Abstract
<title>Abstract</title> <p> The geopolymer mortar has become a viable substitute for the normal cement mortar due to its light carbon footprint, effective use of industrial wastes and its high durability. The effects of different precursor materials and alkaline activator systems on the fresh, mechanical, microstructural, and structural performance of the ambient-cured geopolymer mortar are systematically studied in this work. Alkaline activators based on potassium and sodium were used to evaluate fly ash (FA), ground granulated blast furnace slag (GGBFS), metakaolin (MK), and steel slag (SS) separately and in hybrid combinations. The developed geopolymer mortars were tested for flowability and compressive strength at 7, 14, and 28 days. The mixes were further characterised using scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA-DTG), which were optimised to ascertain the relationship between microstructural development, gel formation, thermal stability, and mechanical performance. To rapidly predict the strength, four machine learning models (Artificial Neural Network (ANN), Gaussian Process Regression (GPR), Random Forest (RF), and Support Vector Machine (SVM)) were developed and compared to the experimental data. The Shapley Additive exPlanations (SHAP) analysis was utilised to explain the ANN network and determine the most important input variables. The 50% FA-50% GGBFS mix exhibited an excellent balance of strength and workability, while the 100% GGBFS mix had the greatest 28-day compressive strength of 68.51 MPa among the mixes examined. The NaOH-Na <sub>2</sub> SiO <sub>3</sub> activator system has exhibited the best geopolymerization and mechanical performance in comparison to the other combinations of activators. The ANN model showed the greatest prediction with the others being compared, and SHAP analysis found that GGBFS content, sodium hydroxide concentration, sodium silicate dose, and additional water were the most influential factors to control the compressive strength. Moreover, nonlinear finite element analysis at ABAQUS revealed that geopolymer mortar jacketing, which is reinforced by three layers of hexagonal wire mesh, enhanced the load-bearing capacity, stiffness, crack resistance and structural behaviour of reinforced concrete beams. The combined experimental, microstructural, machine learning, and numerical study validates the high potential of geopolymer mortar as a high-performance, low-carbon material to be used as a sustainable construction and structural rehabilitation tool. </p>