The production rate of by-product has been greatly exceeded an attempt to reduce this abundant material by its utilization in many segments. The remains become problems when hundred of million tons is disposed on soil foundation and pollutes the biosphere. The application of by-product as cement replacement is considered as a great consensus to obtain some advantage both for concrete performance and environmental issues comprising economical problems. Considering the stability and ensuring their general application to the macro-scale system for long term serviceability are of important contemplation in many fields. Therefore, a comprehensive analysis of the multi-scale thermodynamics stability of by-product applications requires its clarification, simplification and investigation in micro-sized level at laboratory-scaled specimens.

The thermodynamic stability under aqueous medium was discussed for suitable treatment of blast furnace slag (BFS) and fly ash in this research. The discussion was directed to the gas-phase stability coupling with kinematics which is associated with vapor pressure inside the micro-pores of the solidified materials. Concerning the harmful substances to human health, especially boron in fly ash, liquid-phase stability related to ion dissolution and adsorption of boron was also investigated in line with the thermo-hygro stability. A sustainable waste material application in some point of views has immense value to the contribution in society.

Gaseous-phase stability in porous media such as cementitious material is specified with diffusion of humidity for the vapor pressure which represents the micro-climate in pores of hardening cementitious composites. Using BFS as a by-product at low water-to-cement ratio (W/C) to develop high strength concrete can cause early-age cracks as a consequence of autogenous shrinkage when self-desiccation induces more stress under restrained conditions. In this study, moisture distribution in mortar having 40% cement replaced with BFS at low W/C was investigated with a specific measurement. Embedded sensors are introduced in this study to deal with problems on measuring relative humidity in mortars containing BFS since dissolves sulphate during hydration becomes a troublesome to obtain a reliable measurement. The proposed method is verified to be applicable under the sulfate gaseous conditions during the early hydration when BFS is partially mixed with the ordinary Portland cement (OPC), where the previous sensing system is impossible. Moreover, a comprehensive procedure with detailed explanations to measure internal relative humidity was proposed. The experimental results were then compared with the analytical ones by the thermo-hygo simulation system named DuCOM. Lower W/C has a considerable effect on moisture diffusion in concrete since the pore structure of concrete becomes finer, especially when BFS is used. The moisture loss and drying shrinkage of mortar specimens having W/C of 25% and 35% made with 40% blast furnace slag is much greater than those made with pure OPC.

The rapidity of hygro-states of BFS was identified in terms of the volumetric mechanistic stability which investigated with shrinkage measurement using two types of embedded strain gauges. The purpose of this study is to investigate autogenous shrinkage of mortar using different commercial slag cements, which are categorized in slag cement type B (JIS standard). A caution procedure to use embedded gauges was proposed in detail. A problem to deal with accuracy results has been considered comprehensively to obtain a reliable measurement. In this study, mortar specimens made from seven industrial slag cements were prepared with the same mix proportion and curing condition. The results were then compared with the shrinkage of OPC mortar and the one made with 40% BFS replacement. Compressive strength and autogeneous shrinkage were analyzed at a certain age. The effect of high temperature of curing to shrinkage was also considered and was thought to increase the hydration process in the early age. The results show that autogeneous shrinkage of slag cements varies in reactivity and the maximum shrinkage in the slag cement mortar is about three times larger that in the specimen made with OPC. Furthermore, by analyzing the results, a comprehensive benchmarking was considered on slag content in the mixture, the particle size distributions and chemical properties of cement slag. A linear relation between the autogeneous shrinkage and the compressive strength of slag cement mortar is obtained. This fact may bring comprehensive information to the material designs in practice, where some influential factors should be considered, such as the creation of the early hydrated products, the greater chemical shrinkage, finer pore structure of blended cement containing BFS, and the particle shapes of blended cement.

Liquid stability of waste material was further examined by investigation of fly ash hydration in aqueous medium. Liquid stability with regard to the ion leaching and adsorption was experimentally investigated by focusing on boron from both the solidified and non-hardened fly ash. In this study, fly ashes obtained from the Japanese district were dissolved with de-ionized water until a certain time. Boron content in suspension was then assessed in time with Inductively Coupled Plasma (ICP) depending on water contact with fly ash. The effect of temperature is considered by mixing fly ash with hot water. The pH of solution was also observed to investigate the tendency of alkalinity of suspension in releasing soluble boron from fly ash in aqueous media. The solid part of the extracted suspension was analyzed with XRD to compare minerals binding boron in fly ash after contact with water. The result was then compared with an initial condition when there was no contact of fly ash with water. The experimental results show that chemical stability of boron ion in aqueous media is rapid so that the solid-liquid relation of boron in solid and saturated conditions can be assessed in a simple equation. Boron ions are also adsorbed rapidly by the surface of fly ash particles. Process of sorption and de-sorption of boron ions was found less than one week. The thermodynamic complexity of leaching is explained by coupling the irreversible ionization process with the recoverable course of adsorption-desorption action.

