Impact of nano-dopants on the mechanical and physical properties of magnesium oxychloride cement composites – Experimental assessment

The importance of the reduction of the World's CO2 emissions due to their non-negligible contribution to climate change is inevitable. As the Portland cement (PC) industry is one of the main contributors to the overall volume of CO2 emissions produced over the World, a sustainable PC substitute must be implemented. Previous scientific studies suggest that magnesium oxychloride cement (MOC) – an eco-friendly binder based on reactive magnesia – could be a suitable alternative. This contribution studies the influence of various nano-dopants on the mechanical and physical properties of MOC-based composites. The nano-dopants introduced to the MOC composite were the following: multi-walled carbon nanotubes, oxidized multi-walled carbon nanotubes, graphene oxide, graphene nanoplatelets, and alumina nanosheets. Ahead of the composite preparation, the nano-dopants were analysed with a wide spectrum of analytical methods to study their composition and microstructure in detail. The used amount of nano-dopant was 1.0 wt.%, relative to the cement paste weight. After a curing period of 28 days, the prepared composite samples underwent a comprehensive analysis of their microstructure, phase, and chemical composition, as well as micro- and macrostructural parameters and mechanical properties. Additionally, the research studied the effects of nano-dopants on the hygric properties and water resistance of the MOC composites after 24-h immersion in water. The findings revealed a noteworthy increase in mechanical parameters with the addition of nano-dopants. The highest compressive strength of 85.4 MPa was obtained for the MOC composite enriched with the addition of oxidized multi-walled carbon nanotubes. MOC doped with alumina nanosheets exhibited the highest value in flexural strength (20.99 MPa) and dynamic modulus of elasticity (38.85 GPa) measurements. The resistance of MOC composites to deterioration in water was also improved by all the implemented nano-dopants. The softening coefficient determined for samples immersed in water for 24 h varied from 62.7 to 74.8%. The best resistance to water degradation was obtained for MOC with alumina nanosheets, which showed a softening coefficient value about 23.2% higher than that of the reference sample. Thus, the incorporation of nanomaterials as functional nano-dopants in MOC-based composites shows promising opportunities in the improvement of both mechanical properties and water resistance, contributing to the development of environmentally sustainable building materials.