Microwave Compressive Strength Estimation of Cement Paste using Monopole Probes


In-situ evaluation of the compressive strength of existing concrete structures using a direct approach is the objective of this investigation. The principle factor affecting the compressive strength of a concrete structure is its water/cement (w/c) ratio. The reflection properties of four cement paste samples with w/c ratios of 0.35, 0.40, 0.50, and 0.55 were measured using several monopole probes at microwave frequencies of 5, 9, and 12 GHz. The effect of several parameters, such as the operating frequency, the probe length (h), and the properties of the cement paste (w/c ratio) on the measurement sensitivity, were studied theoretically as well. For a given monopole probe (fixed diameter), h and the operating frequency can be optimized such that any slight change in the w/c ratio causes a large change in the reflection coefficient. Lower microwave frequencies are shown to be more sensitive in detecting variation in the reflection coefficient of these samples as a function of the w/c ratio. After the reflection coefficient measurements for these samples were conducted, they were tested to measure their compressive strength. Subsequently, a correlation between the compressive strength and the reflection coefficient of these samples was shown. The effect of an air gap around the monopole was investigated as well.


Electrical and Computer Engineering

Keywords and Phrases

Compressive Strength; Concrete Structures; In-Situ Evaluation; Electromagnetic Formulation-Probe Development And Antennas; Infrastructure Testing And Cement-Based Material Evaluation; Material Characterization

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


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© 1995 Taylor & Francis, All rights reserved.

Publication Date

01 Jun 1995