Abstract: The nickel slag-based geopolymer was prepared by alkali activators and the effect of self-made modified fly ash （MFA） on the mechanical properties of geopolymer was investigated. XRD， IR and SEM test techniques were adopted to study microstructure and properties of the products. The results showed that: the addition of MFA is beneficial to the mechanical properties improvement of nickel slag-based geopolymer. The best effect occurs with the replacement of 20% MFA. After maintaining at 50 ℃ for 7 days， the flexural strength and compressive strength of geopolymer increased by 32.0% and 20.2%， respectively. β-C2S on the surface of MFA particles took part in the reaction， which helped to produce more gel phase. Therefore， the structure compactness of geopolymer was improved and the cementation ability with the MFA particle surface production were enhanced. Meanwhile， the introduction of the calcium sources is beneficial to the dissolution of MFA in the alkali solution and accelerates the reaction rate of the system.

Key words: Nickel slag, Geopolymer, Modified fly ash