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The environmental issues caused by solid waste have become increasingly serious. Adding additive is considered as an effective measure to improve the performance of the cemented soil. Therefore, the feasibility study of solid waste such as red mud and desulfurization gypsum used in composite cemented soil is in urgent demand. In this study, the mechanical properties and durability to freezing-thawing cycle of red mud-calcium-based composite cemented soil (RMCC) were analyzed through compressive strength test, resistivity test, and freezing-thawing cycle test. The action mechanism of RMCC was revealed through a series of X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) test. The results show that the optimal red mud content in RMCC is 12%. As the freezing-thawing cycle progresses, the difference in resistivity and pressure sensitivity of RMCC gradually weakens. When the freezing-thawing cycle reaches 7, the pressure sensitivity characteristic of RMCC is lost. The change in resistivity and pressure sensitivity can be used to characterize the damage caused by the freezing-thawing cycle. Combined with XRD and SEM analysis, the presence of minerals such as K2Ca5(SO4)6·H2O and (Ca, Na)2(Si, Al)5O10·3H2O play a key role in fixation of alkali metal elements, and the coordination of CSH gel cementation effect and AFt filling effect has a significant impact on mechanical properties. The study provides an effective way to the utilization of red mud and desulfurization gypsum in subgrade strengthening.

Red mud is a waste product generated by the aluminum industry and its presence has significantly damaged the environment. Interestingly, red mud has some desirable adsorptive properties and can solidify heavy metal ions. Moreover, after processing, red mud has certain cementing properties that have a positive influence on the curing effect of red mud cement-treated soil. This study examined different ratios of red mud, cement and Ca(OH)2 by testing the electrical resistivity and unconfined compressive strength of various soils. The resistivity test indicates that the electrical current frequency has a great influence on the test results. It is recommended that a current frequency between 1 and 50 kHz is used in a resistivity test. The study also indicates that, with increasing Cu2+ content, conductive tunnel effect occurs. However, when the ratio of curing agent and content of Cu2+ are different, the time causing the conductive tunnel effect varies. The unconfined compressive strength of different cement-to-soil ratios decreases with increasing Cu2+ content and the reduction extent is related to that ratio. Lastly, the study results suggest a good linear relationship between unconfined compressive strength and electrical resistivity, which is dependent on the specific ratio of contaminating materials.

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