Magnesium oxychloride (MOC) boards have gained attention as low-carbon construction materials, yet their durability depends on moisture-driven changes in their internal chemistry. The dominant binding phase, the 5-phase (5Mg(OH)₂·MgCl₂·8H₂O), is susceptible to water and its stability can be compromised when the board is exposed to high humidity environments for prolonged duration. This effect also influences the behavior of embedded fasteners. [BR1] [BR2] [BR3] Despite this, there has been no systematic nondestructive method to evaluate the corrosion performance of fasteners inside MOC boards. Industries have relied on woodrelated testing approaches that only reveal damage on the stud, not the fastener, at the end of exposure. Existing MOC standards, such as PAS 670, focus on physical and mechanical durability under constant high humidity and temperature, yet they do not represent field conditions, which is characterized by cyclic wet/dry conditions that activate corrosion or influence the stability of the 5-phase in service. This study introduces an electrochemical methodology and controlled humidity and temperature cycles to assess and accelerate the corrosion of galvanized fasteners with and without coating in MOC boards, respectively. Physical-chemical tests included water absorption, capillary uptake, permeability, and resistivity to describe moisture transport. X-ray diffraction (XRD) identified the crystalline phases present in the boards, including the 5-phase. Scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to characterize the condition of the fasteners before and after exposure. These measurements describe the state of the boards and fasteners and provide the basis for interpreting the electrochemical response. Nondestructive electrochemical monitoring using open-circuit potential (OCP) and linear polarization resistance captured changes in fastener activity during exposure. The OCP was used to identify when the steel was protected, when the Zn was being depleted, and when the steel was actively corroding, which was confirmed by visual inspection. Boards with higher moisture uptake and lower electrical resistivity showed earlier transitions to active steel corrosion, whereas boards with more restricted moisture transport exhibited delayed activation under cyclic exposure. The proposed cyclic protocol provides reproducible measurements and allows for a comparative assessment of both board quality and fastener performance.This approach offers a practical and nondestructive method to evaluate corrosion in MOC fastener assemblies and supports the development of testing procedures that reflect the moisture-dependent behavior of MOC materials and their primary 5-phase.
