Synthesis and characterization of geopolymers for infrastructural applications

In this study, the synthesis process, composition, and microstructure as well as mechanical properties of geopolymers generated by 3 different kinds of raw materials (i.e., metakaolin, mixture of red mud and fly ash, mixture of red mud and rice husk ash) was explored. For geopolymers from identical raw materials, variable parameters involved in the synthesis were examined to investigate the extent and degree of geopolymerization. Uniaxial compression testing was used to examine the mechanical properties (i.e. compressive strength, stiffness, and failure strain). Then the composition and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well as energy-dispersive X-ray spectroscopy (EDXS). The results demonstrates that the geopolymeric products are not pure geopolymer binders, but geopolymeric composites, which generally comprise pure geopolymer binder as the major matrix, a small amount of unreacted source materials and nonreactive crystalline phases (e.g., quartz, anhydrite, and hematite) from parent materials as inactive fillers. Moreover, the study also shows that geopolymeric products can be used as a cementitious material to replace Portland cement in certain engineering applications, such as roadway construction, which brings environmental and economic benefits. Owing to the consistent properties of metakolin-based geopolymers, they were selected to be examined as smart adhesives for the infrastructure health monitoring. A distributed geopolymer-fiber optic sensing (G-FOS) system was proposed, where metakaolin-based geopolymers are used as smart adhesives to affix optical fibers to existing in-service structures to form the integrated G-FOS sensor for infrastructure health monitoring. The concept of such a G-FOS system was explained, and laboratory experiments as well as prototype testing were conducted to validate the concept and its feasibility. The results showed that varying the geopolymer composition (e.g., SiO2/Al2O3 ratio) and adding sand filler can both alter the tensile cracking strain for tailored sensing applications for both steel and concrete structures. Further prototype testing on steel and concrete demonstrated the feasibility of the proposed G-FOS system that can be used to monitor tensile strain and crack width for steel and concrete structures, respectively