Determination of Surfactant Content for Optimum Strength of Multi-Walled Carbon Nanotube Cementitious Composites

Abstract

This paper proposes a method for the determination of the optimum surfactant amount to achieve the highest strength for carbon nanotubes (CNT) cementitious composites. The method is based on combining the results of a chemical and a mechanical test. The chemical test was used to determine the remaining amount of surfactant after sonication by analyzing solutions containing CNTs, polycarboxylate surfactant, and water. On the other hand, the mechanical test was used to determine the optimum polycarboxylate surfactant amount that achieved the composite’s highest strength by conducting flexural and compressive tests on cement paste specimens prepared using various surfactant concentrations (i.e., 0.03%, 0.08%, 0.12%, 0.15%, 0.32%, and 0.60%). The results show a strong relationship between the paste’s strength and the surfactant’s concentration. The mixes prepared using 0.08% surfactant-to-cement weight fraction achieved the highest flexural and compressive strengths. Increasing the surfactant-to-cement weight fraction beyond 0.08% resulted in a reduction in the flexural and compressive strengths. This shows the importance of the proposed method in determining the remaining amount of free surfactant in the solution after sonication, and in preventing overdosing that will adversely affect the flexural and compressive strengths of CNT–cement composites.