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Making concrete with glass

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AUSTRALIAN scientists have given the green light to using waste glass in concrete construction. This means local councils, recyclers, municipal engineers, and private contractors can look at using glass concrete for a range of construction applications.

Dr Kwesi Sagoe-Crentsil of CSIRO Sustainable Materials Engineering said his department has carried out extensive field and laboratory testing which had shown waste glass that was crushed and screened was strong, safe and economical when used as a sand substitute in concrete.

"We have been studying the use of waste glass because despite being a product that is a recycling success story, around 16 per cent or some 20,000 tonnes each year of all glass in Victoria (for example) is not reprocessed into containers or used in other primary markets and is currently dumped as unsuitable for recycling.

“Our studies have shown that new uses for waste glass in concrete means there is a chance that nearly all glass now being dumped can be ground and put to good use."

CSIRO has prepared a guide for pre-mix concrete utilising this ground glass (cullet).

Dr Sagoe-Crentsil said data for the guide had been generated from CSIRO's extensive short-term material performance tests involving laboratory and field evaluation of pre-mix concrete incorporating up to 20 per cent crushed glass blended with conventional sand to meet industry grading specifications.

The guide sets out preliminary requirements for material supply, placing and curing of concrete incorporating glass cullet as sand replacement for municipal and building construction works.

Other common uses for glass cullet include:

· Abrasives: Finely ground container and non-container glass for sandblasting.

· Aggregate substitute: Container and non-container glass utilised in concrete, road beds, pavement and parking lots, as well as drainage medium, backfill or landscaping purposes.

· Utility construction: Varying levels of cullet up to 100% proposed for general backfill applications such as underground facilities, trenches and landfill applications.

· Fluxes/additives: Glass powders used as lubricants, core additives and fluxes in metal foundry work and fabrication, as well as flux in the ceramics industry.

· Filtration and drainage applications in foundations and retaining walls and high rate filtration media and hydroponic rooting medium.

· Architectural applications including glass bricks and paving blocks.

· Fibreglass insulation and foam insulating glass products.

The benefits of glass in concrete include:

· Saving on landfill cost for recovered glass cullet in concrete.

· Savings on unit cost of concrete.

· Saving on freight cost.

· Environmental benefits of replacing natural aggregate resources with recycled material.

· Benefits to recyclers in rural communities i.e. establishment of secondary markets.

While glass cullet can now be used as a concrete aggregate, it also means a wider range of aesthetic (decorative) applications for concrete is now possible.

However, Dr Sagoe-Crentsil said more work needed to be done before glass cullet could be recommended for use in structural concrete applications.

The development of the research program and the guide (specification) was prepared by CSIRO for EcoRecycle Victoria, ACI Glass Packaging and Alex Fraser Recycling Industries. A copy of the specification can be found at www.ecorecycle.vic.gov.au.

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