Quarry Southern Africa November 2018 - Page 27

240ℓ and thereafter 250ℓ – meaning the concrete strength is variable – a ready-mix plant cannot use it because the plant will lose credibility,” says Du Plessis. “With recycled aggregates, consistent grading is not something you can guarantee unless you get your recycled material from one reliable source.” Therefore, to write a specification will be challenging, while to adhere to it will be even more challenging. The specs will have to be even more strict than for natural aggregates, because people will cut corners in what they put in, adds Du Plessis. The challenge, he says, is that the trade is struggling to get approval for ordinary natural aggregate samples. Each aggregate has to go through vigorous testing worth nearly R20 000 to ensure compliance to all specifications as set out in SANS 1083. For instance, for a major project like a power station a supplier can expect hundreds of thousands or up to a million rand of testing throughout the project life to ensure consistency and performance. has been taking place for over a hundred years and a number of techniques have been developed and continue to be developed to provide economically and environmentally suitable methods to suit various projects and locations. In South Africa, asphalt from existing road pavements has been used since the mid-1970s for the production of millions of tonnes of recycled mix that have the same performance characteristics as hot mixed asphalt made with all virgin materials. Saied Solomons, CEO of the South African Bitumen Association (Sabita), says that recycled or reclaimed asphalt (RA) refers to the portion of asphalt which, once removed from an existing road surface, is reclaimed and re-used for the purposes of new road building, maintenance or repair. RA typically consists of 95% high quality aggregate and 5% of aged bitumen. “Over time, road surfaces either deteriorate or the road requires an upgrade for other reasons, but these require the existing road surface to be demolished or “We have old mines in Secunda, Witbank and Middelburg which have to be filled. We can pump self- compacting or self-levelling concrete into the mines to fill the cavities, and for this we can quite efficiently use recycled aggregates because it’s cheaper, and in the case of fly ash it would be free. In fact, some of the mines will pay you to take it off their hands.” Aggregate from a quarry is relatively predictable because it comes from solid rock in which one wouldn’t expect organic material. In comparison, aggregate from a recycling plant where everyone simply dumps their concrete and rubble will represent a wide variety of quality of material from multiple sources. “We have different specifications for aggregates from different sources to be used in construction – to guarantee consistency. With recycling they’re all mixed together. There is definitely a use for recycled aggregate, but not for high-spec construction,” says Du Plessis. Asphalt’s long history of recycling The reuse of road material across the globe www.quarryonline.co.za  repaired. Although the road surface may no longer function as a whole, the asphalt component of the road surface can be re-used and provides a valuable source of material that can be reclaimed. It is important to note that prior to reclamation the asphalt is always tested to determine if it is suitable for reclamation and there are a number of standards which are used for this,” says Solomons. In the past few years this technology has received much more attention as the world puts more emphasis on environmental conservation and carbon footprint reduction. In addition, the costs of building this type of infrastructure have also increased and economic reasons are a driver. The method is to accommodate over 90% of recycled asphalt producing materials TECHNOLOGY Kate Stubbs, director, Business Development and Marketing from Interwaste. at a low energy cost with an appropriate design life. Future trends As an example of what the future holds, Qatar has set itself a target to recycle 15% of solid waste generated in the country over the next four years, according to the Qatar Second National Development Strategy (NDS2). The state is making significant efforts to increase the waste recycling rate and promote environmental awareness on reducing the quantity of domestic solid waste. The generation of total solid waste (construction, domestic and others) on the country increased from 8Mt in 2008 to 12Mt in 2013. As the infrastructure works of the FIFA World Cup and related demolition and rebuilding of enterprises is nearing completion, the generated amount of construction waste is expected to decrease. A high proportion of construction waste, especially cement, brick and tile waste, is fully suitable for crushing and recycling as a replacement of gravel extracted from new quarries in some lower applications. Stubbs concludes, “It is critical that any business going forward needs to incorporate its environmental impact into its business processes from cradle to grave. From the sourcing of various raw materials, to the production and final consumption or route to market, companies need to understand the generation of waste in each process to ensure the long term commercial and environmental viability of the business.”  QUARRY SA | NOVEMBER/DECEMBER 2018_27