Long-term durability and microstructure of low-carbon concrete with high-volume ternary blend SCMs (GGBFS, fly ash, silica fume)

This study reports experimental and analytical investigation on long-term durability and microstructures of Low-Carbon Concrete (LCC) developed using optimized ternary blends of ground granulated blast furnace slag, fly ash, and silica fume as sustainable alternatives to Ordinary Portland Cement (OPC). Three LCC mixes compliances for 40, 32, and 25 MPa grades concretes were designed with high-volume of 80%, 85%, and 90% OPC replacement, respectively. Their durability performance, including abrasion resistance, chloride penetration, water absorption, and total shrinkage was evaluated up to one year and benchmarked against similar grade OPC concretes. Results showed that all three LCCs mixes outperformed the OPC concretes in compressive strength by 2-4% at 28-days (28d) and 36-65% at 365d. Similarly, LCCs mixes reported 19% and 68% improvement in abrasion resistance, 84% and 89% in chloride penetration resistance, 38% and 66% in water absorption resistance, and 53% and 47% reduction in total shrinkage when compared with OPC concretes at 28d and 365d, respectively. More importantly, it is found that unlike OPC concretes for which their long-term strength and durability performances were positively correlated to the concrete grade and OPC content, the long-term compressive strength of LCCs was only weakly correlated to the OPC content while their durability performances are positively correlated to the percentage of supplementary cementitious materials (SCMs) rather than their concrete grades. Microstructural analysis of LCCs identified the synergistic effects of high-volume ternary SCMs blends which resulted a denser, more refined matrix, and explained their correlations with the improved long-term strength development as well as superior durability. Furthermore, a new empirical model was proposed for the total shrinkage of LCCs. The findings confirm that these developed LCCs could provide a low-carbon alternative for infrastructure applications that demand high durability performance.