SUSTAINABILITY

CO2-SUICOM is resistant to harsh environments because its surface
becomes denser due to curing by CO2. It is also aesthetically pleasing since
the carbonation process prevents efflorescence, or the appearance over timeof white deposits on the surface.

“Developing a new type of concrete takes time. We
would like to keep on making products to protect
people and enrich their lives by fully utilizing theaccomplishments of our many years of research,” says
ONO Kayoko, senior manager of the Technology
Development Department of Kajima Corporation’s
Civil Engineering Management Division.

CARBON-NEGATIVECONCRETEA GAME CHANGER FOR A SUSTAINABLE FUTURE
Carbon Recycling, which recasts the role of carbon dioxide as a resource to be put to good use, has been positioned by
Japan as a key technology for realizing its goal of carbon neutrality. Pioneering this new role, a domestically
produced type of concrete that absorbs carbon dioxide during the curing process has already been commercialized.
The more structures that are built with it, the morethat carbon dioxide emissions can be reduced fromthe planet—this almost magical product, a concretecalled CO2-SUICOM, was created in 2008, withKajima Corporation leading its joint developmentwith three other companies. “The idea originatedwhen we focused our attention on the 5,000-yearold concrete that was excavated from the Dadiwan
Ruins in China, as part of our research on concrete
durability,” says ONO Kayoko, senior manager of theTechnology Development Department of Kajima
Corporation’s Civil Engineering Management
Division. The study led to the realization thatcarbonation, until then considered to be a cause ofthe corrosion of structural steel frames, was actually
the key to concrete’s durability. With that serving
as a hint, in 2006, Kajima developed EIEN (Earth,Infinity, ENvironment), a concrete with an estimatedlife span of 10,000 years. Then, the company adapted

EIEN technology to give rise to CO2-SUICOM(CO2-Storage and Utilization for Infrastructure by
COncrete Materials; the name was also inspired by
the Japanese word suikomu, which means “absorb”),
thinking that it could also reduce CO2 emissions
since it absorbs CO2 during carbonation.
Concrete is made by mixing cement—whichhardens in reaction to contact with water—withCO2 Emissions[ kg/m3 ]350
300

288kg/m3

250-197kg/m3200

Reductionof cement amountby changing materials

150
100-109 kg/m350

aggregates such as sand and gravel. However, thecement production process emits large quantities
of CO2 as it involves heating limestone to very hightemperatures. In order to reduce these emissions,
CO2-SUICOM uses γ-C2S, a special material thatsolidifies when it comes into contact with CO2. Not
only does the material’s use help to cut the amount ofcement needed to about one-third the usual volume,
but the concrete’s net CO2 emissions fall below zerothrough its absorption and fixation of CO2. That
process has made CO2-SUICOM the world’s firstcarbon-negative* concrete. While other types ofCO2-absorbing concrete are available, the product’s
strength lies in the amount of CO2 it absorbs: theact of producing one cubic meter of the concrete initself absorbs more carbon than one cedar tree can ina year. “Our expertise and many years of experience
have enabled us to develop the optimum mixture ofingredients and timing for CO2 absorption,” says Ono.
Although the concrete became commerciallyavailable in 2011, it did not enjoy widespread usageat first due to its high cost and the special equipment
needed in its production that prevents casting-inplace, among other reasons. However, along with theglobal trend toward decarbonization, demand for theproduct has heightened in recent years, including
inquiries from abroad. The market size for CO2absorbing concrete is forecast to grow to between
15 and 40 trillion yen by 2030, which has led to a
current acceleration in global competition to develop
such a product.
The “Green Growth Strategy Through Achieving
Carbon Neutrality in 2050”—the Japanese
government’s industrial policy for realizing carbon
neutrality by 2050—has set several ambitious goals,
such as lowering the price of CO2-absorbing concrete
to the same level as that of ordinary concrete by 2030,
and, as part of the “Roadmap for Carbon Recycling

CO2 fixation

0-50

GeneralConcrete
Products-18kg/m3
CO2 - SUICOM*a state in which reductions of CO2 exceed emissions.

Technologies,” the concrete’s use will be promoted
in such high-demand generic products as building
beams, starting from around 2040. In January2022, as one of its projects, a consortium including
Kajima Corporation was adopted by a governmentalorganization as the implementing body for a projectbased on the 2-trillion-yen Green Innovation Fundto develop concrete that maximizes the level of CO2
emissions reduction and CO2 fixation, as well as todevelop related quality-control technology. For its actualsocial implementation, issues such as cost and on-site
placement will need to be tackled.
As emerging economies grow, the global demandfor concrete and cement is projected to rise by as muchas 23% in 2050 over fiscal 2014 levels. That projection
will have a different meaning altogether, however, if
carbon-negative concrete comes into widespread use.
“Concrete is an indispensable foundation of our lives.
That is precisely why we want to deliver products
to the world that both respond to the social issuesof the time and offer high quality,” says Ono. “Thefirst construction site that I visited when I joined thecompany was that of one of the largest concrete damsin Japan. I was deeply impressed by the scale of thecivil engineering project and the technological skillof the experts involved, as well as by their attention todetail. I look forward to the day when such a dam isbuilt with CO2-SUICOM.”
Top: In the field of architecture, the product is used in such places as theceilings of apartment balconies (photo). Since its dense surface prevents
water intrusion, concrete skeletal structures can be effectively protected, evenin areas exposed to the elements. KAJIMA CORPORATION
Bottom: The CO2-SUICOM products are currently made at precast
concrete plants with special equipment. Among the concrete’s mainapplications are paving blocks in parking lots (photo) and road demarcation
blocks. KAJIMA CORPORATION