Concrete is the primary material utilized for infrastructure construction. Globally, the usage of concrete has been increasing as developing countries have begun investing in their infrastructure. Further growth and urbanization will increase the demand for infrastructure and thus the usage of concrete will increase. However, this growth and urbanization is also responsible for environmental deterioration. The environment is one aspect of sustainable development, along with society and the economy. These three are not separate entities, but rather a hierarchy exists whereby changes in the environment affect society, and changes in society affect the economy. Sustainable development, therefore, is concerned with how to develop modern societies while reducing the negative impacts felt throughout these systems and allow future societies the same chance at development.

As part of the sustainability movement, the concrete industry has also begun to consider its environmental impact. Concrete's negative impact comes primarily from greenhouse gas emissions, consumption of natural resources, and waste disposal. Approaches to considering sustainable practice in the concrete industry include enhances durability, utilization of industrial waste, and recycling of construction demolition. Concrete materials form an important part of sustainable practice but, like sustainability itself, it is difficult to determine exactly what constitutes sustainable concrete. There is oftentimes a trade-off between different performance aspects, such as how increasing strength also increases CO2 emissions. A definition for sustainable concrete which includes both a reference state and balance between evaluation criteria is necessary for the development and implementation of sustainable concretes. Just as concrete construction requires cooperation and interaction between many different groups, so too should the definition of sustainable concrete be developed considering the diversity of perspectives and goals within the concrete industry.

The objectives of this research are to develop a framework which can be used to define and evaluate the sustainability of concrete materials based on the perspectives of the relevant social groups; to investigate the perspectives on sustainable practice and materials in the Japanese concrete industry and the differences between social groups; and to apply these perspectives to the framework to establish a definition and weighted evaluation criteria for sustainable concrete.

Sociology of technology theory, which considers the technology development process as driven by the negotiation of differing perspectives on the technology, was combined with a technology formation model, which visualizes the formation of technology as the transcription of design information on media, to produce a framework which could transition from the undefined concept of sustainable concrete to a specific form and balance of criteria. This framework consists of three parts: the identification of relevant social groups, the evaluation of the social groups' perspectives on sustainable concrete, and the integration of the perspectives into the formation model.

To apply this framework for the Japanese concrete industry, relevant social groups were identified by considering the industry's structure and the relationship between social groups. The perspectives on sustainable materials were investigated using a top-down approach, via interviews with industry researchers, and a bottom-up approach, via surveys across a wide group of concrete industry members. Sustainable concrete practice and materials could be divided into two aspects: concrete performance and sustainability. The most importance was placed on durability, cost, and life cycle cost for concrete performance, and on atmosphere, land, consumption and production, and institutional framework for sustainability, and these were selected as key indicators for defining sustainable concrete. The concrete parameters were given higher importance than the sustainability indicators. Few differences between the social groups were observed; in the cases were conflict occurred, the contractor's viewpoint was selected as most appropriate.

To convert the importance factors for the key indicators into knowledge which could be applied to the formation of sustainable concrete, the multi-criteria decision-making tool Analytic Hierarchy Process was applied. Most of the weight was given to the concrete parameters, with cost and life cycle cost carrying the highest weight. These weights don't provide information about the absolute sustainability - only relative sustainability - so general-use concrete was set as the baseline which the concrete industry should aim to surpass. Sustainable concrete could therefore be defined as concrete which exceeds the performance of general-use concrete, and the evaluation of this performance could be conducted using the weights given to each indicator. An example calculation using this methodology and a simplified set of weights from the social perspectives was conducted using five concretes with different approaches to sustainability. It was found that durability was the key to achieving high sustainable value, and the trade-off between reducing amount of recycled materials and increasing strength nearly balanced out overall. Normalizing these performances by the general-use concrete provided an easy-to-interpret means for understanding the trade-off between different performances.

The methodology proposed in this thesis can be used to overcome several barriers to the implementation of sustainable concrete. First, it provides a means for balancing different performance criteria by allowing that balance to be defined by the relevant social groups. In addition, this thesis directly addresses the problem of how to define sustainable concrete by a combination of social investigations, Analytic Hierarchy Process, and the establishment of general-use concrete as the baseline performance. These techniques may be useful to all members of the industry who are concerned with evaluating the sustainability of concrete materials.

