Multi-performance assessment of sodium carbonate-based low-alkali binder concrete under ambient and controlled ambient curing conditions

The extensive utilization of conventional cementitious materials has increased environmental concerns associated with carbon emissions and energy-intensive clinker production. This study developed Low-Alkali Binder Concrete (LABC) using GGBS and Class F FA activated by a hybrid sodium carbonate–sodium silicate (Na₂CO₃–Na₂SiO₃) activator system. The influence of binder composition, target strength grade, and curing condition was evaluated under ambient laboratory conditions and Controlled Ambient Curing (CAC) conditions (27 ± 2°C and 60 ± 5% relative humidity). Three GGBS:FA ratios (60:40, 50:50, and 40:60) were evaluated in M30, M40, and M50 mixtures using a hybrid Na₂CO₃–Na₂SiO₃ activator (1 M Na₂CO₃, activator ratio 1:1, liquid-to-binder ratio 0.40). The mixtures were evaluated for fresh, mechanical, and durability properties, including UPV, compressive strength, tensile strength, flexural strength, water absorption, and acid resistance. In addition, Alkali Efficiency Index (AEI) and Curing Efficiency Index (CEI) were used to assess activator utilization and curing effectiveness. Higher GGBS contents improved mechanical performance, whereas higher FA contents enhanced workability and durability. Among all investigated mixtures, L50–6040-C achieved the highest 90-day compressive strength of 64.9 MPa, while L50–4060 exhibited the lowest acid-induced mass loss of 4.96% under controlled ambient curing. CAC improved strength and durability performance compared to Ambient Curing (AC). L40–4060-C may be considered a balanced trade-off mixture under low-alkali activation conditions. The results demonstrate the potential of low-molarity Na₂CO₃ activation for producing sustainable structural-grade LABC under practical curing conditions. The findings are limited to laboratory-scale evaluation under AC and CAC conditions.