Impact of alkaline activator concentration on mechanical properties and microstructure of a ternary blended one-part geopolymer cement

Abstract

Geopolymers offer a sustainable alternative to Portland cement (PC), which significantly contributes to global greenhouse gas emissions. One-part geopolymers (GP), which are synthesized by mixing solid precursors and dry activators with water on-site, present a promising alternative to conventional cement. This study investigates the impact of alkaline activator dosage (6–16%) on the mechanical properties and microstructure of a ternary blended one-part geopolymer cement, incorporating diatomite, feldspar, and ground granulated blast-furnace slag (GGBS) as raw materials. The materials were first evaluated for pozzolanic reactivity through strength activity index, lime saturation, and Frattini tests. Results revealed that activator dosage significantly influenced geopolymer performance. While all mixes exhibited minimal workability, the mechanical properties improved up to an optimal activator dosage. The mix with 10% activator and a sodium silicate (SS) to sodium hydroxide (NH) ratio of 1.5 demonstrated the highest compressive strength (46 MPa), split tensile strength (4.69 MPa), and flexural strength (7.448 MPa) after 28 days of curing. Microstructural analysis showed a dense, well-formed structure at the optimum mix, while lower activator dosages led to a less compact structure, and higher dosages caused brittleness and cracking. This study highlights the importance of optimizing activator dosage for enhanced geopolymer performance.