Curing regime controlled performance of basalt-modified alkali activated slag: phase composition, porosity profile, microstructure and compressive strength.

Abstract

The transition from traditional cement to low-carbon alkali-activated materials is no longer an environmental obligation but a materials-design challenge requiring precise control of reaction kinetics. In this study, basalt-modified alkali-activated slag was cured under various conditions to demonstrate how mix design and curing regimes affect gel formation and strength development. Ground-granulated blast-furnace slag (GGBFS) was replaced with 5-20 wt% basalt (BT) and then activated with 6 wt% NaOH. The developed materials were cured under normal conditions (1-28 days), hydrothermal conditions (135-170 °C/5 h) and microwave conditions (450 W/5-15 min). Advanced microstructural analyses (XRD, FTIR, SEM/EDX and BET/BJH) elucidated the phase evolution, morphological features and porosity profile within the matrices. The results reveal that BT has a slight effect on the fresh properties (workability and setting time) of the alkali-activated slag. Despite diluting reactive calcium phases in GGBFS, the AAS-20BT (80% GGBFS + 20% BT) composite delivered robust, structural-grade compressive strengths: 49.5 MPa under normal curing, 56 MPa after 170 °C/5 h hydrothermal treatment, and a rapid 37 MPa after just 10 min at 450 W of microwave exposure. From the compressive-strength results and advanced analysis techniques, it can be concluded that the curing regime strongly controls the composition of the load-bearing capacity phases, microstructural development and pore refinement. Overall, hydrothermal curing provides the most favorable balance between reaction kinetics, zeolitic phase formation, hydrate morphology and microstructural development. Under normal conditions, BT particles act as fillers and nucleation seeds, while hydrothermal curing increases their reactivity, facilitating Si and Al dissolution and participation in geopolymeric products. Accordingly, the AAS-20BT can be considered a promising low-carbon binder that offers a highly scalable, eco-efficient pathway for next-generation construction materials.