Geopolymer Modified with Insoluble Calcite and Various Silica Fumes Originated from Different Manufacturing Processes

Area of Science:

• Materials Science
• Civil Engineering
• Geopolymer Chemistry

Background:

• Silica fume (SF), a by-product of silicon manufacturing, improves geopolymer mechanical properties, durability, and workability by dissolving into silicate phases.
• The exact reinforcement mechanism of SF in geopolymers is not fully understood due to geopolymer complexity and variations in SF types.
• Limited calcite solubility in alkaline environments hinders calcium-based gel formation, complicating geopolymer systems containing SF and calcite.

Purpose of the Study:

• To investigate the modification mechanisms of silica fume (SF) on geopolymer materials incorporating insoluble calcite.
• To evaluate how different types of SF influence the properties of fly ash/limestone-based geopolymer materials.
• To understand the role of SF's chemical composition, crystallinity, and activity in geopolymer activation.

Main Methods:

• Two distinct types of silica fume (SF) were utilized as replacements for fly ash in a fly ash/limestone geopolymer system.
• Geopolymer materials were synthesized and characterized to assess the impact of SF on their properties.
• Analysis focused on the influence of SF's chemical composition (Si, Ca, Al, Mg content), crystallinity, and activity on material performance.

Main Results:

• The reinforcement effect of SF on geopolymer materials is highly dependent on the specific type of SF used, even with similar particle sizes and compositions.
• Geopolymer mechanical properties are governed not only by the elemental ratios (Si, Ca, Al, Mg) but also by the crystallinity and activity of the SF.
• The nature of hydration products formed can vary based on the reaction environment influenced by SF characteristics.

Conclusions:

• The study clarifies that SF's effectiveness in modifying geopolymer properties is intrinsically linked to its type, crystallinity, and activity, not just its bulk composition.
• Findings contribute to the optimized design and application of geopolymer materials, particularly those incorporating insoluble components like calcite.
• This research provides a foundation for the sustainable upcycling of industrial solid wastes, including SF, fly ash, and other aluminosilicate materials.