Geopolymer: A Systematic Review of Methodologies

Area of Science:

• Materials Science and Engineering
• Sustainable Construction Materials
• Geopolymer Chemistry

Background:

• Geopolymer technology is gaining international recognition as a sustainable alternative to ordinary Portland cement (OPC).
• Lack of standardized definitions and mix design methodologies creates inconsistencies and confusion in geopolymer research and application.
• Existing literature lacks a clear understanding of unary and binary geopolymer systems, hindering standardization.

Purpose of the Study:

• To clarify existing geopolymer definitions and diverse mix design methodologies.
• To provide a comprehensive understanding of unary and binary geopolymer systems.
• To identify key factors for developing sustainable geopolymer design standards.

Main Methods:

• Systematic literature review based on the Preferred Reporting of Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist.
• Data retrieval and analysis from the Scopus database.
• Synthesis of information on geopolymer reactions, material utilization, and mix design approaches.

Main Results:

• Geopolymers are tecto-aluminosilicate matrices formed via polycondensation reactions.
• Binary geopolymer systems exhibit complex structures influencing workability, strength, and durability compared to unary systems.
• High-calcium industrial by-products (slag, fly ash, phosphogypsum) optimize geopolymer properties, forming C-S-H or C-A-S-H gels.
• Current mix designs predominantly use trial-and-error, with limited application of advanced methods like Taguchi or response surface methodology.
• Alkali activators like NaOH have lower CO2 emissions than sodium silicate (Na2SiO3) but raise sustainability concerns due to causticity and energy demand.

Conclusions:

• Standardization of geopolymer definitions and mix designs is crucial for its adoption as an OPC alternative.
• Optimizing the use of industrial by-products and understanding geopolymer system complexities are key to sustainable development.
• Further research is needed to address innovation gaps and foster robust geopolymer standards for environmental and societal benefits.