Mechanistic insights into synergistic strengthening and shrinkage mitigation of alkali-activated materials via natural halloysite nanotubes: a dual-perspective evaluation of tubular nanostructure and calcination-induced reactivity

2026-05-02

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Fangli Zhao

Baomin Wang *

Songlin Yang

Junnan Han

DOI：10.1016/j.cemconcomp.2026.106655

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Alkali-activated materials (AAMs) are promising low-carbon alternatives to Portland cement, however, their widespread application is hindered by inherent brittleness and pronounced drying shrinkage. This study investigates the use of natural, cost-effective halloysite nanotubes (HNTs) as an additive to enhance the strength and mitigate drying shrinkage in AAMs. The key innovation lies in the dual-regulation mechanism involving the inherent tubular nanostructure of HNTs and their calcination-induced reactivity. The effects of HNTs content (0.5∼3 wt%) and calcination temperature (0∼900 °C) on the performance and underlying mechanisms of AAMs were systematically evaluated. The results show that 2 wt% HNTs yielded optimal performance, with 28-day compressive and flexural strengths of 106.8 MPa and 9.2 MPa, representing increases of 9.27% and 26.08%, respectively, compared to the control, and an 11.3% reduction in 84-day drying shrinkage. Thermal activation further enhanced HNTs reactivity, with higher calcination temperatures promoting dihydroxylation and increasing Si/Al dissolution in alkaline media. Notably, HNTs calcined at 750 °C accelerated the reaction kinetics, inducing an additional exothermic peak and reducing setting time by approximately 45%, while simultaneously enhancing compressive strength and reducing drying shrinkage. Microstructural analysis revealed that the performance enhancement was due to matrix densification driven by reduced capillary porosity and gel-structure rearrangement. Compared to commercial carbon nanofibers, HNTs offer a more cost-effective, eco-friendly, and efficient alternative. This research clarifies the microstructural mechanisms of HNTs modified AAMs, offering novel insights for the design of high-performance, sustainable composite building materials.

Keywords:

halloysite nanotubes

alkali-activated materials

drying shrinkage

strength enhancement

calcination temperature

Mechanistic insights into synergistic strengthening and shrinkage mitigation of alkali-activated materials via natural halloysite nanotubes: a dual-perspective evaluation of tubular nanostructure and calcination-induced reactivity

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