Mechanical performance, strength deterioration, and salt freeze-thaw response of concrete containing sodium carbonate-treated secondary aluminum dross

초록

To enable the safe and value-added utilization of secondary aluminum dross (SAD), raw SAD was pretreated by Na2CO3-assisted alkaline leaching and then used alone or in combination with silica fume (SF) as a partial cement replacement in concrete. The effects of SAD incorporation on the ambient mechanical properties, compressive stress-strain response, microstructural characteristics, and deterioration under salt freeze-thaw cycles (SF-tC) were investigated. XRD results showed that the characteristic peaks assigned to crystalline aluminum nitride (AlN) were no longer detected after pretreatment, indicating a substantial reduction in XRDdetectable crystalline AlN rather than complete removal or overall chemical stabilization. The incorporation of SAD altered the failure patterns of concrete and generally deteriorated its ambient mechanical performance, with splitting tensile strength being the most sensitive index. At a SAD replacement level of 10%, the compressive, flexural, and splitting tensile strengths decreased by 9.44%, 16.06%, and 47.59%, respectively, relative to the control. The stress-strain results further showed a reduction in peak strain and changes in both pre-peak and post-peak deformation characteristics. SEM-EDS observations showed visible spherical pores and localized Al enrichment in the selected SAD10 regions, suggesting that pore-related defects and local Al-rich heterogeneity may have contributed to the strength deterioration. SF partly compensated for these adverse effects. Among the two blended mixtures investigated, S/SF5 exhibited the most favorable compressive and flexural performance, although its splitting tensile strength remained below that of FC. Under SF-tC, SAD aggravated visible surface damage, mass loss, and the loss of residual mechanical properties, whereas the co-incorporation of SF alleviated the late-stage deterioration to some extent. These results indicate that Na2CO3-treated SAD can be used as a partial cement-replacing component in concrete when its dosage is properly controlled and combined with SF.

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