Magnesium oxychloride cement boards are light and fire resistant, but their behavior in humid environments raises concerns. Moisture can enter the boards, degrade them, and release chloride ions. This process can generate corrosion on the stud and on the fasteners that support the boards. Buildings depend on these connections, so it is important to understand how this corrosion starts and develops. The objective of this project is to create an accelerated testing standard that can copy the moisture and corrosion interaction that happens in real field conditions, but in a shorter and more controlled time. The work follows the guidance of PAS 670:2021. This standard gives a framework to evaluate magnesium cement boards under moisture exposure. It explains how to measure water uptake, size change, material loss, chloride release, and visible damage during extended periods of high humidity. PAS 670 uses steady exposure, for three months, to track slow changes in the boards and does not include corrosion testing of studs or fasteners. This project extends the ideas of PAS 670 to a complete board, stud, and fastener system and adds nondestructive electrochemical methods (Linear Polarization LPR and Open Circuit Potential OCP) to study corrosion during the tests. Earlier test methods used continuous high humidity similar to the steady exposure idea in PAS 670. A previous study at The University of Texas at San Antonio showed that these methods can start corrosion but often keep the boards fully water saturated. When the boards stay saturated, oxygen cannot reach the fastener surface, and the corrosion slows down. Then an alternating wet and dry cycle was developed, which showed behavior that is closer to real conditions. In this paper, the results from the last six environmental cycles that were designed to mimic field exposure are going to be presented. The cycles use short exposure periods at high humidity and warm drying stages at lower humidity, and some cycles also include a short water contact event. Electrochemical tests such as open circuit potential and linear polarization resistance measure corrosion activity, while resistivity tests measure moisture in the boards. Tests were performed on three boards with different filler compositions and on galvanized fasteners with different ceramic coatings. The results show that controlled drying lets oxygen reach the fastener surface and keeps corrosion active. The corrosion data show differences between the boards and coating systems and support the creation of an accelerated cyclic standard.
