Microwave non-destructive testing of cement concrete using free - space technique / Mazni Munir

Since the existence of moisture in concrete is a major cause of damage to pavements and other concrete structures, there is an increasing need for non-destructive detection and monitoring of moisture content before failure opcurs. Thus, we have developed a free-space measurement system at microwave frequenties in the frequency range of 8.0 -12.5 GHz. for the measurement of reflection and transmission coefficients, S„ and S2l of concrete samples. The dielectric constant and loss tangent values are calculated from the measured data via a C++ language program. Dielectric properties are correlated to water content by dielectric mixture theory. Water content will be measured for different wet specimens of cement concrete, with varying values of air void content. The key components of the measurement system are a pair of horn lens antennas, Wiltron Vector Network Analyzer, mode transitions and a printer. Brrors due to multiple reflections between antennas via the surface of the sample are corrected by using a free-space LRL (Line, Reflect, Line) calibration technique.