Waste glass in concrete
This is a part of the Building envelope feature
A scarcity of locally produced construction aggregate and growing stockpiles of waste glass are being addressed in a unique building project currently under construction in South Auckland.
Project Century, Lion Nathan’s new brewhouse in East Tamaki, is using recycled waste glass as aggregate in the building’s concrete structures. The new concrete, sometimes called ‘glasscrete’, is being used to replace natural fine aggregate in many elements of the brewery project.
Award-winning partnership
The building contract and supply of concrete for Project Century is a partnership between Mainzeal Property & Construction Ltd and Holcim Concrete. Responsibility for ensuring the concrete will meet all applicable standards is being accepted by the Holcim Construction Materials Testing Laboratory in Auckland. This IANZ-accredited lab is an independent testing facility used by a large number of industry participants.
The project won Mainzeal and Holcim the inaugural 2008 Concrete3 Sustainability Award. The award, part of the Concrete3 initiative from the Cement and Concrete Association of New Zealand, acknowledges companies whose product, programme or initiative demonstrates excellence in environmental, economic and social sustainability.
Gaining strength
Replacing some of the aggregate used to make concrete with product from recycled glass was initially proposed over 30 years ago. However, studies had shown that putting recycled glass into the concrete mix had unexpected effects on the strength of the concrete.
Only in relatively recent times did attention turn to solving these issues, driven by the increasing availability of recycled glass, issues around supply of aggregate and a desire for achieving environmental sustainability by both the supplier and the customer.
Sourcing the glass
With thousands of tonnes of waste glass collected annually for recycling in Auckland there was no shortage of raw material, but deciding on what kind of glass and how much should be added to the concrete posed a number of major technical challenges. Glass is often thought to be inert, but its high silica content can react with the alkalis in cement to affect its strength, so a low-alkali cement is called for. After a lengthy testing regime, the right proportions and form of the glass were specified and production samples of the concrete were sent to Australia for standards testing.
Attention then turned to sourcing the waste glass in bulk, according to the strict specifications of the lab. Once again, this was breaking new ground, but Holcim Concrete formed a partnership with the recyclers, Visy NZ, to work on producing the glass in the sand-like form that was required.
Pouring underway
In August, five concrete pours had been made, with a further seven left to complete the 50,000 m2 floor. Large pours took 9 hours to complete, using up to 12 trucks on a continuous cycle.
Fittingly, the glass used in building the brewery, due for completion in 2010, includes recycled beer bottles.
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