Impact of oxidized carbon nanotubes on the mechanical, thermal, and hygric properties of Portland cement- and magnesium oxychloride cement-based mortars: A route to advanced building composites

Carbon nanotubes (CNTs) have gained attention as nano-reinforcement for cementitious materials due to their exceptional mechanical, thermal, and self-sensing properties. While extensively studied in Portland cement (PC) composites, their application in magnesium oxychloride cement (MOC) remains underexplored. However, challenges such as CNTs agglomeration and MOC’s moisture susceptibility limit their effectiveness. This study investigates the impact of oxidized multi-walled carbon nanotubes (CNTox) on the mechanical strength, durability, and water resistance of MOC, with PC composites included for comparison. Two sets of PC- and MOC-based samples were prepared and analyzed in detail, focusing on elemental composition, phase composition, fracture surface microstructure, mechanical properties, thermal, and hygric properties. The results indicate that low CNTox concentrations enhance mechanical strength and retard water ingress. In MOC composites containing 0.1 wt.% of CNTox, an 8.4% increase in compressive strength, a 14.0% enhancement in flexural strength, and a 0.5% increase in Young’s modulus were recorded. In PC-based composites, the addition of CNTox led to an improvement in flexural strength by 10.6-20,0%, while the maximum compressive strength increased by up to 50% in the composite with 0.05 wt.% of CNTox. Thermal conductivity and heat storage increased in all composites containing CNTox. Furthermore, the moisture resistance of CNTox-reinforced MOC composites improved by approximately 1.9–21.4% compared to the control mix. The results highlight the potential of CNTox as an effective nanoadditive for enhancing the properties of cement-based construction materials.