Civil Engineering August 2021 | Vol 29 No 7

16 August 2021 Civil Engineering M odern civilisation is built on concrete and its positive social impacts are immense, but this extensive usage means that concrete has a relatively large environmental footprint. However, this could be reduced by in- creasing the volumes of recycled concrete, says Bryan Perrie, CEO of Cement & Concrete SA (CCSA). “At least 10 billion tons of concrete are used annually – twice as much as any other building material. This means the potential for recycling is enormous, but sadly unacceptably high volumes of concrete now end up in landfills together with other construction and demolition waste (C&DW) – completely ignoring their recycling potential.” Perrie says the demolition of in-situ, precast and tilt-up reinforced concrete can be achieved relatively easily by modern cutting, breaking and lifting equipment. Once demolition of reinforced concrete has been completed, the concrete and reinforcing steel can be separated for recycling. “Internationally, the most common usage of recycled concrete currently is in roads, but concrete can be recycled for many other purposes such as aggregate for building products such as bricks, blocks, layer works in road construction, or land reclamation. Recycling reduces the need for virgin materials, thereby saving resources and the energy required to process them. Crushed concrete furthermore absorbs carbon dioxide. Precast components from structures can be reused in new buildings without having to be demolished and recycled. Structures using precast elements should, in fact, be designed for such reuse,” explains Perrie. “In former industrial areas and inner-city precincts, there are many old concrete structures such as unused of- fices, factories and warehouses that can be retrofitted and converted into residential space. Effective building retrofitting usu- ally requires the building structure to be left largely intact.” BENEFITS AND CHALLENGES The benefits of recycling and retrofitting include: Q Q Saving of natural resources, including raw materials, energy and water required for new structures Q Q Reducing the quantity of solid waste sent to landfill Q Q Lowering the energy consumption and pollution that would result from the extraction, manufacturing and transportation of virgin materials Q Q Increasing employment opportuni- ties – an important element in a country such as South Africa with its high unemployment rate. Perrie concedes that there are still some challenges to be overcome in the quest for using higher volumes of recycled concrete. “Included are aspects such as irregularity of supply, contamination and lack of consistent quality, site sorting, noise and pollution resulting from recovery and processing on site, as well as potential legal aspects. “But the benefits – particularly for countries with shrinking economies – by far outweigh the challenges. CCSA be- lieves there should be legislation banning construction and demolition waste from landfills, or taxation to limit the volumes of C&DW ending up in landfills. This must be coupled with increased policing to stop illegal dumping of construction waste. Architects and specifiers also need to increasingly consider the use of recy- cled concrete or concrete unit reuse when designing new buildings,” he adds.  The benefits of recycling and retrofitting concrete Enormous economic and environmental benefits could be achieved globally by placing more emphasis on the recycling and retrofitting of concrete, the most commonly used building material on earth. The quality of the concrete in demolished structures will determine the concrete’s suitability for reuse