Can alternative raw material usage be better implemented?

CEMBUREAU's recent webinar on '2050 ambitions and the role of secondary materials in the European cement sector' indicated how challenging it will be to meet the CEMBUREAU 2050 Carbon Neutrality Map decarbonising targets through an increased uptake of alternative raw materials (ARMs). While Europe has clear sustainable and net zero ambitions, enshrined in its Green Deal legislation, obtaining these goals has several barriers regarding the availability of materials, political challenges or societal approvals to win before they become the norm.

To get a better picture of how the cement sector could improve one of the routes to net zero through the increased usage of ARMs, ECRA was assigned the task of carrying out a study entitled the ‘status and prospects of ARMs in the European cement sector’. Dr Volker Hoenig, managing director of VDZ, shared the study’s results to a wider audience in the CEMBUREAU webinar.

ECRA’s study focussed on different types of ARMs resulting from industrial processes as by-products and not naturally occurring ARMs, such as pozzolans or calcined clays, which can be defined as supplementary cementitious materials (SCMs). ARMs can be used as alternatives to traditional raw material ingredients in cement manufacture, as clinker substitution material or as concrete additives. While the study covered seven European countries (Austria, France, Germany, Italy, Poland, Spain, UK) as well as Europe as a whole, it was clear that Austria is by far the leader in this field and the benchmark for ARM use in cement production.

Austria is the benchmark in ARM usage
Austria has a well-developed recycled waste market that supplied 790,000t of ARMs for clinker production in 2019, corresponding to 15 per cent of total raw material requirements. By comparison, across the whole EU-28 countries, the use of ARMs in cement production accounted for just 3.8 per cent in 2019.

The main types of waste that Austria processes as ARMs are waste ceramics and tiles, spent bricks, fly ash, used foundry sands, bottom ash (slag and boiler dust), lime waste, waste from slag, mill scale, secondary sand, other materials. The top 10 most-used recycled materials account for 82 per cent of Austria’s ARMs. Ceramic bricks and waste construction products account for 50 per cent of the ARMs used.

The mean annual CO₂ avoidance with clinker substitution in Austria reached 35,000t in 2019 with waste ceramics and granulated blastfurnace slag (GBS) being used most. This was up from 15,000t of mean CO₂ avoidance in 2013.

The use of ARMs in Austrian cement manufacture has risen from 0.95Mt in 2013 to 1.1Mt in 2019. However, the substitution ratio has fallen from 21.7 per cent in 2013 to 21.2 per cent in 2019. In 2019, 75 per cent of the ARMs used for cement production was GBS and 11 per cent was fly ash. However, these resources are in decline in the mid- to long term.

Moreover, when ECRA looked at ARMs in concrete production in Austria the trend has been falling since 2013, when it reached a peak of 2.8 per cent substitution ratio. By 2020 ARM content in concrete had declined to 2.1 per cent. Most of the ARM used in concrete comes from fly ash, the availability of which has declined in line with the closure of coal-fired power generation. Therefore, recycled aggregates may increase their role as ARMs for concretes.

EU need to raise recycling of ARMs 
So why aren’t more EU countries able to make better use of ARMs in cement production? ECRA’s study points to some societal barriers, arguing that more work is needed to convince public opinion of the benefits of recycling ARMs. There is also a need for increased capex in cement plants for the handling and storing of ARMs and licensing costs. Austria has invested in advanced emission abatement techniques for high organic compounds with regenerative thermal oxidation (RTO) technology to process a variety of ARMs.

CO₂ avoidance through the use of ARMs in Austria amounts to 10kg CO₂/t of clinker, while Poland achieves 7kg CO₂/t of clinker. CO2 abatement for the rest of the European countries studied average only 3kg CO₂/t of clinker. Even if the EU cement industry achieved Austria’s level, an increase by a factor of more than four is required until 2050 to reach CEMBUREAU’s targets for recycling and the circular economy. CEMBUREAU's goal is to reach 20kg CO₂/t clinker by 2030 and 45kg CO₂/t of clinker by 2050. CEMBUREAU envisages this would lead to a 3.5 per cent fall in CO₂ (2.6Mt of CO₂) in cement production using ARMs by 2030, rising to an eight per cent reduction (5.9Mt of CO₂) by 2050.

Conclusion
The use of ARMs as raw material ingredients for clinker production, in cement production or as a concrete additive is proven. However, their potential has not yet been fully realised in the EU despite 36 types of ARMs being available. Just 7.78Mt of ARMs were recycled in the EU28 cement sector in 2019. Austria has made better use of ARMs than other European countries. Countries are also at different stages of development for the use of ARMs. ARMs can play a part in reaching the decarbonisation targets, but there is a big gap in reaching the required recycling targets. Natural pozzolan cements, limestone Portland cements and calcined clay cements will likely fill most of this void.

“Further research is required into the potential sources of ARMs and more data is required, especially for their use in concrete,” said Dr Hoenig. Many of the waste collection, sorting and fractioning systems from industrial facilities are not yet in place. Access to landfill with fly ash reserves also need to be established as these are valuable resources that could be used in future low-carbon cement production. New ARMs data on the use of ashes from sewage sludge, bottom ashes, slags from steel and artificial aggregates and demolition waste is still required.