The effects of Fe3O4 and Fe3O4/SiO2 nanoparticles on the mechanical properties of cement mortars exposed to elevated temperatures.

This study investigates the effects of Fe 3 O 4 and Fe 3 O 4 /SiO 2 nanoparticle admixtures on the behavior of cement mortars exposed to elevated temperatures. Pristine nanoparticles of magnetite (Fe 3 O 4 ) were coated with a solid silica shell (via the Stöber method), to form a core-shell nanostructure (Fe 3 O 4 /SiO 2 ). The cement mortars were incorporated with an optimized ratio of 3 wt% Fe 3 O 4 and 5 wt% of Fe 3 O 4 /SiO 2 admixture. The specimens were exposed to elevated temperatures of 200, 300, 450, 600 and 800 °C. After cooling, the mass loss and flexural and compressive strengths of the specimens were determined. The results demonstrated that the presence of magnetite-silica (Fe 3 O 4 /SiO 2 ) nanostructures is much more beneficial for improving the thermal resistance of cement mortars than pristine Fe 3 O 4 nanoparticles. The silica (SiO 2 ) shell in the nanoparticles improves residual compressive strength and prevents crack extension in cement mortars exposed to elevated temperatures. The investigations undertaken in this study were supported by optical and scanning electron microscopic studies. [ABSTRACT FROM AUTHOR]