以簡易直流電阻評估鋼筋混凝土受高溫後之殘餘握裹

A RAPID DC APPROACH FOR ASSESSING THE POST-HIGH-TEMPERATURE RESIDUAL BONDING STRENGTH OF REINFORCED CONCRETE ELEMENTS

10.6652/JoCICHE.202209_34(5).0006

王楚弦(Chu-Hsien Wang)；詹凱任(Kai-Ren Zhan)；侯琮欽(Tsung-Chin Hou)

混凝土 ； 高溫 ； 殘餘握裹 ； 直流電阻 ； 非破壞檢測 ； concrete ； post-high-temperature ； residual bonding strength ； DC resistance ； nondestructive testing

中國土木水利工程學刊

34卷5期（2022 / 09 / 01）

407 - 414

英文

高溫火害影響鋼筋混凝土的物性與化性，其造成的改變通常是不可逆的，不僅混凝土本身的強度受到影響，混凝土與鋼筋的界面亦遭弱化，最後導致鋼筋混凝土構件的力學行為產生變化。混凝土強度與鋼筋握裹力兩者皆為高溫火害後進行修復、補強或拆除時之重要評估指標，亟需有效且快速的檢測法對其進行評估。本研究以簡易二電極直流電阻探討混凝土受高溫作用後其內埋鋼筋之殘餘握裹強度，試驗中混凝土試體設計涵蓋三種常見之水灰比，承受低溫（100°C）、中溫（250°C）與高溫（400°C）三種溫度分別延燒30至120分鐘，並量測其高溫前後之混凝土抗壓強度、單筋拉拔強度及直流電阻值。研究結果顯示隨熱負載程度（溫度與延燒時間）增加，上述三種指標皆有明顯下降趨勢，其中電阻值對熱負載之變化相對較敏感，雖然用以評估鋼筋殘餘握裹之表現不如抗壓強度指標，但其仍具有簡易且快速之優勢，並能在低熱負載時反映出混凝土產生之微裂縫。

High temperature damage affects reinforced concrete's physical and chemical properties, and the changes caused by it are usually irreversible. Not only the strength of the concrete itself is affected, but also the interface between concrete and rebars is weakened, resulting in changes in the mechanical behavior of reinforced concrete components. The strength of concrete and the bonding strength of rebars are both important evaluation indicators for repair, retrofitting, or demolition after high temperature fire damage. There is an urgent need for an effective and rapid detection method to evaluate them. In this study, a simple two-electrode DC resistance was used to investigate the residual bonding strength of the embedded rebars in concrete subjected to high temperatures. The design of concrete specimens in tests covered three common water-cement ratios and were subjected to various thermal loads with low (100°C), medium (250°C), and high temperature (400°C) lasting for 30 to 120 minutes. The corresponding compressive strengths, single rebar pull-out strengths, and DC resistivities before and after high temperature conditioning were measured, compared and analyzed. Our results indicated that all the above mentioned three measurements decreased with the degrees of thermal loads (temperature and burning time). Among them, DC resistivity values were relatively sensitive to the changes of thermal loads. Although the performance used to evaluate the residual bonding strength of rebars is not as good as the compressive strength, it still has the advantage of being simple, fast and nondestructive. It also shows the ability to reflect the changes of porosity as well as microstructures caused by light thermal loads at early stages.

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