Performance of fly ash with electroplating waste and cement for geotechnical applications

The rapid pace of urbanization and industrialization necessitated setting up of large number of coal based Thermal Power Plants in the country to meet the energy requirements, resulting in a huge production of fly ash. Fly ash, a waste product of Thermal Power Plants is generally disposed off in vicinity of the plants as a waste material covering several hectares of valuable agricultural land. This affects the ecology of land, water and air in the region. The Indian Government enacted a law in October, 2005 stating that a minimum of 25 percent fly ash must be used in the manufacturing of clay bricks for use in construction activities within a 50 km radius of coal based Thermal Power Plants. There were also restrictions on the excavation of top soil for the manufacture of bricks. This necessitates effective utilization of this accumulated waste material. The electroplating industries are one of the oldest industries. These industries discharge highly toxic wastes, which include heavy metals and chemicals like cyanide. According to a report, in the year 2006 about 7,00,000 electroplating units were operating in India, out of which about 5000 units are located in Aligarh. The wastewater generated in Aligarh by lock industries, specially electroplating industries is around 250 million litres per day. The present investigation attempts to explore the possibility of best utilization of the these two industrial wastes viz., fly ash and electroplating waste sludge, after converting them into a non hazardous material through an economical process, leading to an effective waste management applications such as, construction products and structural fill material etc. Fly ash, procured from Harduaganj Thermal Power Plant, Harduaganj, 16 km from Aligarh, India, was used as the test material. This fly ash is classified as Class F type which is having low pozzolanic properties. The fly ash resembled with the particle size of silts and classified as ML. Electroplating waste sludge was collected in the form of filter cake fi-om one of the electroplafing industries in Aligarh City, India, in which Nickel, Chromium, Zinc and Cadmium plating were done, associated mostly with lock and other allied industries. The waste sludge comprises of 70% solid waste and 30% waste water, having pH as 1.2, specific gravity as 1.022. The waste sludge was having enormous quantity of heavy metals such as Ni, Cr, Zn, Cd, Cu and Pb. The finely powered white coloured lime was used as precipitator for electroplating waste sludge. The cement used in this study was OPC-43 grade. Compressive strength tests were carried out on lOOxlOOx 100mm cubes prepared with various combination of fly ash (FA)-waste sludge (S)-cement (C), at 7, 14, 21. 28 and 90 days of curing. The toxicity characteristics leaching procedure (TCLP) leaching tests were conducted on the samples at 28, 60, 90, 120, 150, 180, 210, 240. 270, 300, 330 and 365 days of curing. On the basis of compressive strength and TCLP leaching tests on various combinations of fly ash-waste sludge-cement mix, the most effective percentages of waste sludge was obtained in the range of 30% to 45%, whereas, for economical considerations the cement percentage was fixed as 8% in the fly ash for carrying out further studies. The maximum compressive strength was obtained for 60% to 55%FA, 30% to 45%S and 8%C composition. The average compressive strength for this range of mix has been observed to be 38.4 MPa at 28 days of curing. The pH values of different mixes are found in the range of 6.9-10.9. The analysis by atomic absorption spectrophotometer (AAS) reveals that the concentration of heavy metals in the leachates is reduced by 97%-100%. When the experimental results of leaching are compared with US EPA (1992), EEC (1991) and DIN (1984), it is found that the heavy metals in the waste sludge were completely stabilized by fly ash-cement system. On the basis of compressive strength and leaching tests, the range of most effective percentages of fly ash-waste sludge and cement were determined. Further, experimental investigations such as compaction tests, shear strength, California bearing ratio and plate load tests were carried out on the most effective percentages of fly ash, waste sludge and cement. Compaction parameters, namely maximum dry density (MDD) and optimum moisture content (OMC), determined fi-om Proctor compaction test serve as the benchmark