Intelligently designed fly-ash based hybrid composites with very high hardness and Young's modulus

- Alkali activated samples prepared from mixture of 80 wt% fly ash (FA), 18 wt% WCC and 2 wt% chopped glass fibre.
- Synthesized alkali activated samples showed a characteristic load independence of nanohardness and Young's modulus.
- Unique strain tolerance behaviour.

Currently, India generates annually about 112 million tones of fly ash (FA), as an industrial waste from thermal power plants. As part of the global journey to convert waste to wealth here we report the intelligent design based synthesis of FA based hybrid composites with spectacular improvement in Young's modulus and nanohardness. The novel design approach utilized alkali activation as well as simultaneous reinforcements of the porous FA matrix with a layered white china clay (WCC) and chopped E glass fiber. The developed materials were subsequently characterized by nanoindentation technique, pH measurement, alkali dissolution, FESEM, etc. techniques to evolve the structure-property correlation. The optimized design and optimal alkali activation lead to achievements of about 233% and 545% enhancements in Young's modulus and hardness, respectively. These results are rationalized in terms of chemical analysis, Si:Al ratio, presence of silicate network modifiers e.g., Na2O and CaO, microstructure, density, extent of polymerization due to alkali activation, processing condition and elastic recovery as well as the ratio of energy spent in elastic and plastic deformations during the nanoindentation processes. Finally, a schematic model is proposed to explain the experimental observations.