Mateusz Szymków

This article shows the results of research into the damaging effect of high temperature on the structure of fibre-cement boards. Samples of fibre-cement boards were exposed to high temperatures over various lengths of time and then they were investigated under the three-point bending and acoustic emission methods. In this way, the critical temperature and the duration of its influence on the structure of a fibre-cement board were determined. An artificial neural network was used to analyse the results obtained using the acoustic emission method. The investigations showed a marked fall in the number of registered AE events for the tested series of boards exposed to high temperature in comparison with the reference boards. Moreover, in the boards exposed to high temperature, a marked increase in the energy of AE events occurs during the bending test, whereby the registered events, by and large, come down to a single pulse induced by a brittle fracture. It is also demonstrated that the determination of the damaging effect of high temperature on the structure of fibre-cement boards solely on the basis of bending strength (MOR) is inadequate.

This paper presents the results of investigations into the effect of the use of recycled waste paper cellulose fibers on the properties of fiber cement boards subjected to contamination by moisture. Four series of fiber cement boards were tested. A reference fiber cement board manufactured without the use of recycled cellulose fibers constituted as one of the series. The other three series consisted of boards differing in their recycled cellulose fiber content-ranging from 10% to 50% of the total cellulose fiber content. Specimens of the fiber cement boards were subjected to contamination by moisture by storing them in water for 1–96 h. Subsequently, their basic physical and mechanical parameters, i.e., mass moisture content, absorbability, and modulus of rupture (MOR), were tested. Then, the specimens were investigated by means of acoustic emission during three-point bending. Artificial neural networks were employed to analyze the acoustic emission test results. The tests clearly showed the amount of recycled waste paper cellulose fibers and the length of storage in water to have an adverse effect on the boards, contributing to their degradation. This was reflected in the decrease of the acoustic emission (AE) events count recognized by the artificial neural networks, accompanying the rupture of fibers during the three-point bending of the specimens. In order to gain a more detailed insight into the changes taking place in the structure of the tested fiber cement boards, optical examinations were carried out by means of a scanning electron microscope. Interesting findings crucial for building practice were noted.

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.