AI paves the way towards green cement
The cement industry produces around eight percent of global CO2 emissions - more than the entire aviation sector worldwide. Researchers at the Paul Scherrer Institute PSI have developed an AI-based model that helps to accelerate the discovery of new cement formulations that could yield the same material quality with a better carbon footprint.
The rotary kilns in cement plants are heated to a scorching 1,400 degrees Celsius to burn ground limestone down to clinker, the raw material for ready-to-use cement. Unsurprisingly, such temperatures typically can't be achieved with electricity alone. They are the result of energy-intensive combustion processes that emit large amounts of carbon dioxide (CO2). What may be surprising, however, is that the combustion process accounts for less than half of these emissions, far less. The majority is contained in the raw materials needed to produce clinker and cement: CO2 that is chemically bound in the limestone is released during its transformation in the high-temperature kilns.
One promising strategy for reducing emissions is to modify the cement recipe itself - replacing some of the clinker with alternative cementitious materials. That is exactly what an interdisciplinary team in the Laboratory for Waste Management in PSI's Center for Nuclear Engineering and Sciences has been investigating. Instead of relying solely on time-consuming experiments or complex simulations, the researchers developed a modelling approach based on machine learning. "This allows us to simulate and optimise cement formulations so that they emit significantly less CO2 while maintaining the same high level of mechanical performance," explains mathematician Romana Boiger, first author of the study. "Instead of testing thousands of variations in the lab, we can use our model to generate practical recipe suggestions within seconds - it's like having a digital cookbook for climate-friendly cement."
With their novel approach, the researchers were able to selectively filter out those cement formulations that could meet the desired criteria. "The range of possibilities for the material composition - which ultimately determines the final properties - is extraordinarily vast," says Nikolaos Prasianakis head of the Transport Mechanisms Research Group at PSI, who was the initiator and co-author of the study. "Our method allows us to significantly accelerate the development cycle by selecting promising candidates for further experimental investigation." The results of the study were published in the journal Materials and Structures.
The right recipe
Already today, industrial by-products such as slag from iron production and fly ash from coal-fired power plants are already being used to partially replace clinker in cement formulations and thus reduce CO2 emissions. However, the global demand for cement is so enormous that these materials alone cannot meet the need. "What we need is the right combination of materials that are available in large quantities and from which high-quality, reliable cement can be produced," says John Provis, head of the Cement Systems Research Group at PSI and co-author of the study.
Finding such combinations, however, is challenging: "Cement is basically a mineral binding agent - in concrete, we use cement, water, and gravel to artificially create minerals that hold the entire material together," Provis explains. "You could say we're doing geology in fast motion." This geology - or rather, the set of physical processes behind it - is enormously complex, and modelling it on a computer is correspondingly computationally intensive and expensive. That is why the research team is relying on artificial intelligence.
AI as computational accelerator
Artificial neural networks are computer models that are trained, using existing data, to speed up complex calculations. During training, the network is fed a known data set and learns from it by adjusting the relative strength or "weighting" of its internal connections so that it can quickly and reliably predict similar relationships. This weighting serves as a kind of shortcut - a faster alternative to otherwise computationally intensive physical modelling.
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