Concrete is one of the most utilised man-made materials in the world. An essential construction element of modern buildings, roads and bridges, it underpins urban development across the globe. Consequently, as concrete-based infrastructure is replaced with new structures, an enormous amount of building waste is produced, much of it steel-reinforced concrete.
There was a time when this building rubble would often end up as landfill, but thanks to construction industry professionals devoted to sustainability, new waste minimisation strategies have emerged. Here, concrete recycling processes are proving invaluable, both economically and environmentally.
One company leading the way in this field is Australian construction and demolition materials recycler Alex Fraser Group. With technical expertise in producing a comprehensive range of recycled construction products, including specification road bases and civil construction materials, Alex Fraser Group has established itself as a recycling pioneer.
With demand for its recycled building products increasing steadily in recent years, Alex Fraser Group decided to establish a new concrete recycling facility at its Laverton North site in western Melbourne, Victoria. Earmarked to replace the company?s existing concrete recycling operation at the same site, the new facility features a sophisticated materials handling system, founded on the latest geared motor technology from drives solutions group SEW Eurodrive.
LOAD, CRUSH, CONVEY
The new concrete recycling facility has been designed with reliability, efficiency and safety at its core. Underpinned by the latest crushing and conveying technologies, it is capable of throughput rates of 550 tonnes of product per hour, a significant increase on the existing plant?s production capacity of approximately 150 tonnes per hour.
Front end loaders transfer raw feed (comprising various grades of steel-reinforced concrete up to 1.5 metres in diameter) into the plant?s main feed hopper, which rises out of the process pit. An extensive network of conveyors transport the feed through a succession of jaw crushers, magnets (for metal removal), screens and a cone crusher to reduce the raw feed into the fragment sizes of less than 20mm grade crushed rock final product.
Finally, a 76m conveyor transfers the product out of the process pit. Once out of the recycling plant, a 125m conveyor transports the product to a computer-controlled telescopic Thor stacker for stockpiling. After further processing in a separate blend plant, the wet mix is ready to be loaded on to trucks and transported to construction sites for use as base material in pavement and road applications.
The entire process is controlled and monitored from a central management centre in the process pit. Operators are able to interrogate the process via a plant-wide SCADA system, which is fed by a central Ethernet communications loop.
The new facility comprises over 600m of heavy duty belt conveyors, providing fast and efficient transfer of concrete through the recycling process. With all conveyors requiring geared motors, Alex Fraser Group chose to implement SEW Eurodrive?s drive solutions plant-wide. Over 30 IP66-rated geared motor combinations of up to 55kW provide the driving force for the concrete recycling facility?s conveyor applications.
?There?s never any shortage of building waste to recycle, so the more time we?re on-line, the more concrete we can process,? said Dean Walsh, the plant projects manager for Alex Fraser Group. ?It was crucial that we implemented a dependable geared motor solution to ensure our process is up and running. SEW Eurodrive was able to provide us with reliable geared motor combinations, which go some way to ensuring our recycling process stays on-line.?
According to Dean, one of the biggest challenges in keeping the process on-line is the inconsistency of the feed. ?It?s not like processing quarried rock, which displays the same size and consistency characteristics day in, day out,? he explained. ?When recycling concrete, there are a number of variables, such as the steel content and concrete density. Both can affect throughput.?
To ensure that the conveyors are supplied with a consistent feed, the crushers have been designed to accommodate concrete of varying material make-ups. This means conveyors can be kept running and the process kept on-line. However, there are bound to be disruptions. Invariably, a bit of metal will get caught, requiring conveyors to be turned off to clear blockage.
?If there is a blockage, we are able to quickly switch the conveyors off from the central control centre, or via the pull-wire safety stops that run alongside the length of each conveyor,? said Dean. ?Importantly, the SEW Eurodrive geared motors have an impressive duty cycle. We are able to turn them on and off frequently, and have them still come up to speed and torque quickly.?
Safety is a primary consideration across all of Alex Fraser Group?s sites and operations. As a result, all of the geared motors used on the conveyors at the new concrete recycling facility feature direct-coupled geared motor/shaft arrangements. Previously, v-belt to gear box arrangements were employed on-site, which presented some safety issues, such as extra guarding and maintenance requirements.
?By direct coupling, we can avoid this,? said Dean Walsh. ?However, in the past, we?ve shied away from direct-coupling gearboxes. In a corrosive environment, it is very hard, and often impossible, to remove the gearbox from the shaft. In fact, once it?s time to take them off the shaft, it?s not uncommon to have to cut them off with a gas axe. We knew there had to be a better way.?
