Properties of Ultra-High Performance Geopolymer Concrete: Influence of Silica Fume

Haonan Huang¹Liu Yang^2*Kai Pan²Wen Jiang^3*Chen Yu³Xianghua Hou³

• ¹Zhejiang University, Hangzhou, China
• ²Guangxi Institute of Industrial Technology, Nanning, China
• ³Institute of New Functional Materials, Guangxi Institute of Industrial Technology, Nanning, China

Research regarding the influence of silica fume content on ultra-high-performance geopolymer concrete (UHPGC) remains limited, and therefore this study investigates the effects of silica fume on the properties of UHPGC synthesized through the alkali-activation of a ground granulated blast furnace slag (GGBFS)-fly ash-silica fume ternary system. A comprehensive assessment of the properties of UHPGC, encompassing flowability, setting time, mechanical performance, and water absorption porosity, was conducted, while the reaction products were subsequently analyzed to elucidate the underlying microstructural enhancement mechanisms. The results reveal that unlike in Portland cement systems, the dissolution of silica fume raises the activator modulus, which chemically hinders the reaction kinetics and strictly limits the optimal dosage to 5%. The addition of silica fume significantly enhanced the flowability of the mixtures; however, the initial and final setting times were delayed due to the retardation of the geopolymerization process. Regarding mechanical performance, a reduction in compressive strength was observed when the silica fume content exceeded 5%, while the incorporation of silica fume was also found to negatively influence the flexural behavior. Microstructural analyses revealed that silica fume did not refine the pore structure but instead increased the overall porosity. While the addition of 5% silica fume promoted the formation of C-A-S-H type gels without generating new crystalline phases, the optimal silica fume dosage typically used for conventional UHPC (20%–35%) was found to be inappropriate for enhancing the hardened properties of UHPGC.