Fly ash-dominated High-Strength Engineered/Strain-Hardening Geopolymer Composites (HS-EGC/SHGC): Influence of alkalinity and environmental assessment

In this study, fly ash (FA)-dominated High-Strength Engineered Geopolymer Composites (HS-EGC) were designed and developed. The influence of alkalinity and the underlying mechanism on the mechanical performance and microstructures were investigated through a systematic study. The developed HS-EGC presented high compressive strengths (over 100 MPa) and high tensile ductility (over 4%). Specifically, results showed that HS-EGC with 6% alkalinity possessed the highest compressive strength of 122.7 MPa, the largest tensile strain capacity of 8.0%, and the highest tensile strength of 12.9 MPa. Tensile over-saturated cracking was observed for HS-EGC with alkalinities of 6% and 8% through crack analysis. Back scattering electron and nanoindentation further confirmed that higher alkalinity resulted in higher reaction degrees, but a strength loss was observed at an alkalinity of 8% due to the deterioration of the reaction product. From the comprehensive review of high-strength Engineered Cementitious Composites (ECC) with similar compressive strength and the existing FA-dominated EGC/ECC, it was found that the developed HS-EGC recorded the lowest embodied carbon, embodied energy, and material cost per MPa compared to all the counterparts. Notably, the HS-EGC with 6% alkalinity in this work pushed the performance envelope of FA-dominated EGC. The findings of this study provided useful knowledge for the design and development of HS-EGC for sustainable and resilient infrastructure.