Mechanical Performance of Hybrid Fibre Reinforced Magnesium Oxychloride Cement-Based Composites at Ambient and Elevated Temperature

Magnesium oxychloride cement (MOC) is often recognized as an eco-friendly cement and has found widespread application in various sectors. However, research on its resistance against elevated temperatures including fire is very limited. This paper thoroughly investigated the mechanical performance of fibre reinforced MOC-based cementitious composite (FRMOCC) at ambient and elevated temperatures. A recently developed water-resistant MOC was used as the base matrix which was further reinforced using hybrid basalt and polypropylene fibres at various proportions, and a systematic study on the effect of fibre dosage on compressive and tensile strength of FRMOCC was conducted. The specimens were exposed to elevated temperatures ranging from 200 to 800 °C; mechanical performance and phase composition from a microscale study were analysed. The findings revealed that compressive strength, with the increase in temperature, substantially decreased, with values of 30–87% at 400 °C and over 95% at 800 °C. Specimens with 1.5% basalt and 0.5% PP fibre showed the least reduction possibly due to the vacant channels created as a result of the melting effect of PP fibres. Tensile strength was also completely lost at 600 °C and the specimens suffered substantial mass loss exceeding 30% at this temperature, indicating significant matrix decomposition. Additional analysis using X-ray diffraction (XRD) and scanning electron microscope (SEM) revealed the decomposition stages of the matrix and highlighted the instability of the main hydration phases of FRMOCC at elevated temperatures.