About 40 per cent of overall waste in Australia comes from construction and demolition, underscoring both the substantial impact circular economy principles can have on carbon footprints, as well as the value opportunity it presents for the industry.
By replacing new materials with recycled or re-adapted ones, the construction sector can take advantage of circularity and reduce waste and new resource production, boosting the sustainability of its projects.
Comprising about 9 per cent of GDP, Australia’s construction industry represents more than 18 percent of all carbon dioxide emissions. Steel and concrete foundations make up a quarter of Australia’s total emissions.
It is estimated that with circular economy approaches integrated into its operations, the Australian construction industry could reduce 165 million tonnes of carbon emissions each year by 2040.
Adopting a proactive approach to waste reduction requires a comprehensive strategy that begins during a construction project’s planning and continues through to the final stages, encompassing deconstruction methods, material optimisation, and improved on-site practices.
Reversible and sustainable design approaches from the outset of construction ensure a building canbe deconstructed at the end of its life, with its various materials reused and recycled in a circular economy that mitigates or eliminates waste material.
For example, recovered construction and demolition waste, such as concrete, brick, and glass, are suitable alternatives to natural aggregates and sand in road bases, and can divert up to 8,000 tonnes of waste from landfill per kilometre of road.
Effective waste management is a critical aspect of sustainable design and to support a circular economy, conserve resources and reduce environmental impacts.
Queensland is currently developing a new waste strategy targeting a significant reduction in waste sent to landfills and a major boost to recycling through identifying waste reuse and manufacturing opportunities.
The strategy was welcomed by industry groups inthe sunshine state, including the Waste Management and Resource Recovery Association of Australia, the Waste and Recycling Industry of Queensland, and Cement Concrete & Aggregates Australia (CCAA).
The CCAA voiced some concerns, however, warning the government that unless current regulatory barriers were addressed, particularly those around the end-of waste(EOW) code framework, the strategy risked falling short of its ambitious goals.
The CCAA said: “The Queensland heavyc onstruction materials industry is ready to lead Queensland’s transition to a circular economy, but we are being held back by outdated and cumbersome waste regulations.”
While the draft strategy aims to boost recycling and reduce landfills, CCAA warned that the current EOW code framework was overly complex, with costly and confusing compliance requirements. Further, inconsistent permit rules made it unclear how and when certain waste materials became resources, creating unnecessary duplication in regulatory approvals.
CCAA also pointed out that the regulatory burden for reusing materials was often greater than for simply disposing of them, contradicting the strategy’s hierarchy of reduce-reuse-recycle.
As the most widely used construction material, 25billion tonnes of conventional concrete are produced each year, consuming about 30 per cent of non-renewable natural resources, emitting about 8 per cent of greenhouse gases, and comprising up to 50 per cent of landfill.
Concrete typically has a cement content ranging from15 to 20 per cent, and 90 per cent of global concrete emissions come from clinker production to make cement.
Clinker is the key constituent of concrete and is produced at very high temperatures from materials such as limestone. This process induces the calcination of the limestone, a chemical process that accounts for 55 per cent of carbon dioxide emissions in the sector.
Reducing clinker will need a fundamental shift across the entire supply chain, as well as a flexible approach towards achieving required outcomes through the different pathways.
Supplementary cementitious materials, cement substitutes such as blast furnace slag from steel production and fly ash from coal-fired electricity production, are increasingly used to produce lower-carbon concretes withen hanced product performance.
In a study published by Engineering Proceedings, researchers pointed out that fly ash was abundantly available and could be used to make upcoming-generationgreen concrete for contemporary buildings.
They said: “In the presence of water, fly ash becomes a pozzolanic material with high alumina and silica content that has a cementitious attribute.“As a result, geopolymer concrete based on fly ash appears to be a superior alternative to normal concrete that should be pursued.”
Fly ash makes a durable geopolymer, a relatively new and long-lasting design of composite material with a number of advantages, including high early strength and an increase in durability qualities (such as reduction in permeability) in harsh conditions.
A recent project led by Flinders University in Adelaide and researchers from the US and Turkey has demonstrated how geopolymers reinforced with renewable natural fibres and made with industry by-products and waste based sands can match the strength, durability and drying shrinkage qualities of those containing natural sand.
A geopolymer is a hard and durable man-made substance, and its production generates up to 90 per centless carbon dioxide emissions than conventional concrete.The properties of geopolymer concrete have been tested in the laboratory and real-world conditions through chemical analysis, compressive strength and workability, and have met Australian Standards and specifications.
The results showed that geopolymers using waste glass sand exhibited superior strength and lower water absorption than those containing natural river sand, while lead smelter slag-based geopolymers had lower drying shrinkage compared to geopolymers prepared with river sand.
