In an effort to achieve carbon neutrality by the year 2050, expectations are growing surrounding the sequestration of CO₂ from the atmosphere and exhaust gases through the carbonation of cement and concrete. In light of this, various R&D and practical applications are being promoted worldwide. This review introduces state-of-the-art technological developments related to CCUS using cement and concrete, including: Transition of CO₂ emissions in the construction and cement/concrete industries; Outline of measures for carbon neutralization; Outline of various technologies for low-carbonization; Decarbonization at each stage of the concrete lifecycle; Development of additions and aggregates made of artificial calciumcarbonate; Development of cement/concrete binders that react and harden with CO₂; and Development of calcium carbonate concrete. Requirements are also indicated for concrete to develop into a carbon-neutral construction material.

A consortium comprised of Kajima Corporation, Denka Company Limited, and Takenaka Corporation, along with 44 companies and 11 research institutions, has proposed the development of “Innovative carbonnegative (CN) Concrete: Materials, Construction Techniques, and Quality Control Technology.” This proposal has been selected for funding by the Green Innovation Fund project, managed by the New Energy and Industrial Technology Development Organization (NEDO) in Japan. It involves companies from all sectors of the construction industry, pooling their research and execution capabilities, to transform the Japanese concrete industry. The consortium aims to bring together various technologies that contribute to the reduction and fixation of CO₂ and implement expertise acquired over the years to promote the development of environmentally friendly concrete. The goal is to integrate the various techniques to create a new generation of concrete that is carbon-negative by the year 2030. This ambitious project is driven by the shared determination to combat climate change and promote sustainable construction practices.

Carbon Pool Concrete, which is being developed under the NEDO Green Innovation Fund Project, is a new carbon-neutral concrete that uses concrete waste as a recycled resource. Concrete mass totals 36.9 million tons per year, with 2.25 million m³ of residual and returned concrete being generated annually. Each material is expected to come close to achieving the targeted fixation amount of CO₂ gas together with moisture. In the future, we plan to study more efficient fixation methods and methods for fixing the materials to concrete, but it will be necessary to first fully evaluate not only the fixation amount of the materials used, but also: the treatment method, the state of CO₂ used, and the selection of a suitable site for the treatment plant from the viewpoint of LCA.

Various CO₂ fixation technologies are under development in the cement and concrete fields. In line with this, many organizations have been studying mass evaluation technologies for sequestrated CO₂ that are currently in the process of being JIS standardized. This paper outlines differential thermal-thermogravimetric analysis, wet analysis, total organic carbon analyzer, and coulometer methods. It presents examples of their application and discusses the issues surrounding these. Although all of the CO₂ fixation evaluation techniques are currently capable of quantifying CO₂ fixation with a certain degree of reliability, further research and development will be required. This will include revision of testing methods, as it is expected that more types of CO₂ fixation materials and concrete can be developed in the future.

One of the methods for recycling returned concrete, of which 1 to 2 million m³ is generated annually, is to use granulated recycled aggregate in concrete. RRCS (Ready-mixed & Returned Concrete Solution Association) conducted tests at 42 ready-mixed concrete plants nationwide with the aim of promoting the use of granulated recycled aggregate. The test results showed that the physical properties of granulated recycled aggregate almost satisfied the standard values equivalent to recycled aggregate Class L. In addition, it was found that the compressive strength of concrete produced by replacing ordinary aggregate with granulated recycled aggregate decreased little when the replacement ratio of granulated recycled fine aggregate was less than 30% and that of granulated recycled coarse aggregate was less than 100%. Furthermore, the RRCS has proposed the concept of a returned concrete station for the widespread use of granulated recycled aggregate, since not only the technical aspects but also the facilities for granulation and production of granulated recycled aggregate concrete and its utilization are issues to be addressed.

“Fresh ready-mixed concrete waste” at construction sites is defined as fresh concrete that is leftover after castingbecause the amount of ready-mixed concrete ordered by the construction site was larger than the required amount.When the ordered quantity of ready-mixed concrete falls short of the required quantity, it has a significant impact on the construction schedule. This is a problem which is difficult to completely eliminate whether the quantity is small or large. It is therefore an issue to be solved from the viewpoint of sustainability in concrete distribution, especially from the viewpoint of waste recycling. Possible reuse methods are beingstudied from various angles by various companies, and one of the most common methods is to use fresh ready-mixed concrete waste to make concrete blocks. In this manuscript, based on the fundamental research presented so far, this paper describes the factors necessary for the advanced utilization of fresh ready-mixed concrete waste.

This paper introduces the content of the CRER project being implemented in the Republic of South Africa under the Science and Technology Research Partnership for Sustainable Development (SATREPS). The CRER project is scheduled to be implemented over a five-year period starting in fiscal year 2021 and is primarily targeting the cement industry in the Republic of South Africa. It aims to develop mineral carbonation technologies in order to reduce CO₂ emissions and environmental remediation technologies using byproducts. One of the projectʼs other main objectives is to develop young talents and implement the technologies in the partner country. Hence, this paper presents an overview of the activities in the field and the academic results obtained from the project.