Mechanical activation of halloysite as a sustainable precursor for cementitious materials

This work presents a comprehensive investigation of the mechanical activation (MA) of halloysite (Hal) as a sustainable method to enhance its reactivity for the development of cementitious materials in construction applications. Hal, a 1:1 aluminosilicate clay with tubular morphology, is particularly valuable in regions where kaolinite (Kaol) is either scarce or entirely absent. High-energy planetary ball milling was applied to induce structural, morphological, and chemical modifications in a commercial Hal. The study systematically compares the effects of mechanical and thermal activation, employing a suite of advanced characterization techniques to monitor amorphization and microstructural changes. The most intensively milled sample (at 350 rpm for 120 min, H-350-120) reached 86% amorphous content, slightly higher than metahalloysite (MH, 84%). Reactivity was quantified using the modified Chapelle test, the R 3 test, and alkaline solubility in 8 M NaOH. The H-350-120 sample achieved 1659 mg·g −1 of Ca(OH) 2 fixation, 570 J·g −1 of cumulative heat release, and 10.98% bound water content, values closely comparable to those of MH. These findings enable the use of Hal-rich clays in regions with limited Kaol availability, and contributing to the development of supplementary or alternative cementitious materials. • Mechanical activation induces high amorphization in halloysite at low energy input. • Mechanically activated halloysite achieves high pozzolanic reactivity. • Activated halloysite is a promising candidate as a cement precursor. • Mechanically activated halloysite can be used in regions where kaolinite is absent.