Understanding the role of carbon nanotubes in low-carbon concrete: From experiment to molecular dynamics

This research aligns with green and sustainable development principles, aiming to augment concrete's mechanical properties and durability. The low-carbon reactive powder concrete was developed by substituting ordinary Portland cement with sulfoaluminate cement. Additionally, an effective method was proposed to enhance the interfacial transition zone (ITZ), involving the pre-saturation of sand particles in a dispersion of carbon nanotubes (CNTs). The role of CNTs on the concrete's mechanical property, hydration process, and microstructure was extensively explored using experiments and MD (molecular dynamics) simulations. The results indicated a 27.8% and 10.1% increase in 28-day compressive strength, along with a 16.7% and 6.3% rise in 28-day flexural strength for the sample with pre-saturated sand dispersed in CNTs (CS2), in comparison to samples without CNTs (C0) and those with dispersed CNTs (C2). The primary enhancement mechanism is ascribed to the CNTs' ability to improve the ITZ through adsorption and nucleation. The CNTs facilitated the generation of AFt (ettringite) and AH3 (gibbsite), enhancing the hydration degree. This mechanism was corroborated by MD simulations that analyzed the effect of CNTs' on the mobility of calcium ions (Ca2+). When dispersed at the ITZ, CNTs had a seeding effect, leading to the generation of AFt and AH3 around the CNTs. This, in turn, reduced the ITZ's width and dramatically improved the bonding between the CNTs and the ITZ, thus effectively enhancing the ITZ's microscopic structure.