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When cost and environmentally conscious construction and demolition companies combine, everyone benefits. By MARK CATHIE and HEATHER ROBERTSON
“As the construction industry looks toward the future, one of the issues that it cannot ignore is the move toward recycling and sustainability” says Peter Ward of Ward Demolition. “At Ward Group our philosophy is to achieve zero percent waste.” This commitment to recycling is not just a philosophy for Ward Group. While recycling the components of a building provides a commercial interest, it is the land and the concrete content where this commitment produces evidence of taxpayer savings and environmental benefits. “We give back the land to be used again, by developers to develop, builders to rebuild and people to reuse,” says Peter. “In the States, recycling land is recognised for its importance. In Auckland where land is in short supply, it should take priority.” From a cost viewpoint, the durability of recycled concrete is evidenced in the traffic loading limits in repeated load triaxial testing of Ward recycled crushed concrete aggregate dry/drained and saturated/undrained against other base course aggregates, as published in a report by Dr Greg Arnold of Pavespec in January 2010. The findings in the Pavespec report show Ward’s RCC AP40 aggregate at the density tested is above average performance for the dry/drained test and well above average performance for the saturated/undrained test for a basecourse aggregate (see charts), further evidencing “the cement that remains in the crushed concrete aggregate is known to provide an additional beneficial binding property not present in natural aggregates”. This durability provides true dollar savings, but the real value comes from the environmental impact. The Nordic Innovation Centre published a report, “C02 Uptake During the Concrete Life Cycle”, showing that, “C02 present in air reacts with the calcium in the cement forming calcium carbonate (CaC03). This reaction takes place within the concrete and is called concrete carbonation. Concrete carbonation is a natural process and helps reducing the atmospheric C02.” Alan Kirby of the Cement and Concrete Association says that not only does the use of recycled crushed concrete attract credits under the New Zealand Green Building Council’s Green Star Building rating scheme, but crashing concrete for use as either road metal or reuse as aggregate in concrete exposes more surface area to the atmosphere for greater C02 uptake. The Nordic Innovation Centre report takes this further, stating that “the carbonation of concrete increases significantly after demolition because of the reduction in particle sizes due to crushing… In fact, crushing demolished concrete results in a total C02 uptake that is two to 2.5 times higher than the C02 uptake that is not recycled”. The construction and demolition industry is one of New Zealand’s largest waste producers, contributing around 17 percent of waste that is sent to landfill. Concrete represents approximately 30 percent of this amount. This recycling development now presents considerable cost saving opportunities for Auckland councils who are struggling to minimise cost impacts on ratepayers for roading and refuse disposal, with the added bonus of being able to build more durable, eco-friendly streets and motorways. If New Zealand is committed to recycling it should look at established practice overseas, which has demonstrated the cost and environmental benefits of recycling of not only the more commercially redeemable components – but also the concrete. Although there is momentum and an appetite in New Zealand, as a consequence of various government and industry initiatives and societal expectations, the benefits are slow to be realised here, for reasons unapparent.
Contractor Vol.34 No.5 June 2010 |
The combined vision, resources and experience of Brookfield Multiplex and Ward Demolition turned the demolition of the BNZ Tower/Jean Batten Post Office in Auckland into re-usable land and material that provide cost savings to the taxpayer, as well as carbon credits and C02 absorption for the environmentalist.