SEW Eurodrive?s TorqLOC keyless hollow shaft mounting system presented the ideal solution for direct-coupling the geared motors on to the conveyor shafts. The TorqLOC system provides a keyless connection with a shrink-disc, with the interfacing surfaces relying on two conical tapered bushings, made from bronze and nickel-plated steel (or stainless steel).
?Traditional hollow shaft securing solutions – the keyed hollow shaft and smooth parallel-bore hollow shaft – have suffered from corrosion problems, which, in turn, can create disassembly difficulties,? said Andrew Kurzem, SEW Eurodrive?s technical sales representative. ?TorqLOC components are designed to counteract the impact of corrosion. You only have to loosen the steel bushing taper a little, and it will fall away. And this is still the case after a long running time.?
?The TorqLOC system was one of the key reasons we chose SEW Eurodrive,? said Dean Walsh. ?It allows us to install and remove the geared motor units quickly and easily, a real advantage when you are installing big bits of gear. It?s all about reducing downtime and keeping the plant running, so we can get them on and off quickly with no fuss. This is a real advantage, especially during installation and commissioning, and for major servicing.?
AN ENVIRONMENTAL BENCHMARK
Inherently environmentally friendly, Alex Fraser Group?s concrete recycling operation is setting the benchmark for the provision of sustainable building materials. Since obtaining VicRoads certification in the early 1990s, Alex Fraser Group has provided Class 2 cement-stabilised road base for some of the country?s most important roadways, including the Albert Park Grand Prix track and numerous sections of Victoria?s Western Ring Road.
Recently, an Alex Fraser Group-funded Royal Melbourne Institute of Technology research programme highlighted the environmental benefits of recycled concrete when compared with concrete made from virgin quarried rock. It was found that the carbon impact of recycled concrete produced by Alex Fraser Group was 65 per cent less when compared with the impact of manufacturing concrete from freshly quarried material.
?This is no surprise, given the amount of energy consumed during the extraction, processing, manufacturing and transportation activities that are associated with the production of concrete from raw materials,? Dean Walsh remarked. ?Furthermore, by recycling concrete, landfill space can be conserved, gravel mining reduced and the carbon footprint minimised.?
According to Andrew Kurzem, efficiency was a key parameter when specifying the SEW Eurodrive geared motor combinations. ?Each gear motor has been selected to match the performance requirements of each conveyor to deliver optimal operational efficiency,? he said. ?All motors are MEPS-compliant, high efficiency varieties. In combination with Alex Fraser Group?s recycling process, real environmental savings can be made.?
Like many heavy industrial applications, Alex Fraser Group?s concrete recycling process is a 24 hours a day, seven days a week operation, employing numerous full-time on-site engineers, technicians and operators. ?We need our conveyors and our process to operate uninterrupted,? said Dean Walsh. ?This, of course, is dependent on the ongoing performance and maintenance of the geared motors.?
Before selecting a geared motor supplier for this project, Alex Fraser Group posed some hypothetical replacement/repair scenarios to all potential suppliers and compared the response capabilities of each. ?SEW Eurodrive were able to provide overnight turnarounds on gear unit repair/replacement,? Dean said. ?In fact, SEW Eurodrive took us on a comprehensive tour of their assembly plant. We were extremely impressed with their stock of spare parts and assembly facilities. It really backed up their claims and sealed it for us.?
Support is something SEW Eurodrive prides itself on. ?SEW?s ability to supply total project lifecycle support in Australia and across the globe sets us apart,? said Andrew Kurzem. ?By assembling locally, stocking a comprehensive range of spare parts and providing 24 hour, around the clock technical support and service, the company has gained a reputation as one of the world?s most dependable drive solutions providers.?
With the new concrete recycling facility on-line and on schedule, Alex Fraser Group is looking to the future. The new concrete recycling plant has performed well above expectations during commissioning trials, and is on target to achieve a production rate of 600 tonnes per hour. Here, the conveyors and geared motors have been sized to accommodate this increase. ?Alex Fraser Group is looking forward to bringing the plant up to full production capacity,? said Dean Walsh. ?By working alongside like-minded, environmentally aware industry partners like SEW Eurodrive, we?re confident of reaching our 2014 production target of 40 million tonnes of recycled concrete.?
Sources: Relate Technical Communications/SEW Eurodrive