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凍結融解と塩化物の複合作用によるスケーリングに対する耐久性設計法に関する研究
| Title: | 凍結融解と塩化物の複合作用によるスケーリングに対する耐久性設計法に関する研究 |
| Other Titles: | A Study on Durability Design Method for Control of Scaling due to Combined Action by Freeze-Thaw and Chloride |
| Authors: | 遠藤, 裕丈1 Browse this author |
| Authors(alt): | Endoh, Hirotake1 |
| Issue Date: | 24-Mar-2011 |
| Publisher: | Hokkaido University |
| Abstract: | コンクリート構造物は住民の生活と安全を支える重要な役割を担っている．構造物を長く使いこなすには，ライフサイクルコストの低減に配慮した合理的な維持管理計画を策定する必要がある．そのためには，コンクリートの劣化予測を適切に行うことが大切である．寒冷地における代表的な劣化因子に凍結融解が挙げられる．さらに，沿岸部や凍結防止剤の散布地区では塩化物の作用も合わせて受ける．コンクリートが凍結融解と塩化物の作用を複合的に受けると，コンクリートの表面がうろこ状に剥がれ落ちるスケーリングが促進されることが知られている．スケーリングは構造物の美観の低下や，かぶりの減少による鋼材の早期腐食を引き起こす．しかし，スケーリングは，ひび割れの進展が主な一般の凍害とは劣化の形態が異なるため，既往の凍害の予測・評価に関する研究成果をそのまま適用することができない．これらの背景をふまえ，まず本研究の前半では，スケーリングの進行性の定式化およびスケーリングに対する耐久性設計法の確立を目的に，ASTM C 672 に準じた室内実験および実構造物での調査を行った．室内実験では，水セメント比と使用するセメントの種類の影響が特に大きいこと，また，スケーリングの進行性は水セメント比とサイクルを無次元化させた変数を用いることで予測・評価が行えることを示した．さらに，スケーリング促進の危険性はコンクリートの弾性係数とコンクリートの表層で発生する凍結圧の圧力勾配とのバランスに強く依存すること，そして弾性係数は細孔の含水状態，凍結圧勾配は透水係数の影響を受けやすいことを明らかにした．防波堤上部の天端面の調査では，供用年数を凍結融解の履歴を表す変数（室内実験ではサイクルに該当）とみなすことで，室内実験で提案したスケーリングの進行性に関する評価式は実構造物にも応用できることを実証した．また，本研究の範囲ではあるが，水セメント比の設計値が53～60%の場合，ASTM C 672 における300 サイクルのダメージ（実験水：人工海水）は，実環境の最大20～33 年分のダメージに相当することを確認した．これらの知見を総合的にとりまとめて，スケーリングの進行を抑制するための耐久性設計の考え方を整理した．次に後半では，スケーリングの抑制対策について検討を行った．本研究ではシラン系表面含浸材に着目した．シラン系表面含浸材は，凍結融解と塩化物の複合作用によるコンクリートの劣化の抑制が期待される材料の一つで，経済性と施工性に優れ，施工実績は増加傾向にある．しかし，耐久性の照査法および施工後の劣化予測手法の確立には至っていない．そこで，効果の持続性の評価を目的に，北海道の道路橋地覆での試験施工ならびに沿岸部での暴露実験を行った．実験・調査の結果，先行劣化を受けていない部材ではスケーリング抑制効果の持続が確認された．さらに，取得したデータの範囲でライフサイクルコスト縮減効果の評価も行った． | | Concrete structures play an important role in supporting the lives and safety of those who use them. To extend the service life of such structures, it is necessary to develop a rational maintenance and management plan that considers life cycle cost reduction. Accordingly, it is important to be able to predict concrete deterioration in an appropriate way. While freeze-thaw are typical deterioration factors in cold regions, areas where antifreeze is used as well as coastal areas are also affected by chloride. It is known that the combined effects of freeze-thaw and chloride act to accelerate the progress of scaling (i.e., scale-like peeling on the surface of concrete). Scaling may lead to a deterioration in the appearance of structures, and the early corrosion of steel materials due to reduced covering. However, since the form of scaling-related deterioration differ from those caused by ordinary frost damage in which cracking progresses, it is difficult to apply the results of past studies on frost damage prediction and evaluation to design without modification. Against this background, at the first period of this study, laboratory experiments and surveys on deterioration in actual structures were conducted in this study in accordance with ASTM C 672. The model of scaling progress and the concept of a design method to resist scaling were summarized. The laboratory tests confirmed that the influences of the water-cement ratio and the type of cement used were significant. It was found that scaling progression can be predicted and evaluated using variables found by non-dimensionalizing the water-cement ratio and freeze-thaw cycle through division by the average of the values obtained from the experiments. And, it was found that the risk of scaling acceleration depended strongly on the balance between the young’s modulus of concrete and the freeze pressure incline by unfreezing water in concrete surface layer. It was closely related to the pore saturation state and the coefficient of permeability. In the deterioration survey on actual structures, it was demonstrated that the variables (cycles) representing the freeze-thaw history used in the laboratory test can be applied to the prediction of scaling progression at the crowns of breakwaters by replacing them with the number of in-service years. Within the scope of this study, it was found that the damage after 300 cycles in accordance with ASTM C 672 (using artificial seawater) was equivalent to the damage that would be sustained over a period of 20 to 33 years in an actual environment for a design water-cement ratio of 53 to 60%. The concept of design to control scaling progression was comprehensively summarized. At the second, as for countermeasure, it paid attention to surface penetrants (silane-type). The surface penetrants (silane-type) are expected to help control the deterioration of concrete caused by combined action due to freeze-thaw and chloride. Although the method offers high economic efficiency and workability and cases of its implementation are increasing, no durability verification method and deterioration prediction method after construction have yet been established. A field test and exposure test were conducted on the wheel-guard concrete of a road bridge and seaside testing ground in Hokkaido to evaluate the persistence of the effect of these materials. As a result, persistence of the scaling control effect was confirmed in the case of application to a replacement member. In addition, the effect on the reduction of the life cycle cost was evaluated based on the findings of the study. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第9940号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Degree Affiliation: | 工学研究院 |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/57097 |
| Appears in Collections: | 学位論文 (Theses) > 博士 （工学）
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Submitter: 遠藤 裕丈
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