Chemical fundamentals of geopolymers in sustainable construction

Abstract

The rising environmental toll of traditional cement production, marked by substantial resource consumption, high greenhouse gas emissions, and low energy efficiency, drives the need for alternative, sustainable building materials. This review advocates for a shift towards geopolymers as a sustainable alternative, focusing on their chemical fundamentals, which are key to this transition. The study affirms that geopolymers support multiple Sustainable Development Goals (SDGs) through their lower carbon footprint and reduced resource usage, addressing the critical need for eco-friendly construction options. Further, the review refines the classification of aluminosilicate raw materials into true precursors and auxiliary materials and details their reactivity profiles, essential for enhancing geopolymer formulations and thereby improving their quality. The review clarifies common misunderstandings in geopolymer chemistry, such as the differences between chemical alkalination and alkali activation, activators versus hardeners, and gels versus geopolymers, as well as dissolution versus depolymerization, improving the foundational knowledge needed for material science innovation. Examination of key composition ratios such as SiO₂/Al₂O₃, M₂O/SiO₂, SiO₂/Fe₂O₃, Na/Fe, Al/Fe and H₂O/M₂O highlights their significant impact on the mechanical properties and longevity of geopolymers. Furthermore, the distinctions between alkali-aluminosilicate (AAS) and aluminosilicate phosphate (ASP) geopolymers are elucidated, showing that AAS geopolymers offer better early-age strength, whereas ASP geopolymers provide greater thermal stability and dielectric properties. The review also specifies that curing processes are crucial to geopolymer performance, with high-temperature curing boosting early strength at the potential cost of long-term durability, and ambient curing enhancing durability and environmental resistance. The review further advocates for standardized testing procedures and regulatory frameworks to promote wider adoption of geopolymers in sustainable construction. Overall, this review underscores the importance of advancing geopolymer technology through a deep chemical understanding and regulatory support, facilitating their broader integration into sustainable construction practices and establishing geopolymers as a fundamental component of eco-friendly building solutions.