Sustainable Construction Using Biochar

SUSMICS Series

The SUSMICS (SUstainable + SMI (“charcoal” in Japanese）+ Carbon Storage) series is the collective term for environmentally-friendly construction technology that uses biochar made by carbonizing woody biomass. This technology removes CO₂ from the atmosphere and realizes long-term stable carbon storage (CO₂ fixation). We look here at the products in the SUSMICS series that are suitable for an extensive range of construction and civil engineering applications.

Index

Removal of CO₂ from the Atmosphere Using Biochar
SUSMICS-C（Concrete）
SUSMICS-A（Asphalt）
SUSMICS-G（Ground Improvement Method）
SUSMICS-S（Soil Cement）

Removal of CO₂ from the Atmosphere Using Biochar

Woody biomass can be considered carbon-neutral material. That is because there is balance between the amount of CO₂ absorbed from the atmosphere during the course of the tree growth and the amount of CO₂ emitted into the atmosphere after the woody biomass has been used. Meanwhile, when woody biomass is converted into biochar, the CO₂ originally in the atmosphere is fixed in the biochar as carbon (C). That means it is possible to reduce the amount of CO₂ emitted into the atmosphere (to reduce the amount of CO₂ in the atmosphere). Therefore, we can call biochar a carbon-negative material.

However, simply converting woody biomass into biochar does not reduce CO₂ in the atmosphere. For example, using biochar as a fuel results in CO₂ being emitted into the atmosphere. All the technologies in the SUSMICS series are capable of preventing CO₂ being emitted into the atmosphere by stably storing biochar in the long-term and removing CO₂ equivalent to the amount of carbon in the biochar from the atmosphere.

Long-term storage of biochar can lead to carbon negativity

It is possible to maximize the functionality of the SUSMICS series by selecting the applicable technology according to the application and conditions.

SUSMICS-C (Concrete)

Use of Biochar to Fix Carbon in Concrete Structures

Cement, the main ingredient in concrete, emits CO₂ in large amounts when it is manufactured.

Replacing part of the fine aggregate with biochar fixes carbon in concrete structures and thus realizes a substantial reduction in the CO₂ emissions accompanying concrete production.

Taking advantage of the strengths of SUSMICS-C given below has already resulted in an expansion in the introduction of the technology into various construction and civil engineering sites.

Strengths

Performance equivalent to general concrete
Various tests have been conducted on concrete made using biochar to compare it to the general concrete used in construction sites. These tests confirm that SUSMICS-C’s fresh properties and performance after hardening are equivalent to general concrete.
Highly versatile, so it enables manufacturing and construction anywhere
In addition to application to secondary concrete products, SUSMICS-C can be manufactured in general ready-mixed concrete plants. Therefore, cast-in-place is possible in the same way as with general concrete.
The amount of CO₂ fixation has been reported in the National Greenhouse Gas Inventory Report of JAPAN
The amount of greenhouse gas absorbed (amount of CO₂ fixation) by three types (four products) of environmentally-friendly concrete were calculated for the first time in the world in Japan’s National Greenhouse Gas Emissions and Removals in Fiscal Year 2022. The report covers SUSMICS-C as a type involving the use of biochar among the three types.

SUSMICS-A^*(Asphalt)

Biochar Asphalt Pavement That Realizes Carbon Negativity

Adding biochar as a substitute for the sand in the asphalt mixture offsets the amount of CO₂ emitted at the time of the asphalt mixture manufacturing with the amount of CO₂ fixed by the biochar. This results in a carbon-neutral and carbon-negative asphalt mixture.

Developed jointly with THE NIPPON ROAD CO., LTD.

Strengths

Achieves both carbon neutrality and economic efficiency
The amount of CO₂ fixed by biochar (addition rate: 3%) is approximately 14 times the amount of CO₂ reduced by the conventional low-carbon asphalt carbon technology of warm-mix asphalt (modified type II). This keeps down the cost to reduce 1 kg of CO₂ to approximately 10% of conventional technology.
Performance equivalent to mixtures that use modified type II asphalt
The fluidity resistance of SUSMICS-A was evaluated in a wheel tracking test. The results show that SUSMICS-A has the equivalent fluidity resistance even when biochar is added compared to a normal modified type II asphalt mixture.
It is possible to carry out construction as before
It is possible to carry out construction with conventional machinery configurations without using special equipment or heavy machinery when paving.

SUSMICS-G^*(Ground Improvement Method)

Realizing Carbon Neutrality by Mixing Biochar and Melt-Solidified Slag

This is a decarbonized ground improvement method that virtually eliminates CO₂ emissions in ground improvement work employing the mixed treatment method. This ground improvement method involves evenly spreading melt-solidified slag and biochar in addition to the cement and cement-based stabilizer before mechanically mixing, stirring and compacting the mixture.

Developed jointly with Toyo Stabi Co., Ltd.

Achieving carbon negativity by mixing biochar and molten slag

Strengths

Improves soil properties and contributes to CO₂ reduction
Mixing melt-solidified slag into soil to be improved has the effect of lowering the moisture content and raising the sand content. This improves the soil properties and increases the strength of the ground. Therefore, it is possible to reduce the amount of the cement and cement-based stabilizer used to thereby enable a reduction in CO₂ emissions.
Effective use of waste
Using melt-solidified slag, made by melting general waste at high temperatures of over approximately 1,300°C and then cooling it, and sawdust, a byproduct at the time of sawing, as a biochar contributes to reducing the environmental impact.
It is possible to carry out construction as before
The ground mixing and stirring are performed using conventional construction methods. Therefore, it is possible to apply existing methods without changing the processes or the machinery used.

SUSMICS-S (Soil Cement)

Ensuring Backfill Ground Quality while Reducing CO₂ Emissions

Slurry-type cement treated soils, such as soil cement and fluidized soil, are made by mixing soil produced during construction or on-site soil with water and the cement that serves as the stabilizer. Adding biochar suppresses the bleeding (phenomenon involving the separation and settling of the constituent materials) at the time of solidification to thus make it possible to improve the soil quality. It also contributes to reducing the actual CO₂ emissions accompanying the production of soil cement.

Strengths

Takes advantage of high-water absorption properties to ensure quality across the depth
Adding powdered biochar with its high-water absorption properties absorbs the excess water in the soil cement that arises over time and thereby suppresses bleeding. Moreover, it has been confirmed that the quality (for example, the unconfined compression strength) across the depth is equal to or greater than that of conventional fluidized soil.
Manufacturing process and construction performance as before
It is possible to carry out manufacturing just by simultaneously adding the stabilizer and powdered biochar using existing fluidized soil manufacturing devices. The flow values in the pre-mix tests are equivalent to that of the conventional fluidized soil. There is no impact on fluidity when the mixture is poured in even in actual construction. Accordingly, it is possible to carry out construction as before.
Realizes carbon negativity
A large amount of biochar is added to the stabilizer. Therefore, it is possible to significantly reduce CO₂ (carbon negativity).

Relationship between the amount of CO2 emitted and stored at a site that has achieved carbon negativity — Relationship between the amount of CO₂ emitted and stored at a site that has achieved carbon negativity

Sustainable Construction Using Biochar

SUSMICS Series