Effect of Carbon Nanotubes on Chloride Diffusion in Cementitious Materials Under the Marine Environment of the Arabian Gulf

Abstract

Chloride-induced corrosion is a significant concern under the aggressive environmental conditions of the Arabian Gulf Region, where high ambient temperatures and the high salinity of seawater intensify the concentration of chloride ions in the atmosphere. These conditions exacerbate the diffusion of chloride ions in cementitious materials, impacting their durability. Specifically, the presence of temperature gradient conditions across sections enhances chloride diffusion through the dual mechanisms of mass and thermal diffusion. This study proposes the use of carbon nanotubes (CNTs) to mitigate chloride ion diffusion under these local temperature conditions.

CNTs were incorporated at concentrations of 0.05%, 0.10%, and 0.15% by weight of cement in mortar specimens with an aggregate-to-binder ratio of 2.75, a water-to-cement ratio of 0.60, and 0.5% superplasticizer content. The aggregates used were a blend of dune sand and crushed sand, typical for local construction practices. Specimens were Ø96mm x 80mm for all tests except compressive strength, which used 50mm cubic specimens. The temperature conditions considered were room temperature (22°C), high ambient temperature (50°C), and a temperature gradient (TG) condition.

The experimental program was conducted in two stages. The first stage identified the optimal mix based on compressive strength, absorption, porosity, and chloride diffusion under a temperature gradient. The second stage assessed the chloride diffusion performance of the optimal mix compared to a control mix under varying temperature conditions. For chloride analysis, specimens were immersed in a chloride solution for 30 days. Subsequently, a 36mm core was extracted from each specimen and sliced into 10mm layers, excluding the top and bottom 5mm. Chloride analysis involved precipitation titration to measure total and free chloride content. The free chloride content was compared between the control mix and the optimal mix exclusively during the second stage.

Results indicated that a CNT concentration of 0.05% is optimal, showing over a 24% increase in strength, a 17.55% reduction in porosity, improved porous structure, and reduced chloride content across all temperature conditions. Notably, the critical chloride content was substantially lower in the optimal mix than in the control, suggesting that 0.05% CNT effectively delays chloride ion diffusion and corrosion initiation in the marine environment of the Arabian Gulf region.

Date of Award	20 Jul 2024
Original language	American English
Supervisor	Tae Yeon Kim (Supervisor)