Carbon Nanotubes in Cementitious Materials: Structure, Dispersion, and Limitations

This state-of-the-art review examines the use of carbon nanotubes (CNTs) in cementitious materials, with emphasis on CNT structure, dispersion mechanisms, and the practical limitations hindering large scale implementation. Experimental findings from the literature are synthesized to evaluate CNT types, structural characteristics, and dispersion strategies. Attention is given to physical and chemical dispersion approaches, including ultrasonication and polycarboxylate based superplasticizers, with respect to effectiveness, repeatability, and compatibility with cementitious matrices. Although several methods have demonstrated improved CNT dispersion at the laboratory scale, persistent challenges related to agglomeration, re-agglomeration, workability reduction, and scalability remain unresolved. Key gaps include the absence of standardized dispersion protocols, limited understanding of CNT cement interactions at the nanoscale, and inconsistencies in dispersion characterization techniques. Based on these limitations, future research directions are identified, focusing on dispersion reliability, mix design optimization, durability, and the development of practical guidelines for large scale application. This paper provides a foundational reference for advancing the effective and responsible integration of CNTs into next generation cementitious materials.