Abstract
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.
Highlights
The use of fiber-reinforced polymers (FRP), those comprising carbon fibers (CFRP), has anchored its position within researchers and practitioners as an effective retrofitting technique for reinforced concrete (RC) flexural members
It becomes evident that the maximum attained slip at failure decreased almost by half after freeze-thaw cycles (FTC), 43% and 57%, respectively for the unstressed and prestressed cases, indicating that the reduction in deformation capacity was more pronounced in prestressed specimens
Strain values obtained from the block that was exposed to 100% RH were used as the input for the finite element (FE) model
Summary
The use of fiber-reinforced polymers (FRP), those comprising carbon fibers (CFRP), has anchored its position within researchers and practitioners as an effective retrofitting technique for reinforced concrete (RC) flexural members. To this day, the most common strengthening approach is the application of either fabrics or pultruded strips on the tensile face of the member, often referred to as externally-bonded reinforcement (EBR). Prestressing is a potential method to postpone, or in some cases even eliminate, the abrupt debonding failure mode and allow the flexural. A number of metallic and non-metallic mechanical anchorage techniques have been developed and are in use today within the industry [3]. As an alternative to mechanical approaches, gradient anchorage is a non-mechanical technique developed at
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