Nanoscale modification of MOC-based composites: the influence of alumina nanosheets on the microstructure and material properties

The presented study deals with the optimization of alumina nanosheets (ANS) content in magnesium oxychloride cement (MOC)-based construction composites filled with silica sand. The experimental setup was designed in such a way that the optimal content of ANS in these composites was determined while ensuring the highest possible values of mechanical parameters (compressive and flexural strength, and Young's dynamic modulus) while maintaining good water resistance of the prepared composite, which is a crucial parameter in terms of MOC-based materials. The designed composites were studied concerning the changes in their structure after the addition of ANS, especially in their porosity and density. The prepared composites were also examined in detail using scanning electron microscopy in order to show changes in their microstructure. It was revealed that the addition of 0.1 wt% of ANS was the most beneficial, causing an 8.4% increase in compressive strength, a 3.4% increase in flexural strength, and an 8.4% increase in the dynamic Young's modulus compared to the sample with no additives. On the other hand, the sample containing 0.5 wt% of ANS showed the best hygric properties with a water absorption coefficient of 3.21 kg m² s^−1/2 and 24-h water absorption of 68.3 kg m⁻³ and the best resistance to water damage defined by the softening coefficient (78.3%) and the residual compressive strength (61.3 MPa) after 24 h immersion in water.