Obayashi Corporation announced on September 29, 2026, that it has developed a technology to use biochar made from wooden formwork used at construction sites as a CO2 absorption and fixation material in its “Clean Crete N” carbon-fixing concrete. The company also applied Clean Crete N made with this biochar-derived material for the first time in precast concrete curtain wall panels (exterior wall panels) at the experimental building “Open Lab 3 (OL3),” constructed at its Technical Research Institute (Kiyose City, Tokyo).
Clean Crete N is a concrete that achieves further CO2 emission reductions by mixing CO2 absorption and fixation materials into the company’s low-carbon concrete, “Clean Crete.” Depending on the amount mixed in, it is reportedly possible to bring the CO2 emissions generated during manufacturing to effectively net zero or below.
To expand the application of Clean Crete N, the company has been working to diversify the raw materials that can be used as CO2 absorption and fixation materials. In addition to the calcium-carbonate-derived materials it has used to date, the company has been verifying new materials and confirmed that biochar made from the wooden formwork used in concrete structural work can be used as a CO2 absorption and fixation material. This biochar is produced by carbonizing waste from used wooden formwork in a carbonization furnace, making effective use of materials that had previously been discarded. Carbonizing biomass such as wood is recognized as having a carbon storage effect.
OL3 is an experimental construction building that reuses steel-frame and concrete structural components taken from demolished buildings in new construction, incorporating a range of environmentally conscious technologies. It is being developed as a facility to put circular construction practices into effect and verify their benefits.
For this project, OL3’s exterior wall panels used a total of 67.3 m³ of Clean Crete N: 58.3 m³ made with calcium-carbonate-derived material and 9.0 m³ made with biochar-derived material. Compared to conventional concrete, the CO2 emission reduction rates were approximately 104% and approximately 79%, respectively, achieving a total CO2 emission reduction of 19.3 tonnes through this construction work. In addition, since the calcium-carbonate-derived material is white and the biochar-derived material is black, the difference in color between the two was incorporated into the design of the exterior walls.
Other efforts to use biochar in concrete can also be seen elsewhere in the construction industry. In March 2026, Shimizu Corporation announced that its environmentally conscious concrete incorporating biochar, “SUSMICS-C,” had obtained a construction material technology performance certification from the General Building Research Corporation of Japan. As “SUSMICS-Cs,” a version specialized for structural building materials, it was first applied to gates and walls in the rebuilding plan for the company’s Tokyo Woodworking Plant. Additionally, in November 2024, Fujita Corporation and Tokuyama Corporation jointly developed “Biochar Interlocking Blocks,” a sidewalk paving material that mixes large granular charcoal—a byproduct of woody biomass gasification power generation—into concrete products, achieving effectively net-zero greenhouse gas emissions from materials such as cement.
※Image sourced from the press release
【Press release】Developing Clean Crete N® using biochar derived from used wooden formwork
【Reference】Expanding the environmentally conscious concrete SUSMICS-C for use as a structural building material
【Reference】Jointly developing “Biochar Interlocking Blocks” to contribute to a carbon-neutral society
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