One-Part Alkali-Activated Materials Derived from Natural and Designed Blends of Clay and Calcium Carbonate Sources

The design and development of environmentally oriented cements with predominant content of widespread noncalcined precursors contribute to a more promising future for constantly evolving alkali-activated materials (AAMs). In this study, natural and designed blends of calcined clays and abundant raw calcium carbonate minerals were investigated as binary precursors for one-part AAMs using standard techniques, thermal, X-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy (EDS) analyses. The influencing factors to set optimal parameters were the mineralogical assemblage, precursors fineness, formulation details, means of alkali reactant incorporation, and curing regimes. It was stated that hydraulic one-part AAMs can be derived from calcined marl incorporated with limestone powder containing 5.8%-7.0% of calcined clay minerals and 54.6%-60.5% of calcite or nonhydraulic one-part AAMs from a mixture consisting of 20%-30% metakaolin and 70%-80% limestone powder. It was found that, compared with a metakaolin-limestone-based binary precursor, alkali activation of calcined marl-limestone results in the formation of a higher amount of binder gel with a greater extent of Ca incorporation into the structure of Na aluminosilicate gel and the formation of Ca aluminosilicate and Ca silicate hydrogels. This provides an alkali-activated calcined marl-limestone binder system with better mechanical properties and continuous strength development, including under wet conditions.