Fresh state, short and long-term mechanical properties of ternary supplementary cementitious material-based low-carbon concretes

This study investigates the fresh state and short to long-term mechanical properties of three optimized Low-Carbon Concretes (LCCs). These LCCs use a ternary blend of supplementary cementitious materials (SCMs) consisting of ground granulated blast furnace slag (GGBFS), fly ash (FA) and silica fume (SF) to achieve a high (80 %-90 %) ordinary Portland cement (OPC) replacement ratio. Their fresh state properties and short (3 days, 3d) to long term (96d) mechanical properties were compared with traditional OPC C40 concrete with 40 MPa 28d cylinder characteristic compressive strength and three single blend SCM concretes (using SF, GGBFS, FA only) with 70 % OPC replacement ratio. Tests results confirmed that the optimized LCCs showed good slump values with balanced initial and final setting times when compared with C40 and single blend SCM concretes. For mechanical properties, while the optimized LCCs showed lower early (3d and 7d) compressive strength gain than C40 and single blend SF SCM concrete, they showed higher long-term strength gain from 28d to 96d. For flexural and indirect tensile strengths and elastic modulus, the optimized LCCs showed better short and long-term performances when comparing with C40 and all single blend SCM concretes. Finally, microstructural analysis using field emission scanning electron microscopy and x-ray diffraction confirmed the existence of a denser matrix, continuing hydration and pozzolanic actions supporting their enhanced flexural and tensile strength performance.