The recycled concrete aggregate produced met the requirements for typical structural applications.

RESEARCHERS at the Indian Institute of Technology Madras have developed a treatment process involving solar thermal energy to recycle concrete debris from construction sites and demolitions.

A team of researchers from IIT Madras has developed a treatment process involving solar thermal energy to recycle concrete waste. Here, at the trial site in Rajasthan, with the solar reflectors in the background. | Photo Credit: IIT Madras

Waste concrete was heated using solar radiation to produce recycled concrete aggregate (RCA) that was higher in quality compared to that obtained from mechanical crushing, according to the IITM release, and met the requirements for typical structural applications.

Full-scale trials of the process were carried out at the “India One Solar Thermal Power Plant”, located in “Shantivan”, the headquarters of the Brahma Kumaris organisation in Rajasthan, using two solar concentrators.

By using concentrated solar energy for heating, the thermo-mechanical beneficiation of the concrete waste resulted in high-quality recyclable materials, which can substitute broken stone aggregates and sand in concrete. In this 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 recycled concrete aggregate (RCA). The findings of this work were published recently in the journal Materials and Structures.

Elaborating on this study, Ravindra Gettu of the Department of Civil Engineering, IITM, said: “The main intention of the present study was to develop the proof-of-concept that solar radiation could be used… to produce good quality recyclable material for new concrete.”

The study demonstrated that (1) the required temperature of about 500 °C could be achieved and maintained for a long duration with the reflector-receiver solar-thermal energy set-up that was used; (2) the properties of the aggregates produced were comparable with those of RCA produced in an electric furnace, with the total yield of recycled products being 90 per cent of the feed concrete; and (3) preliminary results on concrete made with the RCA indicate its suitability for typical concrete applications.

Concrete is the most common material used in construction universally with an annual production estimated to be 10-30 billion tonnes. According to the release, the global consumption of construction aggregates, including that needed to make concrete, is projected to reach 63 billion tonnes in 2024.

Practically all aggregate demand is currently met by extensive quarrying and mining, leading to the depletion of primary mineral resources. Moreover, there is a severe shortage of fine aggregate in many countries owing to bans on the mining of river sand.

On the other hand, construction activities generate considerable waste, estimated to be about 3 billion tonnes a year. Some developed countries recycle up to 90 per cent of the construction and demolition, waste whereas others continue to dump it in landfills.

R. Ramachandran