DEVELOPMENT OF A MICROWAVE FREQUENCY SENSOR FOR THE LONG-TERM LOCALISED MOISTURE MONITORING OF CONCRETE

Monitoring the moisture levels in concrete over long periods of time is important, as moisture plays a pivotal role in the corrosion process of embedded reinforcement steel in concrete. It is also key in a number of other deterioration processes, and can be used as an indication of changes in the conditions, thus providing a useful early warning system for potential chemical attack. Maintenance needs are thus flagged up before damage is caused. Following an overview of these deterioration processes in concrete, this paper outlines the development of a microwave frequency sensor operating at around 1 GHz and utilising a transmission line either embedded into the concrete at the time of production or encapsulated in a porous medium and inserted into the concrete. It has been amply demonstrated that the method is capable of measuring the moisture content over a wide dynamic range, up to saturation. Trials showed that the encapsulating medium has necessarily to have a microstructure similar to the concrete to...