Yas Mall in Abu Dhabi is one of the largest projects aiming for a Pearl Two Rating under Estidama, which requires it to divert at least 70% of the waste it produces from the landfill. Meeting this requirement has required innovation from the design and operation team, including crushing and screening more than 39,000 tonnes of concrete on site.
The Yas Mall construction site on Yas Island in Abu Dhabi is the first commercial project of its size to strive for a Two Pearl rating within the Estidama system.
Compared to the LEED system, a Pearl Two is slightly below a LEED Gold, although it is not an exact comparison, and it depends which categories are prioritised.
Within the construction and demolition waste management component of Estidama, a Two Pearl rating calls for 70% of waste produced on on-site to be diverted from the landfill and used elsewhere.
For the developer, Aldar, and the designing consultant, AECOM, this has meant a construction site focused on the waste management hierarchy of ‘reduce, reuse, recycle and compost’.
Alternative uses have had to be found for thousands of tonnes of concrete, hundreds of tonnes of wood, as well as tens of tonnes of plastic and cardboard produced during construction.
Douglas MacAskill, senior project manager – Yas Retail, Aldar, says that a decision was made within the company to support the government’s initiative of Estidama, developed through the Abu Dhabi Urban Planning Council (UPC).
“Although there are costs involved with trying to achieve Two Pearls, there are other benefits, intangible and non-financial, which we all know are a result. The mandate on a project this size is Two Pearls. There was a lot of discussion internally as it is a demanding target, but we decided that we will go with the wishes of the UPC and achieve Two Pearls.”
Across the GCC, waste from the construction industry is thought to be account for 55% of all waste produced, according to a report last year by Vishnu Sankaran, industry manager of chemicals and materials at Frost and Sullivan, the business research and consulting firm. And this is despite construction activity accounting for only 5.6% of GDP in the region.
Tarik Tadmori, a sustainability consultant at AECOM, and one of the designers of the Yas Mall C&D waste management plan, says that while steel has always been recycled on construction sites due to its value, materials such as concrete, plastic and wood would generally just get sent to a land fill.
“It’s quite depressing if you ever go out to the landfill and you see what is just a vast wasteland. [For Yas Mall] we looked during the design phase at what would come on site, and what could be recycled. We formed a construction waste design plan as a part of the submittal. The contractor [Six Construct] took that on board, and is obviously implementing it.”
When PMV visited the site, the volume of waste diverted from the landfill stood at 96.93%; or in volume terms, of the 44,860.2 tonnes of waste produced, 43,482.2 had been diverted from being dumped. “Right now we’re at 97% diverted waste from landfill, and that is a high number in any country, but here in the UAE it’s actually quite amazing,” says Tadmori.
Waste to be diverted includes steel, concrete, wood, cardboard and plastic, as well as materials such as plasterboard and glass that will likely be produced in the later phases of construction. Food and general waste is not being diverted, while hazardous waste is not counted towards the total.
In order to cope with the requirements, a segregation area was built to house the waste, and a weigh-bridge was built to measure trucks when they are taking waste off site, in order to document the amounts.
At the end of the project the documentation must be produced to account for the waste. The process and systems are also occasionally audited by the UPC and Estidama officials, and Tadmori says that so far they have been happy with the systems that are in place on site.
By far the greatest volume of construction waste material has been concrete, with 39,936.4 tonnes of concrete waste produced on site, accounting for approximately 89% of the total waste material produced on site.
This came from a variety of sources, but after the project was scaled back due to the Global Financial Crisis there were a number of elements on the site – existing piles and pile caps – that needed to be demolished under the revised plan.
This has meant that the volume of concrete waste produced is larger than what would normally be expected from a project of similar size.
While the waste management plan has been running since March 2011, the concrete waste was all produced in a relatively short time space of four months this year.
On a smaller site, that volume of waste – nearly 20,000 tonnes was produced in June alone – could have proved to be a logistical nightmare. However the large footprint of the Yas Mall site allowed the rubble to be stored before it was crushed with a mobile crusher, to be reused in the construction.
Uses have to be found for the other waste products, such as wood, plastic and cardboard, that have no conceivable use within a construction project.
