Metakaolin-red mud/carbon nanotubes geopolymer nanocomposite: mechanical properties and structural studies

Abstract

Abstract In this research, the mechanical properties and structural studies of the geopolymer nanocomposite of metakaolin-red mud/carbon nanotubes were investigated. The geopolymer was designed by using metakaolin and red mud as aluminosilicate sources. Red mud replaced between 10 to 30% of the metakaolin. The mass ratio of the solid material and activator liquid was optimized in 1.5:1. Afterward, 1, 2, and 3 wt% multi-wall carbon nanotubes (MWCNTs) were dispersed in a polycarboxylate-based superplasticizer and were added to the geopolymer, which was mixed homogeneously. Geopolymer nanocomposites were characterized by XRD, FTIR, SEM, compressive and flexural strength measurements. The results indicated that the compressive and flexural strengths of the samples increased with curing time. The addition of red mud decreased the compressive and flexural strength of the geopolymer samples due to less reactivity and presence of a non-reactive impurity in red mud. By adding 2% MWCNTs, the compressive and flexural strengths increased to 37.05% and 36.06%, respectively, owing to the crack-bridging mechanism and filling of the cavities and porosity. FTIR spectra demonstrated the growth of the asymmetric stretching vibrations of T–O–Si (T: Si or Al) at approximately 995.85–1083.55 cm−1, confirming the realization of the geopolymerization process in the structure.