Harmanci Yunus Emre, Michels Julien, Chatzi Eleni
Institute of Structural Engineering, Department of Civil, Environmental & Geomatic Engineering, ETH Zürich, 8049 Zürich, Switzerland.
Structural Engineering Research Laboratory, Swiss Federal Laboratories for Materials Science and Technology, Empa, 8600 Dübendorf, Switzerland.
Polymers (Basel). 2018 May 23;10(6):565. doi: 10.3390/polym10060565.
The long-term performance of externally-bonded reinforcements (EBR) on reinforced concrete (RC) structures highly depends on the behavior of constituent materials and their interfaces to various environmental loads, such as temperature and humidity exposure. Although significant efforts have been devoted to understanding the effect of such conditions on the anchorage resistance of unstressed EBR, with or without sustained loading, the effect of a released prestressing has not been thoroughly investigated. For this purpose, a series of experiments has been carried out herein, with concrete blocks strengthened with carbon fiber-reinforced polymer (CFRP) strips, both unstressed, as well as prestressed using the gradient anchorage. The gradient anchorage is a non-mechanical technique to anchor prestressed CFRP by exploiting the accelerated curing property of epoxy under higher temperatures and segment-wise prestress-force releasing. Subsequently, strengthened blocks are transferred into a chamber for exposure in dry freeze-thaw cycles (FTC). Following FTC exposure, the blocks are tested in a conventional lap-shear test setup to determine their residual anchorage resistance and then compared with reference specimens. Blocks were monitored during FTC by conventional and Fabry⁻Pérot-based fiber optic strain (FOS) sensors and a 3D-digital image correlation (3D-DIC) system during gradient application and lap-shear testing. Results indicate a reduction of residual anchorage resistance, stiffness and deformation capacity of the system after FTC and a change in the failure mode from concrete substrate to epoxy-concrete interface failure. It was further observed that all of these properties experienced a more significant reduction for prestressed specimens. These findings are presented with a complementary finite element model to shed more light onto the durability of such systems.
外部粘结增强材料（EBR）在钢筋混凝土（RC）结构上的长期性能高度依赖于组成材料的性能及其与各种环境荷载（如温度和湿度暴露）的界面性能。尽管已经投入了大量精力来了解这些条件对无应力EBR锚固抗力的影响，无论有无持续荷载，但释放预应力的影响尚未得到充分研究。为此，本文进行了一系列实验，用碳纤维增强聚合物（CFRP）条带对混凝土块进行加固，既有无应力的，也有使用梯度锚固进行预应力处理的。梯度锚固是一种非机械技术，通过利用环氧树脂在较高温度下的加速固化特性和分段释放预应力来锚固预应力CFRP。随后，将加固后的混凝土块转移到一个试验箱中，进行干冻融循环（FTC）试验。在FTC试验后，对混凝土块进行传统的搭接剪切试验，以确定其残余锚固抗力，然后与参考试件进行比较。在梯度施加和搭接剪切试验期间，通过传统的和基于法布里-珀罗的光纤应变（FOS）传感器以及三维数字图像相关（3D-DIC）系统对混凝土块在FTC试验期间进行监测。结果表明，FTC试验后系统的残余锚固抗力、刚度和变形能力降低，破坏模式从混凝土基体破坏转变为环氧-混凝土界面破坏。进一步观察到，预应力试件的所有这些性能下降更为显著。这些发现通过一个补充有限元模型进行了阐述，以便更深入地了解此类系统的耐久性。
