Tetsuo Harada

The Design Method for the Demolition of Concrete with Expansive Demolition Agents

Recently, some chemical expansive agents have a tendency to be used for demolition. With these agents, demolition work can be done in safety almost without any pollution, since high expansive pressure is obtained gradually by only mixing the agents with water and pouring the slurry into boreholes. To estimate the time for demolition works, it is necessary to clarify the amount of the expansive pressure acting on the inner surface of the boreholes and the mechanism of fracture of materials to be demolished. The authors carried out experimental and theoretical studies to clarify the problems mentioned above, and proposed a demolition design method.

STUDIES ON ANCHORING MECHANISM FOR CFRP STRANDS AND PC STRANDS AS TENDON USING HIGHLY EXPANSIVE MATERIAL

The authors have developed a new anchorage method for continuous fiber reinforcing materials such as carbon fiber reinforced polymer (CFRP) strands using a highly expansive material (HEM). Experiments have confirmed that this method offers great utility for anchoring tendons of both steel strands and CFRP strands in prestressed concrete (PC). The new anchorage method offers the following features: (1) solid adhesion of various FRP/steel tendon types; (2) no stress concentration at point of adhesion due to uniform expansive pressure, which acts similarly to a fluid and can reach up to 50 MPa; (3) sustained prestressing force over the long term with negligible loss over time.

DURABILITY DESIGN AND THERMAL CRACKING CONTROL OF CONCRETE PIERS OF SHIN-KITA-KYUSHU AIRPORT BRIDGE

新北九州空港連絡橋の海中橋脚を対象として第1種防食法による耐久性設計およびマスコンクリートとしての温度ひび割れ制御の検討を実施した. アルカリ骨材反応性試験で無害と判定される粗骨材であっても高アルカリ環境下では異常膨張を示すこと, これに対して高炉スラグ微粉末を置換率50%で使用すればアルカリ骨材反応が抑制されることを確認した. 高炉スラグ微粉末高添加の低発熱セメントによるコンクリートの発熱量の低減と保温型枠による放熱量の制御とを併せて実施することで, ひび割れ指数を感潮帯では1.0以上, 海中・海上大気中では0.7以上としひび割れ幅を0.1～0.3mmに抑制できた. また, ひび割れ幅・間隔には配力鉄筋比および構造体温度と外気温との温度差の影響が大きいことを明らかとした.