Effect of incinerator bottom-ash composition on the mechanical behavior of backfill material

This study explores the influence of the chemical composition (SiO₂, CaO, Fe₂O₃, and Al₂O₃) of incinerator bottom ash on its friction angle. Direct shear tests were performed to measure the strength of bottom ash with two distinctly different compositions. Then, an empirical equation was regressed to determine the correlation between each composition and the friction angle. The experimental results showed that the main constituent material of the incinerator bottom ash from general municipal wastes is SiO₂, and the friction angle is 48.04°-52.66°. The bottom ash from incineration plants treating both municipal wastes and general industrial wastes has a high content of iron-aluminum oxides, and its friction angle is 44.60°-52.52°. According to the multivariate regression analysis result, the friction angle of bottom ash of any composition is influenced mainly by the Fe₂O₃ and Al₂O₃ contents. This study used the friction angle of the bottom ash from four different incineration plants to validate the empirical equation, and found that the error between actual friction angles and the predicted values was -1.36% to 5.34%. Therefore, the regressed empirical equation in this study can be employed in engineering applications to preliminarily identify the backfill quality of incinerator bottom ash.