Sustainable application of waste eggshell as fillers in alkali-activated solid waste-based materials: Varying treated methods and particle sizes

The incorporation of waste eggshells as fillers in construction materials is currently constrained by factors such as shell-membrane separation, particle size, and proportion of incorporation. This study aims to assess the feasibility of utilizing non-calcined eggshell particles (EPs) in alkali-activated solid waste-based materials. Initially, the micro characteristics of water-treated and alkali-treated eggshells were evaluated. Subsequently, nine groups of alkali-activated slag-based paste samples were prepared by using EPs as fillers, and the influence of the particles on the physical and mechanical properties of the materials was assessed based on flowability, density, and compressive strength. Furthermore, the impact of shell-membrane separation and particle size on the microstructure and composition of the alkali-activated materials (AAMs) was characterized by using a combination of SEM-EDS, XRD, FTIR, and TG-DSC techniques. Finally, six groups of alkali-activated slag-red mud-fly ash-based mortar samples were prepared with EPs as fillers, which demonstrates the feasibility of EPs in multiwaste-based materials and expands the application range of non-calcined eggshells. The results show that water treatment and alkali treatment of EPs provide viable methods for shell-membrane separation, albeit with some loss of fine particles. The physical filling of membranes in AAMs does not affect the chemical composition. The EPs (with a particle size less than 0.5 mm) can be used as fillers in AAMs without shell-membrane separation. Moreover, when the EPs content is increased to 33%, the 90-d flexural strength of the AAMs increases by 60% compared to the control group (without EPs), while the compressive strength remains unchanged. Thus, it is feasible to directly crush and sieve non-calcined eggshells for use as fillers in alkali-activated waste-based cementitious materials without the need for shell-membrane separation, and this method does not produce any negative impact. The findings of this research provide an effective technical approach for the application of waste eggshells in eco-friendly construction materials.