Ambient Temperature Curing Stimulated One-Part Engineered Geopolymer Composites with Extremely High Ductility and Low Thermal Conductivity

Achieving high tensile strain capacity in practical, ambient-cured one-part engineered geopolymer composites (OP-EGCs) remains a critical challenge, with previously reported tensile strain capacities typically below 5%. This study introduces a novel ambient-cured OP-EGC incorporating expanded polystyrene (EPS) beads that achieves extremely high tensile strain capacity and low thermal conductivity, and experimentally investigated the effects of curing conditions and the sizes of EPS beads on the properties of the composites. Four OP-EGC mixtures were formulated with equal water-to-binder ratios and anhydrous sodium metasilicate proportions. Polyethylene (PE) fibers were employed as reinforcement for the OP-EGC at a volume fraction of 1.2%. A comprehensive series of experiments was conducted to evaluate mechanical and thermal properties, impact resistance, and chemical constituents. Experimental results confirmed that all mixtures satisfied the criteria for lightweight concrete, exhibiting densities below 1.87 g/cm3. Although the incorporation of EPS beads relatively lessened strength, it dramatically improved the tensile strain capacity of the OP-EGCs. Notably, the air-cured OP-EGC incorporating EPS beads with diameters of 1–2 mm achieved a maximum tensile strain capacity of 20.9%, surpassing the extensibility of rebar, and exhibited high thermal insulation, with a thermal conductivity of 0.58 W/mK. This superior tensile strain capacity was concomitant with pseudostrain-hardening behavior and distributed microcracking. Furthermore, the ratio of tensile strength to compressive strength for the OP-EGCs ranged from 18.1% to 24.5%, approximately double that of conventional concrete. In impact tests, the OP-EGCs layers survived more than 60 cycles of repeated drop-weight impacts. Based on the chemical examination, the predominant geopolymeric products of the OP-EGCs were confirmed to be C─ (N)─ A─ S─ H and N─ A─ S─ H gels.