Effects of halloysite-decorated basalt fiber on mechanical properties and microstructure of iron tailings-based cementitious mortar

Abstract

As one of the largest solid wastes, iron tailings pose a serious threat to the safety of personnel and environment. The lack of toughness in the iron tailings-based cementitious mortar significantly restricts the comprehensive utilization of these tailings. Basalt fibers are widely applied in cementitious composites, but their excessively smooth surfaces render them ineffective in improving the flexural strength of cement-based composites. In this study, we enhance the surface roughness of basalt fibers by modifying them with halloysite (HNTs), thereby improving the mechanical properties of iron tailings-based cementitious mortar. The grafting of HNTs onto the basalt fiber’s surface was achieved via a synergistic modification involving alkali etching and coupling agent. The effects of alkali etching concentrations and etching time on the grafting of HNTs were analyzed by using SEM and IR characterization techniques. The results indicate that the grafting effect intensified with the increase of etching concentration and time. The best grafting of HNTs onto the basalt fibers was achieved after 5 h of etching with a 1.0 mol/L NaOH solution. The resulting halloysite-decorated basalt fibers significantly improve the flexural strength of iron tailings-based cementitious mortar. The iron tailings-based mortar with HNTs-BF attained a 28-day flexural strength of 10.56 MPa, which is 70.6% higher than the control iron tailings mortar without fiber, and 18.1% higher than the iron tailings mortar containing original basalt fiber. Importantly, this study provides a novel and stable solution for surface decoration of basalt fibers, further offering an effective scheme for toughening iron tailings cement mortar.