“When we’re designing, we study where we can use the waste that we’re producing – we ask ‘Where is it going to go?’ It’s part of what UPC and Estidama asked for, they don’t want you just to recycle 70% of the wood, they want to ask you where that wood will go,” explains Tadmori.
The intent, he says, is that the waste products from one industry – for example construction – are used in another industry such as manufacturing.
Wood can be chipped and dyed, and used as a locally produced product for landscaping; cardboard can be turned into paper at the local paper factory; and there a number of options for plastic, including breaking it down into small pellets and compressing it into plastic lawn furniture.
“Once the process becomes more cohesive, when we can start taking waste from other industries, and waste from our industry goes to other industries, it becomes a full circle.
And I think that’s the ultimate goal that the UPC is thinking of, but we’re not there yet, to be quite honest. I hope that in another 10-15 years we are. That would be a fantastic accomplishment.”
For the concrete, the project was lucky that it was able to process the waste on site, and also that there was a demand for that volume of recycled aggregates to be used on the project. Six Co initially used the services of a local waste management company, but their crusher proved to be too small.
Instead a larger Keestrack Destroyer 1312C impact crusher was used, rented from ILE Rental. Capable of crushing up to 450 tonnes per hour, and used in conjunction with a screening unit, the crusher was able to process the piles of material, producing two grades of aggregate, a 0-63mm grade for recycled road base, and 0-100mm for recycled backfill.
And while renting the crusher and screen of course had a cost, this was mitigated by the fact that a huge stockpile had been built up – “a huge area of the site covered by mountains of thousands tonnes of concrete” – and was able to be quickly processed. The recycled aggregate was to be used on site, mainly for back fill for the roads that will service the mall.
Once again the large site foot print proved to be a blessing, as the crushed aggregate was able to be stored until it was needed in construction.
Future projects may see an expanded role for recycled aggregates. But Tadmori says that there are limitations to what it can be used for.
“Structurally-speaking, with recycled aggregate you can pretty much do what you want as long as it’s going horizontal. Any time you want to go vertical that’s mission impossible, it’s just not structurally sound.”
Another factor is that if aggregate is crushed on-site to be used for anything other than pipe bedding, backfill or temporary road base, the crushing process would have to be monitored by the consultant, which would be an extra cost for the contractor, not a factor if RCA is sourced from a commercial supplier.
“Until the technical expertise for that is up to par, and more common, it won’t be cost effective to do it. But obviously if the client insists on it, we will do it,” says Tadmori.
Indeed, the requirement may not be voluntary. With all major projects in Abu Dhabi required to be at least One Pearl, which requires that at least 30% of the waste be diverted, in theory a project could be required to find innovative uses for the recycled aggregates on site. Any ‘cutting edge’ use of RCA would have to be shown to the municipality to be structurally safe.
“Structurally we’d have to prove that it was sound enough for the municipality to approve it. That hasn’t been the case yet. Any time that we’ve presented our designs to the municipality we haven’t had an issue with it,” says Tadmori.
However the RCA could also be trucked to another work site, and with the current pace of infrastructure development in the UAE, there is plenty demand for backfill.
“Fortunately the UAE is still developing aggressively, we’ve got lots of roads, lots of transportation projects – Etihad Rail for example,” says Tadmori.
“If projects and consultants start working together, flagging up that projects will produce a certain waste, such as RCA, and projects can procure that waste, it becomes a benefit for everyone. They can procure it at a reduced price, and the company can sell it and recap some of their operational costs.
“Right now it’s easier as there are a lot of projects that could be using this backfill. In maybe 10 or 20 years, when there is a lot more infrastructure in place, it will be a little more difficult to pull this off, and that will be the challenge we will have to face then. But right now, we’re comfortable.”
While the final percentage of diverted waste may drop from its current high figure, Tadmori says they’re on target to achieve the target.
“We’ve got a year left to go, that number could go down a little bit, [but] we’ve got quite a comfortable buffer, but obviously if we can keep it at 90 or 95% we will all be happy, it will be quite an accomplishment for the entire team.
This is one of the newer aspects, and it’s always a challenge. It’s a team-driven aspect, all of us are just cogs in the waste management system. I have to say that everyone has been doing an excellent job.”