Advancing Cementitious Composites with Biopolymer-Treated Halloysite Nanotubes: An Innovative Approach to Enhancing Engineering Properties

Achieving a uniform and stable dispersion of halloysite nanotubes (HNTs) in cementitious systems remains a major challenge due to their strong tendency to agglomerate, which limits their reinforcing potential. To address this issue, this study presents an environmentally friendly and sustainable approach that employs natural biopolymers—xanthan gum (XG) and guar gum (GG)—to achieve stable colloidal dispersions of HNTs without relying on chemical surfactants. The novelty of this study lies in the dual functionality of biopolymers, which not only stabilize HNTs through electrostatic repulsion and steric hindrance but also act as viscosity-modifying admixtures that enhance cement hydration and durability. In this method, HNTs were first dispersed in water using ultrasonication and subsequently treated with dissolved biopolymers before incorporation into the cement matrix. The experimental results revealed that the HNT–XG mix exhibited the highest performance among all studied formulations. Although the inclusion of XG-treated HNTs reduced the workability of the mortar, it significantly refined the microstructure of the hardened matrix. After 90 days of curing, the HNT–XG mixture achieved a 29.4% increase in compressive strength and a 9.4% increase in flexural strength compared with the control mixture. Furthermore, it showed reductions in porosity (23.4%), initial and secondary capillary absorption coefficients (30.1% and 43.2%), and rapid chloride penetration charge (38.0%). These findings emphasize the significance of biopolymer-assisted HNT dispersion as a green and effective alternative to conventional chemical admixtures, enabling more efficient utilization of HNTs in cementitious composites while substantially improving mechanical and durability performance.