Synergistic effects in ground granulated blast furnace slag‒steel slag-based geopolymer

To promote the efficient and high-quality use of steel slag (SS), a geopolymer was innovatively developed from ground granulated blast furnace slag (GGBFS) and SS using an optimized alkali equivalent method. As SS-based geopolymer content increases, trends in compressive strength and total admittance modulus of the GGBFS‒SS-based geopolymer reveal distinct synergistic effects. To investigate these effects, electrochemical impedance spectroscopy, a relatively novel technique, was employed alongside other analytical methods. From a physical perspective, the synergistic effects manifest through the encapsulation of C-S-H gels by C-A-S-H and N-A-S-H gels, the filling of microdefects by C-S-H gels, microdefects truncation, and reinforcement by SS microaggregates. Chemically, the effects include the microaggregation of inert components and competitive activation induced by hydrated Ca(OH)₂. However, these chemical effects have a dual nature, making it unclear whether they positively or negatively impact the binary geopolymer. Thus, the physical synergistic effects are considered predominant in the GGBFS‒SS-based geopolymer.