Structure, dispersion, properties and multifunctional applications of natural halloysite nanotubes: Recent progress and future challenges

In the context of the carbon-reduction strategies and sustainable engineering, nanomodification is proposed as an approach to design and optimize cementitious materials. Halloysite nanotubes (HNTs), natural hollow tubular aluminosilicates, have attracted increasing interest in cementitious materials due to high aspect ratio, inner-outer charge asymmetry, and easily modified surfaces. This study systematically reviews the structural characteristics, tubular formation mechanisms, and dispersion behavior of HNTs, with particular emphasis on the effects of thermal treatment, acid/alkali treatment, and surface functionalization on crystal structure, surface chemistry, dispersion stability, and interfacial compatibility. On this basis, the reinforcing effects and regulatory mechanisms of HNTs on the mechanical properties, durability, and microstructure of diverse cementitious systems are critically assessed. Unlike conventional nanofillers or supplementary cementitious materials (SCMs), HNTs serve not only as a nano-reinforcing phase to enhance rheology, crack propagation resistance, and multi-scale interfacial structures, but also enable multifunctional applications including self-healing, controlled release, corrosion resistance, energy storage, and smart responsiveness through lumen loading, surface functionalization, and reactive activation. Current evidence indicates that the engineering performance of HNTs is governed jointly by morphological parameters, dispersion behavior, surface activity, and the chemical environment of the matrix. Their contribution extends beyond physical filling or bridging effects and instead arises from the coupled action of structural, interfacial, and functional mechanisms. Nevertheless, several issues still limit the engineering application of HNTs, including stable dispersion in highly alkaline environments, the long-term service reliability, and the lack of quantitative structure-property relationships. Finally, future research directions are proposed from the perspectives of structural regulation, interfacial engineering, functional integration, and application expansion toward intelligent construction, with the aim of providing a systematic theoretical basis and research framework for the development of low-carbon, high-performance, and multifunctional cementitious materials incorporating HNTs.