The ongoing study, led by University of Dundee in collaboration with the UK Quality Ash Association (UKQAA), LKAB, Master Builders, and the Scottish Research Partnership in Engineering, is investigating how CDFA performs as a constituent in concrete across a range of durability and long-term exposure tests. These tests replicate the various requirements of concretes across various applications in the construction of large-scale infrastructure.
Now two years into the three-year programme, initial data is giving encouraging results for various properties, including aspects of durability, across a range of mixes. Importantly, the findings indicate that processed CDFA from stockpiles performs similarly to freshly produced fly ash, supporting its viability as a sustainable construction material for future infrastructure applications. All CDFA samples tested so far have met the fineness, loss on ignition (LOI) and chemical requirements of EN450, the European standard for fly ash in concrete.
Dr Mike McCarthy, Reader in Civil Engineering at the University of Dundee, who is supervising the research, said: “This important study has assessed a wide range of durability properties relevant to CDFA’s applications in construction. By extending our testing across a broad range of concrete formulations, we are beginning to build a clear picture of how processed CDFA behaves in real-world conditions and how it can support the development of low-carbon concrete mixes that meet established performance expectations.”
The study is evaluating CDFA across a range of binary and ternary concrete mixes produced at water–cement ratios from 0.35 to 0.55.
Nigel Cooke, UKQAA Director, said, “These early findings from the University of Dundee highlight the significant opportunity we have to bring stockpiled fly ash back into the construction supply chain in a meaningful way. What is particularly encouraging is the consistency we’re seeing across durability, strength development and overall performance. The Atritor (drying and deagglomeration) and STET (carbon removal) pilot plants that provided the processed CDFA which was used in the study are enabling stockpiled material to deliver performance comparable to fresh ash.
“With the construction sector focusing on lowering embodied carbon, this research will give specifiers real confidence that CDFA can deliver both the sustainability benefits and the technical performance that designers, engineers and contractors depend on.”
Early results include:
- Similar strength development properties for concrete containing dry fly ash and recovered CDFA.
- Comparable carbonation and chloride migration performance between dry fly ash and recovered CDFA. These qualities are particularly key for the use of steel-reinforced concrete and long-life infrastructure in coastal regions or highways projects.
- In ternary blends, incorporating Portland cement, Ground Granulated Blast Furnace Slag (GGBS) and fly ash, chloride resistance improves with higher GGBS content, although this is accompanied by increased carbonation depths, in line with expected trends.
- To date, minimal deterioration or expansion has been recorded in sulphate exposure tests (up to 12 months) and alkali-aggregate reaction tests (6-9 months).
These early indications suggest that CDFA has credible potential for specification in long‑life infrastructure, with a positive performance trajectory across key durability metrics.
Dr McCarthy said, “It’s great to see this collaboration between research and industry. The support the UKQAA has provided has been very beneficial to the ongoing study. As the programme progresses, our focus will turn to validating these early trends through extended exposure testing, as well as assessing additional engineering properties.”
These results remain preliminary, and further long-term exposure testing, particularly for carbonation, chloride ingress and sulphate resistance, is currently in progress. However, the early performance indicators are positive and reinforce the potential for CDFA to contribute meaningfully to the future of sustainable construction.
University of Dundee
Nobel Prize winning poet and honorary graduate Seamus Heaney has described the University of Dundee as ‘having its head in the clouds and its feet firmly on the ground.’ The ability to be both aspirational and down-to earth and to blend ground-breaking intellectual achievement with practical applications, has given the University its distinctive character.
