Core particle morphology effects on granulation and performance of cold-bonded core-shell aggregates from recycled concrete fines

The crude disposal of construction wastes generates recycled concrete fines ('4.75 mm) characterized by complex morphologies and high heterogeneity. Although cold-bonding granulation combined with the alkaline activation method can convert such wastes into uniform core-shell artificial lightweight aggregates (CLWAs), the role of particle morphology in governing granulation behavior and performance remains unclear. To clarify this effect, recycled concrete fine aggregate (RFA), glass fine aggregate (GFA), and quartz fine aggregate (QFA) with identical size ranges but distinct morphologies were selected as core materials, while recycled concrete powder was used as the shell material to prepare CLWAs. Morphological parameters were quantified via image analysis, and principal component analysis was employed to extract key morphological features. By monitoring the particle size growth rate and adhesion rate at multiple time intervals, the granulation kinetics of CLWAs were elucidated. Multiscale characterizations were conducted to assess the physical, mechanical and microstructural properties of CLWAs. Results indicate that the highly irregular RFA morphology induced mechanical interlocking and capillary adhesion between the core and shell, leading to rapid yet unstable growth, high water absorption (15.5%), and low bulk crushing strength (9.6 MPa). GFA’s inert and smooth surface produced weak interfacial bonding and the widest ITZ (8 μm), constraining aggregate performance. In contrast, QFA’s spherical and moderate roughness promoted stable granulation, enabling strong core-shell bonding and facilitating abundant C-A-S-H gel formed in the shell matrix to fill voids, thereby imparting superior performance of aggregate. This study provides a theoretical foundation for turning construction wastes into high-performance CLWAs.