Recycled aggregates use set to grow
The use of recycled concrete aggregate is set to grow in Abu Dhabi
The use of recycled concrete aggregate is set to grow in Abu Dhabi, with specification of RCA for major infrastructure projects
The use of recycled concrete aggregates (RCA) is set to soar in Abu Dhabi, after having been specified in a number of major projects, including in the Etihad Rail project in Abu Dhabi.
Produced by the Al Dafra waste plant, use of RCAs all but came to a halt, and the plant was forced to shut down, with a stockpile of 1.6 million tonnes of material ready to be crushed.
But it roared to life again, when Al Jaber engineering ordered 750,000 tonnes of aggregate for use on the Etihad Rail project. This was followed by further orders, and according to Tim Harwood, executive general manager of Leighton Services, which manages the plant, the total orders of RCA for Etihad Rail total 1.2 million tonnes.
Demand is set to grow, and next year in Abu Dhabi, 40% of the aggregates used in the construction of new roads will be recycled, something that will be written into the specification, though the exact details will vary between projects.
Tim Harwood says that contractors can use RCA in projects in order to meet their Estidama requirements.
“One of the main barriers [for greater use of recycled materials] to overcome is ensuring that recycled materials are actually specified for use in contracts.
“Fortunately, there is a long track record of the use of recycled materials internationally, so you are not starting from scratch when you can adopt specifications that work elsewhere in the world.
In Abu Dhabi, the government has issued decrees approving specifications for recycled products and these have been adopted by various departments and municipalities across the Emirate.”
The specification for road construction follows a trial use of RCA in a road built for the development of the Baniyas Sports Club, where Al Jaber was the contractor and AECOM was the consultant.
Before work began, the RCA was tested to ensure it met the Abu Dhabi Municipality’s specifications, when it was found that the RCA from Al Dafra had a sulfate content of between 0.97 and 1.37%, higher than the 0.5% maximum allowance.
According to Ramin Yazdani, of the material quality section, internal roads and infrastructure division, at ADM, this final specification was adjusted to allow for the higher sulfate levels, in line with practices overseas.
The higher sulfate levels can be explained by the decades-old concrete – produced from concrete rubble taken from demolished buildings – absorbing sulfates through exposure to groundwater or airborne salts, and it may also be the case that the concrete had higher sulfate levels when it was originally poured.
When used on the test patch, the RCA met all required material properties for road base and subbase courses.
And while the use of RCA prevents concrete waste going into the landfill, there can also be cost advantages for operators, largely due to Al Dafra’s location, south-east of the capital, and the relative remoteness of the sources of virgin aggregates, which have to be sourced from quarries in Fujairah or further afield.
With transport costs the biggest cost factor, operators will find that material from the Al Dafra plant is priced better as far as Ghantoot, on the border with the Dubai emirate.
Yet RCA can also be produced on-site, and some in the machinery industry see the use of mobile crushers as a major opportunity for contractors to lower operation costs.
Bob de Weerd, managing director of ILE Rental, believes that the key driver of on-site recycling of building waste is costs.
For a contractor to dump demolition waste at a landfill, and at the same time have virgin aggregate brought to the job site from a quarry in Ras al Khaimah or Fujairah, adds an enormous cost to a project, says de Weerd, through the cost of the truck and the driver, and the diesel, on top of any costs to dump at a landfill, or to buy new aggregates from a quarry.
“A major site, such as an airport or port, can dump as many as 3,000 cubic metres per day of building waste in a landfill. That’s a huge amount of trucks – with 40 cubic metre trailers, that can be a hundred trucks daily, dumping material.”
Crushing on-site and reusing reduces site traffic, and as well as meaning that contractors are not reliant on trucks arriving to deliver aggregate.
De Weerd currently rents out his crushers for a fixed rate per tonne, of 15 dirhams, in part to allow contractors to easily calculate cost savings for crushing and re-using material on site.
He expects that recycling construction and demolition waste on site will become more common in the future, but says that one obstacle is that contractors are currently limited in what they can use recycled aggregates for, namely building of temporary roads for site access, backfill, and pipe bedding. He would like to see consultants opening up more uses for recycles aggregates.
Harwood says that perception is also barrier to uptake.
“Another barrier is the perception that recycled products are somehow inferior to virgin material. However this is not the case and recycled products, once made to specification, can actually outperform virgin materials, or at the very least are just as good.
It always takes time for a new product to gain broad market acceptance however as time goes on the use of recycled products in the UAE will become the norm.”