Manufacturing and evaluation of mechanical and physical properties of green geopolymer composite reinforced with kenaf fibers and carbon nanotubes

The aim of this study was manufacturing and evaluation of the mechanical and physical (water absorption) of a green geopolymer composite reinforced with kenaf fibers and carbon nanotubes. For this purpose, the effect of amount of kenaf fibers, carbon nanotubes and water each in 5 levels (% wt) compared to metakaolin-based geopolymer and steel slag on the mechanical and physical properties of the composite were evaluated. Response surface method and central composite design were used as statistical method to select the mixtures. Bending tests (bending strength, modulus of elasticity and fracture toughness), compression test and water absorption were conducted on the samples. Also, ultrastructure of geopolymer and dispersion quality of carbon nanotubes and kenaf fibers in the composite matrix, was evaluated by FESEM images. The results showed that by increasing the amount of kenaf fibers up to 7.5%, the bending strength, compressive strength, fracture toughness and water absorption increased, whilst at higher amounts of the fibers, the values of mechanical strength decreased. Also, the use of carbon nanotube as a reinforcement up to 0.6%, had a positive effe on increasing the mechanical strengths of the composite. The results of FESEM showed that with increasing the amount of percentage of kenaf fibers, and carbon nanotubes the diameters of pores in matarix highly increased. Generally, in this research accoriding to the statistical results, the sample with the combination of 7.5% kenaf fiber, 0.6% carbon nanotube and 29% water is introduced as the optimal combination.