Ice-cooled ultra-high performance engineered geopolymer composites for ambient temperature curing: Formulation, properties, and microscale investigation

High-performance engineered geopolymer composites (EGCs) are typically limited by excessively rapid setting times and a reliance on elevated temperature curing. To overcome these kinetic limitations, this study proposes a novel formulation of ice-cooled ultra-high performance EGCs (I-UHPEGCs) to enable ambient temperature curing and regulate reaction kinetics. This thermodynamic control strategy retards the initial geopolymerization rate, optimizing the fabrication process while extending the final setting time by approximately five times compared to conventional EGCs. Systematic experimental evaluations demonstrate that most I-UHPEGC mixtures achieved a compressive strength higher than 120 MPa and a tensile strain capacity approaching 10% at 28 days of age. Remarkably, the mixture incorporating 1.0% PE reinforcement cured in water obtained an outstanding compressive strength of 142 MPa alongside a robust tensile strain capacity of 10.6%. Micromechanical and microstructural analyses attribute this ultra-ductile, strain-hardening behavior to optimal frictional fiber-bridging, the absence of sudden fiber rupture, and dense C-(N)-A-S-H gel precipitation. Consequently, I-UHPEGCs quantitatively outperform all existing high-performance EGCs across comprehensive performance indices governing strength, ductility, and microcrack width.