Optimisation of Supplementary Cementitious Materials for Enhanced Mechanical and Durability Performance of Geopolymer Concrete

This research provides an extensive experimental and predictive study of ambient-cured geopolymer concrete developed with fly ash (FA), ground granulated blast furnace slag (GGBS), and silica fume (SF). Eleven combinations of geopolymers were developed through systematic variation in the proportions of FA-GGBS-SF and the alkaline activator modulus (Ms = 1.5-2.0). At 7, 14, and 28 days, we assessed compressive, split tensile, and flexural strengths and evaluated durability performance using RCPT, sorptivity, and water absorption. Silica fume (up to 10%) was further added to the mixture to perfect the pore structure and achieve lower permeability and greater durability. A mixture C10 (50% FA, 40% GGBS, 10% SF, Ms = 2.0) showed the best performance, with a 28-day compressive strength of 72.5 MPa, the lowest water uptake (2.95%), and the lowest chloride permeability (820 Coulombs). The paper establishes that the optimised FA-GGBS-SF geopolymer concrete can be strengthened and sustained at high strength under realistic ambient curing conditions.