Reviewing 211 studies and seven regulatory documents, Adelaide University researchers found that fuel made from non-recyclable waste holds real promise for cement plants, and that inconsistent definitions and quality standards are holding it back.

Cement is one of the hardest industries to decarbonise. It accounts for an estimated 8 per cent of global carbon dioxide emissions, and the reason is partly chemical and partly thermal. Making cement requires heating limestone to around 1,450 °C, and reaching those temperatures has traditionally meant burning coal.

Meanwhile, a great deal of combustible material that cannot practically be recycled goes into landfill. A review published in the International Journal of Building Pathology and Adaptation by researchers at Adelaide University examines the obvious idea that connects those two problems, and finds that the obstacles are less about engineering than about paperwork.

Fuel from the bin

The material in question is refuse-derived fuel, or RDF. It is made by sorting and processing waste, removing what can be recycled and what will not burn usefully, then shredding and drying the remainder into a fuel that can be fed into an industrial furnace.

Cement kilns are unusually well suited to burning it. They run extremely hot, which destroys organic pollutants, and they hold material at high temperature for a long time. The mineral ash left behind is incorporated into the cement rather than becoming a waste stream of its own. Burning RDF alongside conventional fuels in a kiln is known as co-processing, and it is already practised in parts of Europe and Asia.

Emissions are the obvious concern with burning mixed waste, and it is why the composition of the fuel matters so much. Chlorine-bearing plastics, in particular, are associated with the formation of dioxins in poorly controlled combustion, and heavy metals present in waste streams have to go somewhere. The high temperatures and long residence times of a cement kiln address much of this, which is the technical basis for co-processing, but only if what goes in is known.

“Previous research has highlighted the potential of refuse-derived fuel to turn suitable waste materials into a useful resource rather than sending them to landfill,” said Geethmi Thisakya, a PhD candidate in Adelaide University’s School of Civil Engineering and Construction.

What the review covered

Thisakya and colleagues surveyed 211 scholarly articles published between 1991 and July 2025, examined 48 of them in detail and also reviewed seven regulatory documents. The aim was to map what the research has established, where the gaps are and what the rules actually say.

Global interest in the approach is growing, the review found, driven by the twin pressures of reducing landfill volumes and cutting fossil fuel use in a sector with few easy options for either.

But the literature itself proved to be part of the problem.

Two names, no agreement

The review identified widespread confusion between RDF and a related material called solid recovered fuel, or SRF. SRF is a more standardised product, produced to specifications that set limits on properties such as energy content, moisture and chlorine. RDF is a looser category, and in practice the two terms are often used interchangeably.

That might seem like a semantic quibble. It is not. If two studies describe their fuel as RDF but one used a well-characterised, consistently processed material and the other used coarsely shredded mixed waste, their results on emissions, kiln performance and clinker quality are not comparable. Inconsistent terminology makes it difficult to pool findings, and difficult to interpret regulations written with one definition in mind and applied to another.

“However, our review shows that realising this potential requires more than simply replacing coal with waste,” Thisakya said. “We need consistent fuel quality, clear regulations and stronger evidence about the environmental and economic impacts.”

What plant operators need

The practical consequence falls on the cement producers. A kiln is a continuous, capital-intensive piece of equipment, and variability in fuel is a genuine operational risk. Fluctuating energy content makes temperatures harder to control. Chlorine can corrode equipment and interfere with the chemistry of the clinker. A batch of unexpected composition can affect both the plant and the product.

“Cement manufacturers need confidence that alternative fuels will perform consistently, meet environmental requirements and support safe, reliable production,” Thisakya said.

“Developing stronger quality assurance systems and clearer regulatory frameworks will help industry make informed decisions about using waste-derived fuels.”

The review sets out priorities for research accordingly: better classification of fuels, stronger quality control, systematic comparison of regulations across countries, and more detailed assessment of environmental, economic and social impacts. It also notes that more work is needed on how RDF performs under different industrial and geographic conditions, since waste composition varies enormously between countries and even between cities.

Not a substitute for recycling

The researchers are explicit on one point that often gets lost when waste-to-energy schemes are discussed. Recycling and reuse should remain the priority. RDF is for the combustible fraction that cannot practically be recycled, not an alternative to recovering materials that can be.

That ordering matters because the economics can pull the other way. A cement plant with a long-term contract for waste-derived fuel has an interest in a steady supply, which can create pressure to divert material that recycling systems could otherwise have captured. Waste policy in the European Union addresses this through a hierarchy that places prevention, reuse and recycling above energy recovery, with disposal last.

There is also a limit to how much the approach can achieve. Roughly half the carbon dioxide from cement production does not come from fuel at all. It comes from the limestone itself, which releases carbon dioxide when it is heated and converted into lime, a reaction that happens regardless of what is burning in the kiln. Substituting fuels addresses the combustion half of the problem; the process emissions require different solutions, such as carbon capture or alternative cement chemistries.

Within that limit, though, co-processing is one of the few options available to cement producers now, using equipment they already have. The review’s argument is that the technology is not what is holding it back.

Thisakya’s supervisory team comprised Dr Navodana Rodrigo, Dr Chamitha Wijewickrama and Professor George Zillante.

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Notes

1. Thisakya, G., Rodrigo, N., Wijewickrama, C., Zillante, G. “Refuse-derived fuel in cement manufacturing: a systemic review of research trends, gaps and future research directions.” International Journal of Building Pathology and Adaptation, 2026. DOI: 10.1108/IJBPA-08-2025-0200.
2. Adelaide University. “Turning waste into fuel could help cut cement’s carbon footprint.” EurekAlert!, 20 October 2026. https://www.eurekalert.org/news-releases/1148445.

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