Groundbreaking: Recipe for zero-carbon cement discovered

27 May 2024 CW Team

Concrete production is a significant contributor to global CO2 emissions, accounting for approximately 8% of the total. However, recycling concrete into a usable form for new structures has been challenging.

Efforts to make concrete more environmentally friendly have included altering its composition to reduce pollution, such as substituting less harmful ingredients like limestone, or designing concrete to absorb more CO2 from the atmosphere over time. In this study, researchers from Cambridge explored the conversion of waste concrete back into clinker, the dry component of cement, for reuse.

Dr Cyrille Dunant, the lead author of the study, mentioned having a notion from previous research that crushing old concrete, removing sand and stones, heating the cement to eliminate water, and then forming clinker might be feasible. They experimented with using an electric arc furnace, commonly employed for recycling steel, to aid this process.

In traditional steel recycling using an electric arc furnace, a flux material, typically lime, is utilised to purify the steel. This substance captures impurities, rises to the surface, and forms a protective layer to prevent exposure to air. Afterward, the used flux is discarded as waste.

In the Cambridge method, the lime flux was replaced with recycled cement paste. Remarkably, not only was the steel successfully purified, but the leftover slag could be rapidly cooled to produce new Portland cement. The resulting concrete exhibited similar performance to conventional concrete.

A breakthrough from Cambridge aimed at tackling CO2 emissions from concrete and steel production simultaneously. It suggests that throwing old concrete into steel-processing furnaces could yield both purified iron and reactivated cement as a byproduct, potentially leading to carbon-zero cement production if renewable energy is used. Concrete production is a significant contributor to global CO2 emissions, accounting for approximately 8% of the total. However, recycling concrete into a usable form for new structures has been challenging. Efforts to make concrete more environmentally friendly have included altering its composition to reduce pollution, such as substituting less harmful ingredients like limestone, or designing concrete to absorb more CO2 from the atmosphere over time. In this study, researchers from Cambridge explored the conversion of waste concrete back into clinker, the dry component of cement, for reuse. Dr Cyrille Dunant, the lead author of the study, mentioned having a notion from previous research that crushing old concrete, removing sand and stones, heating the cement to eliminate water, and then forming clinker might be feasible. They experimented with using an electric arc furnace, commonly employed for recycling steel, to aid this process. In traditional steel recycling using an electric arc furnace, a flux material, typically lime, is utilised to purify the steel. This substance captures impurities, rises to the surface, and forms a protective layer to prevent exposure to air. Afterward, the used flux is discarded as waste. In the Cambridge method, the lime flux was replaced with recycled cement paste. Remarkably, not only was the steel successfully purified, but the leftover slag could be rapidly cooled to produce new Portland cement. The resulting concrete exhibited similar performance to conventional concrete.

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