Mechanisms of Chemical and Autogenous Shrinkage in Alkali-Activated Hybrid Systems

This study aimed to investigate the role of chemical and autogenous shrinkage as well as microstructure of a hybrid system composed of alkali-activated ash blended with portland cement. Three alkali-activated binders were produced with 30% portland cement and different types of ash (70% of bottom ash, 70% of rice husk ash, or 35% of each type of ash). Chemical shrinkage was measured by the buoyancy method. The microstructural and surface analysis were investigated by scanning electron microscopy (SEM), nitrogen adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. Autogenous shrinkage, rather than chemical shrinkage, was mainly responsible for the shrinkage observed in these sealed systems. The results showed that the main mechanism involved in the shrinkage of this hybrid system is associated with the microstructural reorganization of the aluminosilicates phases resulting from polymerization.