Development of one part sustainable alkali activated binder system using slag, flyash and micro calcined kaolin

A one-part alkali-activated binder system is a sustainable, low-environmental-footprint binder. However, optimising this binder using industrial by-products for reliable performance remains a challenge. Conventional cement production is a major source of global CO₂ emissions, challenging the achievement of the Paris Agreement targets and net-zero goals by 2050. To align with Sustainable Development Goals 9 and 11, the development and adoption of low-carbon alternative binder materials is essential for sustainable infrastructure. This study investigates the formulation and optimisation of a novel One-Part Ternary Alkali-activated Binder (OP-TAB) using Box-Behnken Response Surface Methodology (RSM). A ternary blend consists of Ground Granulated Blast Furnace Slag (GGBS), flyash (FA) and Micro Calcined Kaolin (MCK) in varying proportions, mixed with solid activators. The properties of the binder depend on the proportions of the precursors, activator dosage and water-to-binder ratio. A three-level Box-Behnken design was employed to evaluate the influence of FA, MCK, and water-to-binder ratio (W/B) on key performance indicators, namely flowability, setting time, and compressive strength. GGBS served as the primary precursor, with sodium metasilicate as the solid activator. Optimisation via desirability function yielded an ideal mix comprising of 23% FA, 24% MCK, 53% GGBS, and a W/B ratio of 0.265. This formulation achieved a flowability of 130.12%, initial and final setting times of 114.58 and 186.47 min, respectively, and compressive strengths of 28.12 MPa at 7 days and 55.45 MPa at 28 days, respectively. Analysis of Variance (ANOVA) is performed to evaluate most significant parameters and accuracy in DOE. Microstructural analysis using Scanning Electron Microscope (SEM), with Energy Dispersive X-ray Spectroscopy (EDS), and X-Ray Diffraction (XRD) confirmed the formation of reaction products consistent with the observed mechanical performance. The proposed one-part binder system exhibits a reduced environmental footprint and lower reliance on cement, offering a sustainable and durable alternative for construction applications while supporting circular economy principles.