# Magnesium Oxychloride Cement: Development, Opportunities and Challenges
## 7 Application of MOC as a Fire-Resistive Material  
MOC has been regarded as inherently fire-resistant in past studies [11; 34; 109]. Regarding the fire-resisting mechanism of MOC, there is very limited literature available, and the complete understanding of its mechanism is still uncertain and needs further investigation. [PERSON] et al. [110] conducted a study on the elevated temperature behavior of pure MOC mixes, noting a complete loss in compressive and flexural strength as temperatures rose from 100 to 500 \({}^{\circ}\)C. To enhance the elevated temperature performance of MOC, [PERSON] et al. [35] investigated the incorporation of hybrid fibers (basalt fiber and polypropylene fiber) into MOC. Results showed a substantial deterioration in compressive strength, ranging from approximately 30% to 87% at 400 \({}^{\circ}\)C and over 95% at 800 \({}^{\circ}\)C (Figure 12), with no observed cracks or spalling. Tensile strength was entirely lost at 600 \({}^{\circ}\)C, accompanied by a significant mass loss exceeding 30%, indicating notable matrix decomposition. The study suggested future research incorporating various admixtures into MOC to generate more thermally stable hydration phases. Moreover, a few studies regarding the use of MOC as a fire-resistive coating material were also conducted, depicting the potential of MOC to resist high temperatures without deteriorating the interior substrate [11; 34]. [PERSON] and [PERSON] [36] studied the performance of MOC as a fire-resistive coating material, and MOC was found to have good insulating properties due to the presence of water of hydration which acts as an insulating agent when used as a coating material. Further, they mentioned that when a cementitious composite coated by MOC was heated to a temperature of 301 \({}^{\circ}\)C, the chemically bonded water within the composite was released, but not discharged outside due to the presence of the MOC coating. Due to the insulating effect of hydration water of MOC, the discharge of entrapped high-water content required a huge amount of energy, approximately 1000 Btu per pound. They also suggested that MgO acted as an excellent reflector, hence, the cement structure remaining after the loss of water of hydration was still an integrally sound structure due to the presence of MgO. Similar findings were also reported by [PERSON] et al. [111] and [PERSON] et al. [34]. [PERSON] and [PERSON] [11] further reported that MOC binders had good heat resistance because of the significant amount of crystalline water (typically about 35% hydrated water by weight) in MOC phases, which is difficult to liberate and requires a lot of energy. This large amount of crystalline water, along with the capacity of MgO to effectively reflect heat, were found to be the two main contributors to its better thermal resistance. Figure 12: Residual compressive strength of MOC reported in previous studies [35; 110]. [PERSON] et al. [109] studied the thermal performance of MOC using comprehensive microstructural analysis such as X-ray diffraction analysis (XRD), thermal gravimetric analysis (TG), infrared spectroscopy (IR), differential scanning calorimetry (DSC), and derivative thermogravimetry (DTG). It was revealed that dehydration occurred up to 200 \({}^{\circ}\)C, whereas the crystals were completely decomposed to MgO up to 600 \({}^{\circ}\)C with the liberation of HCl (Figure 13). Further, they reported that both phase 3 (3.1.8) and phase 5 (5.1.8) disintegrate through stepwise dehydration, followed by degradation and dissociation to MgO and HCl by 600 \({}^{\circ}\)C.  
Table 1 further presents the thermal-analytical findings of the MOCs, indicating that it is transformed into MgO when subjected to 500 \({}^{\circ}\)C. [PERSON] et al. [109] further stated that the release of HCl during heating must be considered when using MOC binders for fire protection in household applications.