The Portland cement industry accounts for approximately 8% of global anthropogenic CO₂ emissions

driving the urgent search for low-carbon cementitious alternatives. Geopolymer concrete (GPC) synthesised from industrial by-products offers a promising pathway toward decarbonising the construction sector while simultaneously valorising residual streams from thermal power generation

iron making

and silicon metallurgy. This study conducts a cradle-to-gate life cycle carbon assessment of four concrete mixtures designed to achieve equivalent 40 MPa compressive strength: an ordinary Portland cement (OPC) reference (M1)

a 100% fly ash-based GPC (M2)

a 100% ground granulated blast-furnace slag (GGBS)-based GPC (M3)

and a ternary blend of fly ash

GGBS

and silica fume in a 6:3:1 ratio (M4). The Australian Life Cycle Inventory (AusLCI) database was used with supplementary Ecoinvent v3.9 data and 2023 National Electricity Market (NEM) grid factors. Impact assessment applied IPCC 2021 GWP100

and uncertainty was quantified through 1

000 Monte Carlo iterations combined with pedigree matrix-based data quality scoring across five indicators. Results show that M2

M3

and M4 achieved 42%

55%

and 61% reductions in global warming potential relative to M1

respectively

with 95% confidence intervals of ±8–11%. Hotspot analysis identified sodium silicate activator as the dominant emission source in all GPC mixtures

contributing 55–72% of total GWP and shifting the primary decarbonisation lever from clinker chemistry to alkali chemistry. Sensitivity analysis confirmed activator modulus and dosage as the most influential parameters (±9–15%). Applied to a precast bridge deck panel scenario

mixture M4 could avoid approximately 212 kg CO₂e per m³

supporting scalable adoption in sustainable infrastructure. The findings provide a transparent

context-specific carbon benchmark to guide mix design and procurement decisions across the Australian construction sector.