# Crystallization-Dominated Rapid Setting of Geopolymers at Low-Preparation Temperature and Low-Modulus Alkali Activators

## TL;DR

A new method for making geopolymers set quickly at low temperatures is developed, reducing setting time by over 90% and offering benefits for cold climate construction and waste utilization.

## Contribution

Introduces a crystallization-dominated setting mechanism using low-temperature and low-modulus alkali activators for rapid-setting geopolymers.

## Key findings

- Setting time of geopolymers is reduced to 20 minutes at 0–10 °C with a 91.63% reduction.
- A distinct reaction sequence of 'hardening stage–dissolution stage–gelation stage' is observed.
- Using vanadium-extraction shale tailings achieves a compressive strength of 38.32 MPa in rapid-setting geopolymers.

## Abstract

What are the main findings?
A novel rapid-setting geopolymer preparation method is proposed.Setting time is reduced by over 90%.An activator crystallization-dominated setting mechanism is revealed.

A novel rapid-setting geopolymer preparation method is proposed.

Setting time is reduced by over 90%.

An activator crystallization-dominated setting mechanism is revealed.

What are the implications of the main findings?
Provides an energy-saving solution for emergency engineering in cold climates.Opens a new avenue for rapid resource utilization of bulk solid waste.Establishes a new paradigm for designing setting-controllable geopolymers.

Provides an energy-saving solution for emergency engineering in cold climates.

Opens a new avenue for rapid resource utilization of bulk solid waste.

Establishes a new paradigm for designing setting-controllable geopolymers.

Current research on rapid-setting geopolymers primarily focuses on accelerating the “dissolution-gelation” reaction process (including dissolution, polycondensation, and hardening) to achieve the faster solidification of the material. In this work, the low-temperature crystallization phenomenon of sodium silicate solution is innovatively introduced into the geopolymer system, and a rapid-setting strategy is proposed by exploiting the synergistic effects of a low preparation temperature and a low activator modulus (the SiO2/Na2O molar ratio) to intentionally induce the rapid crystallization of the alkali activator solution (sodium silicate solution), thereby enabling rapid setting of the geopolymer. Experimental results show that, at a preparation temperature of 0–10 °C and an activator modulus of 1.0, the final setting time of the metakaolin-based geopolymer is shortened to 20 min, corresponding to a reduction of up to 91.63%. Unlike the typical “dissolution stage–gelation stage–hardening stage” route of conventional geopolymers, the rapid-setting geopolymer in this study follows a distinct reaction sequence of “hardening stage–dissolution stage–gelation stage”. Meanwhile, to further enhance performance and expand pathways for solid waste valorization, vanadium-extraction shale tailings (VST) were employed to partially replace metakaolin. The results indicate that, with a tailings replacement of 30%, an alkali-to-solid ratio of 0.4, and an alkali-to-water ratio of 0.7, the rapid-setting geopolymer achieves a compressive strength of 38.32 MPa. These findings confirm the broad applicability and practical potential of the proposed approach for emergency repair in cold regions and solid waste utilization.