Mechanical and microstructural properties of user-friendly one-part alkali-activated mortars via low-grade calcined clay

Alkali-activated materials (AAMs) have emerged as a promising alternative to traditional cement-based binders. However, their adoption is restricted by non-user-friendly production processes, the need for curing at elevated temperatures when higher amounts of aluminosilicate sources are used and the limited availability or regional dependency of precursors and activators. This study focuses on the development of one-part AAMs made with low-kaolinitic calcined clays as the main precursor (between 63–100%wt.) cured at ambient temperature. A comprehensive assessment of reaction kinetics, rheology and mechanical/microstructural properties was conducted. Results demonstrate promising fresh and hardened properties with an optimal AAM formulation including 81% of calcined clay achieving a flow diameter of 17 cm, initial/final setting times ranging from 50 to 116 minutes and 28-day compressive strength of approximately 40 MPa. Low-volume slag governs hydration kinetics and microstructure by supplying calcium-rich species and nucleation sites that activate ambient-temperature reactions and promote hybrid gel formation. It modulates setting time and refine porosity toward meso scales. Alongside an optimized solid-silicate regime, this slag-limited formulation optimizes ambient-cured fresh and hardened properties yielding a site-ready binder for multi-purpose applications. The study represents an attractive opportunity for a broader use of low-grade calcined clays as a practical and sustainable alternative to Portland-cement-based binders.