C4S* Research and Development Project*C4S: Calcium Carbonate Circulation System for Construction
Project Manager (PM) : NOGUCHI Takafumi, The University of Tokyo

Summary

Strength (N/mm2)

Concrete is an indispensable construction material for social capitaldevelopment, but its production uses a large amount of limestone and emitsa large amount of CO2. The estimated age of limestone is 200 years at best,
and 7-8% of the world's annual CO2 emissions come from cement production.
To fundamentally solve the problems of resource depletion and CO2 emissionin conventional concrete, in this project, Ca in concrete accumulated instructures is considered as a potential unused resource that can absorb CO2.
The project will develop a technology to produce an innovative concrete,calcium carbonate concrete (CCC), using only concrete waste generated
from the demolition of structures and CO2 in the atmosphere as raw
Fig.1 Resource circulationmaterials. CCC can be put to practical use as a major construction material
to replace conventional concrete, thereby recovering a large amount of CO2
from the atmosphere and creating a new resource circulation system (C4S:
Calcium Carbonate Circulation System for Construction) (Fig. 1).
In the production of CCC, the crushed powder is used as raw material for
calcium bicarbonate solution, and the particles are filled into a container withpressure as aggregate. The calcium bicarbonate solution is impregnated into
the aggregate particles, and calcium carbonate crystals are precipitated byheating and drying, bonding the aggregate particles together to form CCC. As
Months after project starta result of attempts to use the precipitation method, the pressurization
Fig.2 Strength gain in CCC
method, and the stacked pressurization method, the optimum temperaturefor dissolving calcium from powder, the optimum pressure for filling of aggregate, and the optimum
temperature for precipitation of calcium carbonate have been identified and compressive strengths of
56 N/mm2 for a 1 cm diameter specimen and 23 N/mm2 for a 10 cm diameter specimen have beenobtained. Then studies on ramen structures with prestressed steel tube structures for CCC column
members and wall-type structures with CCC blocks are underway. In addition, for social implementationof C4S, studies are being conducted on the conformity of CCC structures to current laws and standards,
optimal resource recycling scenarios based on the prediction of concrete waste generation, and lowenergy CCC manufacturing methods based on the analysis of LCCO2 reduction effects.
By realizing C4S, global warming will be greatly suppressed, and the global environment will beregenerated, as CCC fixes a large amount of CO2 in the atmosphere and can be recycled many times asa major construction material with energy conservation, just like the uplift process of the Himalayas andthe Alps fixed CO2 and created Cool Earth in prehistoric times.

KPI
FY2022

FY2024FY2029CCC with compressive strengthof 12 N/mm2 or larger will be
realized at the concrete test
specimen level (cylinder with adiameter of 10 mm and a heightof 20 mm).

CCC with a compressive strength of
30 N/mm2 will be achieved at 10 cm
diameter specimen, and CCC column
members with a diameter of 15 cm or
more and CCC beam members with alength of 100 cm or more with acompressive strength of 12 N/mm2 or
more
will
be
continuously
manufactured in a bench plant toproduceasimulated
two-layer
structure of 2 m wide, 1 m deep and 3m high.

Achieve CCC structuralmembers with the same
performance as conventional
concrete, that is, compressive
strength of 30N/mm2, andstart general supply of CCC
low-rise buildings with seismic
resistance and durability.

Implementation
The University of Tokyo, Hokkaido University
Moonshot Research and Development Program［Project Overview］