A site better: How 360 excavator-mounted attachments could reduce construction’s carbon footprint
Malcolm Bates
The equipment used to recycle construction site waste is echoing the ‘downsizing’ trend already common in the construction industry, by developing specific machines for urban applications. But is this the only option? How about utilizing specialist attachments coupled to 360 excavators? The attachments may be small, but the benefits could be big when it comes to increasing recycling ratios
by Malcolm Bates
The whole concept of on-site recycling in the context of the recycling of construction site debris is hardly new. But the worrying growth in global population and the need for trucking and construction companies not only to reduce their carbon footprint, but to be seen to do so, has brought a new vitality to this sector. In fact, along with more recent interest in dedicated food-waste collections, on-site recycling is probably one of the more ‘sexy’ issues in the whole waste and recycling industry at the moment. And it’s worth examining why.
While many people in the plant world expect on-site recycling to develop into a business niche in it’s own right in order to meet the growing need to redevelop downtown ‘brownfield’ sites (rather than use undeveloped land), how that will happen is still open to some debate. One view suggests that specialized contractors, using compact, purpose-built crushers and screens and a matching complement of ‘downsized’ excavators and wheeled loaders designed to operate on crowded urban redevelopment sites will be the dominant force. And there’s already global evidence of this trend, with several manufacturers producing specific urban machines offering reduced noise and exhaust emissions.
But even leaving those developments aside, the fact remains that any waste materials trucking operation that is routed through an urban area is a contributor to traffic congestion and emissions – and is increasingly costly due to fuel price rises. But perhaps the biggest issue here is a public relations one. For new developments to be judged successful – or to even be permitted – developers increasingly need to show that the construction process has a low carbon footprint and that the development is sustainable – every bit as much as any new buildings have to be energy efficient. That’s a big challenge to an industry that is not accustomed to being in the media spotlight.
Two schools of thought
Encouragingly, the on-site recycling of demolition and construction industry waste is increasingly seen as every bit as much a part of the waste and recycling sector as the handling and recycling of domestic, trade and industrial waste. And behind this thinking is the concept of using machinery to transform what would otherwise be an ‘expense’ (landfill tax, diesel fuel, and the like are all costs) into a ‘resource’ – that is to say something that can actually save money, or even make it. But just as in the mainstream waste sector, there are different views as to how this should be done – one being that it’s easier to keep each specific element separate and uncontaminated, the opposing view being that it often isn’t possible to do that. In which case, machine solutions have to be capable of separating specific elements from a mixed stockpile. One of those who hold the latter view is Terry McSweeney of Worsley Plant, based in Cheshire, UK. While acknowledging that purpose-built crushers and screens are essential in a minerals extraction situation, Terry McSweeney suggests that compact, purpose-built machines are not necessarily the best solution for all urban redevelopment applications. He argues that each purpose-built crusher and screen requires its own power unit – adding to emissions – but at the same time, each machine will require a service fitter familiar with its design. Plus, if anything does go wrong, the issue of whether a replacement machine could be readily hired from a rental company has to be considered.
Tool carrier concept
Terry McSweeney suggests there is a simpler solution – and that’s to use the familiar 360 excavator more as a ‘tool carrier’ and utilize a range of specialist recycling attachments. ‘Every demolition or construction site will have at least one 360 excavator employed to dig and load, so why not add a range of hydraulically-powered attachments such as rock crushing and screening buckets?’ he contends. His assertion could offer some advantages over a whole collection of specialist machines. Firstly, an operator sitting in the cab of a 360 can undertake a number of tasks, using easily-changed Q-hitch crusher and screening attachments as required.
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A Volvo 360 excavator working with an S-Series screening bucket processes rough concrete and clay mix, while in the foreground a Doosan mounted R-Series bucket screens recycled topsoil
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On most sites, each specific operation takes place in a logical order (or at least that’s the hope!) from initial demolition, through to processing material for the construction of new foundation footings, for example – so the need to swap attachments back again shouldn’t arise. But even if this was not the case, a number of 360 excavators could work in parallel, one stockpiling, one crushing, one or more screening material as required to different grain sizes and a further machine loading dumpers or trucks for distribution.
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Close-up of R-Series showing one of two bearings
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Technically, the latest generations of 360 excavator are more than capable of working all-shift long powering a specialist crushing or screening bucket – and with the operator seated in an air-conditioned cab, with good all-round visibility, site safety should be enhanced. Recent generations of 360 are readily available on rental, quiet in operation and fuel efficient. So is there any downside to this philosophy? To find out – and to introduce the new line-up of screening buckets marketed in the UK by Worsley Plant – Terry McSweeney had arranged a demonstration of a range of attachments on a tight, busy commercial site in London, UK, just a few miles from the site of the 2012 Olympic village construction site. Here, on the site of a derelict gas works, material from buildings demolished to make way for the new Olympic facilities were being recycled.
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Doosan-mounted R-Series bucket at work, showing mountings, while Scania tipper truck loads recycled topsoil using its own truck-mounted hydraulic loader with clamshell bucket
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The nature of the site underlined Terry McSweeney’s original assertion that having a number of purpose-built crushers and screens on site wasn’t always a practical proposition due to lack of space. In this case, with three 360s working on top of their respective stockpiles, there was only just enough space for a couple of four-axle dump trucks to access the site – and nothing else! In one corner, a Volvo 360 BLC was processing large chunks of concrete – removing reebar in the process – and separating the heavy London clay soil from the rest of the material.
