Abstract: Red mud, a solid waste from alumina industry, contains alkaline oxides with potential activity, which can be used as building materials after modification. In this paper, lime, slag, desulfurization gypsum and other materials were introduced to modify red mud, and its application in highway subgrade filling was studied. The single-doped and double-doped test schemes were designed. The maximum dry density and optimum moisture content of red mud under different mix ratios were determined by conducting compaction test. According to California Bearing Ratio (CBR), rebound modulus and unconfined compressive strength, the optimal mix ratio was selected, and its environmental impact was evaluated. The results show that the incorporation of modified materials improves the mechanical properties of pure red mud. When the total mass fraction of slag and lime is 10% (double-doped with a mass ratio of 1∶1), the CBR strength, rebound modulus and unconfined compressive strength of the modified red mud subgrade material are the most obvious, and the maximum values are 306.22%, 123.58 MPa and 3.02 MPa, respectively. Compared to single-doped modified material at the same content, the CBR strength of the double-doped group increases by 129%, the rebound modulus increases by 28%, and the unconfined compressive strength increases by 148%. The release rates of the characteristic pollutants Cd, V, Se, As and fluoride in the long-term migration process of the modified red mud subgrade material tend to be stable and the concentration values are lower than class Ⅰ standard limit of groundwater.

Key words: subgrade, red mud, characteristic leaching pollutant, modification, engineering characteristic, environmental assessment