Recycling of Marble Sludge into High Strength and Anti-Efflorescence Geopolymers Through the Synergy of Graphene Oxide and Hydrophobic SiO2 Fillers

The reutilization of marble sludge from the marble cutting and polishing process offers economic and environmental benefits. In this work, fly ash is used as an aluminosilicate source to prepare geopolymers with marble sludge. The crystal composition, gel structure, pore distribution, microstructure and Na + ion leaching behavior were investigated to determine the effects of multiscale fillers on the apparent density, compressive strength, and efflorescence performance of the geopolymers. The addition of graphene oxide (GO) filler catalytically promotes geopolymerization reactions, inhibits microcrack formation and increases the compressive strength, albeit with pronounced efflorescence. In contrast, the hydrophobic SiO 2 aerogel (SA) filler effectively eliminates the pores and hinders water permeability and Na + leaching, thus greatly improving the anti-efflorescence properties. The concentration of Na + ions in the leach solution follows an exponential relationship with leach time, indicating diffusion controlled leaching behavior. With the combination of 1‰ GO and 1% SA, the geopolymer achieves a compressive strength of 40.6 MPa and a surface contact angle of 99.1°. After the immersion efflorescence test, the geopolymer shows a mass loss of 4.3% and a strength loss of 7.2%, far superior to those of the unfilled geopolymer. The strengthening and improved anti-efflorescence properties are closely related to the densification and increased hydrophobicity of the geopolymers. The synergistic effect of different fillers provides a simple technical route to produce high strength and anti-efflorescence geopolymers with marble sludge, promising suitability for applications in paving and embankment blocks. Graphical Abstract