Feasibility of Producing Artificial Pozzolana

Cement production is a significant contributor to global CO₂ emissions. The majority of these emissions – around 60% – are produced during the calcination process, where limestone is melted to produce Portland cement clinker. As a result, there is growing interest in the construction industry in using alternative clinkers, known as supplementary cementitious materials (SCMs), to produce lower carbon emissions.

Currently, many SCMs are sourced from industrial waste streams, such as flue ash and blast furnace slags. But, as coal-fired power stations and blast furnaces decrease in number in the UK, these sources do not offer a long-term solution.

Instead, a project led by construction materials manufacturer Mannok Build Ltd, whose sites straddle the border of Northern Ireland and the Republic of Ireland, explored the feasibility of using local clay deposits to produce SCM in the form of Natural Calcined Pozzolans (NCPs).

“These kaolinitic clays calcinate at a much lower temperature – around 750 to 850 °C compared to the higher clinkering temperatures of 1450 °C for Portland cement production – and historical geological maps indicate they are in abundance in the area,” explains Kevin Lunney, Operations Director at Mannok Build Ltd and project lead. “On top of that, we have a mothballed plant at Derrylin that was used previously for clinker production, so the project also explored its potential for manufacturing SCM there with a relatively low capital cost.”

With funding from the Transforming Foundation Industries Challenge, the project team conducted extensive research into historical records of clay and shale excavations to identify suitable sites within the local area. Samples were then extracted for mineral analysis, followed by the production of trial cement blends.

“Many of the clay deposits proved unsuitable or challenging, either due to material inconsistency or high overburden levels, but we did find a number of areas with potential, including a promising site at Tamnamore, near Lough Neagh,” explains Lunney. “We also identified some shale deposits that contain reactive clays. Although these need more processing and higher calcination temperatures, they are easier to access and closer to the factory.”

In trials, the project found it was possible to manufacture a usable SCM that, when blended with Portland cement, could reduce its CO₂ intensity without loss of performance. “We confirmed that we could get to 22.5% substitution of clinker and still meet the necessary strengths to comply with applicable standards. This would represent around 10.5% CO₂ reduction (83kg CO₂e/ton) in our overall cement produced if the project were implemented,” says Lunney.

“If Mannok were to establish the first calcine clay processing facilities on the island of Ireland, it would offer not only the production of lower carbon cement but also the opportunity for industry to share the knowledge, taking us a step closer to sustainable construction.”

When considering the commercial viability of processing the product at Mannok’s Derrylin plant, the team concluded that although some of the equipment, particularly the kiln, is beyond repurposing, the plant is ideally suited to placing a new, energy-efficient Flash Calciner. “This would potentially be able to operate on renewables and would also mean we could utilise significant elements of the material handling equipment currently mothballed at the site,” says Lunney.

A market assessment as part of the project demonstrated that industry demand for these alternative SCMs is strong, particularly with increasing pressure to achieve lower carbon construction. Lunney adds: “There is so much interest in this area. If Mannok were to establish the first calcine clay processing facilities on the island of Ireland, it would offer the production of lower carbon cement and the opportunity for industry to share the knowledge, taking us a step closer to sustainable construction.”

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