The DPR (detailed project report) prepared by Dr K. N. Satyanarayana of IIT Madras and his team for the Corporation of Chennai recommends setting up two construction and demolition (C&D) waste recycling plants as well as transfer stations in each zone to deal with this monumental problem.
This study is the first to scientifically calculate that 1.25 million tonnes of C&D waste is being generated annually in the city. Without a proper policy or a disposal system in place, C&D waste, which is either sent to the city’s dumpyards or illegally deposited in rivers, canals and marshlands, poses a civic conundrum.
Dr. K. N. Satyanarayana, Professor, Building Technology and Construction Management Division, IIT Madras, said that there has been a gross underestimate of the amount of C&D waste generated. “When a building is demolished, the wood, steel and wire components are resold in secondary markets, while masonry and concrete waste is discarded, which ends up in dumpyards or lakes, rivers and marshes,” explained Satyanarayana.
The study recommends setting up two C&D waste treatment plants as well as transfer stations in each zone. “Setting up a recycling plant for C&D waste is an energy intensive project and needs a proper policy for collecting the waste, as these plants benefit from economies of scale.
The C&D waste should be sent to these transfer stations by the developers or builders. Two recycling plants can be installed near Perungudi and Kodungaiyur. This is a way to retrieve some of the aggregates and reuse it, so that it doesn’t end up in the dumpyards or our lakes,” he noted.
Research scholar V. G. Ram, who is also a part of this project, said they were working on C&D waste management, even before they were awarded the DPR six months ago.
“We were creating estimation models that will suit the Indian urban areas, gaining background knowledge and expertise through literature review and visits to other places,” he said, explaining the technology behind the recycling plant.
“Major operations in a recycling plant are sorting, crushing, classification/sieving and washing. Sorting can either be done manually or using advanced devices. Before feeding the material into the crusher, a grizzly can be used to ensure the maximum feeding size of debris for the respective crusher.
Generally, jaw crushers or horizontal impact crushers are used to crush the debris. Size classification is performed using appropriate screens of required sizes. Washing is done to separate fine particles (silt and clay particles) and this operation can be done combined with size classification. Sorted aggregates of specific sizes are stored separately,” he added.
Dr Satyanarayana said that awareness among the public and officials is vital to create a demand for recycled products. “Creating a market for recycled products is crucial for establishing a successful plant. We have recommended to the Corporation to opt for a PPP (public private partnership), since the set-up works like a factory.
The private agency can undertake running of the plant while the Corporation has to ensure a proper supply of material to recycle.
Once the land has been allocated by the Corporation and private contractor identified, setting up the plant will take a year,” he pointed out, adding that the Corporation was serious about finding a solution to tackle this problem.
An official from the Corporation said, “After analysing the DPR, we will look towards forming guidelines and consider setting up infrastructure towards disposal of C&D waste.”
‘No reduction in building strength’
If the C&D waste is properly recycled, it will not affect the building strength. The design of concrete produced using recycled aggregates (M30 or M20 quality used) incorporates the safety factor and the properties of recycled aggregates used. Thus, safety is in-built into the structure, provided the Indian Standards requirements are met during the design and production of concrete.
The recycling activity (processing of C&D waste) can be designed to produce the required quality of aggregate as specified by Indian Standards (IS 383: Specification for coarse and fine aggregates from natural sources for concrete).