This material had already been processed by one of Worsley Plant’s range of crusher buckets. It was then passed over to the next operation to be processed by a rotary screening bucket, mounted on a Doosan 140LCV. This took out any remaining large foreign matter and produced graded ‘fill’ with the ‘fines’ being passed to another stockpile where a third 360 excavator, fitted with a vibrating riddle bucket was producing mixed, reclaimed topsoil. This was being used to help landscape finished developments in the London area – reducing the need to truck in fresh supplies of topsoil from outlying rural locations.
When it comes to selecting a suitable 360 excavator, there are roughly four operating weight classes to consider: 10–14 tonnes, 16–21 tonnes, 21–28 tonnes and 30–35 tonnes, although smaller crusher and screening buckets are available to fit skid steer and wheeled loaders, of course. The use of two or more attachments adds to the utilization of any 360 and as Terry McSweeney suggests, modern 360s are often the quietest, lowest emission machines on any site. ‘One man and one 360 excavator can do every job needed on a demolition site clearance with suitable attachments,’ Terry McSweeney explained.
Three different designs
Worsley Plant offers three internationally available designs of attachment to it’s UK customers – the S-Series, which comes in three ‘duty’ versions spread over the four machine weight classes, comprises a total of eleven different models. This square-sided design of bucket is designed to prevent heavy clay soils ‘sticking’ while being screened, making the S-Series ideal for separating brick and concrete from hardened clay – something not all competitive attachments can achieve, I’m told. The heavy construction of the S-series screening buckets also makes them suitable for composting and soil reclamation projects and removing foreign matter from recycled road planer chippings. Interchangeable blades can be spaced to give a product varying in grain size from 0–70 mm, but such heavy duty construction does come at a weight penalty, with the smallest units weighing 1030 kg and the largest up to 2700 kg. So selecting the right ‘host machine’ is important. The S-Series models can also be used as mixing buckets on soil reclamation.
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Close up of S-Series straight-sided screening bucket
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The R-Series models are rotary screening buckets, but unlike many competitive ‘open-ended’ units on the market which feature a single bearing surface, the R-Series rotates at right angles to the 360 boom and is located by two bearing surfaces, one on each side. This is claimed to provide a more sturdy location, but does require the screen to have a clamshell opening to both load and release material at each cycle. Like the S-Series, it is also available in a specific size to suit each weight class of 360 excavator. The smallest model, the 600R, has a drum capacity of 0.65 m3, the largest, the 1200R, a capacity of 1.45 m3.
Finally, the V-Series Riddle Bucket range is available in the highest three machine weight classes. Using a hydraulic pressure of 140 bar (with a flow-rate of from 70–100 litres per minute), the V-Series design utilizes two framed bar gratings working off an eccentric cam to create the vibrating motion within the bucket itself. This action separates the fines from the product and the conventional bucket shape enables the V-Series models to be used effectively to process and load topsoil, or backfill the product directly into trench reinstatement projects.
Conclusion
So which approach is best? Purpose-built crushers and screens, or crushing and screening buckets fitted to 360 excavators? Attachments are much cheaper to purchase of course, but then, for larger tonnages, a crusher or screen can run constantly, while the excavator or loader is picking up the next bucketful and a second machine is deployed on stockpiling and distributing materials around the site or loading site dumpers. It depends on tonnages.
The name of the game here is to turn what is currently a material that costs money to dispose of (even if it’s only diesel and driver’s wages) and turns it into a resource that can either reduce the dependency on trucking in new materials, or turn it into recycled hardcore, fill for trench reinstatement, ‘fines’ for recycled sand and regraded topsoil that has a market value.
If the economics already make sense with purpose built equipment – which they do – then cheaper, easier-to-deploy attachments must be even more profitable – or make the recycling of smaller quantities of material viable for the first time. But there’s another angle – Worsley Plant has made a business out of sourcing the most suitable equipment from around the world and marketing it in the UK as part of a range of complementary kit. The Dig-a-Crusher crusher buckets come from Meccanica Breganzese srl of Italy, the R and V-Series Dig-a-Screen screening buckets from Rotar International BV based in The Netherlands and the S-Series range comes from Oy ST-Tekniikka of Finland.
What does that prove? It proves there is good business to be had by further developing the on-site recycling philosophy globally. And it also suggests there is scope for a ‘one stop shop’ approach to marketing a range of waste recycling equipment in global markets, without the attachments needing to come from the same manufacturer – the supply of construction plant is after all, an international business.
So what is the common denominator? The answer is easy – it’s that a dedicated service back-up has to be offered. With that in place, the hire/rental sector would be in a position to make recycling attachments readily available to fit existing 360 excavators, thus increasing their utilization, the rental companies’ profits – and speeding up the whole materials recycling business considerably, for a modest capital outlay.
In fact, it could be a ‘win-win’ situation all round.
Malcolm Bates is Transport Correspondent of Waste Management World
e-mail: wmw@pennwell.com
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