place strength evaluation are listed. For a review of in-place methods for estimating concrete strength, refer to ACI 228.1R.


References:  ACI 301-20; ACI 228.1R-19; ASTM C805 / C805M; ASTM C597

Topics in Concrete:  Nondestructive Testing; Specifications


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