EFFECT OF BINDER INDEX AND ALKALINE CONCENTRATION ON SPLIT TENSILE STRENGTH DEVELOPMENT OF AMBIENT-CURED GEOPOLYMER CONCRETE

This study investigates the influence of the geopolymer binder index on the split tensile strength of geopolymer concrete (GPC) produced with varying proportions of Ground Granulated Blast Furnace Slag (GGBS) and fly ash.Experimental variables included GGBS:Fly Ash ratios (20:80, 40:60, 50:50, 60:40, 80:20), sodium hydroxide molarity levels (8M, 10M, 12M), and curing periods (7 and 28 days), while maintaining a constant alkaline-to-binder ratio of 0.38.The binder index, representing the combined reactivity of GGBS and fly ash, was correlated with tensile strength performance. Results showed that higher GGBS content significantly enhanced tensile strength due to increased calcium-alumino-silicate-hydrate (C-A-S-H) gel formation. At28 days, 8M GPC improved from 2.35 MPa at a 20:80 ratio to 3.94 MPa at 80:20, while 12M GPC at 80:20 achieved a maximum of 4.22 MPa.Increased NaOH molarity accelerated early-age strength development, with 7-day strengths reaching up to 3.37 MPa for 12M