Feasibility of Stabilized Titanium Gypsum as Roadway Subgrade Material: Evaluation of Geotechnical Properties and Leachability

Leachates from unlined titanium gypsum (TG) dumps can pose significant environmental pollution risks to surrounding soils and groundwater. Reusing open-dumped TG as construction material is effective in alleviating the risks. This study presents a systematic evaluation of the geotechnical properties and leachability of novel binder-stabilized TG used as a roadway subgrade material. The binder consisted of reactive magnesia (MgO), ground granulated blast furnace slag (GGBS), fly ash (FA), and rice husk ash (RHA). Macroscopic and microscopic tests, including unconfined compression, one-dimensional swell, batch-type leaching, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy with energy-dispersive X-ray analysis, were conducted to evaluate the strength, swelling behavior, leachability, mineralogy, and microstructure of stabilized TG. Based on the consideration of strength and leached concentrations of chloride (Cl − ) and sulfate ions (SO 4 2− ), in TG stabilized with 10% binder (by dry weight), the reactive MgO:GGBS:FA mass ratios in the binder were optimized as 1.3:5.2:3.5. The stabilized TG cured for 7 days under standard conditions possessed an unconfined compressive strength of 3.72 MPa and zero swell strain, whereas TG had an unconfined compressive strength of 0.73 MPa and a swell strain of 7.6%. Compared with TG, the concentrations of Cl − and SO 4 2− leached from stabilized TG cured for 28 days decreased by 54% and 61%, respectively. Microscopic test results revealed that the formation of calcium-(ferrite)-silicate-hydrate and layered double hydroxides in stabilized TG was the primary mechanism for the immobilization of Cl − and SO 4 2− . The results are useful for facilitating safe utilization of TG in roadway construction.