Microstructural insights of geopolymer mortar containing cenosphere: effects on fresh properties and durability

Abstract The intense environmental burden coupled with the manufacturing of ordinary portland cement (OPC) created an urgent need for sustainable alternatives. Geopolymers, known for their ability to incorporate industrial by-products, have emerged as a promising solution to reduce carbon dioxide (CO 2 ) emissions. This study extensively investigated the effects of cenosphere incorporation on the microstructure of ground granulated blast furnace slag (GGBFS)—based geopolymer. A series of tests were performed to compare the microstructural changes with the performance of those geopolymers. Those tests include fresh properties, such as flowability, setting time, and isothermal calorimetry, and durability tests, including alkali-silica reaction (ASR), and carbonation. Microstructural changes due to cenosphere addition were analyzed using scanning electron microscope, and x-ray diffraction techniques. Results showed that the cenosphere created a ball-bearing effect within the microstructure, which improved the fresh properties of the materials. Incorporating cenosphere 25–50% in GGBFS-based geopolymer can significantly improve the flowability, setting time, heat of geopolymerization, while providing higher compressive strength than OPC mortar. Microstructural characterization revealed that adding cenosphere significantly improved ASR resistance by preventing the formation of silica-rich phases thanks to their stable aluminosilicate products and lower alkali content. Additionally, a dense cluster of carbonated products was found in the matrix of cenosphere-dominated geopolymers, highlighting the higher CO 2 capture capability of the cenosphere.