Shrinkage behavior of alkali-activated materials using ground bottom ashes, calcined clays, volcanic ashes, and fluidized bed combustion ashes as precursors

Abstract

The global decline in the availability of fly ash and slag, the most common precursors for alkali-activated materials (AAMs), necessitates the exploration of alternative materials. Alkali activation technology presents an opportunity to utilize a wide range of naturally occurring and industrial byproducts rich in aluminosilicate minerals as precursors, offering a low-carbon alternative to traditional cement. This study investigates the volumetric deformations in AAMs produced from four groups of nontraditional and natural pozzolan-based (NNP) materials: low-purity calcined clays (CC), volcanic ashes (VA), ground bottom ashes (GBA), and fluidized bed combustion ash (FBC). Volumetric deformations—including chemical, autogenous, and drying shrinkage—were characterized using ASTM standards for portland cement. Chemical and autogenous deformations were minimal across most materials, while excessive drying shrinkage was observed in all but the calcined clays. The application of shrinkage-reducing admixtures and internal curing effectively mitigated this shrinkage. Further analyses of total heat release during activation, bound water content, pore solution surface tension, and porosity provided insights into the shrinkage and expansion mechanisms. With effective drying shrinkage control measures, alkali-activated NNPs show promise as viable low-carbon binders.