Physical and Mechanical Evolution of Ternary Geopolymer Mortars Under Various Curing Methods

This study explores the mechanical and microstructural performance of Geopolymer Mortars (GMs) formulated with 50% ground granulated blast furnace Slag (S) from Türkiye and 25% of either Fly Ash (FA), Diatomite (D), or Opacifier Waste (OP) from Kazakhstan, aiming to enhance the material sustainability through ternary alkali-activated systems. All precursors were sieved below 90 µm and activated using a 2:1 blend of 12M sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) with an Activator-to-Binder (A/B) ratio of 0.7 silica modulus (SM = 3.29), producing a water-to-binder ratio of approximately 0.28. GMs were cured under ambient, thermal (80 °C/24h), and electrothermal regimes (30 V, 40 V, 50 V) for 1–24 h. The highest compressive strength (35.03 MPa) was achieved under thermal curing, while 40 V electro-curing reached 31.34 MPa at 4 h, equivalent to 89% of the thermal maximum in only 14% of the time. The flexural strength under 40 V peaked at 5.66 MPa, surpassing the thermal values (5.44 MPa), and delivered the highest flexural strength-compressive strength ratio (approximately 0.20), indicating improved ductility. The water absorption and apparent porosity dropped by 29.2% and 7.2% under 40 V curing, while the bulk density increased to 2.04 g/cm³. The fuzzy logic and Multi-Criteria Decision Making (MCDM) analyses ranked the 40 V condition as the highest overall due to its efficient balance of strength, durability, and energy performance. These findings position the controlled 40 V electro-curing as a rapid, energy-conscious alternative to conventional thermal methods, particularly valuable for prefabricated applications and resource-constrained construction environments.