Red mud stabilization using alternate industrial waste materials- mechanical and microstructural properties

Red mud (RM) is a potentially toxic industrial waste material generated from aluminum processing industries that usually be stored in open ponds. Occasionally spilling of RM to the surrounding areas has been reported either by overflow or due to dyke breach causing severe environmental concerns. Stabilization of RM is considered as an effective means to enhance its utilization as a geotechnical material. Hence, several researchers have attempted to stabilize RM using cement, fly ash (FA), gypsum, and ground granulated blast furnace slag (GGBS) for pavement applications. Though cement stabilization and geopolymer stabilization could result in satisfactory strength requirement (unconfined compressive strength (UCS) more than 10 kg/cm² and California bearing ratio (CBR) more than 10 %), the durability aspects were not supplemented by many researchers. Considering the high carbon footprint of cement stabilization and the similar impact of sodium silicate use in geopolymer stabilization, in the present study an attempt is made to evaluate the influence of lime, FA, and GGBS individually and in combination on the strength and durability aspects of RM. From this study, it is revealed that for 3 %-10 % cement addition, the UCS values obtained for RM mixes for 7 days curing period were 0.8 MPa-6 MPa. The durability aspects were also satisfied for these mixes. Whilst for 5 %-30 % lime stabilization, the UCS values ranged from 0.30 MPa-1.67 MPa at 7 days curing period and 0.65 MPa-3.6 MPa at 28 days curing period respectively. However, the durability aspects were not satisfied for lime stabilized RM samples. Further when FA is used along with lime, the UCS values ranged from 2.98 MPa-5.32 MPa at 7 days curing period and 4.56 MPa-6.62 MPa values at 28 days curing period respectively. For these stabilized RM mixes, the durability was satisfied up to 30 % FA for 20 % Lime addition; beyond which the durability aspects could not be satisfied. The lime-GGBS combinations could impart the UCS values of 5.79 MPa-9.83 MPa for GGBS content of 10 %-40 % and Lime content of 10 %-20 % while satisfying the durability aspects. The UCS values for various stabilized mix proportions as above could satisfy the suggested range of 4.5-7.0 MPa for subbase and base courses of pavements as per Indian Roads Congress (IRC): 37-2018. At higher GGBS and lime additions, the mix of RMGGBSL (503020) resulted in the UCS strength of more than 8 MPa making it even suitable for higher end roads. However, keeping in view, the mixing difficulties of admixtures with such a finer RM, the stabilized materials may be restricted to low volume road construction.