Previous research has shown that the application of externally bonded reinforcements (steel plates, fiber-reinforced polymer (FRP) laminates, overlays, etc.) to strengthen reinforced concrete (RC) beams can lead to brittle debonding failures before the ultimate load is reached. The aim of this study is to develop an analytical approach for the flexural strengthening of existing structures using various types of external reinforcements and predicting the debonding failure. In this study, an analytical model is developed to predict concrete cover separation failure in beams with overlay strengthening that is also applicable to strengthening using other reinforcements, such as steel plates and FRP laminates. An experimental database with various types of beam specimens is used to verify the model’s validity and reliability. A concept for determining the effective strengthening capacity in a strengthening design is presented and the main parameters affecting the strengthening capacity are investigated. Finally, a design proposal is presented for the flexural strengthening of RC beams with respect to concrete cover separation failure. This proposal contributes to the application of external flexural strengthening in practical design.
The release agents currently used to facilitate demolding and protect formworks from corrosion present some risks to users and the environment. This study focuses on a new demolding technique based on polarization, with the aim to eliminate the use of release agents. The tests were carried out on ordinary concrete C25/30 at 20±2°C. The methodology and conditions to obtain a good quality of concrete surface and demolding are presented herein.
A new strain hardening cementitious composite with a dense matrix, Ultra High Performance-Strain Hardening Cementitious Composites (UHP-SHCC), has been developed. This material combines excellent protective performance with a significantly higher tensile strength and strain hardening at tensile strength. Further, the material has controlled fine cracks (less than 30 microns). A low water to binder ratio with silica fume that causes a pozzolanic reaction is used in UHP-SHCC. These characteristic may give advantages for autogenous healing after the cracking. This paper presents autogenous healing behavior of cracked UHP-SHCC, and discusses about recovery of protective performance through air and water permeability test results. It was confirmed that UHP-SHCC has potentially autogenous healing properties. The air permeability coefficient and water permeation were dramatically decreased by increasing of re-curing period. Re-curing in water was more effective than re-curing in air for recovery. The effect of induced damage level on recovery of the used indices was not significant, because crack width was controlled and was almost the same among all the cracks. The repeatability of autogenous healing (twice in this study) was confirmed.
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