Magnesium oxychloride cement-based composites: unveiling fire resistance for structural and non-structural applications

Magnesium oxychloride cement (MOC) is commonly known for its eco-friendly properties and versatile applications across various industries. It is often claimed to be inherently fire-resistant, making it a favourable choice for cladding applications, especially in areas prone to wildfires or buildings requiring enhanced fire safety. Moreover, recent development of ductile and water-resistant MOC based composites (MOCC) utilizing supplementary cementitious material, chemical additives and fibres has further opened new avenues for this material in terms of application. Despite this progress, there exists a noticeable lack of research explaining fire resistance of MOC or MOCC, and the mechanisms involved. Additionally, the distinct advantages it offers over alternatives based on ordinary Portland cement (OPC) in terms of spalling resistance remain unclear. Therefore, this study is focused on analysing the fire performance of MOC based composites. 50 mm cubic specimens were tested after subjecting to 200-800°C at a heating rate of 2°C/min and two-hour dwell duration to obtain the residual compressive strength. The results showed a significant decrease in the strength (>95%) of MOCC specimens after exposure to 800°C, highlighting its poor fire performance and raising concerns about its suitability as a structural component. Building upon this finding and seeking to understand the strength loss, differential scanning calorimetry analysis was employed to delve further into the microstructural investigation of MOCC. Furthermore, its spalling resistance was assessed through a novel one-directional spalling test on panels measuring 300mm × 300mm × 20mm based on ISO fire curve. A subsequent comparison was made to an OPC-based cementitious composite with proven high residual performance to showcase distinctions in crack pattern, emphasizing the superior spalling resistance of MOCC and its suitability for non-structural applications.