Structural characteristics of geopolymer concrete beams using alkali-modified blended ash: a comparative evaluation with conventional beams
ABSTRACT This study evaluates the fresh-state rheology and flexural performance of ambient-cured geopolymer concrete (GPC) as a sustainable alternative to M35 grade concrete. Using fly ash and GGBS activated by sodium hydroxide (SH) and sodium silicate (SS), the research investigated a parametric molarity range from 4M to 12M. Fresh-state analysis showed that increasing SH concentration significantly raised dynamic viscosity, reducing slump by up to 79%. An 8M threshold was identified for optimal workability and compaction. Mechanical testing revealed 8M as the robust performance optimum, achieving a 28-day compressive strength of 57.53 MPa (23.7% above control) and a flexural load of 112 kN. While GGBS enabled rapid early-strength gain (reaching up to 93% of 28-day strength within 7 days), the 4M configuration was insufficient for structural use. All GPC beams exhibited an under-reinforced failure mode with extensive strain-hardening, yielding capacity ratios between 1.43 to 2.50. Despite the superior ductility and energy absorption of GPC-8M, the findings are presented as indicative performance trends due to the reliance on single-beam specimens per configuration. Furtheremore, the absence of quantitative Life Cycle Assessment or durability profiles necessitates a cautious interpretation of GPC. These findings establish a deterministic benchmark for optimizing molarity in structural geopolymer applications.