Review Study on the Durability of FRP-Confined Concrete

The use of Fiber Reinforced Polymer (FRP) composites has recently experienced a steep increase in civil engineering applications, because of the high mechanical and low density properties of such materials. Over the last few decades, concrete columns externally confined with FRP sheets were largely investigated for their use in structural rehabilitation and seismic strengthening of civil constructions. Scientific literature is rich in experimental results and both analytical or empirical models, focusing on such phenomena. There exist, in fact, several numerical models and analytical procedures able to predict the behavior of FRP-confined structural elements subjected to axial or seismic loads, and researchers worldwide have experimentally studied and analytically calibrated a wide range of significant variables. Nevertheless, there are still a few results concerning the durability of FRP-confined concrete exposed to severe environmental conditions, even if this is a main topic in design. The objective of this study is to raise awareness about the durability of FRP-confined concrete. To do so, the authors collected and analyzed the results of about 760 pure axial compression tests, taken from 17 different experimental studies published in the scientific literature, in order to present a critical comparison between the results of experimental studies and the theoretical models provided by design guidelines and codes. The study was conducted according to the following steps: at first, experimental data available in literature was collected; secondly FRP-confined concrete cylinders subjected to axial load were classified according to the different experimental variables investigated (mainly according to the type of environmental agent they were exposed to); thirdly, experimental results were compared with the provisions proposed by the American Concrete Institute and contained in ACI 440-2R/2008, and with the guidelines presented on CNR DT-200/2012 and proposed by the Italian National Research Council. Finally, strength and limits of the technical codes were analyzed in terms of safety factors, and formulation of design equation in the short and long-term was critically studied.