Enhancing sustainability in construction: Mechanical, carbon emission, and microstructural analysis of activated slag binders incorporating silica fume and nepheline syenite

This research presents the first comprehensive investigation into the development of binders utilizing activated slag, silica fume, and nepheline syenite, addressing the urgent need for sustainable alternatives to traditional Portland cement, which is known for its high carbon emissions. The performance of these manufactured binders was systematically compared to conventional cement binders to evaluate their mechanical and environmental properties. After 28 days of curing, tests assessed compressive, tensile, and bending strengths and water absorption and microstructural features via Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX). The binder activated with silica fume (water-to-binder ratio of 0.45) achieved compressive, tensile, and bending strengths of 45 MPa, 4.7 MPa, and 4.9 MPa, while the binder activated with nepheline syenite showed lower strengths of 37 MPa, 3.3 MPa, and 3.5 MPa. The cement binder yielded strengths of 50 MPa, 4.9 MPa, and 5.2 MPa under the same conditions. Microstructural analysis indicated the highest density and calcium-to-silicon ratio in the cement binder, closely followed by the binder activated with silica fume. Binders activated with a 10 M sodium hydroxide solution exhibited superior performance compared to those with 15 M. Notably, the binder activated with nepheline syenite, formulated at a 1:2 ratio with sodium hydroxide, proved most sustainable, with a carbon footprint of 986 kg CO₂ per unit, significantly lower than the cement binder's 1984 kg CO₂. These findings underscore the urgent need for sustainable construction materials and contribute to addressing environmental concerns associated with cement production.