Researchers in Italy say they have improved the performance of concrete by replacing 5% of the cement with recycled concrete powder. They also found concrete with 75% recycled materials also displayed good mechanical performance, durability and water absorption.
Concrete can perform just as well if three-quarters of its content has been recycled, a team has found.Concrete is made from granular materials such as sand and crushed stone – known as aggregates – bound together by a cement paste.
Cement has a high carbon footprint due to the chemistry of its production and the high processing temperatures, while the aggregates have a high ‘resources footprint’ because they come from finite natural sources. With global construction rates predicted to rise by 35% by 2030, researchers are looking for ways to reduce both footprints through recycling or using other materials.
A team led by Italian engineers has refined the processing of demolition waste on site and tested ways of using the resulting streams of powders and aggregates in fresh concrete.‘We have shown that it’s possible to achieve astonishing percentages of construction and demolition waste embedded in our precast concrete elements,’ said Dr Anna Paraboschi, a civil engineer at RINA, an industrial consulting firm, and coordinator of the project, VEEP.
Previous research by members of the consortium – Spanish R&D company Tecnalia and the University of Delft in The Netherlands – had indicated it might be possible to push the limits of old concrete used in new – so VEEP has built on this at large scale she adds.While construction and demolition waste is often recycled into aggregates to be used for road bases or as backfill after excavations, a large quantity of the 850 million tonnes produced annually across Europe still goes to landfill.
Recycling of construction and demolition waste has increased across Europe, with most countries reaching a 2020 target of 70% recycling rates. However, many have done this by increasing its use in road bases and backfill, while other possibilities, like using it in concrete again, remain untapped.