New Method Confirms Direct Air Capture in Concrete

Carbon capture is important to decrease the influence of human carbon dioxide emissions on the climate.

New Method Confirms Direct Air Capture in Concrete
Sacred Torii Gate in Wajima, Japan. Japan’s concrete production has remained about the same for the past decade, used widely for buildings, bridges, breakwaters, and even sacred shrine gates. Image Credit: Sean Pavone, Envato Elements

Scientists at the University of Tokyo and Nagoya University in Japan have established a technique to check whether carbon in concrete originates from the raw materials, or from carbon in the air, which has been stuck when it reacts with the concrete to form the mineral calcium carbonate.

The group has magnificently authenticated that direct air carbon capture has happened by measuring the ratio of particular carbon isotopes exposed to the air and concrete that had not. This analysis is helpful for the industrial sector and countries forwarding to balance their carbon emissions.

2023 is shaping up to be the hottest year ever documented, with rice crops withering in Japan and roads liquefying under the heat in the US. Despite international agreements and urgent calls for action, greenhouse gas emissions from fossil fuels have persistently risen. To avert the planet’s trajectory toward surpassing the critical 2 ℃ increase by 2100 (compared to preindustrial levels), additional measures are imperative.

As per the United Nations’ Intergovernmental Panel on Climate Change, merely cutting emissions will not suffice. Alongside reducing emissions, it is imperative to actively extract carbon dioxide from the atmosphere to meet the target goals.

Direct air capture (DAC) involves extracting carbon dioxide directly from the air through chemical or physical processes. The International Energy Agency (IEA) advocates for an increased utilization of DAC technologies as part of its net-zero emissions scenario.

This scenario aims to enable the global energy sector to remove as much carbon dioxide (CO2) as it emits by 2050. In 2022, the industry accounted for a quarter of global energy system CO2 emissions, with cement, the second-most widely used industrial product, carrying a substantial environmental impact.

As much as 800 kilograms of CO2 is emitted per ton of cement during its production, so reducing emissions has become a significant issue in the concrete industry. Concrete has long been known to react with CO2 in the air to form calcium carbonate, an undesirable phenomenon because it induces corrosion of the steel bars inside concrete structures. However, the concrete industry is now considering ways to make effective use of this reaction.

Ippei Maruyama, Professor, Department of Architecture, University of Tokyo Graduate School of Engineering

While the reaction that leads to the formation of calcium carbonate is challenging for construction processes, it has the beneficial effect of capturing or trapping CO2, effectively removing the gas from the atmosphere. Additionally, calcium carbonate is naturally present in rocks like limestone, commonly used in concrete production.

This makes it difficult to distinguish whether or not CO2 identified in concrete has been freshly extracted from the air or comes from rocks. So we developed a method to verify this, which could be used to determine whether the concrete produced can be certified as offsetting CO2 emissions.

Ippei Maruyama, Professor, Department of Architecture, University of Tokyo Graduate School of Engineering

To conduct the study, scientists created samples of hydrated cement paste to mimic concrete. After allowing the paste to adequately hydrate, they ground one set into powder, keeping the non-exposed powder contained while exposing the other to the air. After a week and 28 days, they dissolved the powder in acid, collected the gas, and used accelerator mass spectrometry to analyze the ratio of carbon isotopes—carbon-12, carbon-13, and carbon-14.

This allowed the group to determine the source of carbon and whether it was already present in the raw materials, as the carbon ratios reflected the known proportion of carbon isotopes in the air during gas sealing.

The scientists planned to apply this lab-based method to real-world locations and check the varied quantities of ingredients in local concrete production affecting the outcomes.

Fixing carbon dioxide from the air is certified as an act of offsetting CO2 emissions, so it is economically valuable in terms of emissions trading. Digging up calcium carbonate for use in concrete is not, so the distinction is very important and this research can help to support a healthy market. We believe that the carbon neutrality and a circular economy in the construction industry are essential to our future, particularly in Japan where this industry has a role in supporting business continuity and recovery from natural disasters.

Ippei Maruyama, Professor, Department of Architecture, University of Tokyo Graduate School of Engineering

Journal Reference:

Wang, Z., et al. (2023). Verification Method of Direct Air Capture by Cementitious Material Using Carbon Isotopes. Journal of Advanced Concrete Technology.

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