Carbon nanotube reinforced cementitious composites: A comprehensive review

During the past decade, researchers investigated the incorporation of carbon nanotubes (CNTs) as a reinforcement for cementitious materials to achieve multifunctional properties. Nevertheless, the mechanisms by which CNTs affect various properties of the cementitious composites including the fresh and hardened states remain elusive. Furthermore, conflicting experimental results have been reported. The discrepancy is attributed to the variability in dispersion, bonding states, and the inconsistencies in the fabrication process (e.g., matrix composition and material characteristics) of the various research conducted. To overcome these challenges, few researchers have investigated the development of analytical equations that could capture the complex interactions between CNTs and the cementitious matrix in order to predict the final properties. This review presents a comprehensive discussion on the research that has been conducted to this date, and provides a detailed insight into the various reinforcing mechanisms of CNTs. To this extent, first, the extraordinary multifunctional properties of CNTs alongside with their various production methodologies are discussed. Also, potential applications of CNT-reinforced cementitious composites are illustrated. Furthermore, the dispersion methodologies implemented to achieve a well-dispersed and homogenized material are presented including the surfactant-assisted ultrasonication procedure. Moreover, the impact of surface treatment of CNTs on the dispersibility and bonding characteristics of the nano-reinforcement within the cementitious matrix is provided. Then, the latest investigations on the microstructure and fresh properties of CNT-reinforced cementitious composites are discussed. In addition, a statistical analysis on data gathered from the available literature is conducted to search for optimal experimental parameters that can achieve the desired mechanical properties (i.e., compressive strength, flexural strength, elastic modulus, and toughness). Also, recently developed prediction models to estimate the mechanical properties are presented. Finally, the impact of CNTs on the dimensional stability (i.e., shrinkage and creep), durability (e.g., resistance to freezing and thawing and corrosion), and smart applications (i.e., self-sensing, electromagnetic shielding, and energy harvesting) is investigated