Recycling concrete

The use of recycled concrete aggregates here is in the early stages, but the practice of producing aggregates from demolished and reprocessed concrete is expected to grow.

Recycled_concrete.jpgThe construction and demolition industry is one of the country’s largest waste producers, contributing around 17 percent of waste that is sent to landfill. Concrete represents approximately 30 percent of this amount, with the majority of it ending up as cleanfill.

Processing waste concrete to produce recycled concrete aggregate (RCA) or recycled crushed concrete (RCC) has the potential to greatly reduce the quantity sent to landfill each year, and complements the government’s sustainable development and waste minimisation policies.

There can also be economical advantages: The commercial value of RCC or RCA as construction materials; the recovery of reinforcing steel as scrap metal; savings in dumping charges; and a reduction in transportation distances (e.g. hauling the waste material to landfill and hauling virgin aggregate from the quarry or gravel pit to the construction site).

The practice of recycling demolition waste to produce aggregate or road metal is well established overseas, dating back to the rebuilding of Europe after World War II. In the Netherlands, crushing waste concrete to recycle it has been common practice for many years due to a shortage of natural aggregates and a lack of available landfill space.

Europe is currently leading the way in the reprocessing of waste concrete.  European directives in conjunction with other political and economic initiatives are driving the uptake on a pan-European basis.

The recycling rate of construction and demolition waste in Denmark, for example, increased from under 25 percent in 1987, when a landfill tax was introduced, to 90 percent in the following 14 year period, during which it was increased ten-fold.  

In 2002, the UK introduced a levy on natural aggregate of £1.60 per tonne, which was increased this year to £1.95 per tonne ($5).  This tax increased the cost of virgin aggregate from around 15 percent in London and the Home Counties to over 60 percent in some rural areas.  Some 25 percent of the UK’s aggregate demand is now produced from recycled and secondary sources. 

The UK is now ahead of previous leaders the Netherlands in the European recycling league. While the Dutch manage to satisfy about 15 percent of their aggregate needs through recycling, the UK is close to 17 percent.

The practice of recycling waste concrete as aggregate is also well established in the US, but not to the extent that it is in Europe. This may be due to the fact that the USA is not a signatory to the Kyoto Protocol and there is not a national landfill or virgin aggregate tax.

The main drivers for recycling concrete as aggregate or road metal in the US are regional shortages/depletion of virgin material (and related transportation costs) and the potential to claim credits under the LEED certification for buildings by the US Green Building Council. Credits are awarded for diverting demolished concrete from landfill disposal by recycling it into aggregate for road bases or construction fill (Materials and Resources Credit 2) and for using a proportion of recycled concrete aggregate for the project (Materials and Resources Credit 4).

The New Zealand scene

The current scene regarding the recycling of waste concrete in New Zealand is generally concentrated in or around areas of high population where the bulk of construction and demolition waste is generated. The industry tends to be run by demolition and recycling contractors using mobile crushing and screening plants, although one major demolition and recycling contractor has a large purpose built facility in Penrose, Auckland. Quarry and landfill operators are also becoming increasingly active. 

There are a number of government policies and initiatives promoting or encouraging waste minimisation/recycling in New Zealand, including waste minimisation, environmental and sustainability policies, possible product stewardship legislation, Ministry of the Environment and REBRI recycling initiatives, proposed landfill levies, and Green Star New Zealand initiatives.

Other drivers include perceived aggregate shortages due to shutting out quarry operations, with consequential increases in transportation costs. And the importance of public awareness and corporate governance cannot be overlooked. At the time of writing, recycling of waste concrete was also being driven by the high value of scrap metal recovered as reinforcing bars.

Recycled concrete aggregate concrete is being trialled by a number of ready mixed concrete producers.

There is still no specific mention of recycled crushed aggregate in any New Zealand Standard for concrete or aggregates for concrete. However, the NZ Transport Agency and the Aggregate and Quarry Association of New Zealand have produced a specification for basecourse and best practice guidelines for the supply of recycled concrete material for use in pavements, respectively.

NZTA has also published best practice guidelines for the use of alternative material and processes in road construction, and recently let a contract for the supply of 60,000 cubic metres (loose volume) of recycled crushed concrete for AP 65 subbase to be used on the construction of the Christchurch Southern Motorway Extension project. This is New Zealand’s largest recycled crushed concrete contract.

Lessons from overseas

New Zealand’s regulatory environment on the management of construction and demolitions waste is less challenging than Europe’s but more onerous than the US’s.

Despite its modest population density, the demand for aggregates in New Zealand is high per capita and growing, and the recycling of waste concrete will form a small but important element in the strategy to meet future aggregate demand.

New Zealand’s production of aggregate per capita is relatively high at 11 tonnes. In UK and the US for example, the figures are five tonnes and eight tonnes respectively.

In Europe and US, it is evident that where the demand for aggregates is high, there is correlation between scarcity and the level of recycling activity. This is becoming the case in Auckland where virgin aggregate reserves are abundant, but inaccessible because of resource consent issues.

Some of the drivers seen in Europe are not yet prevalent in New Zealand, and yet the market for recycled concrete aggregate, whilst embryonic, is growing.

There is momentum and an appetite for the recycling and indeed up-cycling of waste concrete. This is sensible from a number of perspectives, not least of which is societal expectation surrounding the issue.

  • This article is taken from a presentation by Alan Kirby and Rob Gaimster, project managers with the Cement and Concrete Association, at the recent concrete industry conference. 

 

Contractor Vol.32  No.10  November 2008
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