Utilization of sodium carbonate activator in strain-hardening ultra-high-performance geopolymer concrete (SH-UHPGC)

In this study, strain-hardening ultra-high-performance geopolymer concrete (SH-UHPGC) was produced using Na₂CO₃, Na₂SiO₃ and their hybridization (1:1 in mole ratio) as alkaline activators. An ultra-high compressive strength was achieved for all the developed strain-hardening ultra-high-performance geopolymer concrete (i.e., over 130 MPa). Strain-hardening ultra-high-performance geopolymer concrete with hybrid Na₂CO₃ and Na₂SiO₃ activators showed the highest compressive strength (186.0 MPa), tensile strain capacity (0.44%), and tensile strength (11.9 MPa). It should be highlighted that very significant multiple cracking can be observed for all the strain-hardening ultra-high-performance geopolymer concrete even at a very low tensile strain level (e.g., 0.1%). According to the reaction heat, microstructures, and chemical composition analyses, strain-hardening ultra-high-performance geopolymer concrete with hybrid activators had the highest reaction degree, while that of Na₂CO₃-based strain-hardening ultra-high-performance geopolymer concrete was the lowest. It was found that the Na₂CO₃-based strain-hardening ultra-high-performance geopolymer concrete showed the best sustainability, and the strain-hardening ultra-high-performance geopolymer concrete with hybrid Na₂SiO₃ and Na₂CO₃ presented the best overall performance (considering the mechanical performance, energy consumption, environmental impact, and economical potential). The findings of this work provide useful knowledge for improving the sustainability and economic potential of strain-hardening ultra-high-performance geopolymer concrete materials.