Impact of carbon nanotubes on chloride diffusion in cement mortar under temperature gradient conditions

Reinforcement corrosion induced by chloride ingress is a major durability issue in cementitious materials, particularly in harsh marine environments. Incorporating carbon nanotubes (CNTs) has emerged as a promising solution to mitigate chloride ingress. However, their performance against chloride diffusion under elevated temperatures remains unexplored. This study explores the influence of adding CNTs in cement mortars, aiming to mitigate chloride ion diffusion under temperature gradient conditions. CNTs were incorporated at 0.05%, 0.10%, and 0.15% by weight of cement in mortar specimens. Specimens were exposed to a 3% NaCl solution at room temperature of 22 °C (CT22), a high ambient temperature of 50 °C (CT50), and under a temperature gradient (TG). The experiment was carried out in two stages: the first stage aimed at finding the optimal mix based on the compressive strength, absorption, porosity, and total chloride concentration profile under the TG condition, whereas the optimal mix was thoroughly analyzed under different temperature conditions along with the assessment of the free chloride concentration profile in the second stage. The results indicated that adding 0.05% CNTs yielded the best performance, showing over a 24.6% increase in strength, about 17.5% reduction in absorption and accessible porosity, improved porous structure, and reduced chloride content. Notably, the critical chloride content based on the accelerated laboratory experimental results was substantially lower in the optimal mix than in the control, suggesting that 0.05% CNTs effectively delays chloride ion diffusion and corrosion initiation, enhancing the durability in marine environments.