DESIGNWORKS Vol.19

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Topic極薄コンクリート打増工法によるモダニズム建築の保存・再生・継承 / 名古屋大学 豊田講堂改修Preserving, restoring and passing on modern architecture by means of the ultrathin layers of concrete placing method. / Restoration of Toyoda Auditorium, Nagoya University1960年の竣工以来、日本の重要なモダニズム建築として、歴史的、文化的価値を高く評価されている豊田講堂を、竣工後半世紀経た2007年、55mm厚でコンクリートの表面部分を打ち替える極薄コンクリート打増工法という創造的技術により保存・再生が図られた。豊田講堂は、正門を持たない名古屋大学の、象徴としての「正門」であり、また地域から大学へのゲートして都市景観を形成しているが、コンクリート打放しの劣化、建築本体の老朽化のみならず、時代の変化による機能面での限界も見え始めていた。解体・新築も視野に入れた検討が行われたが、名古屋大学は豊田講堂を市民交流の拠点となる文化施設として再生すべく、意匠の保存・継承、機能の強化・拡充を柱にコンセプトをまとめた。建築本体の保存・再生では建設当時のスリムなプロポーションを維持するため、打設可能な最小厚でコンクリートを打増し再生する工法の確立と質感復元のため杉板目転写技術の工法の両立を目指し、極薄コンクリート打増工法を開発した。これは躯体表面を30mm削り、メッシュ筋を配した杉板本実型枠に今回工法のために大臣認定を取得した高流動コンクリートを漏斗を用い55mmで打設する工法で、既存躯体に対して25mmの打増しでコンクリート打放し仕上げを再生した。また杉板の厚さを僅かにかえて小幅板の表現を強調し、杉板表面に浮造り加工を施しSince its completion in 1960, the Toyoda Auditorium has been one of Japan's most important examples of modern architecture, highly regarded for both its historical and its cultural value. In 2007, nearly half a century after it was completed, Takenaka embarked on a preservation and restoration project for the building. A creative new technology called the ultrathin layers of concrete placing method was developed to replace the surface concrete to a thickness of 55 mm. This method preserved the smooth proportions of the building at the time of its original construction and restored the texture of the cedar panel formwork exposed concrete finish. Different restoration techniques were used in accordance with the level of deterioration on the outer wall surface as determined by a survey of the existing building. The ultrathin layers of concrete placing method was used in areas of the outer periphery exposed to rain, both from a design and durability standpoint and due to the significant surface deterioration in these areas. A surface touch-up finishing method was used on the pilotis and eave soffits where there was little surface deterioration. The goal of the project was to establish a method that enabled concrete placing only to the minimum thickness to which concrete could be 質感の復元を図った。ファサードと一体をなす前庭広場の整備も行われ、その結果「新生」ともいえる爽やかな緊張感を与える姿を甦らせることができた。ホールの性能改善による機能強化と、講堂に背面に建つシンポジオンとの間にアトリウムを増築し、二つの建物を複合施設とする機能拡充とを実現し、講堂の正面性や、背面自然林への視線の抜け等、建設当時の精神を保持しながら、より豊かな空間への再生が図られた。老朽化した多くの貴重なモダニズム建築が修復・保全の機会を得ずに姿を消していく中、今回の事例は、モダニズム建築の新たな再生手法として社会的にも大きな意味を持つと言える。2011年、設計者が現役である建築物としては初めて、国の登録有形文化財に指定された。(町田 伊左雄)所在地:愛知県名古屋市延床面積:7,112.99㎡構造:RC造・S造(増築部)階数:地下1階 地上3階 搭屋3階設計:槇文彦改修設計:槇総合計画事務所改修プロジェクトマネジメント:トヨタ自動車プラント・エンジニアリング部建築計画室改修施工:竹中工務店改修工期:2006.12~2007.12Location: Nagoya-shi, AichiTotal floor area: 7,112.99㎡Construction: Reinforced concrete, steelNumber of stories:3 floors above ground and 3 penthouse floors plus 2 basement floorsArchitects: Fumihiko MakiRepair design: Maki and AssociatesRepair project management: Toyota Motor Corporation Building Planning Dept Plant Engineering Div.Repair construction work: Takenaka CorporationRapair construcion term: December 2006 to December 2007改修後西側外観 27placed, and to balance this with a technique for transferring the grain of the cedar board in order to restore the building’s original texture. Repeated studies and trial constructions finally succeeded in establishing the method. In order to preserve the slim proportions of the building with their outstanding design, ultimately 30 mm of the skeleton surface was removed, and a highly fluidized concrete — for which Ministerial approval for use with this technique had been obtained — was applied through a funnel to a cedar board formwork with mesh reinforcements, up to a thickness of 55 mm. To maximize the transferal of the cedar grain, the cedar boards were soaked for 30-40 minutes in lime supernatant water with a pH value of 10-11 to uniformly remove scum. In addition, the thickness of the cedar panels was changed slightly to emphasize the joints of the narrow panels, and the surface of the cedar was embossed to restore its original texture. The result was placing a layer of 25 mm with respect to the existing skeleton, and the achievement of a "rebirth" of the original form that exerts a pleasing tension. Since many modernistic buildings are disappearing without being restored or preserved, this project can be said to have a great significance, also socially, as a case of applying new techniques to restore modernistic buildings. In 2011, the building was designated as a national registered tangible cultural property while the designer was still alive, the first time such designation was made. (Isao Machida)30Topic