Ultra-ductile behavior of fly ash-based engineered geopolymer composites with a tensile strain capacity up to 13.7%

This study introduces ultra-ductile fly ash-based engineered geopolymer composites (UD-EGCs). Four mixtures of UD-EGCs with different ratios of sodium metasilicate pentahydrate (SMP)-to-sodium hydroxide (SH) were designed and prepared at an identical water-to-binder ratio. Polyethylene (PE) fibers at 1.75 vol% were used as reinforcements. Experimental and analytical investigations of mechanical properties, micromechanical analysis, and chemical characterization of UD-EGCs were performed at both meso- and micro-scales. The UD-EGC mixtures were found to strain-harden with ultra-high ductility. Notably, the mixture using an SMP/SH ratio of 1.5 achieved a tensile strain capacity of 13.7% and a tensile strength of 6.8 MPa. Moreover, all mixtures were lightweight, with density below 1.83 g/cm³. From the chemical analysis, C-(N)-A-S-H and N-A-S-H were verified as the primary geopolymeric products of fly ash-based engineered geopolymer composites.