Japan's Kajima Corp. is well on its way to supplying the world with carbon-negative concrete.

A little over an hour from Tokyo, nestled in the mountains near Nagano, a house has been built in Karuizawa with the world's first carbon dioxide-removing concrete walls produced by replacing a percentage of the cement content with an industrial byproduct and adding a CO2-absorbing admixture of dicalcium silicate.

Karuizawa is one of Japan's oldest and most famous forested mountain resort towns. The house, designed by Japanese studio Nendo, has panel walls made of new eco-friendly concrete blocks called CO2-SUICOM, short for CO2-storage and utilization for infrastructure by concrete materials, jointly developed by Kajima Corp. and the Chugoku Electric Power Co., Denka, and Landes Co.

Kajima Corporation

This special concrete's carbon reduction is twofold: cutting down cement content by substituting industrial byproducts and soaking up CO2 in the curing process.

The special admixture used in CO2-SUICOM absorbs CO2 and solidifies it through a calcium carbonation process. This significantly reduces the amount of cement and accelerates the permanent absorption of CO2 inside the concrete.

Generally, concrete hardens through a chemical reaction between cement and water. During the CO2-SUICOM manufacturing process, concrete is formed with byproducts such as coal ash or blast furnace slag, then placed in a curing chamber fed with CO2 to be absorbed into the concrete, a reaction which hardens the concrete mix without needing water while retaining the same strength as traditional concrete.

In addition, it has excellent abrasion resistance and is chemically neutral and nontoxic to plants.

CO2 from various sources, including steel, power, and cement plants, could be directly used for this, resulting in reduced emissions and even carbon-negative production, depending on the source of CO2. For example, a thermal power plant or other facility can redirect its carbon-heavy exhaust into a carbon sequestration chamber, where concrete products made with CO2-SUICOM can be placed to capture the CO2 in the gases.

Promoting a green future

Masahiro Ohgami

Privacy, views, and the promise of a greener future.

According to a study published last year, worldwide cement and concrete industries generate approximately 8% of total carbon emissions. Energy-based CO2 emissions from the cement industry in 2020 were about 1.2 % of Japan's total emissions.

For Nendo, the solution was a design concept of concrete block walls that would serve as screens. The designer emphasized that "A creative solution was essential in securing privacy from passing traffic and pedestrians, while acting as a foil for basking in the natural surroundings."

Around 2,050 of these blocks were stacked to make five walls, each three meters high and angled to control privacy and line of sight – a traditional Japanese aesthetic.

Next to modern architects, Kajima's CO2-SUICOM and CO2 sequestrated aggregate have the backing of Mitsubishi, which supports CO2-SUICOM's technological demonstration, business development, global commercialization and marketing as part of the corporation's commitment to the Keidanren Japanese Business Federation's Challenge Zero decarbonization project.

Kajima Corporation

Kajima's main products are precast concrete forms produced in factories, which are already used for public and private construction.

Kajima's main products are precast concrete forms produced in factories, which are already used for public and private construction.

The company's involvement in various building projects includes a broadening list of already completed hospitals, hotels, apartments, research centers, official buildings, and even infrastructure. Projects range internationally from Japan to the U.S., Australia, Indonesia, India, the Czech Republic and more. Customers include Fujifilm, Hilton, Lexus, and the Japanese Red Cross.