- Calcium sulfoaluminate cement clinker containing belite and ferrite has been produced with more than 85% of the raw material mix coming from waste materials.
- The raw materials CO2 emissions of the produced clinker is 90% less than that of traditional Portland cement clinker; overall process CO2 emissions are 60% lower.
- Hundreds of kilograms of clinker have been produced in a pilot rotary kiln for further performance and application testing
Research conducted by academics from the University of Sheffield (UK), Department of Materials Science & Engineering, along with researchers from the University of Oulu (Finland) has allowed for the manufacture of low-carbon alternative cements while also valorising waste material from the metallurgical and chemical industries. Total CO2 emissions are 60% lower than that produced by traditional Portland Cement manufacture.
The cement industry is the world’s largest manufacturing industry and the product generally employed around the world is Portland Cement (PC). Owing to the large demand for cement (4Bt p.a.), the production of cement is responsible for ~8% of global man-made CO2 emissions which are changing our climate. Approximately two thirds of the emissions arise from the calcination of limestone (CaCO3 -> CaO + CO2) and one third are from the combustion of fuels required to reach the high temperature required in conventional cement rotary kilns (~1500 °C).
“New” binders can bring significant emissions reductions, especially when produced from raw materials that do not contain embodied carbon. Among several alternative binders, cements containing ye’elimite, commonly known as calcium sulfoaluminate (CSA) cements have been pointed out as an important alternative with a reduced carbon footprint as the production process requires 1) a lower amount of calcium carbonate to be calcined and 2) a lower production temperature. CSA clinker can also be produced in existing cement plant configuration without major modifications or capital investment.
CSA cements are currently in commercial production throughout the world, but most notably in China and North America where they have been commercialised for decades for use in both structural and non-structural applications. However, the use of CSA cements has been limited in Europe due to the lack of inexpensive raw materials containing alumina.
The properties of CSA cements are often superior to those of standard PC, including; high early strength. Despite their higher costs, CSA cements have found application where extended work-time or closure is not possible; for example, restoration of highway and airfield pavement. CSA cements also find use in special applications such as self-levelling cements, expansive cements, and cements for waste encapsulation/stabilization. However, the feeling is that these cements can have a broader range of applications once certain disadvantages are overcome.
The metallurgical industry generates large amounts of inorganic “waste” which contain the necessary ingredients to produce CSA cement clinker; alumina and lime. In the CECIRE project, these metallurgical industry residues combined with by-products from other chemical industries were successfully used for the pilot scale production of a green and circular cement product.
I am very happy to have been involved in this project, we have successfully created symbiotic solutions for several large industry. We now also enough material which we can use to completely assess the material properties and performance while answering any remaining questions regarding the cement’s behaviour and performance.
Dr Theodore Hanein
Research Associate, Department of Materials Science and Engineering
Visa Isteri from the University of Oulu said: “I truly enjoyed steering this research from lab scale to pilot. Our success shows the importance and benefits of connecting a capable network to support research; with this cooperation we have achieved significant results in solving the challenges of the inorganic circular economy”.
The research project (CECIRE; Cement From and For Circular Economy), partly funded by Business Finland, was led by Timo Fabritius and Mirja Illikainen. The industrial collaborators included: Boliden Harjavalta, Boliden Kokkola, Fortum recycling and waste solutions, Nordkalk, Outokumpu stainless steel, SSAB Raahe, and Yara Suomi. Manatee Consulting Limited (UK) assisted in scale up of the process and design of the trials.