コンクリートは,地球上で最も広く使用されている建設材料であるとともに,その使用量は水に次いで2番目であり,社会生活の基礎となる安全で快適な社会基盤を構築する主要な材料である.世界的に見て,コンクリートの使用量は,発展途上国での需要増加や,都市化の進行に応じた需要増加により,現在でも増加している.これらの成長は,生態系の破壊や地球温暖化ガスの増加などの環境破壊をもたらし,世界的にも,経済に偏った発展ではなく,持続可能な発展の重要性が認識されている.持続可能な発展の基本概念は,将来の社会においても持続可能な発展が可能となるような,現在社会の発展のあり方を議論することにあり,この時,複雑な相互関係のある環境,社会,経済の3つの側面を統合して考慮する必要がある.このような社会状況は,コンクリート産業においても,環境負荷の重要性を認識させるに至っている.コンクリートは環境負荷が大きく,使用量の増加を考慮すれば,環境負荷の低い建設材料となることが重要となる.コンクリート材料および産業の持続可能性を評価するためには,サステナブルコンクリートの定義や評価基準を定めることが極めて重要であるが,発注者,施工者,材料メーカ等の参画者間に存在する,異なる考え方や目標を適切に統合する必要がある.本論文は,これらの問題を解決すべく,日本のコンクリート産業における社会的視座に基づき,サステナブルコンクリートの評価と形成方法を提案するものである.

第1章は序論であり,背景と目的および論文の構成を取りまとめている.

第2章は,本研究の背景となる,持続可能な発展に関する一般的な技術論とコンクリート産業における議論に関してとりまとめている.一般論に関しては,環境性,社会性,経済性の3つの視点からのサステナビリティに関する既往の報告,およびその評価手法に関してとりまとめている.コンクリート産業に関しては,環境負荷,サステナブルな活動のための戦略,評価手法,サステナブルコンクリートの事例などの既往の研究を詳細にとりまとめている.

第3章は,建設産業のイノベーションプロセスをモデル化するために,社会学で利用されているSCOT理論を紹介し,技術開発プロセス評価のために必要となる視点を整理している.

第4章は,第3章で紹介したSCOT理論を活用して,サステナブルコンクリートを開発するための枠組みを提案している.特に,対象技術に関連する社会的グループ(発注者,施工者,材料メーカ,学識者など)の相互関係の重要性,伝統的な知識体系(規準類)とサステナビリティなどの新しい価値のバランスの重要性などを指摘している.

第5章は,異なる社会的グループの価値規範や技術開発に関する障害などを理解するために,インタビュー調査を実施している(トップダウンアプローチ).

第6章は,第5章の分析結果を活用し,アンケート調査(ボトムアップアプローチ)を実施することで,サステナブルコンクリートを評価する際に重要となる視点および具体的な指標を明らかとしている.

第7章は,第6章の結果を用いたAHP分析により,重要となる指標の重付けを行い,サステナブルコンクリートの評価手法を提案するとともに,その活用方法に関して幾つかの事例を用いて説明している.さらに,第5章から第7章の結果を,提案したサステナブルコンクリートの開発フレームに適用し,具体的な技術開発プロセスに関して論じている.

第8章は,提案手法の活用方法に関して論じている.特に,社会的な価値は,社会的グループの構成員,場所や時代などの影響を受けて変化するため,これらの価値変化への対応方法に関する考察を行っている.

第9章は,本研究で得られた成果および今後の課題を取りまとめている.

以上,本研究は,サステナブルコンクリートを評価するために,社会学と技術マネジメントを統合した枠組み(フレームワーク)を構築し,コンクリートの社会的側面の検討を可能としたものであり,コンクリート産業で持続可能な活動を推進することに貢献できる有用性に富む独創的な研究成果と評価できる.よって本論文は博士(工学)の学位請求論文として合格と認められる.