Synthesis of alkali activated mortar using phosphogypsum neutralized bauxite residue

The present study aims at perspective utilization of two wastes, bauxite residue (BR)-an extremely alkaline material and phosphogyspum (PG)-a highly acidic substance, of entirely different in nature. Development of alkali activated mortar targeting pavement applications has been explored. As BR and PG alone proved to be ineffectual in developing geopolymer/alkali activated mortar because of undesirably low compressive strength, the challenge lies in synthesis of alkali activated mortar envisioning high strength using the combination of these wastes. PG in proportions of 10, 20, 30, 40 and 50%, NaOH molarity of 8, 10, 12, and 14, and Na2SiO3/NaOH ratio of 0.5, 1.0, 1.5, 2.0 and 2.5 are chosen as variable parameters to develop the mortar. From the comprehensive experimental results, 30% of PG, 12 M NaOH and Na2SiO3/NaOH ratio of 1.5 are found as optimum parameters to synthesize the mortar. It is demonstrated that the mortar made at 70:30 combinations of BR and PG exhibits superior compressive strength of 31.24 MPa, minimum abrasion loss of 1.52 mm, and water absorption of <7%, apart from constraining leaching of potentially toxic elements. On account of mechanical, durability and environmental performance, the present study recommends the above combination as ideally suitable material in pavement applications.