Determination of compressive strength of concrete using free-space reflection measurements in the frequency range of 8-12.5 GHz

A fast and nondestructive method for measurement of compressive strength and water cement ratio (w/c), will be of great interest to the construction industry because compressive strength is one of the most important parameter in the structural design of concrete structures. Also, compressive strength is specified for building code compliance. In this paper, a study was conducted to apply a free-space microwave technique for determination of compressive strength and w/c ratio of concrete. This technique utilizes the reflection properties of concrete in the frequency range of 8-12.5 GHz. Concrete specimens were prepared using different concrete mix constituents, different w/c ratios and different compressive strengths. The reflection properties of concrete specimens were evaluated over a range of frequency and curing age. The results indicate that free-space microwave sensing has the ability to determine the compressive strength and w/c ratios of concrete. This technique is easy to adapt for in-situ measurements and can determine concrete constituent proportions.