Indian Institute of Technology Madras (IIT Madras) researchers have developed a treatment process involving solar thermal energy to recycle construction and demolition debris. The waste concrete from demolition was heated using solar radiation to produce recycled concrete aggregate (RCA) that was higher in quality when compared to those obtained from mechanical crushing. The concrete made using this technology met the requirements for typical structural applications.

The demonstration was done at the India One Solar Thermal Power Plant located in Shantivan, the headquarters of the Brahma Kumaris organisation in Rajasthan. It has 770 solar concentrators to produce electricity using steam generated at high pressure. The plant has been operational since 2017 and provides power to a community of about 25,000 people at a reasonable cost and low maintenance. Two of the concentrators were used in the full-scale trials for treating the waste concrete, says a release.

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By using concentrated solar energy for the heating, the thermo-mechanical beneficiation of the concrete waste results in high-quality recyclable materials, which can substitute stone (blue metal) aggregates and sand in concrete. In this pioneering study, concrete from a demolition site was heated using solar radiation concentrated through large reflectors and cast iron receivers to more than 550 °C and subsequently, scrubbed mechanically to yield coarse and fine RCA, with properties similar to those of pristine aggregates.

Ravindra Gettu, VS Raju Chair Professor, Department of Civil Engineering, IIT Madras, said that the intention of the study was to develop the proof-of-concept that solar radiation could be used in the thermomechanical beneficiation of concrete waste to produce good quality recyclable material for new concrete. The study presents evidence for the use of concentrated solar energy for recycling waste concrete, with promise for large-scale waste concrete recycling. This would reduce the energy footprint of construction and demolition waste processing significantly, and lead to savings in raw material and electricity, towards a circular economy.

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