以簡易直流電阻評估鋼筋混凝土受高溫後之殘餘握裹

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℃), medium (250℃), and high temperature (400℃) 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.