Effect of TiO₂ Nanofiber Content on Compressive Strength of Geopolymers Fabricated from Waste Clay

The main objective of this study is to enhance the physical and mechanical properties of geopolymers fabricated from waste clay through incorporation of synthetic TiO₂ nanofibers. Firstly, the nanofibers were chemically synthesized, annealed at 550 °C and then characterized by different tools as x-ray diffraction (XRD), FT-IR, scanning electron microscope (SEM) and transmission electron microscope (TEM). Secondly, three geopolymer batches included 0.1, 0.3 and 0.5 wt.% TiO₂ nanofibers were fabricated using waste clay and alkali activator. The prepared air-cured geopolymers were investigated for their phase composition, physical properties, microstructure and compressive strength by XRD, water displacement method, SEM and compressive strength testing machine, respectively. The results displayed that TiO₂ nanofibers were successfully synthesized by the proposed method. After calcination at 550 °C, anatase form of TiO₂ was formed. The addition of TiO₂ nanofibers has positive effect on the physical and mechanical properties as well as the microstructure of prepared geopolymers due to the enhancement of geopolymerization process, pores' filling and interlocking of the microstructure. The apparent porosity of prepared geopolymers was decreased with increasing the amount of added TiO₂ nanofibers while the compressive strength was increased with increasing the nanofibers up to 0.3 wt.%, then slightly reduced after addition of 0.5 wt.%. The obtained values of compressive strength were 31, 38.5 and 36 MPa for the geopolymers that contain 0.1, 0.3 and 0.5 wt.% TiO₂ nanofibers, respectively.