Manufacturing of high-performance light-weight mortar through addition of biochars of millet and maize

Agricultural wastes are environmental hazards, as these wastes can catch fire, resulting in the loss of human and animal lives and properties. Alternatively, the wastes are dumped in large spaces, which are already limited. Cementitious composites are quasi-brittle and develop cracks at the micro and nano level, which affect their strength, durability, and esthetics. Transforming agricultural wastes to biochar and using it as fibers in cementitious materials for crack arresting and enhancing fracture toughness is an environment-friendly approach. In this research, nano to microscale carbonaceous inert fibers (biochar) of millet and maize were prepared through pyrolysis followed by ball milling. The X-ray spectroscopy (EDX) revealed that 82.08% and 86.89% of the carbon content was retained in millet and maize, respectively. The scanning electron microscope (SEM) confirmed the presence of angular, flaky, and needle-like particles in the carbonaceous inerts, which may enhance the strength and the fracture response of the cementitious materials. These inerts were added individually to mortar specimens at dosage levels of 0, 0.025%, 0.05%, 0.08%, 0.2% and 1% by mass of cement. The dispersion of the synthesized nano inerts was ensured by UV–VIS spectroscopy. The compressive strength, flexural strength, porosity, and fracture toughness of cement mortar were evaluated. The carbonized nano intrusions reduced the porosity and density of the mortar specimens. The minimum porosity was noted with 1% and 0.08% dosages of millet and maize, respectively, whereas the minimum density was observed at 1% dosage for both. An increase in compressive and flexural strengths was also noticed. The compressive strength increased by 32% and 28% with 0.2% and 0.5% millet and maize, respectively. An increase of 168% and 114% in fracture toughness was noticed at optimized dosages of 0.5% and 1% of maize and millet, respectively. It is concluded that the addition of carbonaceous inert fibers of millet and maize resulted in light-weight porous mortars with enhanced strength and fracture toughness. The fracture toughness increases with dosage as the nanoparticles enhance the tortuosity.