Stabilization of Red Mud Using GGBS and Fly Ash

Abstract

Extensive amounts of waste materials and by-products are generated by human, industrial and commercial activities. It has become difficult to handle huge amount of waste which leads to environmental problems. Rapid utilization of natural resources, generation of huge amount of industrial wastes and environmental pollution needs new solution for sustainable economic development. During past decades more concern is shown towards the utilization of industrial wastes and by-products in civil engineering works. Utilizing the waste is a partial solution to ecological and environmental problems. If the industrial wastes are used in production of cement, concrete and in some other construction materials as a replacement to conventional materials then the manufacturing /project cost will be reduced and reduces the land fill area.

Geopolymerization is the present technology, which can transform waste materials containing silica and alumina into useful products with excellent physical and chemical properties. The main principle involved in geopolymerization is the chemical reaction between alumino silicate materials and highly alkaline solution to form amorphous to semi crystalline inorganic polymers. Red mud, granulated blast furnace slag and fly ash are the industrial waste materials which have the potential application in civil engineering constructions when they are utilized properly. Red mud is alkaline by-product which is generated during the processing of bauxite. Generally red mud is considered as a waste material which is dumped into large areas. Red mud contains large amount of Fe2O3, Al2O3 and small amounts of CaO, SiO2 and some valuable metals such as titanium. As red mud is highly alkaline, it can be stabilized by adding waste materials rich in aluminosilicates. In the present research work an attempt has been made to stabilize red mud using ground granulated blast furnace slag (GGBS) and fly ash separately. Fly ash is added in the percentages of 0%, 10%, 20%, 40%, 60%, 80% and 100% to the red mud. Similarly slag is added to red mud in the same amounts. For each proportion of red mud-fly ash and red mud-slag Atterberg’s limits, pH values, differential free swell (DFS) value, OMC and MDD corresponding to light compaction and heavy compaction and unconfined compressive strength (UCS) are determined. Cylindrical samples of are prepared by compacting to MDD and OMC. The wax coated specimens are kept for curing about 0, 3, 15, 30 and 60 days. These specimens are tested to determine the unconfined compressive strength. NaOH is added in the percentages of 2%, 4%, 8%, 12% of dry mass to red mud, fly ash, slag and the above proportions of red mud-fly ash, red mud-slag and unconfined compressive strength is determined.

It is observed that as the amount of fly ash increases the liquid limit, plastic limit and shrinkage limit increases. As the amount of slag in red mud is increased then plastic limit and shrinkage limit reduces but the liquid limit is found to be decreased up to 40% slag content thereafter with further increase in slag content the liquid limit increases. Red mud-slag and red mud-fly ash mixes exhibits negative values of differential free swelling. Red mud shows moderate decrease in pH values with increase in slag content. With the replacement of red mud by fly ash in red mud-fly ash mixes, resulted in substantial decrease of pH values. It is observed that, in red mud-fly ash mixture, as the percentage of fly ash increases, the maximum dry density decreases whereas the optimum moisture content increases. In red mud-slag mixture, as the percentage of slag added to red mud is increased, the maximum dry density increases up to 40% slag and further addition of slag resulted in decrease of MDD value. Virgin red mud possesses UCS value of 0.22 MPa which is increased to 5.2MPa with the addition of 40% slag at curing period of 60 days. The addition of fly ash to red mud does not result in an appreciable increase in unconfined compressive strength. For 60% Red mud and 40% fly ash maximum strength of 0.33 MPa is obtained at 60 days. Addition of alkali i.e. NaOH solution enhances the strength remarkably for red mud-slag mixes. With the addition of 40% slag and 4% NaOH, red mud attains an unconfined compressive strength of 14.02 MPa at 60 days of curing. An addition of 4% NaOH to 60% red mud and 40% fly ash results an unconfined compressive strength of 1.21 MPa after a curing period of 60 days. This may be due to absence of sufficient amount of reactive alumina and silica in the fly ash specimen. Red mud is a highly alkaline material which can be stabilized effectively by addition of 40% slag through geopolymerization process. It reduces the environmental pollution and it can be used in the construction works such as embankments, structural fills, etc.