Hydration monitoring and moisture control of cement-based samples through embedded wire-like sensing elements

In this paper, a time-domain reflectrometry (TDR)- based solution for monitoring moisture content in cement-based samples is presented. The proposed system employs a simple flexible biwire, which acts as a distributed sensing element (SE) (as opposed to traditional, local moisture content sensors). Once embedded, the SE remains permanently inside the cement-based sample and can be used both for monitoring the hydration process of the sample structures (ex-ante monitoring) and, successively, for monitoring possible water infiltration during the service life of the structure (ex-post monitoring). In practical applications, the SE could be employed inside building structures at the time of construction, and it could be used for the aforementioned moisture content monitoring purposes. As a preliminary validation of the practical feasibility of the proposed system, in this paper, two cement-based samples (made of mortar and concrete, respectively) were equipped with a SE, and their water content was monitored through TDR measurements, over a 28-day period (thus mimicking the ex-ante monitoring conditions). Furthermore, to verify the potential of the proposed method also for the ex-post monitoring, the air-dried mortar sample was intentionally subjected to wetting conditions and the resulting rising damp was observed through the proposed TDR-based system.