A team of Japanese researchers has discovered that Japan's concrete structures—including buildings and infrastructure—absorb and store about 14% of the carbon dioxide (CO2) emissions generated during cement production.
This research provides vital knowledge to offset CO2 emissions from cement production, a significant contributor to global carbon emissions at approximately 8%. The study was published in the Journal of Cleaner Production.
With the growing urgency of climate change, scientists are focusing not only on reducing CO2 emissions but also on effective methods of capturing and storing atmospheric CO2 to mitigate global warming.
Concrete naturally absorbs CO2 throughout its lifetime through a process called carbonation, also known as CO2 uptake. While this process can contribute to the corrosion of reinforcing steel bars in concrete structures, it also enables concrete structures to function as carbon sinks.
Professor Ippei Maruyama of the University of Tokyo, Professor Hiroki Tanikawa of Nagoya University, and their colleagues conducted a comprehensive material stock-flow analysis of Japan's concrete from 1870 (when Japan began producing cement) to 2070. Material stock-flow analysis is an accounting method that tracks how materials enter a system (flows), accumulate within it over time (stocks), and eventually exit through disposal, recycling, or other means, allowing us to understand the complete lifecycle of resources in our economy and environment. Their analysis aimed to estimate the CO₂ uptake of concrete structures on a national scale.
The researchers used statistical data to estimate annual domestic cement production, the lifespan of various concrete structures, and their disposal methods. They quantified the total amount of CO₂ captured and stored based on the surface area of concrete structures throughout Japan.
To accurately calculate the total surface area, the researchers incorporated data on the surface-to-volume ratio of different types of concrete structures that reflect Japanese building design standards. As an earthquake-prone country, Japan has specific earthquake-resistant standards that needed to be factored into these calculations.
The study also accounted for local environmental conditions, finishing materials, and what happens to concrete after demolition. "The main objective of our analysis is to improve CO₂ uptake quantification by considering time-series changes and local-specific factors," Professor Maruyama explained.
The results revealed that the cumulative CO₂ uptake from 1870 to 2020 was estimated at 137.1 million tons, representing 7.5% of the cumulative CO₂ emissions from calcination during cement production. In 2020 alone, annual CO₂ uptake reached 2.6 million tons, accounting for 13.9% of CO₂ emissions from cement calcination that year.
Projections suggest that annual CO₂ uptake will increase slightly during the 2020s before dropping to 2.3-2.4 million tons by 2070. "These results could easily be reversed, depending on waste management methods and other conditions," the researchers noted.
Professor Tanikawa concluded: "Studies on the detailed assessment of the total CO₂ absorbed by concrete structures on the national scale are of great importance. Concrete buildings and infrastructure keep on absorbing CO₂ as long as they are exposed to the air. Concrete structures act as carbon sinks, even though they absorb less CO₂ than forests. With this in mind, we should take good care of buildings and infrastructure around us so that they have a long service life."