The experimental results were assessed to develop a mathematical model of boron leaching from fly ash. The requirement of mass conservation was formulated to simulate the boron release from fly ash to the natural environment. A computational approach to predict both release and capture of the boron ion is presented based upon the finite element discretization. This computational method was validated by using experimentally identified material parameters. i.e., the final adsorption capacity, dissolution capacity of leaching from solid and their intrinsic half time which represents the stability and transient process of these chemical events. The leaching of boron ion was simulated as a multi-phase equilibrium of adsorption-desorption coupled isothermal equilibrium. For verification, simple one dimensional finite element was used to simulate migration of boron ion into the liquid. The model exposed a good prediction of boron leaching in de-ionized water as compared with the experimental result. The proposed model could be a powerful tool to simulate boron migration in various media. It is also clarified that the proposed test can deal with the overall adsorption-desorption process of cement-soil mixtures. This versatility is regarded as the critical point since the method is intended to be employed to the aqueous underground environment. The model shows that in dense media, boron ion migrates slower than in porous media. When a barrier system is introduced, boron ion is retained in the contaminant area. Boron leaching in time based on different adsorption capacity of media and the variation of ion diffusion in different media can be also predicted. The higher the capacity of media to boron the more boron ion leaching from the contaminant can be shown by the proposed model.

Finally, some efforts in laboratory scale to create the artificial barriers adopted from geopolymer method were applied to prevent the interaction between fly ash and the nature. The specimens were provided by preparing fly ash in containers with the same weight. The top of the surface was injected with a combination of sodium silicate and sodium hydroxide solution. It showed that solidification of fly ash by alkali injection creates a strong barrier. The specimens were then immersed in the water and the boron concentration in time was determined with ICP measurement. The corrosive base solution made with a combination of 2M to 14 Molars of sodium hydroxide and sodium silicate showed variation effect to retain boron leaching from fly ash. It can be concluded that some barriers made from solidified-injected fly ash with different concentration from 4M to 8M of sodium hydroxide demonstrate an optimum result. Mechanistic stability of geopolymer paste was investigated with shrinkage measurement. Based on the same procedure developed to measure autogeneous shrinkage of BFS mortars, shrinkage of geopolymer pastes was then compared with OPC and BFS pastes. As the result shown by shrinkage measurement, geopolymer pastes harden rapidly and show less volumetric deformation. Consequently, the binders formed by injecting alkalis into fly ash are solidified rapidly as the liquid diffused into the powder. Therefore, geopolymer technique is expected to be used as one of the solutions to prevent boron leaching from fly ash.

The idea behind this study to investigate thermodynamic stability is to elucidate the behaviour of by-product both in solid and liquid phases throughout a comprehensive study and above all, to provide a proposed analytical calculation method based on the experimental results.

産業副産物の有効利用は環境負荷低減と省資源化社会の構築に不可欠である。都市と国土を支える社会資本の構成材料は膨大であり,社会経済活動にあわせて更新される。ここに物質循環の環が形成されれば,環境負荷低減に多大な貢献を果たすことが期待される。事実,鉄鋼産業から発生する高炉スラグがセメント原料,混和材,路盤材等を通じて他産業に循環し,温室効果ガス排出低減と省エネルギーに貢献を果たしている。同時に、リサイクルの過程で新たな環境負荷を引き起こさないための物質・材料のフロー制御が肝要であり,中長期間での材料と構造の安定性が重要な課題となる。

本論文は,水硬性ポゾランの水分保持能の時間変化と,産業副産物に取り込まれた自然界由来の微量成分の固定能力に関する安定性の二者に着目したものである。ポゾランには産業副産物の高炉スラグとフライアッシュを取り上げ,水硬性反応で固形化されたポゾラン硬化体中の水蒸気圧(相対湿度)の同定手法とそれに連動する体積安定性,ならびに微量成分の固定・溶出・再吸着の一連の過程を追跡するモデル化手法を提案している。ここでは微量成分としてフライアッシュ中に取り込まれている自然由来のホウ素に着目し,主として地中環境への漏出の観点から安定性を論じている。本論文は以下の章から構成されている。

