Geotechnical Stability of Two Gypsum-Treated Bauxite Red Muds and “Marl” as a Road Base Under Submerged Conditions

Abstract

Under rain, rapid erosion of soft limestone rocks (L) used as road bedding from a quarry in Jamaica causes frequent destruction of extensive road sections. Therefore the stability for road bedding of widely available pre- and post-lithified bauxite wastes was studied and compared with soft limestone. Durability of (1) gypsum-treated atmospherically lithified carbonated red mud wastes (G) and (2) atmospherically lithified red mud waste subjacent to the gypsum-treated red mud waste (R) was examined using a slake-durability apparatus through wet/dry cycles. These cycles induce dissolution, recrystallization, and lead to the deterioration of the stone, and, finally, affect the strength of these rocks. The California Bearing Ratio of the rocks was also studied. The results showed clear differences between, and among all the rocks. Based on these properties, the studied rocks were classified into two relative types (weak and strong). The slake-durability test indicated weight losses ranging from 0.1 % for the gypsum-treated atmospherically lithified bauxite waste (G), to 99.5 % for the atmospherically lithified red mud (R). The soft limestone marl (L) lost 14.0 % of its mass. This test caused also a reduction of compressive strength for these rocks (G = 8 %, L = 50 %, RW = 100 %) when wet/dried with distilled water after 5 week-long cycles. Slaking reduced the strength most greatly for the soft limestone and the subjacent red atmospherically lithified red mud. The two strong rocks were found to be the microcrystalline limestone and the gypsum,-treated pre-lithified red mud. For the post lithified (non-gypsum-treated) bauxite waste (R), this low level of durability and strength after slaking was attributed to the large amount of residual Na⁺ in the unflushed waste, which, despite post-lithification, still exhibited increased particle dispersion typical of the post-Bayer Process.