One of the most important parameters associated with concrete is its compressive strength. Currently, there is no reliable nondestructive testing technique that is capable of robust determination of this parameter. Concrete is a heterogeneous mixture composed of water, cement powder, sand (fine aggregate), rocks of various size or grade (coarse aggregate), and air (porosity). Water and cement powder chemically combine into a cement paste binder which, in due curing time (28 days), produces concrete with its specified compressive strength. Compressive strength of concrete is strongly influenced by its water-to-cement (w/c) ratio as well as its coarse aggregate-to-cement (ca/c) ratio. Therefore, if these two parameters are determined using a nondestructive testing technique, then they may be correlated to the compressive strength. Near-field microwave nondestructive testing techniques, employing open-ended rectangular waveguide (OERW) probes, have shown tremendous potential for evaluating concrete constituent make-up. In this paper, the results of an extensive set of measurements, using these probes, are presented. The results demonstrate that the statistical distribution of the multiple measurements of the magnitude of reflection coefficient of concrete specimens with various constituent make-ups follows two well-known distributions as a function of frequency. It is shown that for the specimens investigated this distribution is Gaussian at 10 GHz and uniform at 3 GHz. Furthermore, the standard deviation of the measured magnitude of reflection coefficient at 10 GHz is shown to correlate well with concrete (ca/c) ratio, whereas, the mean of this parameter at 3 GHz is correlated well with concrete (w/c) ratio. Subsequently, these parameters may be used in conjunction with well established formulae or a look-up table to determine the compressive strength of a given concrete specimen.


Electrical and Computer Engineering


National Science Foundation (U.S.)
Electric Power Research Institute

Keywords and Phrases

Binders; Cements; Compressive Strength; Concrete Aggregates; Correlation Methods; Curing; Electromagnetic Wave Reflection; Microwaves; Mixtures; Nondestructive Examination; Porosity; Sand; Microwave Near Field Reflection; Concrete Testing

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

File Type





© 2000 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Feb 2000