第1章は本論文の目的について述べ,ポゾラン硬化体の熱力学的安定性に関わる工学上の諸問題を整理し,安定性を論ずる時間スケールと対象物質・材料の空間スケールごとに個別の研究項目の位置づけを行っている。熱力学的状態を細孔内の水蒸気圧(湿度)で代表することで,硬化体の自己収縮安定性を検討できることを述べ,新たな湿度センサー開発の必要性と解決すべき課題の明確化を行っている。フライアッシュ硬化体等からの微量成分のイオン溶出に関して,接水後数日で起こる溶出・再吸着現象と,年オーダーの拡散移動現象の両者の組み合わせで,物質固定の安定性を論ずる必要があることを,環境負荷低減への貢献の視点から論じている。

第2章では,細孔構造内の湿度を計測する新たなセンサー開発について述べている。産業副産物を扱うゆえに求められる課題として,高炉スラグ中の硫黄分によるセンサーの機能損傷を取り上げている。細孔湿度の計測は,硬化体の熱力学状態のシミュレーション技術の検証に不可欠であり,高炉スラグの水和と組織形成,これに関連する自己収縮挙動の解明に重要である。本論文では,水蒸気と硫黄ガスの両者に対し異なる透過方向性を有する繊維状シートをセンサー本体と結合させることによって,安定した計測を実現することに成功した。さらに普通ポルトランドセメント硬化体やフライアッシュを基調とするジオポリマーにも適用できる一般性を確認している。

第3章では、高炉スラグモルタルの体積収縮の時間変化と内部湿度変化の両者を検討している。高湿度環境下で精度の高い固体変形を検出可能なセンサーを見出すとともに,強度発現と収縮特性間に現れる関係が,セメントの種類とスラグの混合比率などで大きく異なることを提示している。これは高炉スラグコンクリートのひび割れ対策において,ひび割れ危険度の大小を,高炉スラグ粉末ごとに簡易に判定する上で有益な情報を提供するものと評価される。

第4章では,フライアッシュ単身からのホウ素溶出の時間過程を高精度で計測する手法と,その結果について報告している。熱力学的平衡状態に至るまでの過程は,固体から水分中にイオン化・溶出する非可逆過程と,フライアッシュ固体表面への溶出イオンの吸脱着の可逆過程の組み合わせでモデル化が可能であることを示している。さらに,両者の過程が終結する時間を代表する特性時間を試験によって同定する方法を新たに提案している。この方法は地盤材料とフライアッシュが混入されている条件でも特性値を与えることができる。これにより,複雑に見える溶出イオンの時間的な増減変化を,地盤環境を想定した上で記述することが可能となった。

第5章では,4章で得られたホウ素の溶出と吸着脱着に関する特性時間と等温平衡曲線からホウ素イオンの移動拡散支配方程式を導き,実験結果との検証から適用性を論じている。さらに、地盤環境下にフライアッシュを埋設処分し,環境から隔離する過程を逐次解析によって提示している。自然地盤と処分フライアッシュ間にコンクリートで人工バリアを設置する場合,その水セメント比はホウ素の環境放出の速度に支配的な影響を及ぼすが,平衡状態への影響度は低いことが示された。一方,自然バリアとしての地盤が有するホウ素の吸着容量は,平衡状態でのホウ素分布に対して支配的であることが定量的に示された。自然環境へのホウ素閉じ込めの観点から,人工バリアと自然バリアの特性の違いとそれらの組み合わせで,巨視的な溶出特性を制御できることを示唆している。

第6章は,フライアッシュを高アルカリ噴霧で固定化したジオポリマー遮蔽層の遮蔽性能について検討したものである。強アルカリの注入による固形化が促進され,緻密な構造を形成する一方で,硬化時間の短縮から巨視的な欠損や巨大空隙が形成されるリスクも高まる。その結果,材料特性と施工性の両者から,最適な添加アルカリ濃度と量が存在することを明らかにしている。

第7章で本研究の結論をまとめ、今後の課題について概括している。

本論文の扱うポゾラン硬化体の水分保持機能の安定性と体積変化に対する安定性は,構造ひび割れリスク評価の精度向上に資するものと評価される。また,自然界由来の微量成分の溶出過程と吸着脱着過程の定量化は,石炭灰の地中処分の経年変化予測に適用でき,微細な空隙構造を有する人工バリアと吸着特性を有する自然地盤バリアの組み合わせが達成する隔離性能照査を可能にするものである。実証を中心とした基礎モデルの高度化と実用化を視野に入れた数値モデルの貢献の両者から、本論文の工学上の貢献は大である。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。