Characterization of Concrete Curing Using a Microwave Harmonic Sensor

The paper describes a process to use a microwave harmonic sensor, or frequency doubling reflectenna, to understand the evolution of water content during concrete curing. The harmonic sensor has a 3D form factor, is constructed from printed circuit board pieces, and operates at 1.2 GHz (receive) and 2.4 GHz (transmit). The system operates by interrogating a sensor that is embedded in the concrete under test using a wireless reader and correlating variation in signal strength received back from the sensor with the complex permittivity of the concrete. Empirical results from tests of sand-water mixtures, sand-ionic solution mixtures, and cement mortar mixtures are presented. The data demonstrate high sensitivity in signal strength versus moisture and ionic content for relatively low, realistic moisture conditions.