Alkali activated materials can significantly solve environmental problems such as carbon dioxide emissions and energy demand associated with the production of ordinary Portland cement. As a by-product of the steel production process, ballast plays an important role as a source of aluminosilicate in the alkali activation process. However, the mechanical and microstructural properties of alkali-activated ballast are still being studied. In this study, electropenetration was applied to disillusion and condensation reaction processes in the ballast activated by sodium hydroxide and aqueous glass to produce functional gradient materials (FGM), and due to the potential difference between the anode and cathode, ions migrated to electrodes with opposite charges and resulted in changes in strength at both ends. In this study, the compressive strength was used to evaluate the alkali activated ballast (AAS) slurry in the anode, medium and cathode segments under different charging currents and charging times, when the liquid-solid ratio of AAS slurry was 0.6 (mL̸g) and the volume ratio of sodium hydroxide/sodium silicate was 5:5, under the conditions of 0.05A and 15 minutes of charging, the strength of the positive and negative parts of the compressive strength was the highest, the strength of the middle part was the lowest, and the compressive strength of the non-energized combination was unchanged. In addition, the anode, intermediate and cathode differences of AAS slurry were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and magic angle rotation nuclear magnetic spectroscopy (MAS NMR), and XRD and SEM analysis showed that the reactants were aluminum diatomaceous earth, and the structure was C-A-S-H, C-S-H, calcite and calcium silicate. According to the EDS analysis, the high Ca/Si ratio in the middle represents a higher amount of Ca ions in the charge balance due to Al substitution, as shown in the 27Al NMR spectrum. The deconvolution 29Si NMR spectrum shows the presence of Q0, Q1, Q2 (1Al), Q2, and a small amount of Q3 on all cross-sections, as well as the cathode partial Q4. Q2(1Al) is the primary Si unit in the low FWMH region, indicating that the presence of C-A-S-H as a reactant is due to Si being replaced by Al. Deconvolution 27Al NMR shows a large proportion of Al tetrahedron, octahedral coordination Al, and lower strength pentahexahedron. Tetrahedral Al indicates the presence of Al to replace Si in C-S-H, while Al octahedral indicates that hydrotalite is a reactant but XRD analysis did not identify it, and an electropenetrable effect was observed to affect the compressive strength and microstructure of the AAS slurry.

Alkali-activated materials can significantly solve the environmental issues such as CO2 emission and energy demand associated with the production of ordinary Portland cement. Slag, a by-product during the production of the iron and steel, plays a significant role as a source of aluminosilicate in creating the alkali-activated slag. However, the mechanical and microstructural properties of alkali-activated slag are still under investigation. In this study, an electro-osmosis was applied during the disillusion and condensation reaction of the slag activated by NaOH and water glass to produce a functionally graded material (FGM). The ions migrate to the oppositely charged electrode due to the electric potentials difference between the anode and cathode and lead to strength changes at two ends. The compressive strength was used to evaluate the alkali activated slag (AAS) paste at the anode, middle and cathode section subject to different charging current and charging duration. The AAS paste with a liquid to solid ratio of 0.6 (mL̸ g) and a NaOH to sodium silicate volume ratio of 5:5 showed the highest strength at the anode and cathode sections and lowest strength at the middle section at the 0.05A and 15-minute charging conditions. The one without charge, on the other hand, showed no variation in the compressive strength. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and magic angle spinning nuclear magnetic spectroscopy (MAS NMR) were used to characterize the anode, middle, cathode, of the AAS paste. The XRD and SEM analysis revealed the reaction products to be aluminum tobermorite like structure C ̶ A ̶ S ̶ H, C ̶ S ̶ H, calcite, and calcium silicate. According to the EDS analysis, the high Ca ̸ Si ratio in the middle indicates the higher amount of Ca ion in charge balancing due to Al substitution as it was revealed in the 27Al NMR spectra. The deconvoluted 29Si NMR spectra revealed Q0, Q1, Q2 (1Al), Q2, and a small quantity of Q3 in all sections, as well as Q4 in the cathode section. Q2(1Al) was the dominant Si unit in an area with low FWMH, which indicates the presence of C ̶ A ̶ S ̶ H as a reaction product due to the substitution of Si by Al. The deconvoluted 27Al NMR showed a large proportion of Al tetrahedral, octahedral coordinated Al and less intense pentahedral. The tetrahedral Al indicates the presence of Al in replacement of Si in C ̶ S ̶ H while the Al octahedral indicates hydrotalcite as a reaction product which was not identified by the XRD analysis. The effect of electro-osmosis was observed affecting the compressive strength and microstructure of the AAS paste.

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