Development of Sulphate and Corrosion resistant mortar using coarse fraction of red mud

Abstract

Red mud is a highly alkaline industrial solid waste that
are generated as a byproduct of alumina industries during processing of bauxite mineral through Bayer’s process. Aluminium being a light metal with sufficient strength finds its wide range of utilization in automobile industries, aerospace etc. Because of wide range demand of aluminium the vast market of aluminium present today or will be in future can be easily seen, that means directly the generation of red mud will be high. The high volumetric generation of red mud possess great concern for the industries for efficient disposal. Till date the method adopted for disposal are either in form of slurry in red mud pondor as dry stacks, in both the facilities there is a great loss of vast track of usable land and damage to environment due to leachate generation from the red mud being highly alkaline (pH>11).To attain the objective of sustainable development researchers are working hard to find the potential use of red mud so that optimum utilization of red mud will eliminate the problems related to their disposal.Therefore, to avoid the threat due to storage, it is important to reduce the storage by bulk utilization. Indian red mud constitutes 10-20% of coarse fraction. In the present study, this coarse fraction has been used as fine aggregate in cement mortar replacing the conventional river sand in binder to aggregate ratio of 1:3 and 1:3.5 and has been exposed to different curing condition namely water curing(28 days), sulphate curing(90 days)and water curing (28 days) followed by sulphate curing(90 days).The effect of sulphate (MgSO4and Na2SO4) attack on the compressive strength of mortar prepared using red sand has been investigated and compared with the result of river sand. In order to find passivation ability of the mortar, non-destructive polarization test has been carried out. The compressive strength of red sand mortar is found to increase after sulfate attack and the red sand mortar shows nearly same resistance towards corrosion of the reinforcing bars due to high alkalinity(pH>11) as compared to the river sand. The increase in strength of red sand mortar after sulfate attack is correlated with the microstructural changes.Although the percentage of coarse fraction (>75μm) in the red mud is limited, the present study will help in reducing the storage of red mud by utilizing it as fine aggregate in cement mortar thereby reducing the environmental problem.