*Article* **Mechanical and Non-Destructive Testing of Plasterboards Subjected to a Hydration Process**

**Zbigniew Ranachowski 1, Przemysław Ranachowski 1, Tomasz D ˛ebowski 1, Adam Brodecki 1, Mateusz Kopec 1, Maciej Roskosz 2, Krzysztof Fryczowski 3, Mateusz Szymków 4, Ewa Krawczyk 4 and Krzysztof Schabowicz 4,\***


Received: 29 April 2020; Accepted: 20 May 2020; Published: 23 May 2020

**Abstract:** The aim of this study was to investigate the effect of plasterboards' humidity absorption on their performance. Specimens' hydration procedure consisted of consecutive immersing in water and subsequent drying at room temperature. Such a procedure was performed to increase the content of moisture within the material volume. The microstructural observations of five different plasterboard types were performed through optical and scanning electron microscopy. The deterioration of their properties was evaluated by using a three-point bending test and a subsequent ultrasonic (ultrasound testing (UT)) longitudinal wave velocity measurement. Depending on the material porosity, a loss of UT wave velocity from 6% to 35% and a considerable decrease in material strength from 70% to 80% were observed. Four types of approximated formulae were proposed to describe the dependence of UT wave velocity on board moisture content. It was found that the proposed UT method could be successfully used for the on-site monitoring of plasterboards' hydration processes.

**Keywords:** plasterboards; moisture content; hydration processes; mechanical properties; ultrasound measurements
