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Contractor (December 2011) Concrete and Recycled Materials: Growing Acceptance

01 Dec 2011

Rob Gaimster
Cement & Concrete Association (CCANZ)

The use of recycled materials has become accepted throughout the ready mixed concrete industry in response to an increasing environmental focus and the growing cost of disposing of waste material.

To assist with the continuation of this trend CCANZ will soon release Technical Report 14: Best Practice Guide for the Use of Recycled Aggregates and Materials in New Concrete – a resource for optimising the performance and engineering properties of recycled aggregate in concrete.

BACKGROUND

Concrete is the most widely used construction material on earth, with an estimated 25 billion tonnes manufactured each year. As such, issues have arisen around the management of waste concrete.

In New Zealand 27% of the total waste generated is construction and demolition waste, and of this, concrete represents 25%, i.e. 7% of the total waste generated.

The development of recycling schemes, and in turn the use of recycled aggregate in concrete, has been given impetus by the increasing scarcity of landfill sites and the recent introduction of a $10 per tonne landfill levy.

RECYCLED CONCRETE OPTIONS

The reuse of hardened concrete as aggregate is a proven technology. It can be crushed and reused as a partial replacement for natural aggregate in new concrete.

Hardened concrete aggregate can be sourced either from the demolition of concrete structures at the end of their life (recycled concrete aggregate), or from leftover fresh concrete which is purposefully left to harden (leftover concrete aggregate).

Alternatively, the aggregate from fresh concrete, which is leftover or surplus to requirements,  can be recovered for reuse in concrete manufacture (recovered concrete aggregate).

In addition, waste materials such as crushed glass can be used as secondary aggregates in concrete.

All these processes avoid dumping to landfill whilst conserving natural aggregate resources.

BENEFITS OF RECYCLING CONCRETE

Recycling or recovering concrete materials has two main advantages - it conserves the use of natural aggregate and the associated environmental costs of exploitation and transportation, and it preserves the use of landfill for materials which cannot be recycled.

While crushed concrete can be used as a sub-base material for pavements and civil engineering projects, it can also be used as a higher grade resource, such as aggregate in new concrete.

The Nest, Wellington Zoo’s recently opened animal hospital, is one example where recycled concrete aggregate has been used in structural concrete.

Schemes such as Green Star New Zealand recognise construction and demolition waste reuse and provide credits accordingly.

GLOBAL AWARENESS

Extensive investigations have been carried out in the UK, North America and across Europe on the use of recycled aggregate in concrete.

Globally the concrete construction industry has taken a responsible attitude to ensuring its natural resources are not overexploited. In some cases the preservation of dwindling natural aggregate sources is a significant issue driving the use of recycled aggregates.

Reducing the financial and environmental impact of aggregate cartage is also a factor. Using portable aggregate plant, material can be processed onsite during demolition and then reused on the same site during construction. This is a better option than transporting natural aggregates from distant quarries.

Landfill levies, waste dumping taxes and imported aggregate taxes have also made recycled concrete a viable option overseas. This has predominantly taken the form of ‘low-grade’ road-base material, however the UK, Belgium, Switzerland, Germany and the Netherlands regularly use recycled aggregate in new concrete.

DEVELOPING A MARKET

The key to recycling is to achieve a balance between economic pressures and ecologically sound practices.

Several market constraints and technical challenges exist when developing markets for secondary products. These include consumer uncertainty about the quality and consistency of products. In addition, there can be a lack of practical performance and engineering data on recycled materials.

Developing and adopting performance requirements specifically for secondary and recycled products will promote their specification, and also ensure that externally verified quality certification and compliance systems are adopted.

CCANZ TECHNCIAL REPORT

To this end, CCANZ in partnership with BRANZ and supported by the Aggregate & Quarry Association of New Zealand (AQA) has written Technical Report 14.

TR 14 outlines the processes involved in the use of recycled materials as aggregate in concrete and the effects of these materials on the fresh and hardened properties of concrete made from them.

It is intended to act as a resource to optimise the practical performance and engineering properties of recycled and secondary waste materials as aggregate in concrete supplied in accordance with NZS 3104:2003 Specification for Concrete Production, as well as act as the basis for future revisions of NZS 3104 and NZS 3121 Specification for Water and Aggregate for Concrete to potentially incorporate recycled materials.

TR 14 is also designed to raise awareness of the need for concrete recycling in New Zealand, and presents technical guidelines to specifiers, contractors, aggregate suppliers, and concrete manufacturers on the use of recycled aggregate in concrete, and on the recovery of concrete aggregate and fines from left over fresh concrete.

By providing a general overview of recycled concrete in construction, TR 14 will also be of interest to regulatory bodies offering information on the suitability of recycled material for use in construction projects.
 
To request a copy of Technical Report 14: Best Practice Guide for the Use of Recycled Aggregates and Materials in New Concrete contact CCANZ – admin@ccanz.org.nz. Feedback is welcome in response to this ‘working’ report.

Article appeared in Contractor magazine.