Structural Performance of CNT-Reinforced Cementitious Materials Considering the Effect of Chirality of Nanotubes

Abstract The chirality of carbon nanotubes (CNTs) directly affects their mechanical properties, i.e., compressive and tensile strength, and hence, engineering behavior of the modified composites is dependent on these chirality-controlled characteristics. Despite extensive evaluations, the chirality of CNTs and the corresponding effects on cement-based materials have not been well addressed. Thus, in the present study, multiwall CNTs, including armchair, chiral, and zigzag CNTs, with different chiralities were incorporated separately into cement pastes to investigate the engineering behavior of the resulting composites. Compressive and flexural strength was evaluated; also, a scanning electron microscope (SEM) was applied to analyze the dispersion of the nanotubes, porosity of the paste, and effects of CNTs on the micro-crack progression. In addition, the effects of nanotubes physical characteristics were evaluated based on a comprehensive comparative study; also, the corresponding influence in conjunction with the CNT content was probed. The results revealed that while armchair-modified composites led to undesirable strength development, specimens modified by chiral CNTs demonstrated great structural enhancement. According to the SEM images, the reduction of cracks, bridging effects of the nanotubes, and higher hydration rates were observed. The results of the present study could be utilized for developing CNT-modified composites with optimized engineering behavior.