Unlocking the Interaction Mechanism of CNTs and C-S-H on Enhancing Elastic and Viscoelastic Properties of Alite Paste.

Carbon nanotubes (CNTs) have demonstrated potential in enhancing the elasticity and viscoelasticity of cementitious materials, yet the mechanisms underlying their influence on hydrates remain unclear. This study employs experimental techniques and molecular dynamics simulations to elucidate the impact of CNTs on alite hydration, spanning initial stages to the hardened state. Results show that CNTs exhibit a weak nucleation effect, which is thus not the primary factor contributing to the enhancement of mechanical properties. Instead, improvements stem from refining the calcium silicate hydrate (C-S-H) gel structure and optimizing the spatial distribution of calcium hydroxide (CH) throughout hydration. The CNT-mediated modulation of Ca distributions strengthens C-S-H cohesion, refines pore size, and promotes the formation of high-density C-S-H, thereby improving elastic properties. Additionally, the influence of CNTs on shear deformation and particle orientation among C-S-H particles is highlighted for viscoelastic properties. These insights redefine CNT contributions, emphasizing their role in long-term ionic and structural tuning, and provide a foundation for designing advanced nanofiber-cement composites with superior mechanical performance.